4255623_P5_Final_Report.

4255623_P5_Final_Report.
Bio-based FRP structures:
A pedestrian bridge in Schiphol Logistics Park
Student
Rafail Gkaidatzis
Mentors
Ir. Joris Smits
Ir. Arie Bergsma
10. 2014
Master thesis final report
MSc Architecture, Urbanism and Building Sciences
Building Technology
ACKNOWLEDGEMENT
It wouldn’t have been possible to bring this graduation thesis into realization without the valuable contribution of many people.
Foremost I would like to express my deepest gratitude to my two mentors,
Joris Smits and Arie Bergsma. This project would never have started and
ended without the contribution of the initiator of this project, my first mentor, Joris. I want to thank him for trusting me a topic with the demands of a
real project and for giving me the opportunity to broaden my knowledge
on new fields. It was his imaginative attitude that inspired me in the beginning and introduced me in the world of structures. I want also to thank
him for all his support throughout this process, the unique interest and time
dedicated on the project.
I would also like to thank my second mentor Arie Bergsma for his guidance
and important advices on technical aspects. His critical spirit and attitude
helped me to realize other crucial dimensions that a real structure has.
Furthermore, I am sincerely grateful to the person that had the inspiration of the initial idea and started this project, Myrke van der Meer from
Schiphol Area Development Company (SADC). I thank her for commissioning me such a challenging project, for the trust she has shown on my
abilities and the excellent collaboration we had so far.
During the course of my research I had the good fortune to meet another
inspirational person, who contributed the most to the technical solution
of the project, Jan Peeters from FiberCore Europe. I owe him my deepest
gratitude for being more than willing to help with his valuable advice and
feedback on the detailing and production of the bridge, for sharing his
innovative ideas and knowledge through discussions and for giving me
the opportunity to see all these into real practise in the manufacturing unit
of the company.
I want also to express my sincere gratitude to all Royal Haskoning DHV colleagues that contributed either directly or indirectly to this thesis. First and
foremost, I want to thank Liesbeth Tromp who was my supervisor all these
all months and provided me with all the information and knowledge regarding FRP structures. Under her valuable guidance I had the chance to
learn and perform successfully calculations on technical aspects of laminate composites. I would also like to thank Ton Boeters and Peter Gosselink
for their contribution on the calculation of the structure and the life cycle
assessment. I have also to thank my Greek and Dutch colleagues in the
office for offering me a friendly environment to work and making every
day unique.
Last but not least, I want to thank all my friends and fellow students in the
Netherlands, the ones that were always next to me, giving me the inspiration, courage and the confidence I needed in order to overcome the
difficulties of a twelve month daily and nightly schedule.
Finally, I owe a deep dept of gratitude to all my family for their endless
emotional and moral support throughout all my studies at TU Delft. The
smile from my five little nephews was the greatest source of courage and
power.
TABLE OF CONTENTS
1
INTRODUCTION
10
11
11
12
13
1.1
Problem definition
1.2
Goal of the research
1.3
Research question
1.4
Introduction to fibre-reinforced polymers
1.4.1 Natural fibre-reinforced polymers and biopolymers
3
38
38
39
39
2
FIBRES
16
16
16
18
18
19
20
20
20
21
21
22
22
23
24
25
26
27
28
29
30
31
31
32
33
33
34
36
2.1
2.1.1
2.1.2
2.2
2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.3
2.3.1
2.4
2.4.1
2.4.2
2.4.3
2.4.4
2.4.5
2.4.6
2.5
2.5.1
2.6
2.7
2.8
2.9
2.10
2.10.1
2.10.2
2.10.3
Fibres
Basic terminology
Mechanical properties
Textiles
Woven fabrics
Non-crimp fabrics
Braids
Chopped strand mats and fleeces
Knitted fabrics
Natural fibres
Classification
Plant fibres
Bast/stalk fibres
Leaf fibres
Fruit/seed fibres
Grass fibres
Chemical composition of plant fibres
Mechanical properties
Flax
From plant to fabric
Jute
Basalt
Glass
Mechanical comparison
Durability
Flammability
Moisture absorption and fibre-matrix adhesion
UV-radiation resistance
39
40
43
45
45
45
48
48
48
50
LIFE CYCLE ASSESSMENT
3.1
3.1.1
3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.3
3.3.1
3.3.2
3.4
3.4.1
3.4.2
3.5
LCA approach
Goal of the analysis
Flax/Jute Fibre
Agricultural operations
Fertilizers and pesticides
Fibre-Processing Operations
Fabric production
Glass fibre
Raw material extraction
Fibre processing operations
Basalt fibre
Raw material extraction
Fibre processing operations
Conclusions of LCA
4
RESINS
52
54
54
54
54
55
56
57
58
59
4.1
The discovery and development of polymers
4.2
Classification of polymers (resins)
4.2.1 Thermoplastics
4.2.2 Elastomers
4.2.3 Thermosets
4.3
Biopolymers
4.4
Biopolymers vs. conventional polymers
4.5
Durable bio-based polymers
4.6
Furan
4.7
Natural fibre-reinforced biopolymers
5
CORES
62
63
63
63
63
64
64
65
5.1
5.2
5.2.1
Sandwich construction
Core materials
Polymer foams
5.2.2
5.2.3
5.2.4
5.2.5
5.3
Biodegradable polymer foams
Honeycombs
Aluminum foam (metal)
Balsa wood
Environmental impact and embodied energy
6
PRODUCTION TECHNIQUES
68
68
69
70
71
71
72
72
6.1
6.1.1
6.1.2
6.1.3
6.2
6.2.1
6.2.2
6.3
6.3.1
6.3.2
6.3.3
6.4
6.4.1
6.4.2
6.4.3
6.5
6.5.1
6.5.2
6.6
6.6.1
6.7
6.7.1
6.7.2
6.7.3
6.7.4
6.8
6.8.1
72
73
74
74
74
75
75
75
75
76
76
76
77
77
77
78
78
80
80
7
83
83
84
85
85
87
88
91
93
95
98
Manual lay-up processes
Hand lay-up
Vacuum/pressure bagging
Autoclave molding
Automatic lay-up processes
Automated tape placement (ATP)
Filament winding
Resin transfer processes
Resin transfer molding (RTM)
Vacuum assisted resin transfer molding
Resin film infusion (RFI)
Compression molding processes
BMC molding
SMC molding
Thermoforming
Continuous processes
Pultrusion
Continuous lamination
Spraying processes
Spray-up
Manufacturing cost calculation
Materials
Capital
Time, energy and information
Cost comparisons between processes
Moldmaking
Mold materials
8
STRUCTURAL CALCULATION
102
102
102
102
103
103
104
105
106
107
110
114
114
114
115
115
115
116
117
118
118
119
120
120
122
8.1
8.2
8.2.1
8.2.2
8.3
8.4
8.5
8.6
8.6.1
8.6.2
8.6.3
8.7
8.7.1
8.7.2
8.7.3
8.8
8.8.1
8.8.2
8.8.3
8.9
8.9.1
8.9.2
8.9.3
8.10
8.11
9
MANUFACTURE & INSTALLATION
126
127
128
128
129
9.1
9.2
9.3
9.4
9.5
Structural simplification
Structural analysis approach
Calculation process
Aim of the analysis
Dimensioning of the bridge
Fibre-resin properties
Calculation of ply properties
Definition of the laminate
Stress [σ] - Strain [ε] relations for principal directions
Stress [σ] - Strain [ε] relations for rotated axis
ABD Stiffness matrices
Partial factors
Conversion factors
Material factors
Load factors
Parapet to parapet (deck) calculation
Moment of Inertia about centroidal (neutral) axis
Ultimate limit state
Service limit state
Abutment to abutment calculation
Moment of Inertia about centroidal (neutral) axis
Ultimate limit state
Service limit state
Optimization of the structure
Evaluation of flax, jute, glass and basalt fibre
reinforced laminate
Moldmaking and lamination
Construction of shear web
Direction of the web plates
Injection and final operations
Installation on site
DESIGN
7.1 Case study
7.2 Site analysis
7.3 Design parameters
7.4 Design evolution
7.4.1 Stage 1. First design approach
7.4.2 Stage 2. Second design approach
7.4.3
7.4.4
7.5
7.5.1
7.5.2
Design results
Stage 3. Structural testing
Final design
Architectural drawings
3D Impressions
10 CONCLUSIONS & RECOMMENDATIONS
134
135
10.1 Conclusions
10.2 Recommendations and points of improvement
136
LITERATURE
Introduction
10
Chapter 1 | Introduction
1.1 Problem definition
Plastic industry ranks third in the world amongst
all other industry with composite plastic materials
being already part of our everyday life, and having entered nearly all major industrial, commercial
and domestic sectors. However, the utilization of
long-lasting polymers for short-lived applications
(packaging, catering, surgery, hygiene) is not a
wise practice as the majority of the synthetic polymers is produced from petrochemicals and is not
biodegradable. These persistent polymers became
source of environmental pollution, harming wildlife
when they are dispersed in the nature.
Under the environmental awareness of the recent
years, environmental friendly materials are gradually emerging worldwide. Efficient utilization of plant
species through the use of their smaller particles
and fibres in order to develop eco-friendly composite materials is certainly a rational and sustainable
approach. In this way, natural substances can be
turned through appropriate processes into composite polymer products based on renewable raw
materials and thus replace conventional fossil fuel-based polymers.
Building and
construction
17%
Consumer and
institutional
21%
Exports
15%
Furniture 4%
Transportation 4%
Electrical-electronic
equipment 2%
Packagings
33%
Other 2%
Adhesives,
inks/coatings 1%
Industrial/machinery 1%
1.1 The distribution of major markets for plastics
(http://www.plasticsbusinessmag.com)
These polymers that are based on renewable raw
materials found a variety of applications in different sectors. The automotive industry, for instance,
is a sector that made important steps on replacing
gradually the conventional plastics with natural fibre-reinforced polymers on vehicles. Other industries
that invested on this bio-plastic technology include
packaging, catering, agriculture, telecommunications and medical.
However, in the building industry the use of such biobased polymers is still in an early state of development. According to the graph 1.2 for the year 2012
for construction sector the global production of
bio-plastics was 2.500 Ktons holding the lowest position compared with other sectors. The specific application of these bio-plastics in the building sector
include insulation products, cladding components
for façade, flooring and connections.
1.2 Global production capacities of bioplastics 2012 (by
market segment)
Source: European bioplastics, Institute of bioplastics & Biocomposites
(http://en.european-bioplastics.org)
As far as load-bearing applications are concerned,
the use of environmental friendly polymers is even
more limited as composites used for structural elements consist either of man-made fibres with increased environmental impact or petrochemical
resins.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
11
1.2 Goal of the research
It becomes clear that advanced plastics are increasingly preferred by the building industry as they show high
future potentials. However, the high environmental impact of such fuel-based plastics makes necessary their
replacement from more eco-friendly plastics with similar properties. In that sense, the goal of this graduation
project is to prove that the utilization of composite polymers based on natural and renewable raw materials for
lightweight load-bearing applications is feasible and thus take a step towards the introduction and establishment of such plastics in construction.
As the orientation of the project is on load-bearing structures a main aim is to convince that the mechanical
properties of biocomposites are comparable with conventional composites and thus prove their capability to
receive the loads of a structure. Important is also to research the lasting properties and the durability of these
materials (UV, moisture, fire resistance) through time under the continuous exposure to environmental conditions.
1.3 Research question
Are composite polymers based on renewable raw materials able to fulfil the structural requirements of a lightweight loadbearing structure, such as a pedestrian bridge?
Under this general research question, further subquestions can be the following:
•
What are the mechanical properties of natural fibre-reinforced polymers?
•
What is the most appropriate combination of renewable raw materials in order to get a composite with
the optimum structural behavior for a pedestrian bridge?
•
What are the loading requirements the design criteria for a footbridge?
•
What could be the cost of such a structure?
•
Are there any clients in the Netherlands to absorb this kind of product in the market?
12
Chapter 1 | Introduction
1.4 Introduction to fibre-reinforced polymers
Fibre-reinforced polymers (FRP) are composite materials composed
of a polymer matrix which is reinforced with fibres. The fibres can be
out of glass, carbon, basalt or aramid, although other fibres such as
paper, wood or asbestos have been also used. The polymer is usually
an epoxy, vinylester or polyester thermosetting plastic, while phenol
formaldehyde resins are still in use. Both fibres and the polymer matrix
exhibit significant different physical and chemical properties but when
combined together they create strong and rigid composite materials.
More specifically, the polymer matrix surrounds and supports the reinforcement by maintaining its position while the reinforcement gives
its special mechanical and physical properties in order to improve
the properties of the final product. In this way, the matrix which is a
relatively tough but weak material is reinforced by the fibres that mechanically optimize the strength and elasticity of the polymer. In general, the plastic resins are strong in compression forces and relatively
weak in tensile strength while fibres are strong in tension but tend not
to resist compressive loading. The combination of these two materials
and properties leads to the development of a new composite material that can resist both compressive and tensile forces.
1.3 Scanning electron microscope image of a fibre reinforced composite
composed of carbon fibres (in blue) and silicon carbide (in brown)
(http://www.pbs.org/)
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
13
1.4.1 Natural fibre-reinforced polymers and biopolymers
Composite materials are already a part of our everyday life, and have entered nearly all major industrial, commercial and domestic sectors. Although
several studies have proved that fibre-reinforced
plastics perform better in terms of CO2 footprint in
comparison to traditional building materials such as
steel and concrete, the majority of these plastics is
based on non-renewable sources. Fibre-reinforced
polymers used in structural applications are normally composed of synthetic fibres, such as glass and
carbon combined with petroleum-based resins.
Thus, materials based on renewable raw resources
have entered the composite industry and found
application in various products. Natural fibres replaced successfully other artificial fibres and new
types of resins based on natural substances have
been introduced in the market aiming to reduce
the environmental impact of composite plastics, as
well as their embodied energy.
Natural fibre-reinforced polymers (NFRP) are composites consisted of a polymer matrix made from
petroleum but the reinforcement consists of natural
fibres, usually extracted from plants, which are encased in the matrix. These fibres reinforce the polymer and decrease the environmental impact of the
composite as they come from renewable sources.
Additionally, natural fibres are cheaper than artificial manmade fibres, as usually they remain as a
waste sub-product, and have a high stiffness per
weight (higher than glass), which results in lightweight components. Natural fibres are characterized by low density, characteristic that makes them
important for the automotive industry, while they
are biodegradable, non-toxic and present high insulating properties.
Biopolymers (or organic plastics) are synthetic materials manufactured from vegetable substances,
such as starch or cellulose, instead of petrochemicals like polypropylene (PP) which was largely used
the recent years. Biopolymers are biodegradable
composites as long as their compostability is verified
by the European Standard EN 13432.
1.4 Bioplastic products based on renewable raw natural substances
14
Bio-based FRP pedestrian bridge in Schiphol Logistics Park
Fibres
11
16
Chapter 2 | Fibres
2.1 Fibres
Fibres are generally classified in inorganic fibres
(made from glass and carbon), polymer fibres (synthetic fibres), metal fibres and natural fibres. All manmade fibres are also referred to as chemical or synthetic fibers. Synthetic fibres, excluding only carbon
fibres, are made from solid raw materials by production methods based on melting and stretching
processes. One the other hand, natural fibres such
as wool or plant fibres already occur in the form of
fibres and so they are collected and refined in order
to become an industrial product. The majority of fibres, apart from glass and metal, consist of bundles
of tiny fibres that are visible through the microscope.
2.1.1 Basic terminology
An individual fibre is known as a filament, whereas
a bundle of parallel filaments is known as a roving.
When the bundle of the fibres is twisted, the result
is a yarn (or thread). A twine is made from several
twisted yarns. Rovings are typically used as raw material for reinforcement in polymer composites. One
the other hand, yarns are used for making woven or
knitted fabrics.
Filament
Filament
fibre
Organic synthetic fibres
(polymer fibres)
Flax
Sisal
Hemp
Jute
Ramie
Banana
Asbestos
Polyethylene (PE)
Polyamide (PA)
Polyimide (PI)
Polyacrilonitrile (PAN)
Polytetrafluoroethylene
(PTFE)
Aramid
Metal Fibres
Inorganic synthetic fibres
Steel
Aluminum
Copper
Glass
Carbon
Basalt
Ceramic
Yarn
Filament
Roving
Natural fibres
Yarn
“thread”
Twine
2.1.2 Mechanical properties
Compared with their length, fibres have a very small
cross section, the diameter of which varies depending on the type of the fibre. For instance, the diameter of synthetic fibres is between 5 and 24 μm, while
natural fibres can be up to 500 μm.
The diameter is an important parameter for the
structural capacity of the fibre as it influences their
strength. Thus, fibres with small diameter are stronger. However, this strength is mainly in the longitudinal
direction as fibres are frequently sensitive to transverse compression. The more pronounced is the
longitudinal orientation of the microstructure in the
fibre, the weaker are the mechanical properties in
the transverse direction.
2.1 Glass, carbon and aramid fibres viewed under the microscope (up).
(In: Knippers, J,, Cremens, J., Gabler M., Lienhard J. Construction manual for polymers + membranes. Munich: Institut
für international Architektur-Dokumentation)
2.2 Carbon fibres under the microspope
(http://www.formula1-dictionary.net/carbon_fiber.html)
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
Melting furnace
1540oC
Homogenising
1435oC
1370oC
Melt
1340oC
17
Forehearth
1371oC
Feeding with raw
materials, e.g.
quartz sand
In the case of man-made fibres where melting and
stretching fibre-forming processes are required, the fibres are much stronger than their raw material. This
happens as during the production process the internal
structure of the fibre becomes aligned in the longitudinal direction which improves the strength of the material. In doing so, compression of air inclusions is crucial
as it reduces the negative effect that such flaws have
on the strength in the longitudinal direction of the fibre.
As the application of fibres varies, different requirements, such as strength, buckling sensitivity or low selfweight, comply with different uses. For instance, considering only the tensile strength, carbon fibres show the
highest values. However, they are relatively sensitive to
buckling.
1260oC
Size
Yarn winding
2.3 Production process of typical glass fibre
Spider silk
Steel
Wood
Hemp
PET
Flax
Strenght [N/mm2]
Aramid
Glass
4000
Carbon
PE
3000
0
100
200
300
400
Breaking lenght [km]
2000
1000
0
σ [Ν/mm2]
0
0.02
5000
0.04
0.06
0.08
0.1
0.12
Fibre diameter [mm]
Carbon
fibres
4000
PE fibres
3000
E-glass fibres
Aramid
fibres
2000
Flax
1000
PET fibres
0
0
1
2
3
4
5
6
ε [%]
Specifically for lightweight loadbearing applications the most important property of a fibre
is its’ specific strength which is expressed by the
relationship between strength and self-weight
(strength-to-weight ratio). The specific strength
is also indicated by the breaking length which
is the theoretical maximum length that a vertically suspended fibre, supported only at the
top, could reach before breaking under its
own weight.
For fibres that are used as embedded reinforcement in polymer matrixes the elastic
modulus is of high importance. Therefore, fibres
with minimum elongation and thus high elastic
modulus are preferred as low elastic modulus
values lead to excessive deformations of the
component. Additionally, thermosets that are
normally used can only get a limited amount
of elongation and break before the soft fibres
have reached their maximum tensile strength.
Thus, tensile strength has in most of the cases
secondary priority.
18
Chapter 2 | Fibres
2.2 Textiles
Textiles are semi-finished products made from woven fibres. They are mainly used as primary products
for membrane fabrication and as reinforcement in
polymer composites. The most crucial property of
the textiles that are used in construction is obviously
their loadbearing behavior which is determined by
the orientation of the fibres, their waviness (undulation) and the weight per unit area (g/m2).
With the development of different textile technologies such as weaving, knitting and braiding, a huge
variety of textiles for specific applications is now
available. The most common textiles for fiber-reinforced composites are woven fabrics, non-crimp
fabrics, complex mats, braids, chopped strand mats
and fleeces.
Different arrangements of the fixed warp threads
during the weft insertion produce various types of
weave with different mechanical properties each.
Fabrics are also characterized by the weaving density, which is expressed by the number of (warp or
weft) yarns per unit length. The specific terminology
for used in textiles is tows per centimeter. The weight
and the thickness of the fabric are also influenced
by the dimensions of the filament, which together
with the weaving pattern plays an important role in
the stiffness and the strength of the woven fabric.
The three main types of weave are plain, twill and
satin weave.
Plain weave is the simplest and tightest type of
weave. In this style of weave each warp fibre passes alternately under and over each weft fibre. The
fabric is symmetrical, with good dimensional stability
and reasonable porosity. However, compared with
the other weave types is the one which is the most
difficult to drape, whereas the high level of fibre
crimp imparts relatively low mechanical properties.
With large fibres this weave style gives excessive
crimp and therefore it is not generally used for very
heavy fabrics.
2.4 Fabric woven with carbon fibres in twill weave.
(http://www.hccomposite.com/en/catalog/34/1969.html)
2.2.1 Woven fabrics
Woven fabrics are produced by weaving technics,
which are systems of threads crossing at right angles. The warp threads are parallel to the longitudinal direction, fixed to the weaving loom and the
weft threads pass perpendicularly above and below the warp threads.
weft
weft
warp
warp
warp
Plain
Twill weave is produced when one or more warp fibres alternately weave over and under two or more
weft fibres in a regular repeated manner. This produces the visual effect of a straight diagonal rib to
the fabric. This type of fabric is more water-resistant
and has better drapeability than the plain type. In
addition, because the stain in the warp direction is
lower than in the plain weave, twill is stronger and
stiffer.
Twill
Satin
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
Satin weave is fundamentally a twill weave that is
modified to produce fewer intersections of warp
and weft. After each course, the change is shifted
accordingly by at least two steps. Satin weaves are
very flat, have good water-resistance properties,
good mechanical properties and an excellent degree of drape. Due to its’ great drapeability, satin
weave textile is optimum as reinforcement in fiber-reinforced polymer components with complex
and tight curvatures in three directions.
2.6 Plain
2.7 Twill
2.8 Satin
2.9 Non-crimp
19
2.2.2 Non-crimp fabrics
In contrast to woven fabrics, in which the fibres are
interwoven, in non-crimp fabrics the fibres are in the
form of fibre layers that are laid on top of each other with their fibres being fixed in position only by additional thin sewing threads (stitches).
As no weaving occurs, the fibres of each layer are
straight and not in an undulating form, which makes
them stronger as reinforcement for fiber-reinforced
polymers compared with woven fabrics. Another
advantage is the flexibility in adapting the orientation of the fibres to the load-bearing direction as
the fibres do not necessarily need to be in vertical
arrangement but they can be incorporated at any
angle. In a non-crimp fabric it is also possible to have
not only two layers but several, the one above the
other, which allows for multianglular arrangements.
A typical application of this type of fabric is as reinforcement in textile-reinforced concrete.
2.10 Layers of a biaxial (0o, 2.11 Non-crimp fabric
90o) non-crimp fabric
2.5 Layers of a tetraxial (-45o, 0o, +45o, 90o) non-crimp fabric
Non-crimp fabric
2.12 Detail of the stitch
Braid
2.6-2.9
In: Knippers, J,, Cremens, J., Gabler M., Lienhard J. Construction manual for polymers + membranes. Munich: Institut für international Architektur-Dokumentation
2.10 http://www.utwente.nl/
2.12 http://www.tech.plym.ac.uk/
20
Unidirectional
0o
non-crimp fabric
2.13 Carbon braid
(http://shop1.r-g.de)
Biaxial
0o, 90o
woven fabric
2.14 Braiding
(http://www.makeit-loveit.com)
2.15 Random orientation in glass fibre chopped strand mat
(http://tienda.resineco.com/en/VI00005)
2.16 Knitting (http://en.wikipedia.org/wiki/Knitting)
Triaxial
0o,+45o, 90o
non-crimp fabric
Chapter 2 | Fibres
Tetraxial
-45o, 0o,+45o, 90o
non-crimp fabric
2.2.3 Braids
A braided textile is created by intertwining fibres
from three or more yarns in such a way that they
cross one another and are laid together in diagonal
formation, forming a narrow strip of flat or tubular
fabric. This criss-crossing arrangement of the fibres
results in a higher friction force upon fracture and so
in a better impact resistance. Tubular braids have
the optimum form for elongated, three-dimensional
composite applications such as tubes. For that reason, braiding is usually used as fibre-reinforcement
for pipes.
2.2.4 Chopped strand mats and fleeces
In chopped strand mats the fibres that are bonded
together have a random arrangement. Due to this
random orientation of the fibres, composites that
contain such fabrics show mechanical properties
that are not dominant in any orientation. For that
reason, they find application only in composites
with low mechanical requirements. However, the
fibres of chopped strand mats have the ability to
adapt perfectly to the shape of the component as
during processing when the fibres come into contact with the resin, the bonds are loosened. Additionally, such fabrics can be draped easily over
curved shapes. Fine mats, also known as fleeces or
non-woven fabrics, are used in the outer layers of a
fibre-reinforced composite in cases where smooth
surfaces are required. They have also application
as core materials for infilling sandwich components.
2.2.5 Knitted fabrics
Knitted fabrics are produced by processes similar
to hand-knitting mainly by forming loops or stitches.
The application of these textiles as reinforcement for
composites is limited as they do not have a dominant direction and thus they are only used as backing materials for other reinforcing fibres.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
21
natural fibres
plant
animal
bast (stalk)
silk
leaf
wool
fruit
feathers
mineral
asbestos
grass
straw
other
2.3 Natural fibres
2.3.1 Classification
Natural fibres refer to fibres that occur within nature, and
are found in plants (cellulose fibres), animals (protein fibres)
and minerals (asbestos). However, plant fibres are dominant in use as natural fibre-reinforcement for polymers.
Plant fibres are obtained from various parts of plants, such
as the seeds (cotton, kapok, milkweed), stems (flax, jute,
hemp, ramie, kenaf, nettle, bamboo), and leaves (sisal,
manila, abaca), fruit (coir) and other grass fibres. Fibres
from these plants can be considered to be totally renewable and biodegradable. Plant fibres, which have a long
history in human civilisation, have gained economic importance and are now cultivated on a large scale globally
2.17 Mineral fibres under the microscope
(http://www.niehs.nih.gov)
Animal fibres can be either fur/wool taken from hairy mammals, silk fibres secreted by glands of insects during the
preparation of their cocoons or feather fibre like avian collected from birds. Animal fibres consist largely of particular
proteins such as collagen, keratin and fibroin.
Finally, mineral fibres are naturally occurring or slightly modified fibres procured from minerals and they can be categorized into asbestos, ceramic fibres and metal fibres. Some
types of mineral fibres are considered a possible carcinogen to humans. Specifically, the use of asbestos in forming
fibres is banned in the EU and in Switzerland for its harmful
effects on human health.
2.18 Fibres of cashmere, silk, linen, cotton and polyester from
left to right.
(http://www.alpacasocksrock.
com)
22
Chapter 2 | Fibres
2.4 Plant fibres
Vegetation that produces natural fibres is categorized into primary and secondary plants depending on the utilization. Primary plants are grown specifically for their fibres while secondary plants are the ones where the fibres
are extracted from the waste product.
2.4.1 Bast/stalk fibres
In general, bast fibres (stalk fibres) such as hemp or
flax show better mechanical properties and therefore are preferred from the building industry. In this
plant category, the fibres are concentrated in the
outer skin of the stalks supporting the conductive
cells and providing strength to the stem. Each fibre contains individual fibre cells or filaments. The
filaments are made of cellulose and hemicellulose,
bonded together by a matrix, which can be lignin
or pectin. The pectin surrounds the bundle thus
holding them on to the stem. The length of these
fibres is usually a few centimetres. Therefore, these
fibres are characterized by high tensile strength and
low elongation at failure. Straw fibres also belong in
the same bast fibre family. Straw fibres are an agricultural by-product that is extracted from the dry
stalks of mainly cereal plants. Straw makes up about
half of the yield of cereal crops such as barley, oats,
rice, rye and wheat.
2.19 Flax stalks
2.20 Hemp cross section
2.21 Flax stalk in cross section
(http://www.onetruepants.com)
(http://www.stemergy.com)
(http://greenclothing-style.blogspot.nl)
Hollow core
Hurd
Fibre bundle
Outer skin (bark)
Flax
Flax, belongs to the family of the bast fibres and
grows in cooler regions while it is one of the oldest fibre crop ever. It is the most commonly used material in composite area and especially as natural fibre
reinforcement in the automotive industry. Short flax
fibres are produced almost exclusively in Europe
and they are mainly by-products of the production
of long fibres from the textiles industry.
Flax cross-section
Fibre bundle
Bast fibre
Hemp
It is also member of the bast fibres, specifically from
the Cannabis family and similarly with flex, it is also
grows in temperate regions. Hemp is mainly used
as special cellulose for composites and insulating
materials and has extensive application in the automotive industry. Since 1996, when the cultivation
of low-narcotic hemp species was legalized in Germany, hemp received considerable even more
attention for further development in the entire Europe.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
Jute
Jute is the fibre type with the highest production
volume and the one with the lower price compared to the rest of the natural fibres therefore it
is considered as one of the most “exotic” natural
fibres. Countries where the climate conditions are
ideal for its growth are Bangladesh, India, and China.
Kenaf
Belonging to the genus Hibiscus, it is a relatively new
crop in United States which shows good potentials
for usage as reinforcement in composite products.
Originally coming from Africa and Asia these plants
reach height of about 4 meters. Latest innovations
in decortication processes on the separation of the
core from the bast fibres, have increased the interest on utilizing kenaf as fibre source.
23
2.4.2 Leaf fibres
The leaf fibres are hard, coarse fibres obtained from
thick and fleshy sword-shaped leaves of monocotyledonous plants (flowering plants that usually have
parallel-veined leaves, such as grasses, lilies, orchids, and palms), used mainly for cordage. These
fibres, usually several feet long and stiff, are also
called “hard” fibres, distinguishing them from the
generally softer and more flexible fibres of the bast,
or “soft,” fibre group. The leaves are hand-harvested, and their fibre is separated from the surrounding leaf tissue by decortication, a hand or machine
scraping or peeling process. Finally the fibres are
cleaned and dried. Commercially useful leaf fibres include abaca, cantala, henequen, Mauritius
hemp, phormium, and sisal while applications include ropes, and coarse textiles.
Sisal
Sisal fibres are extracted from the leafs of agave
plants which are mainly flourishing in East Africa
and South America. These stiff fibres are traditionally used in making agricultural twine and rope. Likewise other natural fibres sisal fibres are also used by
the automotive industry as reinforcement for polymer composites.
2.22 Flax fibres
2.23 Hemp fibres
(http://www.baltic-flax.com)
(http://en.wikipedia.org/wiki/Hemp)
Abaca
The Abaca or banana fibre is extracted from the
banana plant and is durable and resistant to seawater fibre. Abaca being the strongest commercially available cellulose is produced in Philippines
and Ecuador. In the past, it was the most chosen
cordage fibre for marine applications due to its
resistant to moisture. Having this special quality,
abaca fibres are is used nowadays at the at the
underbody covering part of cars which is exposed
to moisture, weather conditions and ground stone
impact.
2.24 Jute fibres drying
2.25 Kenaf fibres
(http://en.wikipedia.org/wiki/Jute)
(http://ecotextiles.com.au)
2.26 Sisal plant
2.27 Sisal fibres cross section
(http://en.wikipedia.org/wiki/Sisal)
(http://www.intechopen.com/books)
24
Chapter 2 | Fibres
Pineapple leaf fibre
Pineapple fibres belong to the family of the leaf fibres and are extracted from the plant of pineapple
which is indigenous of tropical climates and mainly
Indonesia, India, Brazil and China. It is rich in cellulose fibres and as the leaf fibres are a waste product
they are relatively cheap. It is mainly used by the
clothing industry but also as natural reinforcement
for polymer composites.
Oil Palm
Oil palms, is vastly produced in South East Asia, particularly in Malaysia and Indonesia. Oil palm empty
fruit bunch cellulose fibres are relatively a cheap
waste product in the industry and therefore, it is
of interest to utilize the cellulose fibres into beneficial products with higher commercial value. Such
products include mattresses, fiberboards, insulating
or paper products. However, research done on the
mechanical properties of the fibres and the ability
to be utilized as reinforcement for polymer composites prove that oil palm fibre is hard and tough and
its porous surface morphology is useful for better
mechanical interlocking with matrix resin for composite fabrication.
2.28 Sisal fibres
2.29 Abaca fibres
(http://www.bhtengda.com)
(http://www.save-on-crafts.com)
2.30 Pineapple fibres
(http://www.pixmule.com)
(h t t p : / / i 0 0 . i . a l i i m g . c o m)
2.31 Oil palm fibres
2.32 Oil palm plantation in Malaysia. About 11% of the
total land area in Malaysia (about 62% of the country’s
agricultural land) is devoted to palm oil.
(http://www.etawau.com)
2.4.3 Fruit/seed fibres
Fibres that are produced on the seeds of various
plants have been called seed hair or seed fibres.
The most important fibre of this class is cotton. Other fibres of this group (kapok, floss from milkweed,
dandelion, and thistle fibres) are not generally spun
into yarns, but are utilized mainly as staffing in pillows and mattresses, and for life belts
Seed fibres normally are light, hairy and relatively
shorter compared to other fibre types.
2.33 Coconut fibre cells
2.34 Coconut fruit
(http://www.superstock.com) (http://sanctuarysoil.com)
Coconut
Coconut fibre or coir fibre is one of the natural fibres abundantly available in tropical regions, and
is extracted from the outer shell of the coconut fruit.
There are two types of coconut fibres, brown and
white ones which depend on the maturity of the
coconut. Brown fibres are thick, strong and have
high abrasion resistance while white fibres are
smoother and finer, but also weaker. Applications
vary mainly between objects of daily use such us
brushes, ropes and mattresses. The material is also
used for insulation, packaging and as upholstery
padding for the automobile industry in Europe.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
Cotton
Cotton is the most common seed fibre and is used
for textile all over the world. Cotton is a soft, staple fibre that grows in a spherical form around the
seeds of the cotton plant, a shrub native to tropical
and subtropical regions around the world, including America, India and Africa. The fibre most often
is spun into yarn or thread and used to make a soft,
breathable textile. In comparison with other natural fibres, cotton is rather weak. It can absorb moist
up to 20% of its dry weight, without feeling wet and
is also a good heat conductor. Cotton is applied
for the manufacturing of clothes, carpets, blankets,
mobs and medical cotton wool.
25
2.4.4 Grass fibres
Grass is an annual plants with bundles of elementary fibre cells and it can be found in large
amounts. These elongated cells occur in different
parts of plants, mainly in the stems and leaves of
grass. The most important representatives in the
group of grasses are ryegrass, trefoil and lucerne.
Grass fibres cover a wide range of applications
such as various domestic goods or handicraft
items like hats and baskets.
2.35 Cotton fibres
2.36 Coconut fibres
(http://informedfarmers.com)
(http://www.ppfenterprises.com)
2.38 Grass stems in section 2.39 Triangular grass stem
(http://www.hiltonpond.org) (http://www.bibalex.org)
2.37 Cotton fibres in section and view through microscope
(http://www.swicofil.com)
2.40 Cross section of a Trefoil stem
(http://www.intechopen.com)
Others (wood/paper)
Wood fibres commonly refer to the tracheid cells
which make up the bulk of the woody tissue in trees.
These fibres are roughly tubular in shape, and are
oriented parallel to the tree stem while their dimensions are quite variable. Wood fibres constitute the
largest component of most pulp and paper products.
2.41 Wood fibres
(http://www.bc.org.nz/purpose.html)
26
Chapter 2 | Fibres
2.4.5 Chemical composition of plant fibres
In order to develop polymer composites from natural resources it is important to understand the microstructure and chemical composition of these fibres.
2.42 Cellulose microfibrils in the microscope
(http://media.noria.com)
2.43 Section on the structure of a plant fibre
(http://images.gizmag.com)
2.44 Lignin (red) keeps plant cell walls study and strong
(https://www.sciencenews.org)
Natural fibres normally have rigid complicated
structures, with crystalline cellulose micro fibril-reinforced amorphous lignin. Generally, natural fibres
are composed of cellulose, hemicellulose, lignin,
waxes, and some water compounds. However, cellulose, hemicellulose, and lignin are the major constituents with percentages that vary depending on
the species and the variety of the plant, agricultural
variables such as soil quality, the weathering conditions, the level of plant maturity and the quality
of the refining process. Typically, natural fibres contain 60-80% cellulose, 5-20% lignin and moisture up
to 20%.
Cellulose is an organic compound with the formula
(C6H10O5)n. It is a polysaccharide consisting of a
linear polymer chain of several hundred to over ten
thousand linked D-glucose units organised into microfibrils. Cellulose consists an important structural
component of the primary cell wall of green plants.
It is the major component which is responsible for
the tensile strength and stability of the natural fibre,
while lignin can take the compression. Cellulose
is by far the most abundant renewable material.
Every year the photosynthesis produces more than
75 billion tons of cellulose on the basis of CO2 and
water.
Hemicellulose is not a form of cellulose and the
name is a misnomer. They comprise a group of
polysaccharides composed of a combination of 5
and 6 carbon ring sugars. Hemicelluloses form the
supportive matrix for cellulose microfibrils and they
are very hydrophilic, soluble in alkali and easily hydrolyzed in acids.
Lignin is a complex hydrocarbon polymer with
both aliphatic and aromatic constituents. They
are totally insoluble in most solvents and cannot
be broken down to monomeric units. Lignin is totally amorphous and hydrophobic in nature, while
it is the compound that gives rigidity to the plants.
Therefore, high consistency in lignin results in a high
degree of lignification which results in stiffer, but at
the same time more brittle, fibres.
2.45 Section of soybean stem, stained with two fluoro
chromes to show distribution of cellulose (blue) and lignin
(yellow) (www.swicofil.com)
The following table compares different portions of
cellulose, hemicellulose, ligning and waxes in specific plant fibres.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
27
Table 2.1 Chemical composition of different natural fibres
Fiber
Abaca
Bamboo
Coir
Flax
Hemp
Jute
Kenaf
Oil palm
Pineapple
Ramie
Rice straw
Sisal
Wheat straw
Cellulose (wt%)
56–63
26–43
32–43
71
68
61–71
72
65
81
68.6–76.2
41–57
65
38–45
Hemicellulose (wt%)
Lignin (wt%)
Waxes (wt%)
7–9
21–31
40–45
2.2
10
12–13
9
29
12.7
0.6–0.7
8–19
9.9
12–20
3
–
–
1.5
0.8
0.5
–
–
–
0.3
8–38
2
–
20–25
30
0.15–0.25
18.6–20.6
15
14–20
20.3
–
–
13–16
33
12
15–31
2.4.6 Mechanical properties
Cellulose is a natural polymer with high strength
and stiffness per weight, and it is the building material of long fibrous cells. These groups of cells are
“designed” for giving strength and stiffness to the
plant.
However, the mechanical properties of plants
are strongly influenced by the growing environment. Conditions such as temperature, humidity,
the composition of the soil and the air affect the
height of the plant and the strength of its fibres or
its density. The way the plants are harvested and
processed results in a variation of properties as well.
Therefore, fibres of the same species may show deviated results after testings.
From the following table that compares different
properties of glass fibres with other natural fibres, it
becomes clear that the mechanical properties of
natural fibres, especially of the ones that belong
to the bast family (flax, hemp, and jute) are good
and may successfully compete with glass fibre in
specific strength and modulus. Natural fibres show
higher elongation to break than glass or carbon fibres, which may enhance composite performance
in case they are used as reinforcement.
Therefore, as flax, hemp and jute seem to be superior regarding their mechanical properties compared
to all natural fibres, they are further researched and
compared in the following subchapters.
Table 2.2 Physico-mechanical properties of natural, E-glass and basalt (mineral) fibre
Fibre
Density
(g/cm3)
Tensile strength
(MPa)
E-modulus
(GPa)
Elongation
at failure (%)
Equilibrium moisture content (%)
Abaca
Bagasse
Bamboo
Basalt
Coir
Cotton
Curaua
E-glass
Eleplant grass
Flax
Hemp
Jute
Kenaf
Stinging Nettle
Sisal
Ramie
Oil palm
Pineapple
1.5
1.25
0.6 - 1.1
2.67
1.25
1.5 - 1.6
1.4
2.55
0.82
1.5
1.48
1.3
1.2
1.51
1.4
1.5
0.7 - 1.55
0.8 - 1.6
400
290
140 - 230
1430 - 4900
220
400
500 - 1150
2000 - 3500
185
800 - 1500
550 - 900
400 - 800
220 - 930
560 - 1600
500- 700
560
248
400 - 627
12
17
11 - 17
71 - 110
6
5.5 - 28
11.8
73
11.3
60 - 80
70
10 - 30
53
24.5 - 87
38
61-128
3.2
1.44
3-1
3.1 - 3.3
2.5
15 - 25
3.7 - 4.3
2.5
3 - 10
3
1.2 - 1.6
1.8
1.6
2.2 - 2.5
2 - 2.5
2.5
25
14.5
15
8.8
8.9
< 0.5
10
8 - 25
9 - 12
0
11 - 13
7
9
12
8
11
9
13
28
Chapter 2 | Fibres
2.5 Flax
Flax, also known as linseed, is an upright annual
plant growing to 1.2 m tall with slender stems. It
consists a food and fibre crop that grows in cooler regions. The species is native to the region that
extends from the eastern Mediterranean, through
Western Asia and the Middle East, to India. However, the plant is cultivated also in other regions of the
world including most Europe.
The life-cycle of the plant is divided into twelve
growth stages, shown in the scheme 2.1, that are
spread in three periods: a 45-60 day vegetative period, a 15-25 day flowering period and a 30-40 day
maturation period.
Flax fibres are extracted from the bast or skin of the
stem of the plant. They exist into bundles of 10–40
fibres bonded together by pectin as shown in Fig.
1 and they are separated individually in order to
become functional. One general feature of all
natural fibres is their non-uniform geometrical characteristics. Flax fibres exhibit a polygonal shape in
cross-section with 5–7 sides and a non-constant
longitudinal view. On average, a fibre is 19 mm
in width and 33 mm in length, while the fibres are
thicker near the root and become thinner nearer
the tip. However, it is important to mention that
due to the dispersal of the geometrical dimensions,
the transverse and the longitudinal dimensions can
vary between 5–76 mm and 4–77 mm, respectively.
The microstructure of all natural fibres is extremely
complicated due to their hierarchical organisation
at different scales of observation and the different
stem
d = 2mm
bundle
d = 200mm
2.46 Distribution of flax global production (2005)
(http://www.jute.org)
2.47 Flax flowers
2.48 Harvested flax stalks
(http://www.csu.edu.au)
(http://www.bellavitabotanicals.com)
materials present in variable proportions. Under a
mesoscopic scale, an individual fibre consists of
two cell walls arranged as concentric cylinders with
a small channel in the middle, which is called lumen and contributes to the water uptake. The outer cell wall designed as the primary cell wall is only
0.2 mm thick while the bulk of the fibre is essentially
constituted by the layer S2 of the secondary wall
cell. In this layer, highly crystalline cellulose fibrils are
spirally wound, with a tilt angle of 10o, in a matrix
of amorphous hemicellulose and lignin. These spiral
fibrils give a unidirectional structure to the fibre, responsible for its tensile strength.
S1S1
10o10o
S2S2
S3S3
10o
cellulose
S2 Layer
d = 50nm
Secondary
Secondary
cell
cell
wall
wall
elementary fibre
d = 20μm
2.49 Flax structure from the stem to the cellulosic fibrils and structure of flax fibre cells
S4S4
Primary
Primary
cell
cell
wall
wall
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
2.50 Flax harvesting
2.51 Decortication of hemp
(http://www.theguardian.com)
(http://en.wikipedia.org/wiki/Hemp)
2.5.1 From plant to fabric
When the plant has grown 1m high and 30 days
have passed from flowering, it is ready to be harvested. Harvest requires the use of simple processes
based on pulling the plants and laying them on the
ground, operated either manually by labour and
animal power or by specific machinery. In general,
harvest time affects the quality and thus the properties of natural fibres. The longer the plant is left,
the coarser the fibre will be. Conversely, harvesting
a few days after flowering, the result will be a fine
flax fibre (Wildfibres, 2014).
After the crops have been harvested, retting of the
fibres follows. Retting is a process using the action
of moisture on plans in order to dissolve the “glue”
that bonds the individual fibres, which consists of
lignin and pectin, and so achieve separation of
the fibre from the stem. There are three ways for
retting fibres by using moisture, i.e. dew-, wet- and
strand retting and one method based on exposure
of the bundles of fibres to specific enzymes, such
as pectinase, that break down pectin. The most
widely used method is wet retting, which is a simple
placement of the fibres into water for
a period of a few
days.
1
2
3
cotyledon growfirst pair
ing
of
point
true
emerged leaves
unfolded
29
When the fibres have been retted and properly
dried, the next step is the decortication. Decortication is the process of separation of the individual
fibres from the core and is a basic common step
for all bast fibre plants, such as flax, hemp and jute.
Similarly with harvesting, the methods are divided
into manual and mechanical. The two main mechanical approaches to decortication are with a
roller breaker and hammer mill systems (Natural
capital resources Inc., 2014).
The fibres are cleaned by removing the shive and
then carding follows. Carding is a process operated
either mechanically or by hand, that aligns and intermixes the fibres, by brushing and combing them
with rollers, in order to produce a continuous web
or sliver suitable for processing. Then the produced
fibres are processed to spinning by getting twisted,
to form yarns and tows. In that form, yarns are a
preliminary product that can be subsequently used
for making weaved, knitted and braided fabrics.
2.52 Carding rollers
2.53 Carded flax fibres
(http://fibercrush.wordpress.com)
(http://www.discovershropshire.org.uk)
4
5
6
7
8
9
10
11
start
of leaf
spiral
stem
extension
buds
visible
first flower
early
branching
full flowercontinuation of
branching
late
flower
green capsulelower leaves
yellow
brown capsuleseeds light
brownbranches, stem
and upper
leaves
green/yellow
2.54 Main growth stages of flax
30
Chapter 2 | Fibres
2.6 Jute
Jute is an annual crop of the bast family that reaches its maximum height at 2,5 – 4m. It could never
grow in Europe, as the suitable climate for growing jute is the tropical (warm and wet), with temperatures from 20˚C to 40˚C and relative humidity
of 70% -80%. To achieve successful cultivation jute
requires 5–8 cm of rainfall weekly, and even more
during the sowing time. Therefore the ideal conditions are created during the monsoon season. Originally grown for centuries in India and Bangladesh,
global jute production is still concentrated in these
two countries.
The plant is ready to harvest in four to six months,
after the flowers are shed and the stems have
reached their maximum height. Jute fields may be
under water at the time of harvest and the workers
often need to wade in the water to cut the stems
at ground level or to uproot the plants. Usually, jute
is planned close together so that the plants grow
tall and straight. Unlike cotton, it has little need for
pesticides or fertilizers.
2.55 Distribution of jute global production
(http://www.jute.org)
Jute fibres are very long (1 to 4 metres), silky, soft,
shiny and golden brown in colour, that can be spun
into coarse, strong threads. The wide variety of uses
that jute fibres have, makes them second, after
cotton, most produced natural fibres.
Similarly with hemp, Jute can also have a beneficial effect to the soil that is cultivated. As it has little
need for fertilisers and pesticides, jute plants enrich
the soil with micronutrients that maintain soil fertility.
This property of jute combined with its short growth
cycle, makes the plant ideal for crop rotation,
which is an old practise of alternating deep-rooted
and shallow-rooted plants in order to improve soil
structure and fertility.
2.56 Harvested jute stalks
(http://celadonathome.com/)
2.57 Hessian jute fabric
(http://asiajute.com/)
Another important environmental impact of jute
plants is their ability to clean the air. Studies show
that during growth they assimilate several times
more CO2 than the average tree, converting the
CO2 into oxygen (Inagaki, 2000). Specifically, one
hectare of jute plants can consume about 15 tons
of CO2 from the atmosphere and release about 11
tons of oxygen in the 100 days of the growing season.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
31
2.7 Basalt
2.8 Glass
Basalt is a variety of hard and dense igneous volcanic rock that originally was created in a molten
state. Although 1/3 of Earth’s crust is covered with
basalt eruptive rocks and the availability from
mines and open-air quarries is high, only specific locations contain basalt suitable for fibre processing
because not all various chemical compositions satisfy the conditions for fibre preparation. Research,
production and marketing efforts regarding basalt
are based in the countries of the once aligned Soviet Union and China as within these regions the largest deposits are located.
Similar to basalt, glass fibre is an inorganic fibre produced from molten glass of specific composition
of sand, limestone, kaolin, calcium fluoride (fluorspar), boric acid, natrium sulfate, and clay. Different variations of the consisting materials result in
different types of glass can be produced. E-glass,
C-glass and S-, R-, T-glass are the types used mainly
for structural reinforcements, with E-glass being the
most commonly used. The letter that characterises
the various types, actually defines the specific field
in which the fibre shows exceptional resistance and
superiority. Thus, letter E (electrical) is used because
E-glass was originally used for electrical applications, C-glass (chemical) due to its best resistance
to chemical attack, A for alkali resistance and S for
high stiffness.
2.58 Molten volcanic rock
2.59 Basalt rocks
(http://www.physicalgeography.net/)
For many years, basalt has found application in the
building industry in tiles, slabs or liner in steel tubing.
For all these applications, manufacturing included
casting processes while in crushed form basalt finds
use as aggregate in concrete.
Only in the last decade, basalt has emerged as an
alternative of fibre reinforcement in composites.
Basalt fibre exhibits superior strength and stiffness,
while its highly resistance to fire, moisture, UV radiation, alkaline and acid make it a good candidate
for the use in fibre-reinforced composites.
Extraction of the raw material is achieved by typical mining operations (described in Chapter 3.4).
Crushed basalt is then loaded in melting furnaces,
from which thin filaments are extruded and processed to yarn and textile fabrication.
In general, E-glass shows good tensile and compressive strength as well as stiffness, good electrical
properties and relatively low cost. However, impact
resistance is relatively poor. Concerning durability,
E-glass has acceptable resistance in moisture, fire,
ultra-violet radiation, acids and weak alkalis.
Due to the high availability of the consisting materials, glass fibres are largely used as reinforcement
in FRP composites. The use of glass fibre products
includes many applications from simple heat insulation up to high technologies and space industry,
including also boats and ships, wings of wind turbines, automobile frames and floors, sports and
medical equipment.
2.61 Glass fibre woven reinforcement
(http://www.bikeoff.org/)
Production of glass fibre includes mixing of the
consisting materials and import into the melting furnace. The procedure of melting, which is similar to
basalt, produces molten glass which by extrusion
forms the filaments.
2.60 Global igneous provinces
(http://blogs.scientificamerican.com/)
32
Chapter 2 | Fibres
2.9 Mechanical comparison
As it was also mentioned in the section Mechanical
properties, one of the main drawbacks of naturally
occurring fibres is that they show much higher variability of their various parameters compared to their
synthetic counterparts. Chemical composition,
crystallinity, surface properties, diameter, cross-sectional shape, length, strength, and stiffness vary
from fibre to fibre as they depend on growth conditions, harvesting and processing. It is therefore very
difficult to achieve precise quality characterization
of these fibres as after repeated testings the results
deviate.
Another important reason for the large spread in
the mechanical properties of natural fibres is the
defects on the structure of the fibre. It is a general rule in materials science that defects determine
the mechanical properties of materials and so it
turns out to be equally true in the case of natural
bast fibres, such as flax, hemp and jute. Fig. 9 shows
examples of cross-marks (deformed zones), called
‘nodes’ or ‘dislocations’. During a tensile test, the
break often occurs where the defect is situated.
Defects in fibres are produced irreversibly either
during plant growth or during the decortication
process, thus they can be hardly controlled.
However, cellulosic fibres have an exceptional advantage over the conventional ones i.e. their low
density and thus their low weight. Table 2.3 (Lilholt
& Lawther, 2000) shows that the three researched
bast fibres are almost 40% lighter than glass fibres.
Therefore, although natural fibres’ mechanical
properties are much lower than those of glass, their
specific properties, especially stiffness, are comparable to the values of glass fibres.
Specific stiffness also known as the stiffness to weight
ratio or specific modulus is a materials property
consisting of the elastic modulus per mass density
of a material. High specific stiffness materials find
wide application in structures where primary design limitation is deflection or physical deformation,
rather than load at breaking and thus low structural
weight is required. Such “stiffness-driven” structures
include airplane wings, bridges, masts and bicycle
frames. Therefore it is highly important that flax fibres almost 1,5 times higher specific stiffness from
glass, hemp and jute.
Specific strength is a second important parameter
after specific stiffness and is the strength of the material divided by its density. Also known as strength
to weight ratio, high specific strength is needed in
applications, that permanent deformation or failure has to be avoided at low weight. As shown in
Table 2.3, natural fibres have lower specific strength
compared to glass. Specifically, flax that shows
again the highest values between the natural fibres
has almost 3 times less specific strength than glass
fibres.
Consequently, although flax fibres show the highest
potential to substitute glass fibres as reinforcement
in composite materials, they would not be suitable
for applications that require high load-bearing capacity due to their lower strength. However, in the
case of lightweight applications where the loads
are sufficient for the structure, flax fibres would consist a more rigid reinforcement with higher resistance to deformation than glass fibres.
2.62 Example of defects on flax fibres
2.63 Break area of a flax fibre after a tensile test
(http://sensiseeds.com)
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
33
Table 2.3 Mechanical properties of flax, hemp, jute, E-glass and basalt fibres
Properties
Fibre
Basalt
E-glass
Flax
Hemp
Jute
Modulus
(GPa)
Strength
(MPa)
Density
(g/cm3)
Specific
Modulus
Specific
Strength
90
72
50-70
30-60
20-55
1430-4900
2000-3500
500-900
300-800
200-500
2.67
2.54
1.4-1.5
1.48
1.3-1.5
33
28
~ 41
~ 30
~ 27
~ 1185
~ 1080
~ 480
~ 370
~ 250
2.10 Durability
2.10.1 Flammability
The flammability of the different types of fibres depends on their chemical composition and structure. Natural lignocellulosic fibres, being composed
of carbon, hydrogen and oxygen are characterized for their high sensitivity to heat, as carbon is a
main highly flammable element. Thus subjection
of plant fibres to a constant temperature of 180oC
can cause decrease of the mechanical properties
while temperatures above 200oC destroy completely the fibres. For that reason, during production
of natural fibre reinforced plastics, only short periods of exposure of the textiles to high temperatures
are allowed, while composite production temperatures higher than 180oC have to be avoided in
order to prevent degradation of fibres.
There are several ways to characterize the flammability degree of textiles. The most common method
is the Limiting oxygen index (LOI), which is the per
centage (%) of oxygen concentration required to
maintain steady burning. The LOI value is measured
by applying an oxygen/nitrogen-mix to the burning
sample. If the sample burns for longer than 180s or
the burning reaches a predefined mark, the oxygen level is gradually reduced. The LOI describes
the minimum concentration of oxygen in the oxygen/nitrogen-mix which supports combustion. Thus,
high LOI values mean good flame-retardancy. Specifically, fibres with LOI greater than 25 are said to
be flame resistant.
As natural lignocellulosic fibres prove to be the
most flammable, flame–retardant treatment has
to be applied on the textile prior to incorporation
in the matrix, in order to improve the fire resistance
of the reinforcement. Flame retardants are generally classified in non-durable, semi-durable and
durable. Non-durable flame retardants are usually
Table 2.4 Behavior in flame by fibres without flame-retardant treatment
Highly Flammable
■ Cellulosic fibers
(flax, cotton, jute)
Once alight, these
burn easily and so
can “propagate”
Intermediate
Less Flammable
■ Acetate, triacetate
■ Protein (wool, silk)
These melt as they
burn;
These do not ignite
easily;
burn slowly; tend to
self-extinguish, except
in very dry air or with
very open fabric.
■ Nylon, polyester,
olefin (polypropylene),
acrylic.
These do not ignite
easily
once ignited, burn and
most melt; tend to drip
(especially nylon); the
drops tend to carry
the flame away, so the
fabric self-extinguishes
in some situations
Flame Resistant
(LOI greater than 25)
■ Modacrylic, saran,
vinyon
These melt;
■ Aramid
These do not melt but
char’ tend to self-extinguish; give little smoke
■ Certain modifications
Some MF fibres are given flame resistance by
agents put in before
the fibre is spun
Non-flammable
■ Novoloid, polybenzimidazole (PBI)
These will not burn; do
not melt; char, but stay
intact
■ Inorganic fibers
(asbestos, glass, metal,
etc.).
These will not burn;
can melt, but at temperatures so high they
do not figure in textile
fire safety
34
Chapter 2 | Fibres
2.10.2 Moisture absorption and fibre-matrix adhesion
Major concern of utilizing natural fibres in biocomposites is their hydrophilic behavior due to their high
content of cellulose which makes them susceptible
to absorb water vapor from their environment. This
hygroscopic characteristic of natural fibres affects
the mechanical performance of the composites
adversely. Water inside the fibres molecules behaves like a plasticizer. It allows cellulose molecules
to move freely, which causes low elastic modulus
and tensile strength. The decrease in mechanical
property might be also because of fungus development due to internal moisture of fibre (Stamboulis et
al., 2001).
2.64 Limiting Oxygen Index (LOI) for different fibres
water-soluble inorganic salts which are inexpensive
and can be easily removed by washing or exposure to water. Thus they are applied to fibres that
are not going to be washed, such as batting for upholstered furniture and insulating fibres. The second
type is semi-durable, and can be removed after repeated laundering. Finally, durable fire retardants
are not affected by water.
There are several methods for applying flame-retardants on textiles, which are based on the four
theories for fire retardant mechanisms. These include thermal (reducing the thermal build-up of
a treated combustible), coating (via an insulating
coating that can melt over the fibre), gas (in which
non-flammable gases, like water or ammonia, are
released), and chemical (in which fire retardance
can be “grafted” to natural fibre or actually built
into products). Common methods of treating materials would be by water-soluble salt impregnation,
a purely physical method of depositing tiny crystals
on the fibre surface. There is also vacuum or pressure impregnation and coating ways to treat materials.
Latest advances in genetic engineering have created the opportunity to obtain transgenic cellulose
(flax, cotton, sisal, etc.) with built-in flame retardant groups inside the structure of cellulose or lignin.
These substitute hydroxyl groups, making cellulose
more flame resistant in its natural state.
Additionally, the hydrophilic nature of untreated
natural fibres results in insufficient compatibility between the fibres and the hydrophobic polymeric
matrix. Due to this poor adhesion between the
two materials, load transfer from matrix to fibres is
not good, which may lead to a low quality product that can meet bonding failure with age. One
the other hand, good adhesion usually reduces the
moisture sensitivity. Therefore, an understanding of
the hygroscopic properties of natural fibres is very
important to improve the long-term performance
of composites reinforced with these fibres.
Fibre surface treatment
To improve fibre-matrix adhesion chemical treatment of natural fibres is essential before they are
used as reinforcement. Chemical treatments clean
the fibre surface, modify the chemistry on the surface and reduce the moisture uptake. There are
different chemical treatments available for producing a good quality fibre. Mercerization (alkali
treatment), isocyanate treatment, acrylation, permanganate treatment, acetylation, silane treatment and peroxide treatment with various coupling agents and other pre-treatments are specific
methods that have achieved various levels of success for improving fibre strength, fibre fitness and
fibre-matrix adhesion(Cristaldi et al., 2010).
However, according to Cristaldi et al., (2010) it is
found that most of the chemical treatments may
decrease the fibre strength due to the extensive
delignification and degradation of cellulosic chains
during exposure to the chemical substances. Only
silane and acrylation treatment does not break the
bond structure, but creates strong covalent bonds,
which consequently enhances the stiffness of the
fibre. Another research on the effect of surface
treatment on the mechanical properties of flax fibres showed that silane, benzoylation and peroxide pre-treatment improved the surface properties
of the fibres and led to a higher tensile strength than
that of untreated flax (Wang et al., 2007). On the
contrary, it is proved that alkali treatment can pro-
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35
2.65 SEM micrograph of the untreated sugar palm fibre
(up)
2.66 SEM micrograph of the sea water treated sugar palm
fibre (down)
(In: Ishak, M. R., Leman, Z., Sapuan, S. M., Salleh, M. Y.,
& Misri, S. (2009). The effect of sea water treatment on
the impact and flexural strength of sugar palm fibre reinforced epoxy composites)
Drying phase
Fibres for further processing in biocomposites are
washed under water after surface treatment and
then dried, as moisture should be removed totally
from the fibre. Drying processes used are based on
removing moisture from the fibres through evaporation by means of heat. Temperatures should not
be very high during drying in order to achieve better fibre quality. If the temperature is high, it can
cause degradation of the material and reduction
in quality (Tripathy, 2009).
duce a drop in both tensile strength and Young’s
modulus of the fibres if a very high percentage
treatment is adopted. This result is attributed to the
damage induced in the cell walls and the excessive extraction of lignin and hemicellulose, which
play a cementing role in the structure of the fibres.
Main drying methods for natural fibres are convection drying and microwave drying. Other drying
methods, such as convection-microwave drying
and microwave-vacuum drying consist combinations of the previous processes. However, drying is
an energy consuming process which in addition
with chemical surface treatment it increases the
environmental impact and the cost of the natural
fibres.
Chemical treatments have also raised concerns
regarding their unsustainable and non-renewable
nature, their toxicity and relatively high price. These
reasons have forced scientists and engineers to
search solutions through biological methods that
substitute chemical treatment for fibre-matrix interfacial adhesion.
Ishak et al. introduce sea water treatment as a biologically based and sustainable low cost treatment
that has minimum environmental impact and is safer than chemical methods. The research that investigates the effect of the treatment on the flexural
and impact properties of palm fibre, proved that
sea water improved the surface morphology of the
fibres and thus the fibre-matrix interfacial bonding.
2.67 Untreated-undried flax fibres (right)
2.68 Silane treated- microwave oven dried flax fibres(left)
(In: Tripathy A. C. (2009) Characterization of Flax Fibres
and the Effect of Different Drying Methods for Making Biocomposites)
36
2.10.3 UV-radiation resistance
Durability of natural fibres under exposure to ultraviolent light is of particular concern. Apart from moisture, lignocellulosic materials tend also to efficiently
absorb sunlight which causes changes in the surface chemistry of the fibres and the resin, commonly known as photodegradation. According to
Dence (1992), photodegradation of natural fibres is
attributed to the degradation of its chemical structural components, and specifically lignin. Lignin
degrades upon exposure to UV- by the formation
of free radicals that cause oxidation of phenolic
hydroxyls. Moreover, singlet oxygen (O2) that can
be formed by oxygen quenching of photoexcited
lignin allows degradation of lignocellulosic natural
fibres. This happens because the formed singlet
oxygen is a source of peroxides, compounds that
contain oxygen, which can initiate the auto-oxidation of carbohydrates and fracture of lignin. The
degradation ranges from mere surface discoloration (light-induced yellowing) which is mainly observed in indoor applications and can even reach
loss of mechanical properties in outdoor conditions
where the combination of light, moisture and temperature can destroy the lignocellulosic network.
To increase the ultraviolent resistance of natural fibres, various treatments, either based on biological
processes or conventional chemical reactions, are
available to be applied. Sparavigna (2008) suggests plasma polymerization methods as multi-purpose solutions for textile treatment. Characteristics
that can be improved with plasma treatment include wettability, flame resistance, adhesive bonding, printability, electromagnetic radiation reflection, surface hardness, hydrophilic-hydrophobic
tendency, dirt-repellent and antistatic properties.
Chapter 2 | Fibres
Bio-based FRP pedestrian bridge in Schiphol Logistics Park
Life cycle assesment
11
38
Chapter 3 | Life Cycle Assesment
3.1 LCA approach
Life Cycle Assessment (LCA) is an environmental
assessment technique with which, environmental
aspects associated with the energy, materials and
emissions of a product or process over its life cycle are assessed. The energy analysis includes four
stages of a life cycle: material production phase,
manufacturing phase, use phase, and end-of-life
phase. The guidelines for an LCA study are defined
by international ISO standards that suggest the subdivision of the study in four phases:
1. The goal definition and scoping
Establishment of the aim and scope of the study
and clear definition of unit under examination and
the method followed including boundary conditions, assumptions and limitations, chosen impact
categories, type of information used and resources
of data.
2. Life cycle inventory analysis (LCI)
Development of an Inventory that is including flows
from and to nature (inputs, outputs) for a product
system.
3. Life cycle impact assessment (LCIA)
Evaluation of the significance of potential environmental impacts over the eight impact categories
listed in ISO/TR 14047:2003 (table 10).
4. Life cycle interpretation:
The results from the LCI and LCIA are summarized
including the outcome of the study in a set of conclusions and recommendations.
3.1.1 Goal of the analysis
The subject of this study is a comparative qualitative life cycle assessment (LCA) on four fibres that
can be used as reinforcement in fibre-reinforced
composites: flax, jute, glass and basalt. The goal of
the analysis is to draw conclusions in regards to the
energy consumption and the environmental impact of the production of these fibres by evaluating
their different production stages. As the fibres chosen are produced from renewable (flax, jute) and
non-renewable (glass, basalt) resources, the study
aims to prove whether this advantage of natural
fibres is followed by efficiency in energy consumption and low environmental impact. Used information and data are based on published sources,
such as researches and LCAs, whereas the Ecoinvent database provided significant data as well.
Table 3.1 The eight environmental impact classification factors (EICF) as outlined in ISO/TR 14047/2003 (2003).
Acidification
impact of acids that are emitted in the atmosphere and consequently deposited in
soil and water
Aquatic toxicity/
Ecotoxicity
consequence of high concentrations of chemicals in air, soil and water which is responsible for contamination of eco-systems
Human toxicity
consequence of high concentrations of chemicals in air, soil and water on human
health
Eutrophication
overfertilization of water and soil by excessive production of specific macronutrients
(mainly Nitrogen and phosphorus)
Global warming/
Climate change
effect of increased reflected heat radiation by greenhouse gases (CO2, N2O, CH4
and volatile organic compounds: VOCs)
Depletion of
resources
extensive consumption of abiotic non-renewable (mineral, fossil fuels and metal ores)
and biotic renewable resources (deforestation, fishing, farming)
Ozone depletion
reduction of ozone in the stratosphere which results in more ultraviolent rays reaching
Earth’s surface
Photochemical
Oxidants
Excessive ozone formation by the degradation of VOCs in the presence of sunlight
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
39
3.2 Flax/Jute Fibre
3.2.1 Agricultural operations
As it was also mentioned in 2.1.2 From Plant to
Fabric, flax fibre is the result of agricultural and fibre-processing process, which together with fertilizers and pesticides consist the primary energy consumption for fibre production. A typical production
cycle of flax fibres includes the stages shown in the
diagram 2.1. However, energy demand of some of
these stages varies depending on different specific methods that can be employed. For instance,
for ploughing (tillage) which prepares the land,
conventional tillage (full tillage program), conservation tillage (reduced number of passes) or no-till
can be used. Similarly, retting of the fibres includes
a wide range of techniques such as warm-water
retting, stand/de retting and bio-retting. Finally, the
extensive use of agricultural machinery and fertilizers/pesticides adds to the production cost and the
consumption of fuel. The table 1.1 shows the energy consumption of the agricultural operations of
flax crop production.
Fibre-processing
processes
Agricultural
processes
1. Tillage
2. Drilling (planting) the seed
3. Weed control
4. Plant growth
5. Desiccation
6. Harvest
7. Rippling
8. Retting
9. Scutching/decortication
10. Hacking
11. Carding
12. Spinning
3.1 production stages for flax fibers (Turner 1987)
Table 3.2 Energy Consumption of Flax Crop Production
Garcia-Torres et al. 2002; Hood and Kidder 1992; Kastens 1997;
Lazarus and Selley 2005; Molenhuis 2001; Downs and Hansen 2006; Dhuyvetter and Kastens 2005)
Agricultural operation
No. of
passes
Diesel
consumption
l/ha
Energy consumption
GJ/tonne of yarn
Ploughing Moldboard
Ploughing—chiselFlax
No-till pass
Harrowing
Cultivating
Applying fertilizer
Spraying pesticides
Spraying desiccant
Harvesting
Swather
Baler
1
1
1
1
1
3
3
1
1
1
1
15.2
9.0
0.9
5.9
4.9
17.4
3.9
1.3
6.3
4.7
3.9
2.3
1.4
0.2
0.9
0.7
2.6
0.6
0.2
1.0
0.7
0.6
3.2.2 Fertilizers and pesticides
The use of fertilizers and pesticides is common and mechanized practice for most agricultural crop production.
According to the Stern Review, fertilizer industry is the fifth most carbon- intensive industry and fourth in terms of
energy intensity, consuming 13.31%, after electricity production (26.70%), gas distribution (42.90%) and refined
petroleum (72.83%). Together with tillage operations, fertilizers and pesticides take about 70 % of the energy
required for crop production whereas fertilizer alone accounts about 40 % (Gautam, 1979). Amongst fertilizers,
nitrogen accounted for maximum energy input in crop production.
40
Chapter 3 | Life Cycle Assesment
Nitrogen (N), phosphorus (P2O3), and potassium
(K2O) are the main fertilizers used for flax. Nitrogen-bearing fertilizers are the most energy-intensive
input to modern agricultural production with values
that vary from from 80 GJ/tonne to 130 GJ/tonne,
whereas the energy required to manufacture phosphorus- or potassium-bearing materials is less per
unit weight of nutrient than nitrogen fertilizers (table
2)( Dissanayake et al, 2009). However, these energy amounts could be reduced by the partial substitution of synthetic fertilizers by organic manure.
High nitrate and phosphate emissions contribute
to increased eutrophication in local water-bodies
and soil as nitrogen and phosphate are main nutrients for algae growth. Excessive production of such
autotrophic microorganisms (algae, cyanobacteria) allows the increase of bacterial populations
that subtract large amounts of oxygen. Low oxygen levels cause extensive deterioration of water
quality which results in the loss of aquatic animals
and hence disruption of the ecosystem. According to the LCA carried out by Turunen and van der
Werf (2006, 2008), the nitrogen and phosphate
emissions from the soil contributed about 90% of
the global eutrophication with the remaining 10%
coming from diesel combustion in field operations.
Flax is a crop that does not compete well with
weeds, making essential an adequate weed control in order to obtain high yields. Weed control is
achieved through the application of herbicides.
Glyphosate (N-(phosphonomethyl)glycine) is a
broad-spectrum systemic herbicide used to kill
weeds. Pesticides are also products with high embodied energy, applied to protect the crop from
various insects-pests that may infest flax by the time
of emergence to maturity.
Finally, agricultural lime (CaCo3) is mainly used during land preparation in order to improve soil fertility
and plant growth by controlling pH level of the soil.
Adding the embodied energies of the mentioned
agrochemicals, gives an energy input that covers
more than 80% of the total energy in agricultural
operations of producing 1 tonne of flax yarn. However, as it was mentioned before there are alternative methods (manure as fertilizer, biological pesticides) for reducing these high energy amounts.
Table 3.3 Amount of Fertilizers and Pesticides Used and Embodied Energy
Dissanayake and Summerscales (2009)
Input
Lime
Ammonium nitrate
Triple superphosphate
Potassium chloride
Pesticides
Total
Ammount used
[kg/tonne of yarn]
Embodied energy in material
[GJ/tonne]
Embodied energy in yarn
[GJ/tonne]
2,45
445,0
238,0
368,0
9,40
1,44
66,0
14,0
9,0
240,0
3,52
29,37
3,33
3,31
2,26
41,79
3.2.3 Fibre-Processing Operations
Harvesting of the plants is followed by rippling which is the removal of the flax seed capsules from the stalks.
Nowadays, harvesters normally operate rippling during the harvest stage. After the crop is harvested retting is
the first process at the fibre processing facility. There are different retting processes with varying energy consumptions. Warm water-retting, dew-retting and bio–retting are three commonly used methods. Enzymes may
be also used to assist the retting process (Dissanayake and Summerscales, 2009).
Warm water-retting is the less energy consuming approach as the process is based on the establishment of good
growth conditions for the development of natural micro-organisms, that are present on the plant from its growth
stage and are responsible for retting the stalks by decomposing the pectin substances. However, the process generates a considerable amount of waste water (approximately94% of water used) which also contributes in water
eutrophication. Turunen and van der Werf (2006, 2008) found that water-retting of hemp has contributed 13% of
the total eutrophication, which is higher than other retting processes such as bio-retting and stand/dew retting.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
41
3.2 Processing of water retting in a concrete retting pool. The bales of hemp sheaves are placed in the pool and secured
with metal bars. The pool is filled with water and the stems are let in to ret for 5 days. (Van der Werf, H. M., & Turunen, L.,2008)
Bio-retting has the highest energy input in the fibre processing stage as it includes postharvest
field operations, scutching, rinsing, drying, and
mechanical softening in order to produce long
fibers. Drying of the fibres after retting stands out
as the most energy intensive part of the process.
The values of energy consumption for retting followed by scutching are shown in diagram below.
Hackling or carding is the process that refines the
raw fibre bundles that are in a form of coarse
strands to produce sliver (see From plant to fabric).
Textile sliver will be prepared for rove, bleached,
and finally spun to produce yarn.
Abiotic
depletion
Terrestrial
ecotoxicity
warm water
retting
stand/dew
retting
herbicides
retting process
Acidification
Land use
Eutrophication
bio-retting
Global Warming
Photochemical
Oxidants
3.3 Energy consumption in different retting and subsequent scutching processes
(Turunen and van der Werf 2006, 2008).
Retting is followed by scutching or decortication,
a mechanical operation that breaks the woody
core of the stems into small pieces (shives) without
breaking the fibre and separates short tow fibres
from long fibres by beating the broken stem with
rotating blades (Turunen and van der Werf 2006,
2008).
Fresh water
aquatic ecotox.
Ozone Depletion
Human Toxicity
Hackled flax
Scutched flax
3.4 Influence of the hackling process on flax fibre environmental impacts
(Le Duigou, Davies and Baley, 2011)
Table 3.4 Comparison of environmental impacts for the production of hackled flax fibres and jute fibres.
Impact category
Acidification Potential [kg SO2 eq]
Aquatic Toxicity Potential [kg 1,4 DCB eq]
Eutrophication Potential [kg PO4 eq]
Global Warming Potential [kg CO2 eq]
Human Toxicity Potential [kg 1,4 DCB eq]
Non-Renewable/Abiotic Resource Depletion [kg antimony eq]
Ozone Depletion Potential [kg CFC 11 eq]
Photochemical Oxidants Creation Potential [kg formed ozone]
Land Use [m2/years/kg]
1
Hackled flax
Jute fibre1
(Le Duigou et al.)
(Ecoinvent data)
2,20 10-2
5,90 10-2
1,40 10-3
1,40
2,10 10-1
11,70
2,40 10-8
7,30 10-5
8,40 10-1
9,89 10-3
7,89 10-2
7,35 10-3
7,94 10-1
1,10 10-1
1,34 10-3
2,68 10-8
6,82 10-5
1,98
Mainly manual cultivation of Jute from conventional production standards. Included steps are soil cultivation, pestizides fertilisation (mineral fertilizer), harvest, loading for transport and extraction of the fibres after retting process (hackling is not included)
42
Chapter 3 | Life Cycle Assesment
Spinning is a major step in the fibre production process that produces filaments or yarns by twisting
the slivers. The total environmental impact of a yarn
increases significantly after spinning as the process
requires large amounts of electric energy. Spinning techniques of bast fibres are generally classified into wet and dry spinning (Dissanayake and
Summerscales, 2013). Nowadays, wet ring spinning
is mainly operated rather than other techniques
(open end rotor spinning and vortex spinning) due
to the good quality of yarns, suitable for textile applications. (Turunen and van der Werf ,2006). 4
short fibre and shives, produced from scutching
and hackling processes and used as animal bedding or in paper production. Dust that is also produced by these processes can be collected and
consolidated as biomass fuel. The diagram below
shows the mass reduction of flax fibre processing
from cultivation until the step of hackling.
Table 3.5 Energy Consumption of Fibre-Processing
Operations
Turunen and van der Werf (2006, 2008)
Processes
Energy consumption
[GJ/tonne of yarn]
Warm-water retting
Scutching
Hackling
Wet spinning
0,59
9,39
2,23
23,90
3.6 Diagram of flax fibre production, from the plant to the
co-products, with yields (kg/ha)
(Le Duigou, Davies and Baley, 2011)
Agricultural
operations
9%
Spinning
28%
Hackling 2%
Scutching
11%
Fertilizers
pesticides
49%
Warm-water
retting
1%
The main environmental impact of flax and jute fibre production is caused by the emission of greenhouse gasses during agricultural operations and
fibre-production, the high nitrate and phosphate
emissions by fertilizers and pesticides whereas extensive land use is also considered to have negative consequences to the environment. Primary
sources of greenhouse gasses in the context of production of fibers include the following:
•
•
3.5 InTotal energy used in production of flax yarn
•
At the end of each process, total mass is reduced due
to the production of co-products. As reported in the
environmental impact analysis of the production of
flax fibre by Dissanayake and Summerscales (2013),
twenty-two tonnes of dry, green flax stems produce 1
tonne of flax yarn. Extensive loss of mass occurs by retting
process in which the pectin substances are being decomposed. Co-products of bast fibre production are
•
•
•
Energy used to power agricultural equipment
Energy used to produce and apply fertilizers
and pesticides
Releases of CO2 from decomposition and oxidation of soil organic carbon (SOC) following
soil disturbance
CO2 and CH4 (methane) from retting
Energy used in fibre-production processing
Emissions resulting from transport for both types
of fibre
Though, agricultural activity poses a positive environmental effect regarding global warming and
climate change, which is the sequestration of CO2
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
from the atmosphere by the process of photosynthesis. Photosynthesis allows plant growth by consuming CO2 from the atmosphere and converting
it by using solar energy to carbon in order to build
the plant skeleton.
43
production process or as shipping of final products.
Optimization of transport distances between the
different production units would reduce the embodied energy and CO2 emissions. Yet, shipping
which is a one of the largest sources of man-made
CO2, could be avoided by orienting textile or fibre-reinforced plastic production to locally available fibres or textiles. Environmental cost by extensive transportation is a main week point of jute fibre
which grows only under the conditions of the tropical climate, in comparison with flax which is cultivated and processed in Europe.
As previously stated eutrophication of local water
bodies is a serious environmental impact of conventional agricultural activities that are supported
by extensive synthetically-produced fertilizing (nitrogen, phosphorus, potasium-bearing fertilizers).
Apart from the effect of fertilizing in water quality,
soil pollution can be extensive, as well. In the study
of Corbiere-Nicollier et al. (2001), cultivation of China reed, a bast-fibre crop cultivated for its fibre,
had a dominant role effect to terrestrial ecotoxicity and human toxicity when cultivation of edible
crops followed the reed in crop rotation system.
3.2.4 Fabric production
Weaving and knitting are the two main methods
for producing technical textiles and apparel fabrics
from yarn. Weaving involves the interlacing of the
yarns at right angles and in the technical textile industry it is used to create woven fabrics with different weaving patterns such as plain, twill or satin (see
2.3 Textiles). Knitting, which is based on looping the
yarn around and through one another, is used for
producing unidirectional and multiaxial textiles that
are primarily used in fibre-reinforced polymes. In this
knitting technique the yarns are maintained parallel
and uncrimped by being knitted by a flexible stich.
Tillage is another influential factor for soil quality.
West and Marland (2002) stated that following notill
method, the minimum tillage route, together with
other practices such as efficient use of pesticides,
irrigation, and heavy agricultural machinery, maintains the existing CO2 storage in soil, enhances soil
quality and decreases CO2 emissions.
Spinning
Land use (7 months per year for flax) is another inherent aspect of agricultural production that results
in gradual reduction of habitats and biodiversity.
Deforestation is a main consequence of increased
on-land activity for agricultural or other activity.
One solution that Le Duigou (2011) suggest for land
use reduction is the improvement of production
yields.
Land clearance
Land clearance
Ploughing
Ploughing
Land clearance
Sowing
Sowing
Ploughing
Water
Water
Sowing
Herbicides
Herbicides
Water
Pesticides
Pesticides
Herbicides
Fertiliser
Fertiliser
Pesticides
Dessication
Dessication
Fertiliser
Harvest
Harvest
Dessication Rippling
Rippling
Harvest
Rettimg
Rettimg
Rippling
Decortication
Decortication
Rettimg
Hackling
Hackling
Decortication Carding
Carding
Hackling
Spinning
Spinning
Carding
Non-Renewable/Abiotic
Resource
Depletion
(NRADP)
Non-Renewable/Abiotic
Non-Renewable/Abiotic
Resource
Resource
Depletion
Depletion
(NRADP)
(NRADP)
Ozone
Depletion
Potential
(ODP)
Ozone
Ozone
Depletion
Depletion
Potential
Potential
(ODP)
(ODP)
Photochemical
Oxidants
Creation
Potential
(POCP)
Photochemical
Photochemical
Oxidants
Oxidants
Creation
Creation
Potential
Potential
(POCP)
(POCP)
Noise
and
Vibration
Noise
Noise
and
and
Vibration
Vibration
Odour
Odour
Odour
Loss
of
biodiveristy
Loss
Lossofofbiodiveristy
biodiveristy
3.7 Trade off matrix of the environmental impact of the agricultural operations and fibre-production processes for flax fibre
(Dissanayake and Summerscales, 2009)
Very high effect
Very
Veryhigh
higheffect
effect
Low
effect
Low
Low
effect
effect
No
effect
No
No
effect
effect
No effect
Low effect
Very
high effect
No effect
Low effect
Global
Warming
Potential
(GWP)
Global
Global
Warming
Warming
Potential
Potential
(GWP)
(GWP)
Human
Toxicity
Potential
(HTP)
Human
Human
Toxicity
Toxicity
Potential
Potential
(HTP)
(HTP)
Loss of biodiveristy
Very high effect
Aquatic
Toxicity
Potential
(ATP)
Aquatic
Aquatic
Toxicity
Toxicity
Potential
Potential
(ATP)
(ATP)
Eutrophication
Potential
(EP)
Eutrophication
EutrophicationPotential
Potential(EP)
(EP)
No effect
Environmental
Impact
Classification
Factor
Environmental
Environmental
Impact
Impact
Classification
Classification
Factor
Factor
Acidification
Potential
(AP)
Acidification
AcidificationPotential
Potential
(AP)
(AP)
Low effect
Environmental Impact Classification Factor
Land clearance
Acidification Potential
(AP)
Land
Landclearance
clearance
Ploughing
Environmental Impact
Classification
Factor
Aquatic
Toxicity Potential
(ATP)
Ploughing
Ploughing
Sowing(EP)
Eutrophication
Sowing
AcidificationPotential
Potential
(AP)
Sowing
Water
Global
Warming
Potential
(GWP)
Environmental
Impact
Classification
Factor
Aquatic
Toxicity
Potential
(ATP)
Water
Water
Herbicides
Human
Toxicity
Potential
(HTP)
Eutrophication
Potential
(EP) (AP)
Herbicides
Acidification
Potential
Herbicides
Pesticides
Non-Renewable/Abiotic
Resource
Depletion
(NRADP)
Global
Warming
Potential
(GWP) (ATP)
Aquatic
Toxicity
Potential
Pesticides
Pesticides
Fertiliser
Ozone
Depletion
Potential
(ODP)
Human
Toxicity
Potential
(HTP) (EP)
Eutrophication
Potential
Fertiliser
Fertiliser
Dessication
Photochemical OxidantsResource
Creation
Potential
(POCP)
Non-Renewable/Abiotic
Depletion
(NRADP)
Global WarmingDessication
Potential
(GWP)
Dessication
Harvest
Ozone Depletion
Potential
(ODP) (HTP)
Human Toxicity
Potential
Harvest
Harvest
Rippling
Noise
and
Vibration
Non-Renewable/Abiotic
Resource
Depletion
(NRADP)
Photochemical
Oxidants Creation
Potential
(POCP)
Rippling
Rippling
Odour (ODP)
Ozone DepletionRettimg
Potential
Rettimg
Rettimg
Loss ofand
biodiveristy
Decortication
Noise
Vibration
Photochemical Oxidants Creation
Potential
(POCP)
Decortication
Decortication
Hackling
Odour
Hackling
Hackling
LossNoise
of biodiveristy
Carding
and Vibration
Carding
Carding
Spinning Odour
Spinning
Spinning
Very high effect
Loss of biodiveristy
Low effect
Finally, another crucial factor with significant environmental impact is transportation either as transfer
of raw material and primary products during the
No effect
Very high
effect
As both weaving and knitting are mechanical processes, energy consumption is a significant parameter. Main factors that influence the energy intensity
of these operations and result in different values are
the energy requirements of the machinery or alter
native techniques and the quality of the yarn. The
table below shows different values of the energy
intensity of weaving, whereas graph 2.65 shows
the environmental impact of jute textile compared
with jute yarn and jute fibre.
44
Chapter 3 | Life Cycle Assesment
However, apart from energy use, weaving involves another environmental concern: prior to the actual weaving
the warp is treated by sizing agents that are applied in order to lubricate and protect the warp during weaving.
These agents are removed by a finisher after the end of the operation. According to Turunen and van der Werf
(2006), the environmental impact of this finishing step is associated with emissions to water by the employment
of chemicals and auxiliaries (1kg per kg of processed textile).
100%
90%
80%
70%
60%
50%
40%
30%
20%
jute
textile
Source
jute textile
20%
40%
60%
jute yarn
Energy consumption
80%
100%
[GJ/tonne]
Koç & Çinçik
Pandita et. al.
Turunen & van der Werf
18
30
15-27
Ozone Depletion
Global Warming
Eutrophicationl
Photochemical Oxidants
Creation
jute fibre
Non-Renewable/
Abiotic Resource Depletion
Table 3.6 Different published values of weaving
energy consumption
Aquatic Toxicity
0%
Human Toxicity
10%
Acidification
It becomes clear that calculating the embodied
energy and the environmental impact of a product is a complex procedure that requires detailed
knowledge of all the energy inputs and co-product
outputs. Alternative techniques, different energy resources (nuclear, fossil fuel, renewable), production
of co-products and the analysis method followed
are some of the parameters that create a significant deviation between the published values. Table 2.1 shows different published values of flax and
jute products. It is noticeable that the results of Dissanayake et al. indicate much higher non-renewable energy consumption values, around 59 GJ/T
for flax fibre. This difference can be attributed to
the lower production yield used (6000 kg/ha compared with 7500 kg/ha used in the study of Turunen
and van der Werf), the different energy source (for
instance French energy has a high percentage of
nuclear energy compared to United Kingdom) and
the fact that the co-products are considered as
waste products.
3.8 Comparison in environmental impact of jute fibre, yarn
and textile production process (Ecoinvent database)
The values of each production step are added to the values of the following production step.
Table 3.7 Different published values of flax and jute products
Source
Product
Energy consumption
[GJ/tonne]
Flax fibre (sliver)
Flax yarn
59,3
85,4
Turunen & van der Werf
Hackled flax fibres
11,7
González-García et. al.
Flax sliver
12,4
CES EduPack 2014 (Granta Ltd)
Flax sliver
Jute yarn
10,5 - 11,6
30,3 - 33,5
Jute sliver
Jute yarn
Jute textile
2,83
24,9
30,5
Dissanayake & Summerscales
Ecoinvent database
jute
yarn
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
45
3.3 Glass fibre
furnace
refiner
molten glass
raw material storage
forehearth
1260oC
1340oC
bushing
cooled air
spray
1370oC
water spray
T < 100oC
surface
coating
coating applied
3.3.1 Raw material extraction
Although there is wide variety of different forms of
glass fibres, 95% of all reinforcements are E-glass.
The composition of these fibres consists of the following minerals (Net Composites, undated):
• Sand - particles of minerals including quartz (silica:
SiO2), mica (complex silicates usually with K, Na, Li,
H, and Mg), and feldspar (aluminum silicates with
varying amounts of K, Na, Ca, and Ba). Although
sand used in glass fibre production is an abundant
and naturally occurring raw material, it should be
considered as a non-renewable resource and be
conserved by reduced use (Waste & Resources Action Programme 2006).
• Kaolin - hydrated aluminum silicate (Al2O3•2SiO2•2H2O)
• Limestone - mostly calcium carbonate (CaCO3)
with other oxides (Si, Al, Fe), carbonates (Fe, Mg),
and calcium phosphate
• Colemanite - hydrated calcium borate (2CaO•
3B2O3•5H2O) (Tottle 1984).
After extraction, the raw materials are transported
either by rail car and track or by drums and packaged, depending on the volume of the supply.
The materials are unloaded by various methods,
including drag shovels, vacuum or vibrator/gravity
systems and conveyed to storage piles and silos by
belts and bucket elevators. The next step is weighing of the material in order to achieve the exact
quantities of the ingredients that the product recipe requires prior to mixing (batching). Batching is
an automated process, using computerized weighing units and enclosed material transport systems.
After well blending of the materials, they are processes into the melting unit. Weighing, mixing, and
charging operations may be conducted in either
batch or continuous mode.
winding
3.9 Glass fibre production processes
3.3.2 Fibre processing operations
Melting of the raw material into high-temperature
glass melting furnaces follows after mixing. Melting
furnaces are normally large, shallow, and well-insulated vessels that are heated from above. Temperatures ranging from 1500 to 1700°C heat and transform
the raw material through a sequence of chemical
reactions into molten glass. In operation, raw materials are introduced continuously on top of a bed
of molten glass, where they slowly mix and dissolve.
Mixing is effected by natural convection, gases rising
from chemical reactions, and, in some operations, by
air injection into the bottom of the bed.
Table 3.8 Energy Consumption of glass fibre Glass
fibre mat production
Diener and Siehler (1999)
Processes
Raw materials
Mixture
Transport
Melting
Spinning
Mat production
Total
Energy consumption
[GJ/tonne]
1,70
1,00
1,60
21,50
5,90
23,00
54,70
46
Chapter 3 | Life Cycle Assesment
There are four different types of glass melting furnaces, depending on their fuel source and heat
application, known as: recuperative, regenerative,
unit, and electric melter. The recuperative, regenerative, and unit furnaces can be fueled by either
gas or oil. Recuperative furnaces use a steel heat
exchanger, recovering heat from the exhaust gases by exchange with the combustion air. Regenerative furnaces use a lattice of brickwork to recover
waste heat from exhaust gases, whereas electric
furnaces melt glass by passing an electric current
through the melt. Finally, unit melters are used only
for melting glass by operating the “indirect” glass
marble melting process, a process in which molten
glass is sheared and rolled into marbles.
Molten glass in extruded through microfine bushings in order to produce filaments of 5–24 μm in diameter (Net Composites, undated). Bushing plates
are heated electronically, and their temperature
is precisely controlled to maintain a constant glass
viscosity. As the filaments exit the bushing plate with
a temperature of approximately 1204oC, they are
cooled down by water jets, a process called attenuation. Then the molten streams are drawn by
a high-speed winder which revolves them at a circumferential speed of ~2 miles/~3 km per minute.
As this speed is much faster than the speed that
molten glass exits the bushings, tension is applied
by the winder, which is drawing molten glass into
thin filaments.
The final stage of the fibre production includes surface treatment with the application of chemical
coating. This coating or size is typically added at
0.5 to 2.0 percent by weight and may include lubri
cants, binders and coupling agents. The lubricants
are applied on fibres produced for technical textile
used as reinforcement as they protect the filaments
from abrading and breaking during collection and
wounding into packages and, later, during weaving or other fabric production processes. Coupling
agents are usually organofunctional silanes that
make the fibre more compatible with particular
resin chemistry, improve resin wet-out and promote
fiber-matrix adhesion.
3.10 Cooling down of molten glass filaments by water jets
(http://binaniindustries.com)
It is noticeable that production of glass fibre involves energy-consuming processes. Considering
the environmental impact of the production of
glass fibre the primary sources of greenhouse gases
during the process include the following: (Dissanayake and Summerscales, 2009):
•
•
•
Energy used in glass melting and spinning
Energy used in fiber forming and curing
Emissions from glass melting, VOCs, raw material particles, and small amounts of CO, NOx,
SOx, and fluorides
Table 3.9 Different published values of glass fibre and glass fibre mat energy consumptions
Source
Product
Energy consumption
[GJ/tonne]
Le Duigou et. al.
glass fibre mat
45
Diener & Siehler
glass fibre
glass fibre mat
25,8
54,7
Corbiere-Nicollier et. al.
glass fibre
48,33
Song et. al.
glass fibre
13 – 32
CES EduPack 2014 (Granta Ltd)
glass fibre
62,2 - 68,8
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
47
Table 3.10 Comparison of environmental impacts of sand extraction and the production of glass fibres
Le Duigou, Davies & Baley (2011), Ecoinvent database
Impact category
Acidification Potential [kg SO2 eq]
Aquatic Toxicity Potential [kg 1,4 DCB eq]
Eutrophication Potential [kg PO4 eq]
Global Warming Potential [kg CO2 eq]
Human Toxicity Potential [kg 1,4 DCB eq]
Non-Renewable/Abiotic Resource Depletion [kg antimony eq]
Ozone Depletion Potential [kg CFC 11 eq]
Photochemical Oxidants Creation Potential [kg formed ozone]
Land Use [m2/years/kg]
Sand extraction1
Glass fibre
1,51 10-5
6,79 10-4
2,34 10-5
2,53 10-3
1,94 10-3
1,62 10-5
2,82 10-10
4,91 10-7
4,89 10-4
1,60 10-2
1,70 10-1
1,20 10-3
2,65
9,10
45,00
2,00 10-7
6,0010-4
7,00 10-3
1
Includes the whole manufacturing process for digging of gravel round and sand (crushing not included), internal processes
(transport, etc.), and infrastructure for the operation (machinery)
Emissions, such as are fugitive dust and raw material particles, are also generated during raw materials handling phase at the transfer points. Such a
point would be where sand pours from a conveyor belt into a storage silo. In order to control such
emissions, wet or moist techniques and fabric filters
are employed. Emissions during glass melting and
refining include, volatile organic compounds from
the melt, raw material particles entrained in the
furnace flue gas, and, if furnaces are heated with
fossil fuels, combustion products. Furnaces using
electric energy generally have the lowest emission
rates in comparison with other furnaces, due to the
lack of combustion products. Variation in emission
rates among furnaces is based on the operating
temperatures, raw material compositions, fuels, and
flue gas flow rates. Emission control for furnaces is
primarily achieved by fabric filtration.
biotic resources. According to Van Oers et al. (2002)
the relative contribution to the depletion of abiotic
resources by the extraction of the consisting materials of glass fibre, is low due to the abundance of
these elements. However, such on-land operations
affect biotic resources through reduction of natural
habitats and biodiversity.
Glass fibre production may involve significant transport distances between the raw materials source,
the industrial-scale production unit and the customer. Diesel used in transportation and running
machinery has potential contaminants of concern
including carbon monoxide (CO), nitrogen dioxide
(NO2), and sulfur dioxide (SO2). The direct impacts
of these gases and pollutants include toxicity, global warming, acidification, human toxicity and ozone
layer depletion.
Very
high
effect
3.11 Trade off matrix of the environmental impact Very
of
the
fibre-production
processes of glass fibre
high
effect
Very
high
effect
Low
effect
(Dissanayake and Summerscales, 2009)
Low
Loweffect
effect
No
effect
No
Noeffect
effect
No effect
Low effect
Very
high effect
No effect
Low effect
Environmental Impact Classification Factor
Raw
material
handling
Rawmaterial
material
handling
Raw
handling
Acidification Potential
(AP)
Raw
material
storage
Raw
material
storage
Raw material
storage
Environmental Impact
Classification
Factor
Aquatic
Toxicity Potential
(ATP)
Crushing
Crushing
Crushing
Eutrophication
AcidificationPotential
Potential(EP)
(AP)
Weighing
Weighing
Weighing
Global
Warming
Potential
(GWP)
Environmental
Impact
Classification
Factor
Aquatic
Toxicity
Potential
(ATP)
Mixing
Mixing
Mixing
Human
Toxicity
Potential
(HTP)
Eutrophication
Potential
(EP) (AP)
Acidification
Potential
Melting
Melting
Non-Renewable/Abiotic
Resource
Depletion
(NRADP)
Melting
Global Aquatic
WarmingToxicity
Potential
(GWP) (ATP)
Potential
Refining
Refining
Ozone
Depletion
Potential
(ODP)
Refining
Human
Toxicity
Potential
(HTP) (EP)
Eutrophication
Potential
Forming
Forming
Photochemical OxidantsResource
Creation
Potential
(POCP)
Forming
Non-Renewable/Abiotic
Depletion
(NRADP)(GWP)
Global Warming
Potential
Sizing
Sizing
Ozone Depletion
Potential
(ODP) (HTP)
Sizing
Human Toxicity
Potential
Binding
Noise
and
Vibration
Binding
Binding
Non-Renewable/Abiotic
Resource
Depletion
(NRADP)
Photochemical
Oxidants Creation
Potential
(POCP)
Spinning
Odour (ODP)
Spinning
Ozone DepletionSpinning
Potential
Loss ofand
biodiveristy
Oven
Dtrying
Noise
Vibration
Oven
Dtrying
Oven
Dtrying
Photochemical Oxidants Creation
Potential
(POCP)
Oven
Curing
Odour
Oven
Curing
Oven Curing
LossNoise
of biodiveristy
Fabrication
and Vibration
Fabrication
Fabrication
Packaging
Packaging
PackagingOdour
Very high effect
Loss of biodiveristy
Low effect
Land clearance
Land clearance
Ploughing
Ploughing
Land clearance
Sowing
Sowing
Ploughing
Water
Water
Sowing
Herbicides
Herbicides
Water
Pesticides
Pesticides
Herbicides
Fertiliser
Fertiliser
Pesticides
Dessication
Dessication
Fertiliser
Harvest
Harvest
Dessication Rippling
Rippling
Harvest
Rettimg
Rettimg
Rippling
Decortication
Decortication
Rettimg
Hackling
Hackling
Decortication Carding
Carding
Hackling
Spinning
Spinning
Carding
Noise
and
Vibration
Noise
Noiseand
andVibration
Vibration
Odour
Odour
Odour
Loss
of
biodiveristy
Loss
Lossof
ofbiodiveristy
biodiveristy
Fugitive
Dust
Fugitive
FugitiveDust
Dust
Loss of biodiveristy
Non-Renewable/Abiotic
Resource
Depletion
(NRADP)
Non-Renewable/Abiotic
Non-Renewable/AbioticResource
ResourceDepletion
Depletion(NRADP)
(NRADP)
Ozone
Depletion
Potential
(ODP)
Ozone
Depletion
Potential
Ozone Depletion Potential(ODP)
(ODP)
Photochemical
Oxidants
Creation
Potential
(POCP)
Photochemical
PhotochemicalOxidants
OxidantsCreation
CreationPotential
Potential(POCP)
(POCP)
Very high effect
Global
Warming
Potential
(GWP)
Global
GlobalWarming
WarmingPotential
Potential(GWP)
(GWP)
Human
Toxicity
Potential
(HTP)
Human
HumanToxicity
ToxicityPotential
Potential(HTP)
(HTP)
No effect
Aquatic
Toxicity
Potential
(ATP)
Aquatic
AquaticToxicity
ToxicityPotential
Potential(ATP)
(ATP)
Eutrophication
Potential
(EP)
Eutrophication
Potential
Eutrophication Potential(EP)
(EP)
Low effect
Environmental
Impact
Classification
Factor
Environmental
EnvironmentalImpact
ImpactClassification
ClassificationFactor
Factor
Acidification
Potential
(AP)
Acidification
AcidificationPotential
Potential(AP)
(AP)
No effect
Very high
effect
Spinning
Soil erosion and compaction is an issue associated
with dredging operations in sand extraction. These
on-land activities result in depletion of abiotic and
48
Chapter 3 | Life Cycle Assesment
3.4 Basalt fibre
3.4.1 Raw material extraction
Due to its natural origin basalt is found in different compositions and classified according to the
content of SiO2. Thus only compositions with SiO2
content about 46% (acidic basalts) are adequate
for producing continuous filaments. After the rocks
are extracted, quarried basalt is crushed on site
into smaller particles (5-20 mm) by mobile crushing
equipment.
Crushing is normally processed into two steps: primary and secondary. Quarried basalt is fed towards the jaw crusher by vibrating feeder in order
to operate a primary crushing. Soon after the initial
crush, the stones are transferred by belt conveyor to a cone crusher for the secondary crushing.
Then the particles that meet the size requirements
are washed, loaded and transported to be stored
otherwise they are processed again to the cone
crusher.
3.12 Basalt three-stage crushing line
(http://stonecrusherplantquote.com)
3.4.2 Fibre processing operations
Similar to glass, basalt fibre is produced in a continuous process. Crushed raw material is transported
into the melting furnace by a loader. However, in
contrast to glass fibre which consists of several elements that are mixed in the melting furnace, basalt
has a simple composition that requires no secondary materials, thus the single feed line carries only
crushed basalt. This contributes in shortening the
entire process as prior preparation of various ingredients by weighting and mixing is not needed.
Inside the furnace basalt reaches its melting point
at 1500oC (Ross, A., 2006). Molten basalt is non-homogeneous in nature and shows non-uniform
temperature distribution during production stage.
Additionally, unlike transparent glass, opaque
basalt absorbs infrared energy rather than transmits. These properties make difficult the uniform
heat distribution by conventional glass furnaces
as the material has to stay in the furnace for extended periods of time in order to ensure uniformity. Therefore, basalt producers have developed
several strategies including the immersion of electrodes in the bath or division of melting process
into separate heating zones. According to Nefedov (2014) electroarc basalt melting furnaces
have average power expenses 25,5 GJ/tonne.
After molten basalt is evenly heated, continuous
filaments with diameter 9~15 microns are formed
by passing through platinum alloy holes of bushing. The filaments are then drawn from the melt
and lubricated with silane-based sizing agents for
Table 3.11 Environmental impact of basalt Mining Stage/Crushing/Washing/Classification
Ecoinvent database
Impact category
Acidification Potential [kg SO2 eq]
Aquatic Toxicity Potential [kg 1,4 DCB eq]
Eutrophication Potential [kg PO4 eq]
Global Warming Potential [kg CO2 eq]
Human Toxicity Potential [kg 1,4 DCB eq]
Non-Renewable/Abiotic Resource Depletion [kg antimony eq]
Ozone Depletion Potential [kg CFC 11 eq]
Photochemical Oxidants Creation Potential [kg formed ozone]
Land Use [m2/years/kg]
Basalt
6,62 10-5
2,14 10-3
1,12 10-4
7,86 10-3
9,70 10-3
5,26 10-5
6,78 10-10
1,13 10-6
8,08 10-3
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
lubricity, integrity and resin compatibility. Finally, filaments are taken by the winders, by which rovings
of continuous basalt fibre are formed. As reported
by the Italian national agency for new technologies energy and sustainable economic development (enea) in 2011, the total energy requirement
for the production of basalt fibre is 17,85 GJ/tonne.
49
Easy recyclability is another dominant characteristic over glass fibres. Basalt fibres have excellent
thermal properties compared to that of E-glass and
can easily withstand the temperature of 1100oC
– 1200oC for hours continuously without physical
damage as the melting point is reached at about
1400°C. This exceptional resistance to fire allows for
extraction of fully usable basalt after incineration of
a composite material. In the contrary, a principal
problem of glass fibre recycling is that they melt
during incineration, sticking to the inside of the incineration chamber.
Concerning environmental impact, basalt fibre
poses a strong characteristic compared to glass.
Having a natural origin, basalt fibre is non-toxic,
which consequently results in low values of human,
terrestrial and aquatic toxicity. In contrast, glass
fibre is linked with hazardous health effects. This is
also proved in the life-cycle assessment performed
by the Flemish Institute for Technological Research
(VITO) in Belgium in collaboration with Basaltex, a
Belgian company that produces technical basalt
textiles. The result of this assessment, shown below,
presents a significant difference between the impact of basalt and that of glass regarding factors
that are linked with toxicity.
3.13 Comparative environmental impact of basalt roving fibres and glass fibre
(Flemish Institute for Technological Research (VITO) & Basaltex, 2011)
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
Basalt fibres
Glass fibres
Fossil depletion
Metal depletion
Water depletion
Natural land transformation
Urban land occupation
Agricultural land ecotoxicity
Marine ecotoxicity
Freshwater ecotoxicity
Terrestrial ecotoxicity
Marine eutrophication
Freshwater eutrophication
Terrestrial acidification
Particulate matter formation
Photochemical oxidant
Human toxicity
Ozone depletion
Climate change
0%
50
Chapter 3 | Life Cycle Assesment
3.5 Conclusions of LCA
Analysing the steps of the fibre production operations for natural fibres and man-made resulted in
the energy consumption and the environmental
impact of the four examined fibres. These results
were critical for the outcome of this project, mainly regarding the use of natural fibres as sustainable
reinforcement in bio-composites. The LCA finally
showed that production of textiles from natural fibres can also be an energy consuming process
and reach or even exceed the embodied energy
levels of artificial fibres.
100%
Considering
the environmental impact of natural
100%
fibres, fertilizing proved to be a serious contribution
on climate
90%change and eutrophication of water.
Retting of the fibres was also linked with similar ef80%
fects. Thus,
it becomes clear that only under specific circumstances natural fibres can be considered
70%
as an essentially sustainable solution. Graph 2.66
shows a comparison
of the environmental impact
60%
of glass, flax and jute fibres.
30%
90%
80%
70%
60%
50%
40%
Regarding artificial fibres, production of glass and
basalt fibre is associated with high energy consumption due to melting the crushed materials.
However, technological advancements focus onimproving the energy intensity of such processes.
jute fibre
10%
jute fibre
Ozone Depletion
Human Toxicity
Global Warming
Eutrophicationl
Photochemical Oxidants
Creation
flax fibre
Non-Renewable/
Abiotic Resource Depletion
glass fibre
Aquatic Toxicity
Acidification
0%
Photochemical Oxidants
Creation
Ozone Depletion
Non-Renewable/
Abiotic Resource Depletion
Human Toxicity
Global Warming
Eutrophicationl
Aquatic Toxicity
Acidification
Spinning of the sliver fibre in order to produce yarns
is also an energy consuming process. Therefore, is
more efficient to use natural fibre as reinforcement
in the form of mats rather than woven or knitted
fabrics. In conclusion the validity of the sustainability of natural fibres depends on the processes followed for production and the form of the chosen
reinforcement.
flax fibre
20%
50%
Environmentally orientated agriculture is the ideal
40% the potential environmental impact
way to reduce
of natural fibres. Preserving and improving water
30%
quality and resources, controlling soil erosion/compaction, preserving
physical/ chemical/ biological
20%
soil quality and air quality, preserving biodiversity
10% energy consumption by using renewand reducing
able energy sources are practices that sustainable
0%
agriculture should promote. Specifically, environmental credentials for flax fibre production could
be improved by adopting no-till method for preparing the ground, using organic agrochemicals and
achieving biological control of pests with traditional water retting.
glass fibre
3.14 Comparative environmental impact of glass, flax
and jute fibre
Digital control of the process allows for measuring
and managing the precise temperature of the
glass as it moves through the furnace as well as
the gas and oxygen flow rates. Control of oxygen
flow rates is crucial advantage of newly developed
furnaces because nearly pure oxygen is burned instead of air. This helps the natural gas fuel to burn
cleaner and hotter, melting glass more efficiently.
It also lowers operating costs by using less energy
and reduces nitrogen oxide (NOx) emissions by 75%
and carbon dioxide (CO2) emissions by 40%.
Bio-based FRP pedestrian bridge in Schiphol Logistics Park
Resins
11
52
Chapter 4 | Resins
4.1 The discovery and development of polymers
The demand for a long-lasting synthetic material,
able to overcome the defects that natural materials show over the years, easy to be produced and
available to everyone, was expressed centuries
ago. The dream of the invention of such a material
was becoming more realistic and feasible with the
gradual evolution of practical alchemy into theoretical chemistry during the 17th and 18th centuries and the development of chemistry as one of
the leading sciences of the Industrial Revolution in
the 19th century. At the same time, the mass production as a result of the industrialization called for
new materials that would replace the natural and
thus expensive ones, as well as for new production
technics.
4.1 George Eastman, the founder of the Kodak company, started producing roll film made from celluloid in 1889
and thus made photography accessible to the masses
(http://nice-cool-pics.com/)
In 1870 the American book printer John Wesley applied a patent for the technical process he had developed for producing celluloid. Being nowadays
concerned as the first thermoplastic, celluloid was
an easily molded and shaped polymer compound
which consisted of nitrocellulose and camphor.
However, two decades before Wesley had introduced his technical method, there was already
a similar compound, called Parkesine, presented
by Alexander Parkes at the 1862 World Exposition
in London, which did not succeed due to its rapid
crack formation.
4.2 Transparent flat cellophane sheets
(http://www.asia.ru/)
By the end of the 19th century the French scientist Hilaire de Chardonnet set the beginning for the
production of synthetic fibres by inventing artificial
cellulose-based fibres that aimed at substituting the
expensive natural silk. Though, as it was made from
cellulose the product was characterized by a high
degree of flammability, and therefore it was unsuccessful.
In general, over the first decades of the 20th century research into chemistry was transforming gradually from individual experiments done by creative
chemists, such as the previously mentioned ones,
into scientific projects developed in large research
departments. One product that was created in this
way is nylon, the first completely synthetically pro
A few years later at the beginning of the 20th century another important step was done with the development of an ultrathin transparent foil by the Swiss
chemist Jacques Brandenberger. Cellophane, as it
was named by the word cellulose and diaphane
(transparent) intended to become a cloth that
would be able to repel liquids rather than absorb
them. Finally, the product found a variety of applications and it is still used nowadays for packaging.
4.3 A 1949 Bakelite black and white television
(http://i.dailymail.co.uk/)
During the same decade, in 1907, the Belgian
chemist Leo Baekeland managed to develop the
first completely man-made polymeric product
based on synthetic raw materials: Bakelite. Bakelite
is mostly consisted of phenol and is formed from an
elimination reaction of phenol with formaldehyde.
The product was used for its electrical non-conductivity and heat-resistant properties in electrical
insulators, radio and telephone casings, and other
products such as kitchenware, jewelry, pipe stems
and children’s toys.
4.4 Nylon filament yarn (http://img.diytrade.com/)
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
duced and commercially exploited synthetic fibre.
Nylon is a thermoplastic material with polyamide
structure (repeated amide bonds). It was first produced in 1935, by Wallace Carothers at the DuPont Experimental Station and it was the result of
11 years of research, while 230 other members involved in the research team. Nylon fibres were first
used commercially in 1938 in a nylon-bristled toothbrush, followed more famously by women’s stockings after being introduced as a fabric at the 1939
New York World’s Fair.
At the same time, in 1939, another group of researchers in I.G.-Fraben industie AG plant in Berlin
managed to produce a polyamide fibre with very
similar structure, which they called “perlon”. Although these synthetic fibres were developed originally for clothing, they found application as the
main material for parachutes during the Second
World War. One year later, in England (1940) polyester fibres were developed by J. R. Whinfield and
J. T. Dickinson, which are still used today in membrane structures.
Another very influential polymer of the century,
which is nowadays considered as the third-most
widely produced plastic, is the polyvinyl chloride,
or PVC. As early as 1912, chemists Ivan Ostromislensky and Fritz Klatte, researchers at the German
chemical company Griesheim-Elektron, patented
a method to produce PVC. However, difficulties in
processing the rigid and sometimes brittle polymer
blocked their plans to commercialize their product.
Mass-production of the material happened only
after Waldo Semon and the B. F. Goodrich Company developed a method in 1926 to plasticize PVC
by mixing it with various additives. The result was a
more flexible and more easily processed material
that soon achieved widespread commercial use.
It becomes clear that during the 20th century polymer chemistry, as part of the field of the material science, saw great advance and changed our
everyday life. Specifically, it was the middle of the
century when the majority of the polymers we know
nowadays, appeared and briefly, they are the following:
Polymethyl methacrylate (acrylic sheet), 1933
Polyethylene (PE), 1933
Polyurethane (PUR), 1937
Polyamide (PA), 1938
Unsaturated polyester (UP), 1941
Polytetrafluoroethylene (PTFE, Teflon), 1941
4.5 PVC tubes
(http://truewellpipes.com/)
4.6 Polyethylene foam panels
(http://www.8linx.com/)
Silicone, 1943
Epoxy resin (EP), 1946
Polystyrene (PS), 1949
High-density polyethylene (PE-HD/HDPE), 1955
Polycarbonate (PC), 1956
Polypropylene (PP), 1957
Ethylene tetrafluoroethylene (ETFE), 1970
4.7 Sliced polyurethane foam
(http://www.pasprayfoam.com/)
53
54
Chapter 4 | Resins
4.2 Classification of polymers (resins)
The polymers are normally categorized according to the way in which the organic molecules are bonded together, which affects their physical properties. Polymers are divided into three groups: Thermoplastics (or thermosoftening plastics), Thermosets (or thermosetting plastics) and Elastomers
Polymers
Thermoplastics
Elastomers
Thermosets
4.8 Molecular structure of thermoplastics, elastomes and thermosets (Knippers et. al, 2011)
4.2.1 Thermoplastics
Thermoplastics are polymers that generally exhibit
relatively low strength and low heat resistance as
their molecules are not cross-linked. They become
moldable when they reach a specific temperature and they can turn solid again when they are
cooled down. This ability to be repeatedly remoulded without deterioration of the initial properties is a
great advantage for industrial manufacturing and
recycling. Therefore, the majority of our everyday
plastic objects, including packaging, are made
from thermoplastics. Common thermoplastic polymers include nylon, polyethylene, polypropylene,
polystyrene, polyvinyl chloride and Teflon.
4.2.2 Elastomers
Elastomers are polymers with viscoelasticity (both
viscous and elastic) and they cannot be melted
again once they have been produced as the molecules of such polymers have cross-linked bonds.
Each of the monomers which link to form the polymer is usually made of carbon, hydrogen, oxygen and/or silicon. The raw material for elastomers
is tough crude rubber, which is made elastic by
cross-linking. However, as they have low young’s
modulus they are inappropriate for structural applications and thus they are preferred to be used
as seals in joints, adhesives or bearing pads in constructions. One main application is also in the automotive industry as common vehicle tires.
4.2.3 Thermosets
Thermosets are polymers with even denser crosslinked molecular bonds than elastomers. For that
reason they present higher strength, better durability compared with other types of polymers while
they can be highly heat resistant. However, they
cannot be melted down again after curing. Before
curing they are usually liquid and after they are
heated up and reach a specific temperature they
become permanently hard and can no longer be
melted back to a liquid form. Consequently, they
are bot recyclable. As they are generally harder
and stronger than thermoplastics they are used in
advanced composite materials for structural applications, such in aerospace engineering. Bismaleide
resins (BMIs), Polyimide and Epoxies are some of the
thermosets, but the epoxy resin is the most commonly used thermoset.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
55
4.3 Biopolymers
As the use of fibre-reinforced polymers in the building industry is increasing rapidly, the users call not
only the fibres, but also the matrix to be replaced
by natural sustainable materials.
Biopolymers, known also as bio-based polymers or
organic plastics, are synthetic materials that are
produced from renewable raw material (RRM)
such as starch and cellulose. Biopolymers are
also known as biodegradable plastics when their
compostability has been verified by the European Standard EN 13432. Bio-based plastics can be
produced directly from natural biopolymers such
as cellulose or starch through modification or they
can also be composed by polymerized monomers
of renewable raw materials. However, these polymers can be also produced from petroleum raw
materials as long as the chemical structure of the
polymer allows for biological degradability. Fig 3.10
shows different biopolymers and their production
capacity for the year 2010. In the same way like
conventional polymers, biopolymers are categorized in thermoplastics, elastomers and thermosets
and they can be processed and machined with
the same machinery.
Bio-based polymers are in fact not generally biodegradable. Compostable biopolymers made either from petroleum or renewable raw materials
are preferred for temporary applications such as
packaging or agricultural purposes. These types of
polymers that can be composted are also known
as second-generation biopolymers. In contrast, the
third-generation biopolymers are maximizing the
content of renewable raw materials and achieve a
long-lasting functionality. These biopolymers compete conventional polymers in properties and allow
for disposal after the end of their life cycle. Figure
3.9 shows the increased rate of use of biobased
polymers with long-lasting properties in comparison
with biodegradable polymers.
Recycling conventional polymers is associated with
a downgrading in properties. With biopolymers this
disadvantage is even more distinct due to their
lower thermo-mechanical and chemical resistance. The disposal method that is used for these
long-lasting biopolymers is incineration, which results in almost zero energy production.
4.10 Biopolymers global production capacity for 2010
(European Bioplastics and University of Applied Scienced
and Arts Hanover, 2011)
(http://www.sustainableplant.com/)
4.9 Global production capacity of biodegradable and
durable (biobased) bioplastics (European Bioplastics and
University of Applied Scienced and Arts Hanover, 2011)
(http://www.sustainableplant.com/)
Under incineration the carbon dioxide (CO2) released is as much as the plant absorbed from the
atmosphere during its growth. Finally, some biopolymers, especially polylactides (PLA), can be broken
down into their monomers and then polymerized
again and thus get recycled without any downgrading of their properties.
The most common biopolymers are briefly described below.
Thermoplastic starch (TPS)
TPS is the most common biopolymer today. Starch,
which water-soluble is mixed with a water-repellent, petroleum-based polymer and the plasticizer
glycerine. In the building industry it is used for insulation but in a limited scale because of the material’s
4% moisture absorption.
Cellulose (tri)acetate (CA, CTA)
Cellulose acectate derives from the chemical reaction of natural cellulose with acetic acid. It is
characterized by its shiny surface which allows light
transmission and by its high resistance to scratches
due to its high surface elasticity. Additives can reduce its flammability or make it weather resistant.
Polylactide (PLA)
PLA is a lactic acid synthetic polymer consisted
of natural monomers and produced by bacteria
from starch or sugar. This biotechnical method of
production allows for developing the chemical
structure of the polylactide and thus adjustment of
its properties. Therefore, the properties of PLA are
comparable with those of PP and PET. Polylactides
are scratch-resistant, waterproof and transparent
thermoplastics while they also show good mechanical properties. PLA can be processed by conventional methods such as injection moulding, blow
moulding, extrusion and film forming operations.
Chapter 4 | Resins
Polyhydroxybutyrate (PHB)
PHB is a high-crystalline thermoplastic polymer
with smooth, shiny and highly waterproof surface.
It is resistant to UV radiation and in a temperature
range from -30oC to +120oC it presents stable
properties. However, because of its high production costs it is one of the most expensive biopolymers in the market.
4.4 Biopolymers vs. conventional polymers
Although thermoplastic biopolymers absorb
more moisture than petroleum-based polymers,
the percentage of this absorption, apart from the
case of thermoplastic starch, remains below 1%.
Moreover, comparing the mechanical properties
of both thermoplastic biopolymers and fossil fuel
based polymers, and especially the modulus of
elasticity and the stiffness of thermoplastic biopolymers it gets clear that both present approximately the same values. Analytically, the diagram 1.1
shows the notched impact strength in relation to
the elastic modulus of different polymer types of
both categories. The higher the value of the elastic modulus is, the less is the toughness of the polymer as it has a high tendency to get elastically
deformed (non-permanently).
Notched impact strength +23oC [kJ/m3]
56
PLA
50
blends
40
Starch
blends
PC
30
PP
Cellulose
derivatives
ABS
20
PA6 PS
10
PE-HD
PHB
PLA
PET
0
0
1
2
3
4
5
Elastic modulus [N/mm2]
4.11 PLA containers for food packaging
(http://projeto-pandora.blogspot.nl/)
4.12 Comparative diagram of biopolymes (green) and
conventional polymers regarding their mechanical
properties (Knippers et. al, 2011)
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
57
Table 4.1 Physical-mechanical properties of biopolymers and conventional polymers
(Knippers et. al., 2011)
One of the advantages of thermoplastic biopolymers compared to conventional polymers is their
lower rate of shrinkage, a fact which affects positively the high precision of the components during the production.
The diagram 1.2 presents the shrinkage rate and
the heat deflection temperature of the same biobased and petroleum-based polymers. The heat
deflection temperature indicates the temperature at which a polymer deforms under a specified load.
Shrinkage [%]
Shrinkage [%]
However, long-lasting, durable biopolymers are
just in the beginning of their development and
so far little new findings, regarding their long-term
properties such as fatigue behavior, UV resistance and creep, have been published.
00
0.5
0.5
11
1.5
1.5
PS
ABS
PS ABS
PLA
PLA
SStarch
tarch
blends
blends
PHB
PHB
C
Cellulose
ellulose
derivatives
derivatives
PC
PC
PET
PA6
22
PP
PP
2.5
2.5
33
40
40
PE-HD
PE-HD
60 80
80 100
100 120
120 140
140 160
160 180
60
180
o
Heatdeflection
deflection temperature
temperature VST
VST B
B 50[
Heat
50[oC]
C]
4.13 Comparative diagram of biopolymes (green) and
conventional polymers regarding heat deflection and
shrinkage (Knippers et. al, 2011)
4.5 Durable bio-based polymers
Bioplastics were initially developed for short-lived
applications such as packaging and consumer
products that could easily biodegrade in contrast to conventional plastics. Soon, other industries, including the automotive and building sector showed their interest in employing bio-resins
in durable applications. Thus, biodegrability was
a drawback, rather than an advantage in such
applications. To overcome low durability, cause
by inherent brittleness, low heat resistance and
moisture uptake, bioplastics were blended with
conventional plastics and fortified with impact
modifiers, reinforcing fillers and nano-additives.
Durable bio-based plastics that are used as resins
in composites include modified polylactic acid
(PLA), polyhydroxy alkanoates (PHBV), industrial starch and resins based on castor oils which
is produced from agricultural waste, such as furan. Additionally, a big number of existing resins
(PEBA, copolyester TPEs, TPUs and even acrylics)
are modified to include a part of renewable content.
Therefore, blending PLA with polyethylene, copolyesters or other bio-resins such as PHBV reduces its brittleness. Mixing with PHBV improves also
the heat resistance.
Additives are also important in improving durability of bio-resins. Nucleating agents speeds PLA’s
crystallization and reduce molding time, whereas
calcium sulfate (dehydrated gypsum) improves
heat resistance. Very fine-particle (0.05-micron) silica increases toughness and maintain
clarity. Reinforcing PLA with a network of polymer-crosslinked carbon fibres adds thermal conductivity for use in electronic applications.
58
Chapter 4 | Resins
4.6 Furan
4.7 Natural fibre-reinforced biopolymers
Furan also called polyfurfuryl alcohol has recently gained attention as a renewable alternative
thermoset resin. Produced from pentose sugars,
furfuryl alcohol or its prepolymers consist the raw
materials of furan thermosets. Furfural, the raw
material for furfuryl alcohol, is produced from
the hemicellulosic part of agricultural wastes.
A controlled, hightemperature digestion of this
pentose-based fraction yields furfural. Thus, technically, furfural can be produced from any raw
material which contains pentose, making it a renewable and CO2-neutral chemical. Corncobs
and bagasse from sugar cane are the major industrial feedstocks for furfural production.
Natural fibre-reinforced biopolymers are composite polymers in which a bio-based polymer,
such as the ones described previously, is used as
a resin and natural fibres constitute the reinforcement. Incorporation of natural fillers into polymer
matrices can optimize mechanical and thermal
properties.
Two basic polymers of this category are described below.
4.14 Furfuryl alcohol
(http://en.silvateam.com/)
Most of the furfural produced world-wide is converted into furfuryl alcohol (FA) by a low cost derivatization process. This latter furanic monomer
can be easily polymerized into polyfurfuryl alcohol (PFA). PFA based-resins have found a range of
useful applications in the foundry industry, wood
adhesives and binders, polymers concretes and
fibre-reinforced plastics.
Compatibility of furan with conventional and natural fibres is also good. However, as furan resins
are generally cured by acid hardeners, natural
fibres have to be protected. Plant fibres, being
lignocellosic, can be degraded by both acid
and alkaline chemicals through various pulping
reactions. In order to compatibilize the acid curing mechanism of a furan resin with natural fibres,
novel catalytic systems have been developed in
order to protect the natural fibre from any degradation reaction.
Natural fibre-reinforced PLA (thermoplastic)
Although the mechanical properties of PLA are
similar or even superior to petrochemical polymers, PLA shows low toughness because of its
brittle nature, but also has much lower molecular
weight compared to conventional polymers. In
order to overcome the brittle nature of PLA, natural fibres are embedded into the polymer matrix.
plasticizers can be used during processing.
Although PLA-natural fibre composites show increased tensile modulus they have lower tensile
strength than PLA, and this has been attributed
to factors such as the weak interfacial interaction
between the hydrophobic PLA matrix and the
hydrophilic natural fibers, and the lack of fiber
dispersion due to a high degree of fiber concentration. However, various methods of modifying
the surface of the cellulosic fibers have been explored in an effort to improve the interaction that
occurs at the interface between the PLA matrix
and natural fibres. Better development of processing technologies and improvements in natural fibre treatments will facilitate the production
of PLA based composites with optimum mechanical and physical performance but also generate
high cost competiveness and greater acceptance of these materials in the market.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
One of the first applications on a real product was introduced by a Japanese electronics
group which developed a virtually non-flammable mobile phone housing. Heat-absorbing metal hydroxides were added as flame retardants
and short kenaf fibres were used as reinforcement. Another experimental approach was the
“S-House” project carried out by the Vienna University of Technology in which a prototype for
non-loadbearing partitions made from natural fibre-reinforced biopolymers was developed. Several layers of fleece made from straw, flax and
polylactide fibres were laid on top of each other
and pressed together giving a compression resistant sandwich panel with insulation properties.
Lignin-bonded natural fibre composites
(thermoplastic)
Lignin is one of the most common naturally occurring biopolymers and its function is to give stability between the cellulose fibres in all plants and
wood. This biopolymer has a dark brown color,
absorbs UV light almost totally and is difficult to be
decomposed either biologically or chemically. It
is also known as liquid wood as in combination
with natural fibres it becomes a composite material with the positive properties of naturally grown
wood and the unrestricted mouldability of a thermoplastic. Therefore, the composite shows similar
mechanical and thermal properties to those of
wood which makes it suitable as a connecting
component in timber construction.
59
60
Chapter 4 | Resins
Cores
62
Chapter 5 | Cores
5.1 Sandwich construction
Structural members composed of two thin, stiff and
strong skins separated by a lightweight and thick
core are known as sandwich panels. The core is
normally a low strength material as its main role is to
maintain a distance between the two facings. This
increases the moment of area of the panel, with little increase in weight and results is an efficient structure with an overall low density and good bending
and buckling resistance.
1
2
3
2
1
Additionally, the role of the core is to take the
shear forces of the structure, support the facings
and maintain the proper distance between them.
Therefore, the core should be a lightweight material
with enough shear and axial stiffness. Otherwise, a
weak core material in shear would result in bending of the facings and too low axial stiffness would
cause buckling. But with the proper choice of materials for facings and core, constructions with high
ratios of stiffness to weight can be achieved.
5.1 Structure of a sandwich composite
1. Facing
1
2
3
5.2 Reactions of core under bending and compression
1. Core weak in shear
2. Core strong in shear
3. Separation of core
5.3 Cross sections of (top) the beak of a Hornbill and (bottom) an avian wing bone
(http://www.virginia.edu/)
2. Adhesive
3. Core
Such structures exist originally in various forms in nature. Trees can support the bending loads applied
by strong winds and our bones are able to support
our weight due to the structural efficiency of shell
sandwich structures based on strong and dense
outer surfaces that enclose a low density and light
material. Figure 6.3 shows examples of the structure
of a Hornbill beak and an avian wing bone which
demonstrate how well nature exploits these efficient design practices to create structures that can
support high bending loads at minimal weight.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
63
5.2 Core materials
Many sandwich structures use synthetic polymer
foams, honeycombs, aluminum but balsa wood
has also been used for many years, and cork is also
now available. Both balsa and cork are produced
from renewable resources, may be partly recyclable and can be composted.
5.2.1 Polymer foams
Polymer foams are composed of a solid polymer
and gas mixed together to form a foam. Polymer
foams are known as either closed-cell or open-cell
structure. In closed-cell foams, each cell is surrounded by connected faces. Partial cells, with cut faces
and edges are visible only in the cross-section of the
foam, whereas complete cells exist in the interior of
the material. On the contrary, the structure of opencell foams allows air to pass freely between the cells
as all the cell edges are partly open. Closed-cell
foams are generally more rigid, while open-cell
foams are usually flexible.
Production of polymer foams can be achieved in a
number of different processes including slab-stock
by pouring, extrusion and different forms of molding. They can be divided into either thermoplastics
or thermosets, which are further divided into rigid
or flexible foams. The thermoplastics can usually be
broken down and recycled, while thermosets are
harder to recycle due to strong cross-linked bonds.
Polymer foam industry faces environmental issues
regarding waste disposal, recyclability, flammability
and the effect of blowing agents on the environment.
Foams that are commonly used as core elements in
fibre-reinforced composites are polyurethane (PU),
polystyrene (PS), polyethylene terephthalate (PET),
PVC and others.
5.2.2 Biodegradable polymer foams
Biodegradable polymer foams were developed as
an environmental solution to the increasing non-disposable waste of traditional polymer foams, and as
an alternative based on renewable raw resources
and not on petroleum products. Similar to biodegradable resins and natural fibres, biodegradable
foams are sensitive to humidity, while traditional petroleum-based foams are more inert to water. Thin
sheets cannot be easily achieved with biodegradable foams as they have a different microcellular
structure. There is also a wide range of bio-base materials that can be used for biodegradable foams,
including ethylene vinyl alcohol, polyvinyl alcohol,
polycaprolactone, polylactic acid and starch.
5.5 Honeycomb from aramid fibre paper
(http://www.acpsales.com/)
5.2.3 Honeycombs
Honeycomb cores are structures consisting of an
array of hollow columnar cells, hexagonal in shape,
formed between thin vertical walls. Having that geometry, honeycombs allow for minimization of the
amount of used material, reach minimal weight
and density while out-of-plane compression properties and out-of-plane shear properties are relatively
high.
Materials used to produce such cores vary from paper to thermoplastics and depend on the intended
application. In sandwich composites, aluminum,
thermoplastic (polypropylene, polycarbonate, polyethylene) or fibre-reinforced plastic (glass, aramid)
are preferred. Nowadays, honeycombs are manufactured by the continuous processes of expansion
and corrugation, whereas extrusion is employed for
production of thermoplastic honeycomb cores.
5.4 Open-cell (left) and closed-cell (right) foams.
(http://www.posterus.sk/)
64
Chapter 5 | Cores
5.2.4 Aluminum foam (metal)
Aluminum foam is the most frequent variant of metal foams. Consisting of solid aluminum it shows a
large volume fraction of gas-filled pores. The pores
can be sealed (closed-cell foam), or they can form
an interconnected network (open-cell foam). The
defining characteristic of metal foams is their very
high porosity as typically 75–95% of the volume contains void spaces making aluminum foams ultralight
materials.
Similar to polymer foams, metallic foams are classified into open-cell and closed-cell. Open cell metal
foams, also called metal sponges, can be manufactured by several ways, especially through foundry or powder metallurgy, whereas closed-metal
foams are made by injecting a gas or mixing a
foaming agent into molten metal. Under certain circumstances metallic melts can be foamed by creating gas bubbles in the liquid.
Closed-cell metal foams are primarily used as impact-absorbing materials for high impact loads.
However, unlike polymer foams, metal foams remain deformed after impact and can therefore
only be used once.
5.7 Microstructure of porous wood
(http://www.scielo.cl/)
5.2.5 Balsa wood
A more environmental alternative for core material is balsa wood. Being produced from balsa tree,
a fast growing type of tree, balsa exhibits properties that make it suitable for use as core material
in sandwich composites. The density of dry balsa is
low, typically around 160 kg/m3, because it consists
of large cells that contain water. After the tree is
cut, moisture evaporates, leaving large areas within
the resulting cells.
Balsa wood has also excellent stiffness-to-weight
and strength-to-weight ratios as well as superior
energy absorption characteristics. These properties
are derived from the microstructure, which consists
of long slender cells with approximately hexagonal
cross-sections that are arranged axially, similar to
honeycomb cores. Under compression in the axial
direction the material exhibits a linearly elastic regime that terminates by the initiation of failure in the
form of localized kinking. The material is less stiff and
weaker in the tangential and radial directions.
5.6 Aluminum foams
(http://www.ergaerospace.com/)
5.8 Wood cell structure of Balsa wood
(http://www2.estrellamountain.edu/)
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
65
5.3 Environmental impact and embodied energy
Embodied energy, primary production [MJ/kg]
350
300
250
200
150
100
50
Aluminum-SiC foam
Aramid paper/phenolic honeycomb
Glass/phenolic honeycomb
Polyurethane foam
0
Polyethylene terephthalate foam
Polymer foams are also toxic and non-recyclable,
creating problems regarding waste management.
Manufacturing of such materials is also energy intensive. On the contrary, balsa wood is based on a
renewable resource with the microstructure of the
materials being naturally present. Graph 5.8 shows
the embodied energy of different core materials.
400
PVC cross-linked foam
Hydrochlorofluorocarbons (HCFC) and hydrofluorocarbons (HFC) are blowing agents with lower impact on the ozone layer and with similar properties.
However, the use of HCFC’s is still linked with ozone
depletion problems. On the other hand, HFC’s have
no contribution on ozone depletion, but on global
warming potential.
MJ/kg
Cork
Production of polymer foams requires use of blowing agents, which are volatile liquids that evaporate, produce CO2 and make the foam expand.
The first generation of physical blowing agents,
CFCs (chlorofluorocarbons) are mostly outruled
nowadays due to their negative environmental impact on the ozone layer.
5.9 Embodied energy of core materials
(CES EduPack 2014, Granta Ltd)
Balsa
Considering the environmental impact of the described core materials, balsa wood offers an advantageous alternative. Conventional polymer
foams, being based on non-renewable fossil fuel resources, have an increased environmental impact
and energy intensity.
66
Chapter 5 | Cores
Production Techniques
68
Chapter 6 | Production Techniques
6.1 Manual lay-up processes
6.1.1 Hand lay-up
Hand lay-up or wet lay-up is the most widely used
technique and one of the oldest for making composite parts. Being a simple process to perform, it allows for design flexibility and so it is more suitable for
components with irregular shapes in small batches
or for elements with large dimensions that cannot
be produced with automated plant.
In hand lay-up process an one-part mold is used for
shaping the component. Simple geometries and
planar pieces can be produced by using metal
sheet or wooden molds, but more complex one-off
items normally can be achieved by molds made
from rigid polyurethane foam. However, as the
foam is often damaged during the first demolding
operation such foam molds are not functional after
a number of reuses. Molds made from glass fibre-reinforced polymers are suitable when more than 100
reuses are required as they are stronger and last
much longer.
The surfaces of the mold are usually coated with a
release agent that can ease demolding while for
the case of a rigid foam mold it prevents the resin
being absorbed into the foam. If the foam has to
be integrated in the composite as a core material,
then the application of a release agent would prevent a good bond between the foam and the first
ply of material and so it is not applied.
The first stage of the process is the application of a
gel-coat of less than 1mm thickness on the mold.
This coat is a special non-fibrous pure resin with
good hardness and impact resistance that is going
to protect the surface of the laminate as a top coat
after demolding. Once it has sufficiently cured, the
reinforcement is laid on by hand and the liquid resin
is applied and pressed by brush or roller to ensure
good contact with the layer below and to remove
all air bubbles. Additives such as flame retardants
Hand lay-up
5
6
5
4
3
1
5
6
5
4
3
2
and inert fillers can be mixed in to reduce weight
and improve mechanical and physical properties.
The process is repeated layer by layer, until the desired laminate thickness is achieved.
In general, the application of hand lay-up method is limited to the thermosets as resins need to
be low in viscosity to be workable by hand. Since
most thermoplastic matrices have a high viscosity
at room temperatures, impregnating the fibres with
a thermoplastic resin becomes difficult. Due to the
high flexural stiffness of thermoplastics it can be difficult to drape such prepregs in or over a mold.
1 Mould
2 Release agent
3 Gelcoat
4 Layer of fleece
(surface layer)
8
1 Mould
5 Resin
2 Release agent
6 Fibre reinforcement (textile)
3 Gelcoat
7 Brush (resin application)
4 Layer of fleece
8 Deaerating roller
(surface layer)
5 Resin
6 Fibre
8
7 reinforcement (textile)
7 Brush (resin application)
1
8 Deaerating roller
e agent
t
f fleece
ayer)
6.1 Basic steps of hand lay-up.
(In: Knippers, J,, Cremens, J., Gabler M., Lienhard J. Construction manual for polymers + membranes. Munich: Institut für international Architektur-Dokumentation)
2
5
6
7
8
Resin
Fibre reinforcement (textile)
Brush (resin application)
Deaerating roller
7
1
5
6
5
4
3
2
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
69
6.1.2 Vacuum/pressure bagging
Hand lay-up is a relatively cheap process as equipment and tooling cost is low and as only one single
mold is needed, which is usually simple in shape
and thus is constructed out of cheap materials.
However, it is a process that requires high labor intensity while the quality of the component heavily
depends on the skill of the operators carrying out
the work. Also, as the mold is a single piece, the
face in contact with the mold has a smooth surface, whereas the inner face is rough. Finally, as
the process is based on manual lamination longer
cure times are required.
The nature of hand lay-up also has health and safety issues as it is an open mold process and because
low viscosity resins can be harmful. The fumes from
the curing process, especially with polyester resin
requires appropriate ventilation systems that provide air extraction which complies with the high
emission levels of styrene.
6.2 Operation of hand lay-up
(http://www.fassmer.de)
1
2
3
4
Vacuum and pressure bagging are basically an extension of the wet lay-up process described above
with the difference that pressure is applied to the
laminate in order to improve its consolidation and
hold the resin-coated component in place until the
polymer cures. The difference between vacuum
and pressure bagging is the fact that in the first process pressure difference is created by air extraction
inside the bag while in the latter, pressure difference is achieved by inserting air inside an airtight
space above the bag. However, both processes
require a single mold which can be made of glass
fibre-reinforced polymer, epoxy, or metal. Components that are mainly produced by these two
processes include shapes with high surface area to
thickness ration and so they are preferred for large
one-off components such as boats or racecars.
In vacuum bagging process the reinforcement
and the resin are applied on the mold manually by
hand or spray lay-up technics. Then the laminate
is sealed within an airtight envelope that consists
of an airtight mold on one side and an airtight
bag on the other. When the bag is sealed to the
mold, air is evacuated by a vacuum pump from
the inside of the envelope, creating an air pressure
difference between the inside and the outside of
the envelope by reducing the air pressure inside.
Atmospheric pressure forces the sides of the envelope and everything within the envelope together,
putting equal and even pressure over the surface
of the envelope.
To ensure consistent, high-quality composite parts
it is necessary that proper components and materials, including specialized equipment and commonly available materials are used by specially
trained operators. The materials usually used in
preparing a lay-up for vacuum bagging are a peel
ply, a release fabric, a perforated film, a breather
material and the vacuum bag that encloses the
laminate inside the envelope.
Vacuum bagging
1
2
3
4
Pressure bagging
1
2
3
4
Flexible bag
Heating
Resin + fibre reinforcement
Mould
70
Chapter 6 | Production Techniques
6.1.3 Autoclave molding
Vacuum bagging offers many advantages over
conventional clamping, stapling or other techniques. Due to the continuous, firm and evenly
distributed atmospheric pressure over the entire
surface, it allows for a wide range of types and
combinations of materials in laminates with a superior bond between them. Vacuum bagging’s uniform clamping pressure across the laminate also results in thinner, more consistent glue lines and fewer
voids.
Autoclave molding is a process similar to vacuum/
pressure bag with the difference that autoclave
machinery is used for curing the composites. The
autoclave machine is basically a large oven that
subjects materials to high pressure, temperature
and vacuum. Autoclaves can reach temperatures
up to about 750 degrees Fahrenheit, and pressures
up to 100 pounds per square inch.
Additionally, the ability to control excess adhesive
in the laminate by the different bagging materials,
results in higher fiber-to-resin ratios. This means that
higher fibre-content laminates can be achieved
than with other processes such as standard hand
lay-up. High fibre-to-resin ratios are crucial as they
are translated into high strength-to-weight ratios
and cost advantages.
Another big advantage of vacuum bagging is in
the simplicity and variety of the molds used. Since
atmospheric pressure provides equal and even
clamping pressure to the back of the mold, the
mold only has to be strong enough to hold the laminate in its desired shape until the epoxy has cured.
Therefore, most molds are relatively light weight,
easy to build and cheap. Concerning health and
safety issues, as vacuum bagging is a closed process the emission levels during the cure are low.
However, compared with hand lay-up process in
vacuum bagging the extra process adds cost both
in labor and in disposable bagging materials. Finally, the final quality of the composite is also determined by the level of the operators’ skill.
pressure
1
2
3
5
6
4
Autoclave
1 Flexible bag
2 Resin + fibre reinforcement
3 Mould
4 Heating
5 Clamps
6 Table
6.3, 6.4 Autoclaves
(http://www.brebeckcomposite.com/)
In the same way with vacuum bagging, the reinforcement and the resin are applied on the mold
by conventional hand or spray lay-up techniques.
The laminate is again covered with a porous film
and a layer of glass-fibre cloth or paper to absorb
any excess resin and then it is covered with a flexible bag which is clamped on a table. The wet laminate and the mold are then placed inside the autoclave and subjected to high pressures of about
0.55 MPa and temperature which cause the back
to be drawn on the laminate.
With the subjection of the material to elevated
pressures and temperatures, higher fibre-to-resin
ratios and removal of all voids (less than 2%) can
be achieved, which leads in a maximization of the
performance of the thermoset composites. Besides,
inside an autoclave, three dimensional, uniform
pressures can be achieved mainly due to the external pressure around the enclosed laminate. The
pressure created by the vacuum inside the sealed
bag that contains the laminate is not enough to
achieve such evenly distributed forces around the
bag. Therefore, autoclaves are used for the fabrication of high quality advanced components such
as high strength aircraft and aerospace components.
Autoclave is a high labor intensive and time consuming process as it requires 1-12 hours for a curing cycle. At the same time, the high manufacturing cost makes autoclaving an expensive process
which is used only for specialized high performance
components.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
71
6.2 Automatic lay-up processes
6.2.1 Automated tape placement (ATP)
Automated tape or tow placement (ATP) is a non-autoclave manufacturing process for advanced composites,
based on lamination by layering pre-impregnated fibres in form of tape. During this process a pre-preg tape or
tow is deposited by a laying head carried by a numerically-controlled multi-axis machine.
1
2
3
4
5
6
7
8
9
Individual tow payout with controlled tension
Band collimator
Fibre placement head
Tow restart rollers
Tow cutters and clamp mechanism
Collimated fibre band
Controlled heat
Compaction roller
Mold surface
6.5 Robotic ATP machine
(http://www.investquebec.com)
ATP machines are normally large gantry style metal
machines which can contain as many as ten independently controlled axes of movement in space
(IHS GlobalSpec, 2006), such as head orientation,
roller angle etc. As ATP machines require a considerable investment, the total capital cost of the
process is high. However, compared to other manual processes, that require intensive labor by highly
skilled personnel, such as hand lay-up, an automated tape-laying machine can provide up to 86% labor savings (Van Tooren, Sinke & Bersee, 1993).
ATP is a highly accurate process with very good
repeatability and maximum utilization of the tape
material. It delivers high quality composite components that have improved structural properties and
thus it is primarily used in the aerospace industry.
High quality is achieved as the tape-laying roller applies uniform pressure during the lay-up which gives
compacted laminates with less entrapped air. Additionally, such machines allow for a variety on the
shape, size and fibre orientation (0o, -45o, +45o or 90o).
The process is used for large scale productions of
large, simple to moderately complex parts thatrequire excellent quality and strength. It is not ef
20000
Relative cost index per unit [EUR]
The pre-preg tapes, stored in reels, are transported
by rollers to the tape-laying head. Pre-preg tapes
consist of reinforcement fibres in form of unidirectional strands that are impregnated with a resin. The
matrix, which is usually an epoxy resin, is only partially cured and stored in cool conditions in order
to avoid complete curing. Since heat accelerates
complete polymerization, only during the process
the tape is heated right on the moment is being applied on the surface.
10000
5000
2000
1000
500
1
10
100
1000
10000
Batch size
6.6 Diagram of cost per unit regarding batch size
(CES Edupack 2014, Granta Ltd)
ficient, also in terms of cost, to lay-up small, complex parts without structural requirements. Hollow
and highly curved surfaces with radii of curvature
less than that of the laying head cannot even be
produced.
Although automated tape placement achieves
exceptionally high quality and control of the layup, it is a slow process with low production rates.
Besides, the high production cost limits the use of
the process in specialized applications that require high performance. Finally, as ATP is an open
process and thus toxic vapor is released during
the cure, forced air extraction through ventilation
systems is necessary.
72
Chapter 6 | Production Techniques
6.2.2 Filament winding
Also known as wrapping, this is a process in which
continuous rovings, tows or tapes are wound over
a rotating mandrel. These rovings or tapes can
be pre-impregnated or impregnated during or after the winding process. When impregnation occurs during the process the fibre tows are passed
through a resin bath, usually polyester or epoxy, before being wound on the mandrel.
The mandrel is made of steel, aluminum or plaster
depending on the batch size and the geometry of
the component. It usually has cylindrical, conical,
round or any other shape without complex curvature that would not allow removal of the mandrel
at the end of the cure cycle. The shape of mandrel should also have no bumps or undercuts that
would not allow for entire wounding of the mold.
2
Despite the shape limitations, with filament winding
1
3
4 5
very large parts can be produced, larger that Thus,
filament winding is ideal for producing axisymmetric
hollow parts such as pipes, tubes, tanks and pressure vessels, turbine blades or rocket noses.
Filament winding
6
5
3
1
2
3
4
Drive
Gearbox
Mandrel
Moving carriage
with resin bath
5 Resin bath
6 Fibres
6.7 Tude product by filament winding
(http://savercompositi.com/)
6.8 Filament winding
(http://www.cstcomposites.com/)
without joints, over the entire component surface
that can be also oriented in the load direction.
As a process it requires less capital investment,
compared to other autoclave processes or automated tape lay-up. However, the cost of large
mandrels can be high. In general it is an economic
process with normal cost for large quantities as the
material costs are relatively low. Fibres, for instance,
are used in a primary form and not as fabrics which
includes a secondary process that would increase
the cost.
4
6.3 Resin transfer processes
2
1
3
4 5
6.3.1 Resin transfer molding (RTM)
6
5
3
Filament winding is an accurate automated
process with high level of mechanization. The produced components have high quality with excel4
lent structural
properties as high reinforcement
content can be achieved. The machine has the
ability to vary the winding angle, the resin content
and the winding tension in each layer of reinforcement until the desired thickness, density, resin content and direction of strength of the composite has
been obtained. Another important advantage of
the process is the capacity to use continuous fibres,
Resin transfer processes are a family of closed mold
low-pressure processes in which the dry reinforcement and the resin are mixed within the closed
mold.Such processes have a wide variety of products that range from simple, low-performance to
complex, high performance components in terms
of complexity and from small to very large in terms
of size.
Resin transfer molding uses a double closed mold
which is usually metal or a glass fibre-reinforced
composite. Dry reinforcement in form of fibre mats
is laid up on the first mold together with other fabric layers, such as a release fabric and a breather.
Then a second mold is clamped over the first, and
a low viscosity resin (usually epoxy or polyester) is
injected into the airtight cavity between the two
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
73
molds. The liquid resin is transferred through a tube
that connects the cavity to the resin supply. During the injection, pressure difference is created inside the closed cavity which forces the resin to flow
through the reinforcement. The mold also has vent
points to allow air to escape from the cavity as the
resin flows through under pressure. After the matrix
has impregnated the reinforcement, the composite
is allowed to cure at room temperature.
RTM is an easy process for manufacturing complex
shapes without high cost tooling. Typical applications include car doors and side panels, propeller
blades, boats, canoe paddles, water tanks, roof
sections, airplane escape doors etc. Besides, as
the process is closed-mold type styrene emission
are reduced and thus exposure of the personnel to
chemical environments is greatly reduced. Another advantage of double mold processes is the fact
that both sides of the component have a smooth
surface finish.
On the other hand, although the relative cost per
unit is low, the fabrication of the two parts of the
double mold can be expensive. Thus, the process is
a cost-efficient option only for large mass productions in which the capital investment for the molds is
balanced by the production profit.
2
3
4 5
1
6
7
8
9
11
10
6.9 Double mold for resin transfer molding
(http://savercompositi.com/)
6.3.2 Vacuum assisted resin transfer molding (VARTM)
Another alternative process based also on resin
transfer inside an airtight closed mold is the vacuum
assisted resin transfer molding or vacuum assisted
resin injection (VARI). The process is similar to typical
resin transfer molding with the difference that the
mold is a single part with a flexible bag clamped
airtight on it, instead of a second solid mold. The
pressure here is created by a vacuum pump that is
connected with the cavity between the mold and
the bag.
In a similar way to resin transfer molding the laminate is created by laying the fabrics of the dry reinforcement and the additional layers on the mold.
Then the laminate is sealed airtight on the mold by
the flexible bag that allows injection of the resin
from a tube at the one side and extraction of air
by the vacuum bag from the other side. The resin is
released and sucked into the bag by the vacuum,
flowing through and impregnating the fabric.
One of the major advantages of VARTM is that it is
an economic process for small butch sizes and not
mass productions while it retains the good quality
of resin transfer processes. This basically lies in the
fact that mold costs are lower than typical RTM, as
molds here can be out of low-cost, disposable materials. However, due to the absence of a second
mold only one good surface with smooth finish is
obtained.
Vacuum assisted resin transfer molding
1 Seal
2 Screw clamp
3 Tensioning frame
4 Perforated plate
5 Channel for excess resin
6 Vacuum bag
7. Layers of fibre reinforcement plus resin
8. Release agent
9. Mould
10. Vacuum vessel for excess resin
11. Vacuum pump valve
6.10, 6.11 Infusion of resin in VARTM
(http://www.ar-engineers.de/)
74
Chapter 6 | Production Techniques
6.3.3 Resin film infusion (RFI)
Resin film infusion is a typical vacuum/pressure bag
process. The reinforcement is again laid on the
mold in form of dry, woven fabrics while the resin is
applied on the laminate as semi-solid film which is
supplied on a release paper. The entire laminate is
again sealed with a flexible bag on the mold and
then heated to allow the resin to melt and impregnate the air-free fabric reinforcement. At the same
time, a vacuum pump extracts the air from the
bag, compressing the dry fabrics on the resin.
6.13 BMC molding
6.14 Bulk molding compound
(http://www.tencate.com/)
(http://smccomposites.com/)
6.4 Compression molding processes
shape. Pressures applied vary between 0.5 and
15Mpa depending on the size requirements and
the material being processed according to CES
Edupack (2013). The mold reaches temperatures
between 140-160oC through steam heating, electricity or hot oil.
6.12 Compression molding technique
(http://www.gopixpic.com/)
Resins that are commonly used for the bulk compound are thermosets, such as polyester, epoxy or
vinyl ester or some thermoplastics like PP or nylon.
The fibres used are normally short (25mm) glass or
carbon fibres with random orientation inside the
compound. As the fibres are not continuous, they
cannot be oriented to certain load directions, and
thus the composite products have low mechanical
properties. Therefore, applications with high load
bearing and durability requirements are restricted
from the process. Common uses, include semi-structural applications such as electrical housings and
car body parts.
Compression molding is a wide family of processes that includes several different technologies in
which molding compounds are formed and cured
in metal molds under heat and high pressure. Most
compression mold processes consist of a two-part,
negative and positive, double mold which is usually
constructed either of aluminum, cast iron, steel or
glass fibre-reinforced polymer. When the two parts
of the mold are closed, their inner matching surfaces create a cavity which is the outline of the desired
product.
The products of such processes have high strength,
and can vary in size and in shape complexity. Besides, due to existence of a double closed mold,
styrene emissions are reduced giving the process
lower emission compared to other forming techniques. However, all compression molding processes require a high initial investment both for mold
construction and tooling used, which makes them
useful only for high volume productions.
6.4.1 BMC molding
Bulk molding compound method is a compression
mold process in which the molding compound is a
sticky dough premixed material that includes the
optimum portions of resin, fibre-reinforcement and
additives. The compound is placed in the heated mold cavity and then pressed into the finished
3
4
1
6
7
2
5
Vacuum assisted resin transfer molding
1
2
3
4
Resin
Lower part of mould
Upper part of mould
Spacer
5 Layers of fibre-reinforcement
6 Finished laminate
7 Heating
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
6.5 Continuous processes
6.4.2 SMC molding
Sheet molding compound method is a similar alternative of BMC. The only difference here is that
the premixed compound is in the form of sheet,
with the short fibre-reinforcement, the resin and
the additives being again premixed in the optimum portions. After the sheet is cut to the desired
dimensions it is placed on the mold. The mold then
closes and applies pressure between 3-7MPa and
constant heating (130oC-160oC) to the compound
in order to initiate curing.
Continuous processes are manufacturing techniques for mass production of high-length components, in which the composite is continuously produced. Thus, with such processes there is no limit
to the length of the fabricated parts. The fibre-reinforced components that are reinforced only in the
length direction can be constant cross-sections,
sheets or integrated panels. Continuous processes
have a high degree of automation and are not as
labor intensive as other production processes.
6.5.1 Pultrusion
Pultrusion is a well-known continuous manufacturing method for producing constant cross-sectional
profiles. The dry fibres or fabrics are pulled from a
series of creels and proceed through a resin bath
before continuing to the forming dies. After passing
the dies, the resin-impregnated fibres pass from a
heated steel forming die that starts curing of the
resin at high temperatures and shapes a rigid composite section. A special cutting device cuts the
product to the desired length. The speed of the
process is depended on the viscosity, thickness and
curing of the resin.
6.4.3 Thermoforming
Thermoforming is also known as thermoplastic
composite molding as it is the base of all the thermoplastic forming processes. Being limited only in
thermoplastic resins, the process is mainly based
on heating and pressing the composite, not at the
same time but in two different stages. First a premixed compound in form of sheet is cut to shape.
The compound consists of fibrous fabric as reinforcement and a thermoplastic resin, such as PS, PE,
PP etc. The laminate is first heated inside an infrared
heater or hot air autoclave until it has reached the
forming temperature. Then, it is transferred into the
double compression mold were it is pressed to the
desired shape. After forming, the laminate is cooled
under the pressure of the matched press until is set.
The matrix that is typically used is a thermosetting
resin, such as polyester, epoxy and the reinforcement mainly consists of glass fibres (60-75%), carbon or aramid in the form of continuous rovings or
fabric mats (CES Edupack, 2013).
The cross-sections produced have thin walls and
constant profile that gives a variety of shapes.
Tubes, rods, channels, hollow rectangles, I-beams
or angles are common extruded profiles. The process also allows for continuous encapsulation of
core materials inside the composite, such as foam,
wood or wire. Additionally, with pultrusion, high fibre content of 70% by vol. can be achieved (Knippers, Cremers, Gabler & Lienhard, 2011). However,
as the unidirectional reinforcement is aligned in the
longitudinal direction, the mechanical properties
perpendicular to the pultruding direction are low.
6.15 Double compression mold
(http://wilbertinc.com/)
4
3
Pultrusion
1
2
3
4
5
6
7
8
Heated mold
Pre-form
Textile reinforcement
Rolls of rovings
Resin bath
Molded section
Pull mechanism
Saw
75
1
2
8
5
6
7
76
Chapter 6 | Production Techniques
6.6 Spraying processes
Pultrusion is an automatic method with low labor
intensity and high degree of mechanization. The
equipment used includes the pultrusion machine
that continuously pulls, consolidates and cuts the
profiles and the steel forming die that heats and
cures the composite in its’ final shape. The capital
cost for setting up a production unit whereas tooling is also expensive. Thus, pultrusion is worthwhile
only for large quantities that exceed at least 1000
production meters.
6.5.2 Continuous lamination
In continuous laminating the reinforcement is mainly in form of fabrics or mats instead of fibre rovings.
In the same way with pultrusion, the cloth sheets
are pulled continuously from a series of creels and
get impregnated with thermosetting liquid resin
through resin baths. The wet fabrics are added one
by one on top of each other and pressed together
until they have reached the desired thickness. The
resulting laminate is then cured by getting subjected to the high temperatures of a closed oven. After
curing, the sheet is cut to the desired length.
The process which is limited to sheets, is used for
producing flat and corrugated architectural panels that have a wide range of applications such as
room separating light walls, composite doors and
glazing, patio covers, greenhouse panels, skylights
or electrical insulating materials.
6.16 Pultruded profile reinforced with carbon fibre
(http://www.secar.at/)
6.17 Spay-up process
(http://www.businessnc.com/)
6.6.1 Spray-up
Spray-up is a simple and inexpensive method for
large parts with complex geometries that is based
on spraying a mixture of short chopped fibres and
resin on the surface of the mold. The process requires a single mold that is usually made of GFRP or
wood and the necessary equipment that includes
a hand-held spray gun and rollers.
The reinforcement is installed in the spray gun as a
continuous roving which is chopped in short fibres
inside the gun. Prior to spraying the mixture on the
surface, a gel coat is applied on the mold as in
hand lay-up. Once this layer has cured, the fibres
and the resin are sprayed on the mold. Air inserts
are directly pressed out with a roller and then the
wet laminate is left to cure in atmospheric room
conditions. For thick laminates, the layering is processed in several stages, allowing the material to
gel after every stage.
Spray-up is suitable for shapes with high surface
area to thickness ratio while lamination of vertical
surfaces or membranes is also possible. Typical
applications include building panels, boat hulls or
bathtubs. Another advantage is that the process
is low labor intensive requiring only the minimum
amount of work necessary.
However, the components produces are composites with low demands regarding their mechanical
properties and load-bearing capacity due to the
short length and random orientation of the fibres.
Additionally, as the laminates tend to be rich in
resin, the fibre-to-resin ratio is very low, resulting in
heavier parts. Resins, also need to be low in viscosity (more in a liquid form) in order to be sprayable,
which generally compromises their mechanical/
thermal properties (NetComposites, 2014).
Regarding the environmental impact of the process, as spray-up is an open mold process the styrene emissions are high. Besides, the low viscosity
resins that are used are typically more hazardous
than other thicker resins. Thus a good ventilation
system that provides constant air extraction is necessary.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
77
6.7 Manufacturing cost calculation
Describing all the different processes showed that
manufacturing a composite component consumes
various types of resources, each of which has an associated cost. The summation of the costs of these
resources results to the final cost of the product.
These resources can be generally classified in the
five following categories: materials, capital, time,
energy, information (Ashby, Shercliff, Cebon, 2010).
6.7.1 Materials
Manufacturing a component that weights m (kg)
includes the cost Cm ($/kg) of the materials and
consumable feed-stocks from which it is made.
Thus, the cost of the materials that primarily contributes to the final cost of the unit is mCm. However,
processes usually do not use the right amount of
material but create a scrap fraction f, such as machinery swarf and rejects. In order to include this lost
material in the cost the material cost per unit has to
be magnified by the factor 1/(1-f). Thus, the material cost per unit is:
6.7.2 Capital
The total capital investment is generally subdivided
into the cost of tooling and the cost of equipment.
The cost of tooling Ct ($), consists the cost of dies,
molds, fixtures, and jigs and is also known as the
dedicated cost because is entirely assigned only to
the production run of a single component. Tool
ing has a certain lifespan, after the end of which
it needs to be replaced. Tool life is defined by the
number of units nt that a set of tooling can produce before being renewed. Every time tooling is
replaced, the cost of the new tools is added to the
total cost and spread over the whole batch size n
of the production run, increasing the cost per unit.
This increase in the total cost caused by the renewal of tooling is expressed by multiplying the cost of
one tooling set Ct by (1+n/nt). Thus, the tooling cost
per unit is:
The capital cost of equipment Ct ($) is in contrast
with the cost of tooling not dedicated only to one
production. By installing different die-sets or tooling,
the same equipment and machinery can be used
to manufacture many different components. The
overall capital cost of the equipment is converted into an overhead “rental” charge per hour by
diving it by a capital write-off time, two, which is
the years the machinery was used from the beginning of its function until the time it was recovered.
Thus, in the exceptional case in which the equipment is used continuously during its lifespan, the
charge per hour is Cc/two. However, as this is not
the case, the write-off time is magnified with a load
factor L, which is the fraction of time for which the
equipment was productive. This hourly cost is then
divided by the production rate/hour ṅ (units/hour)
in order to get contribution of capital cost per unit.
hand lay-up
vacuum assisted rtm
spray-up
thermoforming
resin transfer mold.
cold press mold.
pultrusion
smc molding
bmc molding
centrifugal molding
filament winding
vacuum/pressure bag
resin film infusion
autoclave molding
automatic tape placement
continuous lamination
100
1000
104
Table 6.1 Capital cost of composite manufacturng processes
(CES Edupack, Granta Ltd)
105
106
[EUR]
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Chapter 6 | Production Techniques
6.7.3 Time, energy and information
This category consists of costs of different resources
that are included into the general hourly overhead
rate Coh ($/h). The time required for the production
of a series of components becomes chargeable by
including the cost of labor, administration and general plant costs. Energy consumed for the process
is also included in the Coh. Finally, there is also the
cost of information in the sense of research and development done, royalty or license fees.
6.7.4 Cost comparisons between the processes
After having analyzed the costs of all the different
resources consumed in order to manufacture composite components, the production techniques described previously are compared in the following
tables in terms of these cost categories and other
economic characteristics. All the tables were developed in the material science computer software
CES Edupack 2013.
The tables of the capital and tooling cost show that
processes that require either automated machinery (automated tape placement, continuous lamination) or complex, usually double and expensive
molds (compression molding techniques, RTM), are
the ones that have the higher values. On the other
hand, manual processes that are based more on
hand labor and make use of cheap molds (hand
lay-up, vacuum assisted RTM, thermoforming) have
a lower capital cost.
The total shaping cost for one single unit, Cs is the
sum of these four equotations, C1-C4, which can
be simplified to the following (Ashby, Shercliff, Cebon, 2010):
However, some manual processes, such as hand
lay-up, even if they require low capital investment,
they can be very labor intensive and thus have an
increased cost per unit. Specifically, table 4.3 classifies 10 of the researched processes that require
hand labor into three categories regarding their
labor intensity: low, medium, high. Compared to
hand lay-up, vacuum assisted resin transfer molding is a less labor intensive process that still can be
operated within a low investment on equipment.
The equotation shows that the three main contributions to the cost of one product is the material cost
per unit which is not depending on the production
batch size or rate, the dedicated cost (tooling cost)
per unit which depends on the production volume
(1/n) and a general overhead per unit that is influenced by the production rate (1/ṅ).
vacuum assisted rtm
thermoforming
vacuum/pressure bag
resin transfer mold.
cold press mold.
resin film infusion
continuous lamination
filament winding
hand lay-up
autoclave molding
automatic tape placement
spray-up
pultrusion
centrifugal molding
smc molding
bmc molding
100
1000
Table 6.2 Tooling cost of composite manufacturng processes
(CES Edupack, Granta Ltd)
10000
105
[EUR]
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
Table 6.3 Labor intensity
(CES Edupack, Granta Ltd)
Low
Pultrusion
Medium
High
Vacuum assisted rtm
Autoclave molding
Vacuum/pressure bag
Hand lay-up
Filament winding
Resin tranfer molding
SMC molding
BMC molding
Thermoforming
Normally, processes that require high capital investment become economic only at large batch sizes
and therefore are preferred for large production
series. On the contrary, processes with low tooling
cost are suitable for small batch sizes. Usually, such
techniques use equipment with low tool life which
needs to be replaced after a small quantity of units
produced. Table 4.4 shows the economic batch
size of the researched processes in units and Table
1.1 indicates the life of the equipment before it has
to be renewed.
79
Finally, another important factor is the production
rate. This output rate influences the time required for
producing a series of composite components and
is measured in number of units per hour or length
per hour in the case of continuous processes. The
production rate is associated with hourly costs of labor, charging of the machines and consummation
of energy, while the rate becomes more important
for large scale productions. As table 1.1 also confirms, automatic processes have higher production
rates than their manual counterparts.
In conclusion, comparing the processes in terms
of cost showed that for the case of a production
with less than ten units batch size, such as a single bridge, the optimum methods are the typical
manual ones, such as vacuum assisted resin transfer molding or hand lay-up. Nevertheless, the latter
requires much more labor intensity.
automatic tape placement
vacuum/pressure bag
resin film infusion
hand lay-up
autoclave molding
vacuum assisted rtm
spray-up
cold press mold.
thermoforming
resin transfer mold.
filament winding
centrifugal molding
bmc molding
smc molding
1
10
100
1000
10000
Table 6.4 Batch size capacity of composite manufacturng processes
(CES Edupack, Granta Ltd)
105
106
107
[units]
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Chapter 6 | Production Techniques
6.8 Moldmaking
Mold construction is an influential factor of the tooling cost. Molds are generally expensive in terms
of their materials and production and in cases of
complex shapes the cost of the mold can even exceed the cost of the actual component (Knippers,
Cremers, Gabler & Lienhard, 2011).
6.8.1 Mold materials
The selection of the proper material for a mold depends mainly on the dimensions of the component,
e.g large components need strong materials, the
desired surface quality and the number of reuses
required. Strong materials are normally an option in
cases of high batch sizes whereas cheaper materials allow only for a small number of reuses.
The process of creating the mold is operated into
two steps. The first step includes the production of
the original or master mold. This first prototype is developed by means of adding or subtracting gradually material e.g by milling with CNC machine. The
materials used are easy to work but normally they
have short lifespan and thus are suitable only for a
small number of reuses. Such materials include rigid
foam, balsa wood, clay or gypsum.
Gypsum is an inexpensive and easily formed material that is usually used both for negative or original molds. However, its low strength makes it fragile
and thus the mold is frequently damaged during
demolding. Clay is like gypsum another inexpensive easy to shape material suitable for small components and a few reuses.
The second step is the production of the negative
mold by laminating or casting on the first original
mold. Various materials such as fiber-reinforced
polymers and metals can be used for the negative
mold, depending on the size of the production run.
In order to make easier the demolding of the negative mold, the surface of the original mold is coated
with a release agent such as silicone oil or wax.
Rigid foam (PVC, PUR, XPS) is a frequently used material that functions both as mold and core material. The cost of the material is relatively high and
so the quantity of foam used must be reduced to
minimum. Additionally, the computed-controlled
shaping process by the CNC milling machine requires labor. Molds made from rigid foam have a
short lifespan that makes them functional only for
a few reuses.
Glass fibre-reinforced polymers consist a comparatively more expensive option used for constructing
durable negative molds with a life span of more
than 100 reuses. Polymers without reinforcement
such as polyurethane resin are also an alternative. PUR has an excellent finish and is used where
high-precision molds are needed. However, the
mold itself is comparatively expensive and heavy.
6.18 Foam shaped by a CNC router for a boat hull mold
(http://www.reinforcedplastics.com/)
Metal molds, normally from steel and aluminum are
also durable and strong but expensive to produce
and thus they require very large production runs.
Wooden molds represent another reasonable alternative mainly for large components.
Apart from the two-step process of moldmaking,
the negative mold can be also created directly.
For example, is possible to shape rigid foam with a
CNC milling machine or place wooden boards in
a way that they create a sealed mold hat can be
used directly for producing the composite components. Finally, another special type of mold is the
permanent formwork which remains as the core
material inside a sandwich composite.
6.19 FRP composite mold
6.20 Steel mold
(http://www.pcminnovation.com/)
(http://www.emeraldinsight.com/)
Bio-based FRP pedestrian bridge in Schiphol Logistics Park
Design
11
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Chapter 7 | Design
7.1 Case study
The selected site for designing the bridge is located in
the municipality of Haarlemmermeer, in the province
of North Holland in the Netherlands. Adjacent to the
west border of the municipality at the south side of
Schiphol Airport, the area is currently developed into
a logistics park by Schiphol Area Development Company. Schiphol Logistics Park is 45 hectares in size and
comprises a western section (24 hectare) and an eastern section (21 hectare).
The eastern section is separated into two subareas as
a small ditch runs the entire length of the area. From
the one side of the ditch the area is programmed to
become the business location offered for development and investment while the other smaller area is
designed as a public park. The role of this almost 7
hectare green park, Ringdijkpark, is to stand as a buffer zone between the logistics area and a housing linear zone across Aalsmeerderdijk which is adjacent to
the area. Thus, Ringdijkpark, will work as a refreshing
intermediate zone given both to the employees of the
logistic companies and the permanent inhabitants.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
7.2 Site analysis
The ditch separating the Schiphol logistic park and the Ringdijkpark is the
site that was chosen for designing the natural fibre-reinforced polymer
bridge of this graduation. The width of the dike is 7 meters including the
slopes from both sides while the ground from the side of the Ringdijkpark
is 75cm lower than the other side.
The case study area, as well as the entire municipality of Haarlemmermeer is beneath sea level as for centuries Haarlemmermeer was a dangerously increasing 70 square mile lake which was transformed into land
in the 19th century by using steam pumping machines that drained the
water. Thus, the level of the ground of the logistic park is 4,02 meters beneath sea level, Ringdijkpark is at -4,75 meters whereas Schiphol airport
is at -6 meters.
With the same technique of the polder system that was used in all lake
draining examples in the Netherlands, a ring canal was opened first
around the water surface while the excavated soil was used for building
a dike between the canal and the lake. Then the water was pumped out
from the lake by windmills or later by steam machines and thrown to the
ring canal which was directing the water to rivers through outlet canals.
(Dry feet. Flood mitigation in the low countries, 2010)
7,00m
-4,02m
0,73m
-6,10m
-7,10m
-4,75m
83
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Chapter 7 | Design
Drainage ditches, such as the one in Schiphol logistics park, were then dug on the reclaimed land in
order to convey the remaining water to the perimeter of the lake bed. Once the land was dry, these
ditches were usually used as borders for indicating
and separating the properties. The drained lake required continuous maintenance for removing precipitation and groundwater seepage.
The water level of the ditch is at -6,10 meters with
a seasonal level increase/decrease of 10 centimeters depending on winter/summer situation. The
depth of the water is about one meter.
7.3 Design parameters
As this graduation project is a realistic scenario offered by SADC company as a request for designing and constructing a bio-based plastic bridge,
cost- efficiency was from the beginning a very crucial parameter. The total cost of the construction
should be kept within the limits of the budget offered by the company which was in this case the
“client” of the project.
Apart from the budget limitations, the fact that the
bridge would be a single product and not part of
a large production run, orients the construction towards simple manufacturing techniques suitable
for small batch sizes. Processes that require a high
capital investment either in tooling, equipment or
machinery could even double the cost of a single
element.
According to the results of the research done on
production methods, in terms of cost, moldmaking
is a crucial factor. Not only is the cost of the chosen
material for constructing the framework but also
the labor required for shaping it, that increase considerably the actual cost of a product. Obviously, in
the case of multiple reuses, the mold cost is spread
over the butch size of the production and thus it is
divided and added on the individual cost of each
unit. However, as this is not the case for the bridge
of this present project, moldmaking has to be reconsidered.
Consequently, the solution for minimizing the cost
of making the mold seemed to be in using materials which can be easily found in most of the composite construction companies. Flat boards, simple
molding tables and generally molds that were previously used in other productions and can be easily
adjusted and reused or inexpensive new material
are ideal elements for constructing efficiently and
without much labor a mold that will be used only a
few times.
Apart from the financial criteria, another parameter that is also considered as important for this project is the optimum structural design of the bridge.
In that sense the chosen shape should be a result of
comparison between a series of different possible
solutions operated by a performance driven evaluation process. In order to achieve this optimized
design result, a number of different digital simulations and tools have to be done on a parametric
model that would allow for a continuous optimization of the chosen design based on its flexibility.
The last factor regarding the design is related with
the aesthetical result and especially with the way
that plastic material should influence the shape
of a bridge. If a truss is connected with either steel
or wood then what are the shaping potentials of
plastic and how a plastic bridge should look like?
Plasticity is a word used in plastic arts for describing
the quality of being plastic and able to be molded. It is also characterizes the quality of a sculpture
in terms of its three-dimensional appearance. So
plasticity already including the word plastic, is an
important element that should be reflected on a
bridge that was not welded or drilled but molded.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
85
7.4 Design evolution
The overall design phase can be generally divided into three different parts that follow a gradually
narrowing course that starts from a general first approach and leads to the chosen design.
7.4.1 Stage 1. First design approach
The first part of the design process is characterized
by a freedom in form exploration as a result of a
rough sense regarding production cost. Not only
had these financial topics not been researched by
that moment but also the project was still in a conceptual level and the real construction was only a
possible but not verified scenario. The result of this
phase is a series of design approaches that being released from cost limitations they explore the
shaping potentials of molded plastic.
The main criteria for these preliminary designs were
the structural efficiency of the shape itself and the
reflection of plasticity. Considering that objects
with surfaces that curve in two directions, such as
domes and spheres, are much stronger compared
to other structural systems, the forms try to translate
these ideas in bridge design. Therefore, concerning a better structural performance the forms of this
phase are all characterized by double curvature,
smooth curved corners and a fluid plasticity.
In conclusion, this phase shows interesting results on
how a plastic bridge could look like under different financial and production circumstances. In a
possible scenario where a larger number of bridges
had to be delivered, the option of making a special mold would be more reasonable, as the cost of
moldmaking would be distributed over the batch
size. The research done on the production methods
that could be used for achieving such shapes and
on the financial issues proved that as the geometry becomes bigger and more complex, the cost of
moldmaking increases because stronger and thus
more expensive material are required and more labor is needed.
However, all this knowledge taken from this design
part together with the research done was important in order to rethink issues of shaping and production and continue to more rational and cost-efficient solutions.
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Chapter 7 | Design
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
7.4.2 Stage 2. Second design approach
Design guidelines
Following the direction of having an inexpensive
mold by reusing material that already exists in a
composite company directly influences the design possibilities. Shapes that could be feasibly
constructed without exceeding the given budget
should be simple in geometry and consist mainly of
flat or simply curved surfaces.
As it was previously mentioned in the chapter of the
design parameters, a realistic solution towards low
cost moldmaking would be to actually make use of
already existing molds or in general materials that
are easy to be found and do not require much labor to be used.
For instance, one object that is present in almost
every composite company is a steel flat molding
table mainly used for vacuum assisted resin transfer
molding. This flat table has usually large dimensions,
enough to fit the entire length of an 8 meter bridge.
In some cases, especially in companies that produce composite bridges this flat steel plate is more
flexible, allowing for bending as well.
The design prepositions of this phase actually explore the potentials of using this flat plate either
straight or slightly bended as the mold of the deck
of the bridge. The plate will also be the base for adjusting vertical flat boards for shaping the parapets
and making a single mold both for the dech and
the parapets.
An important decision that is reflected in both design phases was to achieve a one-off uniform composite structure produced by the same production
process from a single mold. The purpose of this intention is to use structurally the parapets as beam
elements and have a coherent and complete
structural system. Separating the structure in one
deck element and two side parapets assembled
together would cause discontinuity of the fibres
and thus subdivision of the system. Additionally,
the connection surfaces in the case of a separate
structure would require special shaping of the joints
that would add complexity to the mold, while in
the final result the connection lines would be visible
depriving the visual continuity and uniformity of the
bridge.
The design of the bridges is inspired by the Japanese paper folding art of the origami. The majority of these concept bridges consist of flat surfaces
and gentle “folding” lines combined in clear geometries that resemble to origami structures. The
results of this phase consist of 6 bridges, which although they follow the same “origami” design concept and they keep the same general dimension,
they all have slight differences.
All the bridge geometries were created in a parametric design software in order to achieve a flexible and adaptable 3D model by controlling its basic parameters. The specific software that was used
is Grasshopper for Rhino.
pt
have
is toahave
uni- a unintinuous
s structure
structure
hections
connections
in
in
cturally
se structurally
the the
ets
parapets
as
as
s.
beams.
dimensions
sions
ke2mx7,5m
deck 2mx7,5m
1m
apets
high
1m high
ftotal
the parapets
if the parapets
topenings
have openings
87
Vacuum
Vacuum
table table
Flat sideFlat
boards
side boards
out of out of
wood, mdf
wood,
etcmdf etc
The concept is to have a uniform Curved
continuous
structure
Curved
cornerscorners
withouth connections in
order to use structurally the
side parapets as
beams.
dimensions
Flat sideFlat
boards
side boards
out of out of
wood, mdf
wood,
etcmdf etc
88
Chapter 7 | Design
7.4.3 Design results
Bridge1
This bridge is characterized by a straight 2 meter in width deck and identically same parapets that have a slight shift in the middle of their length,
which breaks the totally straight direction. This shifting in the geometry of
the parapets results in an inwards turn and an outwards turn of the one
and the other side accordingly. The minimum height of the parapets is 1
meter.
Bridge 2
The second design approach is similar to the previous bridge with the only
difference that the side parapets are placed symmetrically to the horizontal axis of the deck giving an entire symmetry to the design. Both parapets
keep an outward shifting resulting to more clear U-shaped crossections
throughout the length of the bridge.
Bridge 3
Bridge 3 is also an alternative of bridge1 which retains the same general
dimensions and asymmetry. The difference between the two designs is
that in bridge3 the inward segments of the parapets are kept to a vertical
straight position and are not turning towards the deck, whereas the outward parts keep the same position.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
Bridge 4
This design approach has a main difference from the previous examples
as the deck is not straight in z-direction but consists of two planar angled
segments that create a smooth curve at the point that they are joined.
Additionally, the width of the deck increases respectively from both sides,
starting from 1,8 meters of minimum width and reaching 2,6 meters at
the highest point of the deck, where the two planar elements meet. The
parapets keep a symmetrical order and both have segments that turn
slightly outwards.
Bridge5
The 5th design is almost identical to the previous 4th design. Having the
same deck, bridge5 and bridge4 are different only at the parapets. The
only difference is that the parapets of this bridge are triangulated, meaning that they consist of triangular surfaces. Being closer to the origami
structures, this bridge allows for more freedom in shifting the surfaces of
the parapets.
89
90
Chapter 7 | Design
Bridge 6
The last bridge is an alternative of a bridge with a bended deck. In the
same way like the two previous designs, bridge 6 keeps a curved increase
of the width which reaches 3 meters maximum width and 1,8 meters minimum. The maximum height of the bend is 0,7 meters. The parapets here
follow the bended character of the design and avoid having straight
linear folds and geometry shifts.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
7.4.4 Stage 3. Structural testing
In the next phase, the previously presented design results had to
be compared in terms of the structural behavior of their geometry. For that reason special software for structural analysis was
used on the parametric models that were created in Grasshopper. Keeping the flexibility of the model allowed for optimization
of the shapes by changing the dimensions of the geometry. The
software that was used for the structural analysis and calculation
is Karamba, a plug-in tool for Rhino that is fully embedded in the
parametric environment of Grasshopper.
geometry
parameters
boundary
conditions
structural analysis
Boundary conditions
Running the analysis requires the construction of a finite model of
the geometry composed by basic entities such as supports, loads,
material properties and cross section that is applied to all 6 bridges
in order to have an equal comparison based on the same boundary conditions.
Specifically, all the bridges are tested under a uniformly distributed
load of 5.0 kN/m2 which is applied on the loading surface of the
deck. Additionally, the support points are defined together with
their degrees of freedom regarding translation in x-, y- and z- direction (Tx, Ty, Tz) and rotation (Rx, Ry, Rz).
As the goal of the analysis is to compare the structural behavior of
the geometries in terms of deformation and not to extract values
or calculate the composite structure, an assumption was made in
terms of the material selection of the bridges in order to simplify the
process. Thus, the bridges are defined as 100mm thick structures
with the mechanical properties of a composite that consists of an
epoxy resin and E- glass fibres.
results with values
91
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Chapter 7 | Design
Results
The analysis regarding the structural efficiency of the shapes, which is expressed through the deflection of the
geometries brought quite interesting results. First of all, the expectations of the superiority of the bridges with
slightly bended decks over the straight ones obviously proved to be right as the deflection of the first was ten
times less compared to the latter. Specifically, the bridge with the lower deflection was the bended one while
the ones with the angled two-plate deck exhibited slightly higher values.
As the parapets of the given bridges are part of the structure their height and position also proved to be influential. Thus, the higher a parapet gets the more tends to get deformed inwards under uniform loading of the deck.
This tendency also explains the high deflection values of the parapets that already designed to turn inwards to
the deck (bridge1). Finally, the symmetry of the parapets in the longitudinal direction seemed to be a better
option.
The following diagrams illustrate the deflection of the 6 bridges (vertically from bridge1 to bridge 6)
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
7.5 Final Design
The final design is based on bended model
that was chosen during the previous process.
However, due to manufacturing limitations as
well as reasons linked to functionality the deck
could only slightly bended having a radius of
30 meters.
The parapets have a continuous height of 1
meter for most of the length of the bridge apart
from the point where it smoothly turns downwards. At that point the height of the parapet
is approximately 1,3 meters. Finally the parapets are placed with an inclination of 30o on
the deck, while the deck-parapet connecting
edges have a smooth turn.
Similar to the bended tested model, the final
design retains the elliptical shape on top view
that creates a feeling of surrounding space
to someone that stands in the middle of the
bridge and give the sense of an entrance to
the one entering the space from the two edges. The minimum width of the bridge at the two
entrances is 2 meters and it reaches a maximum of 3 meters in the middle, while the span
has a length of 8,2 meters. After performing the
structural calculation, which consists the following chapter, the thickness of the structure was
resulted to be 7 milimeters.
The bridge was chosen to be painted with two
different colours, one from the outer surface
and one from the inner. For the outer side a
warm dark chestnut brown is suggested, while
from the inside surface will be painted in light
beige-grey.
93
94
Chapter 7 | Design
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
95
7.5.1 Architectural Drawings
Longitudinal Elevation
Transverse Elevation
96
Top view
Chapter 7 | Design
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
97
Section A-A
Section B-B
98
7.5.2 3D Impressions
Chapter 7 | Design
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
99
100
Chapter 7 | Design
Structural calculation
102
Chapter 8 | Structural Calculation
8.1 Structural simplification
In order to simplify the calculation of the structure,
the geometry of the bridge was translated into a
more rational shape, that of a straight U-beam. The
general dimensions (width, span, parapet height)
are retained, whereas curved lines are considered
as straight. The parapets are positioned vertically
to the deck while their height is constantly at 1,0m
along the span. Figure shows the shape of the geometry that will be calculated.
1.1m
part are used in the final part, which is the calculation of the ultimate and service limit state.
The entire structural calculation of the bridge was
performed by repeating the described procedure
in order to achieve a continuous optimization of
the structure. The initial calculation assumed values such as thickness or ply orientation in order to
draw and evaluate the first results. Then according
to these results, input was adjusted and new values
were calculated. In this way, optimum thicknesses
for the composite were defined.
8m
2m
8.1 Extruded view of the simplified structural model
8.2 Structural analysis approach
8.2.1 Calculation process
The structural analysis process of the simplified
model is organized into the phases shown in figure.
Starting from the fibre/resin properties, given by the
supplier of the specific fabric and resin chosen, the
properties of one ply with single orientation can be
calculated by using the “Rule of Mixtures”.
Having the properties of a single ply, which consists resin and reinforcement in amounts according
to the fibre volume fraction that the chosen manufacturing method can achieve, the properties of
the laminate can be calculated. This is achieved
by following a process based on the Classical laminate theory. At this phase, the computer software
for laminate calculation, Kolibri, was used to evaluate validity of the manually found results. Important
properties that result from this part of the calculation is the thickness, the Young’s modulus and the
Shear modulus of the laminate.
After having calculated the properties of the composite, the U-beam bridge is analyzed. The first step
includes the calculation of the moment of inertia for
the cross-section of the geometry. The results of this
8.2 Flow of the output of the simplified structural caclulation
8.2.2 Aim of the analysis
The structural analysis was performed for every of
the four chosen fibres (flax, jute, glass and basalt).
The aim of this analysis is to compare the structural
performance of the four composites in regards to
their optimum thicknesses. Through this comparison,
the fibres are evaluated as for their environmental
efficiency. Knowing the exact kilograms of required
material for each composite allows for a comparison between their energy requirements and their
financial cost. Thus this structural analysis combined
with the Life Cycle Assessment will show which fibre
is more suitable for the requirements of this project.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
103
8.3 Dimensioning of the bridge
In order to proceed to the structural calculations of the bridge it is necessary to define the basic geometrical
characteristics of the simplified model. The results of the first analysis are then evaluated and these first input
data are reconsidered and changed according to the results.
Table 8.1 Dimensions of the structural analysis model
Top flange facing thickness
tfacing.top = 7.2mm
Side parapet facing thickness
tfacing.in = 7.2mm
Inner facing deck thickness
tfacing.out = 7.2mm
Outer facing deck thickness
tfacing.side = 7.2mm
Core thickness
tcore = 86mm
Parapet thickness
btop = 116mm
Deck inner width
bin = 1900mm
Deck outer width
bout = 2000mm
Parapet inner width
hin = 1000mm
Parapet outer width
hout = 1200mm
8.4 Fibre-resin properties
The first of the fibres that was chosen to be calculated as reinforcement of the composite was the one with the
highest mechanical properties, thus basalt. The specific textile used in the calculations is a unidirectional fabric
with product name BAS UNI 600, supplied by Basaltex, a Belgian based company that produces basalt technical
textiles. The resin that is used in all the calculations is a100% bio-based furan.
Table 8.2 Basalt-furan mechanical/physical properties
Basalt fibre
Furan
Elastic modulus
Ef= 85 GPa
Em= 2 GPa
Shear modulus
Gf= 35 GPa
Gm= 1.3 GPa
Poisson’s ration
νf= 0.26
νm= 0.35
Volume fraction
Vf= 0.5
Vm= 0.5
Density
pf= 2670 kg/m3
pm= 1100 kg/m3
Weight
mf= 600 gm/m2
104
Chapter 8 | Structural Calculation
8.5 Calculation of ply properties
Calculation of the ply properties is based on the general Rule of Mixtures for composite materials, which is used
to define values such as mass density, elastic modulus and shear modulus. Assumptions done by the rule of mixtures include the uniform distribution of the fibres in the matrix, ideal fibre-matrix adhesion, free of voids matrix,
application of loads is either parallel or normal to the fibre direction, the lamina is initially in a stress-free state (no
residual stresses) and the fact that fibre-matrix both behave as a linearly elastic material. Therefore, by using the
rule of mixtures, the ply density, elastic longitudinal-transverse modulus, shear modulus and poisson’s ratio are
calculated:
Ply density
pFRP = pf ⋅ Vf + pm ⋅ Vm = pf ⋅ Vf + pm ⋅ ⎛⎝1 − Vf⎞⎠ = ⎛⎝pf − pm⎞⎠ ⋅ Vf + pm
kg
pFRP ≔ ⎛⎝pf − pm⎞⎠ ⋅ Vf + pm = 1885 ――
3
m
Longitudinal modulus (loading parallel to the fibres)
Equal strain assumption:
εc = εf = εm
According to Hookes law we get,
Loading parallel to the fibres
E1 ⋅ εFRP = Ef ⋅ εf ⋅ Vf + Em ⋅ εm ⋅ Vm = Ef ⋅ Vf + Em ⋅ Vm
E1 ≔ Ef ⋅ Vf + Em ⋅ ⎛⎝1 − Vf⎞⎠ = 43.5 GPa
Transverse modulus (loading perpendicular to the fibres)
1 + Vf ⋅ ξ ⋅ η
E2 = Em ⋅ ――――
1 − η ⋅ Vf
in which
Ef
――
−1
Em
η = ―――
Ef
+ξ
――
Em
The term “ξ”is called the reinforcing factor and depends on:
1.fibre geometry
2.packing geometry
3.loading conditions
For our case
ξ≔2
Ef
――
−1
Em
η ≔ ―――
= 0.93
Ef
+ξ
――
Em
1 + Vf ⋅ ξ ⋅ η
E2 ≔ Em ⋅ ――――
= 7.2 GPa
1 − η ⋅ Vf
Loading perpendicular to the fibres
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
105
Poisson's ratio
ν12 ≔ νf ⋅ Vf + νm ⋅ ⎛⎝1 − Vf⎞⎠ = 0.31
E2
ν21 ≔ ―⋅ ν12 = 0.05
E1
In-plane Shear modulus
The Halphin and Tsai equation for the in-plane shear Modulus G12 is :
1 + ξ ⋅ η ⋅ Vf
G12 ≔ Gm ⋅ ――――
1 − η ⋅ Vf
in which
ξ≔1
and
Ef
――
−1
Em
η ≔ ―――
= 0.95
Ef
+ξ
――
Em
1 + ξ ⋅ η ⋅ Vf
G12 ≔ Gm ⋅ ――――
= 3.7 GPa
1 − η ⋅ Vf
G12 is matrix dominated and is a series combination like E2.
Partial factors
8.6 Definition of the laminate
Material factors (CUR 96 ;2003)
A laminate is an organized stack of unidirectional
γm1 ≔ 1.35on the fibre orientation
composite plies. Depending
and the sequence of the individual plies the laminates
are
generally
in1.2
isotropic and anisotropic.
Vacuum
infusionclassified
γm2 ≔
Isotropic laminates exhibit equal properties in all directions due to the uniform distribution of plies with different
In the
anisotropic
laminates,
Totalorientation.
material factor
γmcontrary
≔ γm1 ⋅ γm2
= 1.62
also called orthotropic, show different properties in
each axis as fibre orientation is not equally arranged.
In addition, laminates are characterised as balanced
Conversion factors (CUR 96 ;2003)
when for every +θ ply there is an equally thick –θ ply
and symmetric when the plies of the laminate are
γct ≔
1.1 the geometrical midTemperature
stacked
symmetrically
about
plane.
Moisture
γcm ≔ 1.1
0
+45
90
-45
-45
90
+45
0
Considering a first simplified approach for the calculation of the structure an isotropic composite plate was
chosen
for allfactor
the parts
structure.
Total material
γc of
≔ γthe
ct ⋅ γ
cm = 1.21 Specifically the
laminate is Quasi isotropic, which means that it exhibits isotropic in-plane response but it is not restricted to
show isotropic out-of-plane (bending) response. The
suggested laminate is also balanced and symmetric
and consists of 8 unidirectional plies, oriented in 0, +45,
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90, -45 degree angles which are equally distributed
8.3 Chosen fibre orientation for the Quasi-isotropic lamieach at a percentage of 25%. Scheme 1.5 shows the
nate of the project
chosen arrangement of the laminate.
106
Chapter 8 | Structural Calculation
The laminate structure defined above consists a repeated module. Increasing the number (Nmod) of the module increase the thickness of the laminate but it will not influence its mechanical properties. For this simplified first
calculation, equal thickness for all parts of the bridge was chosen, whereas the number of the modules is set to
2,
thus 16 plies.
Knowing the thickness of a single ply, the entire thickness of the laminate can be calculated as
Laminate
Calulation
follows.
Thicness of fabric
mf
tfabric ≔ ――
= 0.22 mm
pf
Thicness of ply
tfabric
tply ≔ ――= 0.45 mm
Vf
Thickness of QI laminate module (8 plies):
tQImod ≔ 8 ⋅ tply = 3.596 mm
Number of modules: Nmod ≔ 2
tlam ≔ Nmod ⋅ tQImod = 7.191 mm
tlam
nply ≔ ――
= 16
tply
Calculation
of laminate
properties
Material requirements
/ Cost
estimation
After having defined the structure of the laminate, the calculation of the properties follows. To this point Classical
laminate theory is employed in order to define the strains and the stresses for the entire thickness of the laminate
by starting from the strains and stresses of a single ply that is loaded parallel to the fibres. By using the stresses and
¤ calculate the force and moment resultants acting at that point and
strains
in of
the
principal
we can
Price
jute
fabric direction
cbasalt
≔ 8.5also
――
2
consequently the total forces and moments
m acting on the edges of the laminate.
Area
of total
surface
(2 facings)
8.6.1
Stress
[σ] laminate
- Strain [ε]
relations
for principal directions
Stress [σ] - Strain [ε] relations for principal directions
Coordinate axes (xyz)=subscripts
(123)
⎛
Atot.lam ≔ L1 ⋅ ⎝bin + 2 ⋅ hin + 2 ⋅ btop + 2 ⋅ hout + bout⎞⎠ = 69.856 m
2
The stress-strain relations on the principal axes can be expressed by the reduced stiffness
constants S which form the stiffness matrix [S] such that
Total mass [kg] of fabrics required
mf.tot ≔ nply ⋅ Atot.lam ⋅ mf = 670.618 kg
⎡ σ1 ⎤ ⎡ Q11 Q12 0 ⎤ ⎡ ε1 ⎤
⎥ ⎢
⎥
⎢ σ ⎥=⎢ Q Q
Total cost of
fabrics required 0 ⋅ ε2
⎢ 2 ⎥ ⎢ 12 22
⎥ ⎢
⎥
0 Q66 ⎦ ⎣ γ12 ⎦
⎣ τ12 ⎦ ⎣ 0
cbasalt.tot ≔ nply ⋅ Atot.lam ⋅ cbasalt = 9500.416 ¤
In which, by inspection of the individual equations, it can be seen that
E1
Q11 ≔ ―――――
= 44.184 GPa
⎛⎝1 − ν12 ⋅ ν21⎞⎠
ν12 ⋅ E2
Q12 ≔ ―――――
= 2.244 GPa
⎛⎝1 − ν12 ⋅ ν21⎞⎠
E2
Q22 ≔ ―――――
= 7.356 GPa
⎛⎝1 − ν12 ⋅ ν21⎞⎠
Q66 ≔ G12 = 3.671 GPa
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The inverse version of the above matrix is expressed by the following compliance matrix and the constant Q
12
21
12
21
E2
Q22 ≔ ―――――
= 7.356 GPa
Q66 ≔ G12 = 3.671 GPa
⎛⎝1 − ν12 ⋅ ν21⎞⎠
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
107
The inverse version of the above matrix is expressed by the following compliance matrix and the constant Q
⎡⎣ σ ⎤⎦ = ⎡⎣ Q ⎤⎦ ⋅ ⎡⎣ ε ⎤⎦
⎡ ε1 ⎤ ⎡ S11 S12 0 ⎤ ⎡ σ1 ⎤
⎢ ε ⎥=⎢ S S
0 ⎥ ⋅ ⎢ σ2 ⎥
⎢ 2 ⎥ ⎢ 12 22
⎥ ⎢ ⎥
⎣ γ12 ⎦ ⎣ 0 0 S66 ⎦ ⎣ τ12 ⎦
1
1
S11 ≔ ―= 0.023 ――
E1
GPa
−ν12
1
S12 ≔ ――= −0.007 ――
E1
GPa
1
1
S22 ≔ ―= 0.138 ――
E2
GPa
1
1
S66 ≔ ――
= 0.272 ――
G12
GPa
8.6.2 Stress [σ] - Strain [ε] relations for rotated axis
Stress [σ] - Strain [ε] relations for rotated axis
Rotation of axe (z) with angle φ of (xyz) gives (x'y'z')
The first step in establishing the lamina strains for off-axis loading is to find the stresses, referred to the fibre axis (σ1, σ2
and τ12), in terms of the applied stress system (σx, σy and τ12). This is done using the equation expressing any second
rank tensor with respect to a new coordinate frame
σij = aik ⋅ ajl ⋅ σ'kl
in which aik is the direction cosine of the (new) i direction referred to the (old) k direction. Obviously, the conversion will
work in either
direction
the direction
cosines
defined correctly. For
example,
the normal stress parallel to
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withprovided
PTC Mathcad
Express.
Seeare
www.mathcad.com
for
more information.
the fibre direction σ11, sometimes written as σ11, can be expressed in terms of the applied stresses σ'11 (= σx), σ'22 (= σy)
and σ'12 (= τxy)
σ11 = a11a11 ⋅ σ'11 + a11 ⋅ a12 ⋅ σ'12 + a12 ⋅ a11 ⋅ σ'21 + a12 ⋅ a12 ⋅ σ'22
The angle φ is that between the fibre axis (1) and the stress axis (x). Referring to the figure, these direction cosines take
the values
z
ϕ ≔ 45 °
⎛⎝a11 = c⎞⎠
⎛⎝a12 = s⎞⎠
⎛⎝a21 = −s⎞⎠
⎝⎛a22 = c⎠⎞
c ≔ cos ⎛⎝ϕ⎞⎠ = 0.71 rad
s ≔ sin ⎛⎝ϕ⎞⎠ = 0.71 rad
Carrying out this operation for all three stresses and tensorial strains
⎡ σ1 ⎤
⎡ σx ⎤
⎢ σ ⎥ = ⎡⎣ T ⎤⎦ ⋅ ⎢ σ ⎥
⎢ 2⎥
⎢ y⎥
⎣ τ12 ⎦
⎣ τxy ⎦
where
⎡ c2
⎢
s
2
2 c⋅s ⎤
⎥
x
and
⎡ ε1 ⎤
⎡ εx ⎤
⎢ ε ⎥ = ⎡⎣ T ⎤⎦ ⋅ ⎢ ε ⎥
⎢ 2⎥
⎢ y⎥
⎣ ε12 ⎦
⎣ εxy ⎦
45o
y
108
⎛⎝a11 = c⎞⎠
c ≔ cos ⎛⎝ϕ⎞⎠ = 0.71 rad
⎛⎝a12 = s⎞⎠
s ≔ sin ⎛⎝ϕ⎞⎠ = 0.71 rad
⎝⎛a21 = −s⎞⎠
Chapter 8 | Structural Calculation
⎝⎛a22 = c⎠⎞
Carrying out this operation for all three stresses and tensorial strains
⎡ σ1 ⎤
⎡ σx ⎤
⎢ σ ⎥ = ⎡⎣ T ⎤⎦ ⋅ ⎢ σ ⎥
⎢ 2⎥
⎢ y⎥
⎣ τ12 ⎦
⎣ τxy ⎦
and
⎡ ε1 ⎤
⎡ εx ⎤
⎢ ε ⎥ = ⎡⎣ T ⎤⎦ ⋅ ⎢ ε ⎥
⎢ 2⎥
⎢ y⎥
⎣ ε12 ⎦
⎣ εxy ⎦
where
2
⎡ c2
s
2 c⋅s ⎤
⎢ 2
⎥
2
⎡⎣ T ⎤⎦ = ⎢ s
c
−2 c ⋅ s ⎥
⎢⎣ −c ⋅ s c ⋅ s ⎛⎝c 2 − s 2 ⎞⎠ ⎥⎦
However, to use engineering strains (γxy = 2εxy etc), |T| must be modified (by halving the
elements t13 and t23 and doubling elements t31 and t32 of the matrix |T| ), so as to give
⎡ ε1 ⎤
⎡ εx ⎤
⎢ ε ⎥ = ⎡⎣ T' ⎤⎦ ⋅ ⎢ ε ⎥
⎢ 2 ⎥
⎢ y⎥
⎣ γ12 ⎦
⎣ γxy ⎦
in which
2
⎡ c2
s
c⋅s ⎤
⎢
⎥
2
2
⎡⎣ T' ⎤⎦ = ⎢ s
c
−c ⋅ s ⎥
⎢⎣ −2 c ⋅ s 2 c ⋅ s ⎛⎝c 2 − s 2 ⎞⎠ ⎥⎦
The procedure is now a progression from the stress-strain relationship when the lamina is loaded along its fibre-related
axes to a general
axis involving
a transformed
compliance
matrix, Q , which will depend
angle φ. The first step is to
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Mathcad Express.
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for moreoninformation.
write the inverse of Eqn.(3.3), giving the strains relative to the loading direction,
in
terms
of
the strains relative to the
| −1|
fibre direction. This involves using the inverse of the matrix |T'| , written as |T' |
⎡ εx ⎤
⎡ ε1 ⎤
−1
⎢ ε ⎥ = ⎡⎣ T' ⎤⎦ ⋅ ⎢ ε ⎥
⎢ y⎥
⎢ 2 ⎥
⎣ γxy ⎦
⎣ γ12 ⎦
in which
2
⎡ c2
s
−c ⋅ s ⎤
⎢ 2
⎥
2
⎡⎣ T' ⎦⎤ = ⎢ s
c
c⋅s ⎥
⎢⎣ 2 c ⋅ s −2 c ⋅ s ⎛⎝c 2 − s 2 ⎞⎠ ⎥⎦
−1
Now, the strains relative to the fibre direction can be expressed in terms of the stresses in those
directions via the on-axis stress-strain relationship for the lamina, Eqn.(3.1), giving
⎡ εx ⎤
⎡ σ1 ⎤
−1
⎢ ε ⎥ = ⎡⎣ T' ⎤⎦ ⋅ ⎡⎣ Q ⎤⎦ ⋅ ⎢ σ ⎥
⎢ y⎥
⎢ 2⎥
⎣ γxy ⎦
⎣ τ12 ⎦
Finally, the original transform matrix of Eqn.(3.2) can be used to express these stresses in terms
of those being externally applied, to give the result
⎡ εx ⎤
⎡ σx ⎤
⎡ σx ⎤
−1
⎢ ε ⎥ = ⎡⎣ T' ⎤⎦ ⋅ ⎡⎣ Q ⎤⎦ ⋅ ⎡⎣ T ⎤⎦ ⋅ ⎢ σ ⎥ = ⎡⎣ Q' ⎤⎦ ⋅ ⎢ σ ⎥
⎢ y⎥
⎢ y⎥
⎢ y⎥
⎣ γxy ⎦
⎣ τxy ⎦
⎣ τxy ⎦
Therefore,
⎡ εx ⎤ ⎡ Q'11 Q'12 Q'16 ⎤ ⎡ σx ⎤
⎢ ε ⎥ = ⎢ Q' Q' Q' ⎥ ⋅ ⎢ σ ⎥
22
26
⎢ y ⎥ ⎢ 12
⎥ ⎢ y⎥
⎣ γxy ⎦ ⎣ Q'16 Q'26 Q'66 ⎦ ⎣ τxy ⎦
Finally, the original transform matrix of Eqn.(3.2) can be used to express these stresses in terms
of those being externally applied, to give the result
⎤ structures: A pedestrian
⎤
⎡ εFRP
⎡ σx ⎤ bridge⎡in
σxSchiphol
Bio-based
Logistics Park
x
−1
⎢ ε ⎥ = ⎡⎣ T' ⎤⎦ ⋅ ⎡⎣ Q ⎤⎦ ⋅ ⎡⎣ T ⎤⎦ ⋅ ⎢ σ ⎥ = ⎡⎣ Q' ⎤⎦ ⋅ ⎢ σ ⎥
y
y
y
⎢
⎥
⎢ ⎥
⎢ ⎥
⎣ γxy ⎦
⎣ τxy ⎦
⎣ τxy ⎦
109
Therefore,
⎡ εx ⎤ ⎡ Q'11 Q'12 Q'16 ⎤ ⎡ σx ⎤
⎢ ε ⎥ = ⎢ Q' Q' Q' ⎥ ⋅ ⎢ σ ⎥
22
26
⎢ y ⎥ ⎢ 12
⎥ ⎢ y⎥
⎣ γxy ⎦ ⎣ Q'16 Q'26 Q'66 ⎦ ⎣ τxy ⎦
Then, the following expressions are obtained
Q'11 ≔ Q11 ⋅ c + Q22 ⋅ s + 2 ⋅ ⎛⎝Q12 + 2 Q66⎞⎠ ⋅ c ⋅ s = 17.678 GPa
4
4
2
2
4
4
2
2
Q'12 ≔ Q12 ⋅ ⎛⎝c + s ⎞⎠ + ⎛⎝Q11 + Q22 − 4 Q66⎠⎞ ⋅ c ⋅ s = 10.335 GPa
Q'22 ≔ Q11 ⋅ s + Q22 ⋅ c + 2 ⎛⎝Q12 + 2 Q66⎞⎠ ⋅ c ⋅ s = 17.678 GPa
4
4
2
2
Q'16 ≔ ⎛⎝Q11 − Q12 − 2 Q66⎞⎠ ⋅ c ⋅ s − ⎛⎝Q22 − Q12 − 2 Q66⎞⎠ c ⋅ s = 9.207 GPa
3
3
Q'26 ≔ ⎛⎝Q11 − Q12 − 2 Q66⎞⎠ c ⋅ s − ⎛⎝Q22 − Q12 − 2 Q66⎞⎠ c s = 9.207 GPa
3
3
2
2
4
4
Q'66 ≔ ⎛⎝Q11 + Q22 − 2 Q12 − 2 Q66⎞⎠ c ⋅ s + Q66 ⋅ ⎛⎝c + s ⎞⎠ = 11.763 GPa
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In similar way we calculate the reduced stiffness constants Q’ for all the different angles of the plies. By doing so,
we create the following table
Table 8.3 Stiffness constants Q’ for each fibre orientation of the laminate
ply
1
2
3
4
5
6
7
8
position from
neutral axis [mm]
φ [deg]
thickness
[mm]
Q11
Q12
Q22
Q16
Q26
Q66
1,8
1,35
0,9
0,45
0,45
0,9
1,35
1,8
0
45
90
-45
-45
90
45
0
0,45
0,45
0,45
0,45
0,45
0,45
0,45
0,45
44,184
17,678
7,356
17,678
17,678
7,356
17,678
44,184
2,244
10,335
2,244
10,335
10,335
2,244
10,335
2,244
7,356
17,678
44,184
17,678
17,678
44,184
17,678
7,356
0
9,207
0
-9,207
-9,207
0
9,207
0
0
9,207
0
-9,207
-9,207
0
9,207
0
3,671
11,763
3,671
11,763
11,763
3,671
11,763
3,671
110
Chapter 8 | Structural Calculation
8.6.3
ABD Stiffness
matrices
ABD stiffness
matrices
The inplane forces are denoted by Ni, (i = 1; 2; 6), for all component of the plane stress condition in i direction. The 3
moments per length are denoted Mi, (i = 1; 2; 6) for the i direction. Mxy is a twisting moment and can be associated to
a distortion of the laminate in the bending mode due to shear stress gradient. Ni and Mi are sometimes called
respectively stress resultants and moment resultants. The cross-sectional forces and moments can be determined by
summation of the integrated stress components over each individual ply.
h
―
2
Nx = ⌠
⌡ σx d z
−h
――
2
h
―
2
Ny
h
―
2
Mx = ⌠
⌡ zσx d z
ABD stiffness
y
−h
――
2
matrices
h
―
2
Nx
z
Nx
Nxy
⌠ denoted by Ni, (i = 1; 2; 6), for all componentNof
The inplane forces
are
xy the plane stress condition in i direction. The
Ny = ⌠
x
y = ⌡ zσy d z
⌡ σy d zmoments perM
Ny
length
are denoted Mi, (i = 1; 2; 6) for the i direction.
Mxy is a twisting moment and can be associated
−h
――
2
h
―
2
−h
a distortion of the――
laminate in the bending mode due to shear stress gradient. Ni and Mi are sometimes call
2
y can be determined
respectively stress resultants
and moment resultants. The cross-sectional forces and moments
h
―
summation of the integrated
stress components over each individual ply. Mxy
2
z
Mxyh = ⌠
Nxy = ⌠
Mxy
h
⌡ σxy d z
⌡ zσxy d z
―
―
My
−h
−h
2
2
――
2
――
2
Nx = ⌠
⌡ σx d z
Mx = ⌠
⌡ zσx d z x
−h
――
2
h
―
ABD-matrix, 2also
−h
――
2
h
―
laminate stiffness
2
The result is the so-called
known as
matrix. The ABD matrix defines a relationship
⌠ zσ the
between the stress resultants (i.e.,
applied
to a laminate,
and
reference surface strains and curvatures (i.e.,
σ
d
z
d
z
Nyloads)
= ⌠
M
=
y
y
y
⌡ extensional
deformations). Specifically, [A] is the
stiffness, [B]⌡is called coupling stiffness, and [D] represents the
−h
−h
――
――
bending stiffness of the laminate.
2
2
h
―
h
―
This form is a direct result of the Kirchhoff
hypothesis, the plane-stress
assumption, and the definition of the stress
2
2
resultants. The laminate stiffness matrix
involves everything that
is used to define the laminate—layer material
⌠
⌠
Mxy = ⌡ zσxy d z
Nxy = ⌡ σxy d z
properties, fiber orientation, thickness,
and location.
−h
――
−h
――
2
2
The figure below shows the influence of some
components of the ABD-matrix.
⎡ Nx ⎤ ⎡ A11 A12 A16 B11 B12 B16 ⎤ ⎡ εx ⎤
⎥ ⎢ε ⎥
⎢ N ⎥ ⎢A A A B
26
12 B22 B26
⎢ y ⎥ ⎢ 12The22result
⎢ y⎥
is the so-called⎥ ABD-matrix,
also known as laminate stiffness matrix. The ABD matrix defines a relationsh
N
A
A
A
B
B
B
xy
16
26
66
16
26
66
xy ⎥ loads) applied to a laminate, and the reference surface strains and curvatures (i.
⎥=⎢
⎥ ⋅ ⎢ ε(i.e.,
⎢
between the stress resultants
B12 B16 D11 Specifically,
D12 D16 ⎥ ⎢ [A]
κx ⎥ is the extensional stiffness, [B] is called coupling stiffness, and [D] represents th
⎢ Mx ⎥ ⎢ B11deformations).
stiffness
of
the
laminate.
⎥
⎢ My ⎥ ⎢ B12bending
⎢
B22 B26 D12 D22 D26
κy ⎥
⎢M ⎥ ⎢ B
⎥
⎢
⎥
B26form
B66is Da16direct
D26 D
κxythe
⎣ xy ⎦ ⎣ 16This
⎦ Kirchhoff hypothesis, the plane-stress assumption, and the definition of the stre
66 ⎦ ⎣of
result
resultants. The laminate stiffness matrix involves everything that is used to define the laminate—layer mater
properties, fiber orientation, thickness, and location.
The components of these three stiffness matrices are defined as follows:
⎡ Nx ⎤ ⎡ A11
⎢ N ⎥ ⎢A
y
12
Axy = ∑ Qxy ⋅ ⎛h − h ⎢ ⎞ ⎥ ⎢
k − 1N
⎝ k
k=1
⎢ ⎠ xy ⎥ = ⎢ A16
⎢ Mx ⎥ ⎢ B11
⎢ My ⎥2 ⎞ ⎢ B⎞12
2
1 n
Bxy = ―∑ Qxy ⋅ ⎛⎛⎝h ⎞⎠⎢ − ⎛⎝h
⎥⎠⎢
⎝
2 k=1
⎣k Mxy ⎦ k⎣−B1⎠16
n
A12
A22
A26
B12
B22
B26
A16
A26
A66
B16
B26
B66
B11
B12
B16
D11
D12
D16
B12
B22
B26
D12
D22
D26
B16 ⎤ ⎡ εx ⎤
B26 ⎥ ⎢ εy ⎥
⎥ h⎢ − h⎥ = t
B66 ⎥ ⎢kεxy ⎥k − 1 k
⋅
D16 ⎥ ⎢ κx ⎥
D26 ⎥ ⎢ κy ⎥
D66 ⎥⎦ ⎢⎣ κxy ⎥⎦
3
3
1 n
Dxy = ―∑ Qxy ⋅ ⎛⎛⎝h ⎞⎠ − ⎛⎝h ⎞⎠ ⎞
k
k − 1⎠
⎝
3 k=1
The components of these three stiffness matrices are defined as follows:
n
Axy = ∑ Qxy ⋅ ⎛h − h ⎞
k − 1⎠
⎝ k
k=1
h −h
k
k−1
=t
2
2
1 n
Bxy = ―∑ Qxy ⋅ ⎛⎛⎝h ⎞⎠ − ⎛⎝h ⎞⎠ ⎞
kSee www.mathcad.com
k − 1⎠
⎝
Created with PTC Mathcad
for more information.
2 k=1 Express.
1
n
⎛⎛
3⎞
⎛
3⎞
⎞
k
⎤ ⎡ A11
⎥ ⎢A
y
⎥ ⎢ 12
xy ⎥ ⎢ A16
=
x ⎥ ⎢ B11
⎥ ⎢ B12
y
⎥ ⎢
xy ⎦ ⎣ B16
x
A12
A22
A26
B12
B22
B26
A16⎡ NBx11⎤ B⎡12A11B16A⎤12 ⎡ Aεx16⎤ B11 B12 B16 ⎤ ⎡ εx ⎤
⎥ ⎢
⎥ ⎢
⎥
⎢
A26⎢ NBy12⎥ B⎢22A12B26A⎥22 ⎢ A
εy26⎥ B12 B22 B26 ⎥ ⎢ εy ⎥
⎥ ⎢
⎥
Bio-based
pedestrian
A B AB
B
εbridge in Schiphol Logistics Park
A66
B66Astructures:
16
⎢ NBxy16⎥ =B⎢26AFRP
⎥26⋅ ⎢ εxy66⎥ 16 26 66 ⎥ ⋅ ⎢ xy ⎥
M
B
B
B
D
D
D
B16⎢ Dx11⎥ D⎢12 11D16 ⎥12 ⎢ κ16
11
12
16 ⎥ ⎢ κx ⎥
x ⎥
⎥
⎢
⎢
⎥ D12 D22 D26 ⎥ ⎢ κy ⎥
B26 M
Dy12 D22B12D26B⎥22 ⎢ Bκ26
y
⎢M ⎥ ⎢ B
⎥ ⎢
⎥
⎥
B66⎣ Dxy16⎦ D⎣26 16D66B⎥⎦26 ⎢⎣ κBxy
66⎦ D16 D26 D66 ⎦ ⎣ κxy ⎦
111
The components of these three stiffness matrices
are defined as follows
The components
these three
stiffness as
matrices
ponents of these
three stiffnessof
matrices
are defined
follows:are defined as follows:
1
n
n
= ∑ Qxy ⋅ ⎛h − h Axy⎞= ∑ Qxy ⋅ ⎛⎝hk − hk − 1⎞⎠
k − 1⎠
⎝ k
k=1
k=1
h −h
k
k−1
=t
12 ⎞ n ⎞
⎛⎛ 2 ⎞ ⎛ 2 ⎞ ⎞
2
1
⎛⎝h―
⎠ ∑ Qxy ⋅ ⎝h ⎠k − ⎝h ⎠k − 1
−=
=―∑ Qxy ⋅ ⎛⎛⎝h ⎞⎠Bxy
⎝
⎠
k
2 kk=−11⎠
⎝
2 k=1
k
hh−
1 h
k
k−1
h2
=t
n
h7
h8
2
3
k
h3
h6
h4
h5
h
4
5
6
7
13 ⎞ n ⎞
⎛⎛ 3 ⎞ ⎛ 3 ⎞ ⎞
3
1
⎛⎝h―
⎠ ∑ Qxy ⋅ ⎝h ⎠k − ⎝h ⎠k − 1
−=
=―∑ Qxy ⋅ ⎛⎛⎝h ⎞⎠Dxy
⎝
⎠
k
3 kk=−11⎠
⎝
3 k=1
n
8
Then, the following expressions are obtained
CreatedExpress.
with PTCSee
Mathcad
Express. See www.mathcad.com
for more information.
Created with PTC Mathcad
www.mathcad.com
for more information.
Axy = Qxy
⎝⎛0⎞⎠
⋅ ⎛⎝h1 − h2⎞⎠ + Qxy
⎝⎛45⎞⎠
⋅ ⎛⎝h2 − h3⎞⎠ + Qxy
+ Qxy
⎛⎝90⎞⎠
⎝⎛90⎞⎠
⋅ ⎛⎝h3 − h4⎞⎠ + Qxy
⎛⎝−45⎠⎞
⋅ ⎛⎝h4⎞⎠ + Qxy
⎛⎝−45⎞⎠
⋅ ⎛⎝h5⎞⎠ +
⋅ ⎛⎝h6 − h5⎞⎠ + Qxy ⋅ ⎛⎝h7 − h6⎞⎠ + Qxy ⋅ ⎛⎝h8 − h7⎞⎠
⎛⎝45⎞⎠
⎛⎝0⎞⎠
2
2
2
2
2
2
2
2
1
Bxy = ―Qxy ⋅ ⎛⎝h1 − h2 ⎞⎠ + Qxy ⋅ ⎛⎝h2 − h3 ⎞⎠ + Qxy ⋅ ⎛⎝h3 − h4 ⎞⎠ + Qxy
⋅ ⎛⎝h4 ⎞⎠ + Qxy
⋅ ⎛⎝h5 ⎞⎠ +
⎛⎝0⎞⎠
⎛⎝45⎞⎠
⎛⎝90⎞⎠
⎛⎝−45⎞⎠
⎛⎝−45⎞⎠
2
2
2
2
2
2
2
+ Qxy ⋅ ⎛⎝h6 − h5 ⎞⎠ + Qxy ⋅ ⎛⎝h7 − h6 ⎞⎠ + Qxy ⋅ ⎛⎝h8 − h7 ⎞⎠
⎛⎝90⎞⎠
⎛⎝45⎞⎠
⎛⎝0⎞⎠
3
3
3
3
3
3
3
3
1
Dxy = ―Qxy ⋅ ⎛⎝h1 − h2 ⎞⎠ + Qxy ⋅ ⎛⎝h2 − h3 ⎞⎠ + Qxy ⋅ ⎛⎝h3 − h4 ⎞⎠ + Qxy
⋅ ⎛⎝h4 ⎞⎠ + Qxy
⋅ ⎛⎝h5 ⎞⎠ +
⎛⎝0⎞⎠
⎛⎝45⎞⎠
⎛⎝90⎞⎠
⎛⎝−45⎞⎠
⎛⎝−45⎞⎠
3
3
3
3
3
3
3
+ Qxy ⋅ ⎛⎝h6 − h5 ⎞⎠ + Qxy ⋅ ⎛⎝h7 − h6 ⎞⎠ + Qxy ⋅ ⎛⎝h8 − h7 ⎞⎠
⎛⎝ ⎞⎠
⎛⎝ ⎞⎠
⎛⎝ ⎞⎠
90
45
0
from which the ABD matrices below are created
⎡ 78.2064 22.6422
⎤
0
⎥
⎡⎣ A ⎤⎦ = ⎢ 22.6422 78.2064
0
⎢⎣
⎥
0
0
27.7812 ⎦
⎡0 0 0⎤
⎡⎣ B ⎤⎦ = ⎢ 0 0 0 ⎥
⎢⎣ 0 0 0 ⎥⎦
⎡ 123.9215 18.5552 10.0678 ⎤
⎡⎣ D ⎤⎦ = ⎢ 18.5552 56.8025 10.0678 ⎥
⎢⎣ 10.0678 10.0678 24.1046 ⎥⎦
It derives that [B]=0, which it was expected as for symmetric laminates all the components of the B
matrix are identically zero. A laminate is said to be symmetric if for every layer with a specific
thickness, specific material properties, and specific fiber orientation to one side of the laminate
reference surface, there is another layer with the identical distance on the opposite side of the
reference surface with the identical thickness, material properties, and fiber orientation. Consequently,
the full six-by-six set of equations of the [ABD] decouples into two three-by-three sets of equations,
namely
112
⎡ 78.2064 22.6422
⎤
0
⎢
⎥
⎡⎣ A ⎤⎦ = 22.6422 78.2064
0
⎢⎣
⎥
0
0
27.7812 ⎦
⎡0 0 0⎤
⎡⎣ B ⎤⎦ = ⎢ 0 0 0 ⎥
⎢⎣ 0 0 0 ⎥⎦
⎡ 123.9215 18.5552 10.0678 ⎤
⎡⎣ D ⎤⎦ = ⎢ 18.5552 56.8025 10.0678 ⎥
⎢⎣ 10.0678 10.0678 24.1046 ⎥⎦
Chapter 8 | Structural Calculation
It derives that [B]=0, which it was expected as for symmetric laminates all the components of the B
matrix are identically zero. A laminate is said to be symmetric if for every layer with a specific
thickness, specific material properties, and specific fiber orientation to one side of the laminate
reference surface, there is another layer with the identical distance on the opposite side of the
reference surface with the identical thickness, material properties, and fiber orientation. Consequently,
the full six-by-six set of equations of the [ABD] decouples into two three-by-three sets of equations,
namely
⎡ Nx ⎤ ⎡ A11 A12 A16 ⎤ ⎡ εx ⎤
⎢ N ⎥=⎢ A A A ⎥ ⋅ ⎢ ε ⎥
⎢ y ⎥ ⎢ 12 22 26 ⎥ ⎢ y ⎥
⎣ Nxy ⎦ ⎣ A16 A26 A66 ⎦ ⎣ εxy ⎦
⎡ Mx ⎤ ⎡ D11 D12 D16 ⎤ ⎡ κx ⎤
⎢ M ⎥=⎢ D D D ⎥ ⋅ ⎢ κ ⎥
⎢ y ⎥ ⎢ 12 22 26 ⎥ ⎢ y ⎥
⎣ Mxy ⎦ ⎣ D16 D26 D66 ⎦ ⎣ κxy ⎦
and
Then the above relation can be inverted to give,
⎡ εx ⎤ ⎡ a11 a12 a16 ⎤ ⎡ Nx ⎤
⎢ ε ⎥=⎢ a a a ⎥ ⋅ ⎢ N ⎥
⎢ y ⎥ ⎢ 12 22 26 ⎥ ⎢ y ⎥
⎣ εxy ⎦ ⎣ a16 a26 a66 ⎦ ⎣ Nxy ⎦
⎡ κx ⎤ ⎡ d11 d12 d16 ⎤ ⎡ Mx ⎤
⎢ κ ⎥=⎢ d d d ⎥ ⋅ ⎢ M ⎥
⎢ y ⎥ ⎢ 12 22 26 ⎥ ⎢ y ⎥
⎣ κxy ⎦ ⎣ d16 d26 d66 ⎦ ⎣ Mxy ⎦
and
where [a] and [d] are the inverted matrices of [A] and [D]
⎡ a11 a12 a16 ⎤ ⎡ A11
−1
Created
with PTC
Express.
⎥ ⎢
⎢ aMathcad
⎡⎣ a ⎤⎦ = ⎡⎣ A ⎤⎦
or
12 a22 a26 = A12
⎢
⎥ ⎢
⎣ a16 a26 a66 ⎦ ⎣ A16
⎡⎣ d ⎤⎦ = ⎡⎣ D ⎤⎦
−1
A12
See
A22
A26
−1
A16 ⎤
www.mathcad.com
for more information.
A26 ⎥
⎥
A66 ⎦
⎡ d11 d12 d16 ⎤ ⎡ D11 D12 D16 ⎤
⎢ d d d ⎥=⎢ D D D ⎥
⎢ 12 22 26 ⎥ ⎢ 12 22 26 ⎥
⎣ d16 d26 d66 ⎦ ⎣ D16 D26 D66 ⎦
or
−1
The inverted [a] and [d] matrices are calculated as follows
⎡ a11 a12
⎡⎣ a ⎤⎦ = ⎢ a12 a22
⎢
⎣ a16 a26
⎡ ⎡ A22
⎢⎢A
⎣ 26
a16 ⎤ ⎢
⎡ A26
a26 ⎥ = ⎢ ⎢
⎥ ⎢ ⎣ A66
a66 ⎦
⎢ ⎡ A12
⎢⎢A
⎣ ⎣ 16
A22 ⋅ A66 − A26
a11 = ―――――
det ⎡⎣ A ⎤⎦
2
A26 ⎤
A66 ⎥⎦
A12 ⎤
A16 ⎥⎦
A22 ⎤
A26 ⎥⎦
⎡ A16
⎢A
⎣ 66
⎡ A11
⎢A
⎣ 16
⎡ A12
⎢A
⎣ 26
A12 ⎤
A26 ⎥⎦
A16 ⎤
A66 ⎥⎦
A11 ⎤
A16 ⎥⎦
⎡ A12
⎢A
⎣ 22
⎡ A16
⎢A
⎣ 26
⎡ A11
⎢A
⎣ 21
A16 ⎤ ⎤
A26 ⎥⎦ ⎥
⎥
A11 ⎤ ⎥
A12 ⎥⎦ ⎥
A12 ⎤ ⎥
A22 ⎥⎦ ⎥⎦
A26 ⋅ A16 − A12 ⋅ A66
a12 = ――――――
det ⎡⎣ A ⎤⎦
A12 ⋅ A26 − A22 ⋅ A16
a16 = ――――――
det ⎡⎣ A ⎤⎦
⎣ a16 a26 a66 ⎦
66
16
16
66
26
12
⎢ ⎡ A12 A22 ⎤ ⎡ A12 A11 ⎤ ⎡ A11 A12 ⎤ ⎥
⎢⎢A A ⎥ ⎢A A ⎥ ⎢A A ⎥⎥
⎣ ⎣ 16 26 ⎦ ⎣ 26 16 ⎦ ⎣ 21 22 ⎦ ⎦
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
A22 ⋅ A66 − A26
a11 = ―――――
det ⎡⎣ A ⎤⎦
2
113
A26 ⋅ A16 − A12 ⋅ A66
a12 = ――――――
det ⎡⎣ A ⎤⎦
A12 ⋅ A26 − A22 ⋅ A16
a16 = ――――――
det ⎡⎣ A ⎤⎦
A11 ⋅ A66 − A16
a22 = ―――――
det ⎡⎣ A ⎤⎦
A12 ⋅ A16 − A11 ⋅ A26
a26 = ――――――
det ⎡⎣ A ⎤⎦
2
A11 ⋅ A22 − A12
a66 = ―――――
det ⎡⎣ A ⎤⎦
2
in which det[A] is the determinant of A, given by the following equation
2
det ⎡⎣ A ⎤⎦ = A11 ⎛⎝A22 ⋅ A66 − A26 ⎞⎠ − A12 ⋅ ⎛⎝A12 ⋅ A66 − A26 ⋅ A16⎞⎠ + A16 ⋅ ⎛⎝A12 ⋅ A26 − A22 ⋅ A16⎞⎠
By calculating the above equations we get
⎡ 0.01395 −0.00404
⎤
0
⎢
⎥
⎡⎣ a ⎤⎦ = −0.00404 0.01395
0
⎢⎣
⎥⎦
0
0
0.03599
Similarly, matrix [d] is calculated
Created with PTC Mathcad Express. See www.mathcad.com for more information.
⎡ 0.008635 −0.002356 −0.002622 ⎤
⎡⎣ d ⎤⎦ = ⎢ −0.002356 0.01965
−0.0073 ⎥
⎢
⎥
0.045599 ⎦
⎣ −0.002622 −0.0073
After having calculated the inverted [a] and [d] matrices the Elastic modulus, Shear modulus and poisson’s
ratio can be calculated by the following equations. The results were also checked by the computer software Kolibri which is used for designing and calculating laminates.
1
ExFRP ≔ ―――= 19.93 GPa
a11 ⋅ tlam
1
EyFRP ≔ ―――= 19.93 GPa
a22 ⋅A
tlam
22 ≔ 78.206 GPa ⋅ mm
−a12
A11
78.206 ⋅ GPa ⋅ mm
vxyFRP ≔ ――
=≔
0.29
a11
A12 ≔ 22.6422 ⋅ GPa ⋅ mm
A66 ≔ 27.7812 ⋅ GPa ⋅ mm
1
GxyFRP ≔ ―――= 7.73 GPa
a66 ⋅ tlam
A26 ≔ −0 ⋅ GPa ⋅ mm A16 ≔ −0 ⋅ GPa ⋅ mm
114
Chapter 8 | Structural Calculation
8.7 Partial factors
8.7.1 Conversion factors
The behavior of polymers and fibres, either there
are natural or synthetic, varies over time as deformation increases (creep) and relaxation occurs
under long-term loads. In addition, polymers are
characterized by lower strengths for permanent
loads than they are for brief loads. Another aspect
is also their temperature –depended behavior as
both the elastic modulus and the strength of a
polymer drop as the ambient temperature rises.
Besides, in the case of natural fibres, moisture is a
very crucial element as natural substances show
high moisture absorption.
Table 8.4 Conversion factors
Therefore, these ambient conditions and the period of use must be taken into account in the design procedure. These criteria are incorporated
directly in the calculations by way of reduction
factors. In order to define the specific safety factors for composites, a research was done in relevant composite design codes. At present in The
Netherlands the codes used for composites are
the following:
•
Eurocode EN 1991 (1) Loads on structures
and load factors
•
CUR Recommendation 96 (2) Composite
properties and material factors
Temperature
γct = 1.1
Humidity
γcm= 1.1
Creep
γck = 1.14
Fatigue
γcf = 1.1
8.7.2 Material factors
The material factor has to be derived from the following formula [CUR96]:
γm=γm1*γm2
Where, γm1= 1.35 which is the partial material
factor, taking into account the uncertainties in
deriving the correct material properties. γm2 is
the partial material factor, which takes into account the uncertainties in the production method. γm2 can be derived from the following table.
Table 8.5 Partial material factors [CUR96]
The CUR Recommendation 96 has been recently
revised and translated into English. It is written in
a Eurocode form and will be proposed in the task
committee TC250, working group WG 4 for the realization of a Eurocode for composite materials.
Production
method
For the current analysis the relevant factors where
the load and conversion factors. Load combinations and load factors are based on the European Standard EN1990 EN1991-2 and. Conversion
factors are reduction factors to the rigidity with
which environmental conditions (humidity, temperature, creep and fatigue) will be charged on
the material properties.
Fully
post-cured
laminate
Not fully
post-cured
laminate
Spray-up
1.6
1.9
Hand lay-up
1.4
1.7
VARTM or RTM
1.2
1.4
Filament winding
1.1
1.3
Pre-preg lay up
1.1
1.3
Pultrusion
1.1
1.3
Table 8.6 Application of different conversion factors for different applications [CUR]
Ultimate limit state
Serviceability limit state
strength
stability
fatigue
strength
stability
fatigue
Temperature
x
x
x
x
x
x
Humidity
x
x
x
x
x
x
Creep
x
x
-
x
-
x
Fatigue
-
x
-
x
x
x
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
115
8.7.3 Load factors
The load factor for FRP composites is the same as for structures made of other materials. It has to be calculated
according to the following quideline, derived from Eurocode 0, Basis of structural Design [NEN-EN 1990:2002,
Load factors
table A1.2(B),p59] and the National Annex to NEN-EN 1990.
Load factors
(National Annex to NEN-EN 1990)
For the ultimate limit state(NEN-EN 1990)
For the serviceability limit state
(NEN-EN 1990)
γG = KFI ⋅ γG
γG = 1.35
(NEN-EN 1990)
γG = KFI ⋅ γG
γG = 1.35
γG ≔ 1.2
(National Annex to NEN-EN 1990)
γG=1.2
(Consequence
class CC2 )
(NEN-EN(NEN-EN
1990) 1990)
(Consequence
class CC2 )
(consequence
class CC2)
γQ ≔ 1.5
γQ=K
γQFI*γ
=QKFI ⋅ γQ
(NEN-EN 1990)
γG ≔ 1.2
γG=1.35
(NEN-EN 1990)
γG=KFI*γG
γQ = KFI ⋅ γQ
(National Annex to NEN-EN 1990)
γQ=1.5
γQ ≔ 1.5
KFI=1.0
γG=1.0
(NEN-EN 1990)
KFI = 1
KFI = 1
γQ=1.0
Parapet to parapet (deck)
Parapet to parapet (deck)
8.8
Parapet
parapet (deck) calculation
Neutral
axistodefinition
Neutral axis definition
Distances from base axis x
Neutral axis definition
Distances from base axis x
Distances from base axis x
tfacing.in
y1 ≔ ―――
+ tcore + tfacing.out = 0.097 m
2
tfacing.in
y1 ≔ ―――
+ tcore + tfacing.out = 0.097 m
2
tfacing.out
y2 ≔ ―――= 0.004 m
2
tfacing.out
y2 ≔ ―――= 0.004 m
2
b=1.0mm
b
∑ ⎛⎝yi ⋅ Ai⎞⎠
yc = ――――
∑ ⎛⎝y ⋅ A ⎞⎠
i
i
∑ Ai
yc = ――――
∑ Ai
y1 ⋅ b ⋅ tfacing.in + y2 ⋅ b ⋅ tfacing.out
yc ≔ ――――――――――
= 0.05 m
b ⋅⋅ ttfacing.in
+ b ⋅ tfacing.out
y1 ⋅ b
⋅ tfacing.out
facing.in + y2 ⋅ b
yc ≔ ――――――――――
= 0.05 m
b ⋅ tfacing.in + b ⋅ tfacing.out
yc
b
8.8.1
Moment
of Inertia
about
centroidal
(neutral)
axis
Moment
of Inertia
about
centroidal
(neutral)
axis
Ixci = Ii + dyi ⋅ Ai
2
b
Moment of Inertia about centroidal (neutral) axis
Ixci = Ii + dyi ⋅ Ai
2
Created with PTC Mathcad Express. See www.mathcad.com for more information.
Created with PTC Mathcad Express. See www.mathcad.com for more information.
neutral axis
x-axis
116
Chapter 8 | Structural Calculation
2
b ⋅ tfacing.in
−5
4
Ixc1 ≔ ――――+ ⎛⎝y1 − yc⎞⎠ ⋅ b ⋅ tfacing.in = ⎛⎝1.567 ⋅ 10 ⎞⎠ m
12
3
2
b ⋅ tfacing.out
−5
4
Ixc2 ≔ ―――――
+ ⎛⎝y2 − yc⎞⎠ ⋅ b ⋅ tfacing.out = ⎛⎝1.567 ⋅ 10 ⎞⎠ m
12
3
−5
4
Ixctot ≔ Ixc1 + Ixc2 = ⎛⎝3.133 ⋅ 10 ⎞⎠ m
8.8.2 Ultimate limit state
Ultimate limit state
qtot = γG ⋅ qG + γQ ⋅ qQ
Dead load
Imposed load
qG = AFRP ⋅ pFRP + Acore ⋅ pcore
Traffic load (NEN-EN 1991-2)
AFRP ≔ b ⋅ tfacing.in + b ⋅ tfacing.out = 0.014 m
Acore ≔ b ⋅ tcore = 0.086 m
pFRP = pf ⋅ Vf + pm ⋅ Vm
2
kN
qped ≔ 5 ――
2
m
2
but
Vf + Vm = 1
kN
qQ ≔ qped ⋅ b = 5 ――
m
pFRP = pf ⋅ Vf + pm ⋅ ⎛⎝1 − Vf⎞⎠ = ⎛⎝pf − pm⎞⎠ ⋅ Vf + pm
kN
qG ≔ ⎛⎝AFRP ⋅ pFRP + Acore ⋅ pcore⎞⎠ ⋅ g = 0.395 ――
m
kN
qtot ≔ γG ⋅ qG + γQ ⋅ qQ = 7.974 ――
m
Bending moment
2
1
Mmax ≔ ―qtot ⋅ L2 = 4 kN ⋅ m
8
Stress
Mmax
σmax = ――
W
Iy
W = ―――
htot − yc
(first moment of area)
Created with PTC Mathcad Express. See www.mathcad.com for more information.
Ixctot
−4
3
W ≔ ――――――――― = ⎛⎝6.242 ⋅ 10 ⎞⎠ m
tfacing.in + tcore + tfacing.out − yc
Stress
Mmax
Iy
Bio-based
FRP structures:WA=pedestrian
Schiphol
Logistics Park
σmax = ――
――― bridge
(firstin
moment
of area)
W
htot − yc
Ixctot
−4
3
W ≔ ――――――――― = ⎛⎝6.242 ⋅ 10 ⎞⎠ m
tfacing.in + tcore + tfacing.out − yc
Mmax
σmax ≔ ――= 6.388 MPa
W
0.012 ⋅ Ex
σmax.allowable ≔ ―――= 122.008 MPa
γm ⋅ γc
CUR 96 ;2003 recommends a stress criterion which limits the maximum stress in the laminate
according to the following formula:
σmax
―――――
≤1
σmax.allowable
σmax
―――――
= 0.052 < 1
σmax.allowable
Service
limit state
8.8.3
Service
limit state
Deflection
kN
qrep ≔ qG + qQ = 5.395 ――
m
Acore.deck ≔ b ⋅ tcore = 0.086 m
(The loads without partial factors)
2
Gcore ≔ 183 MPa
Created with PTC Mathcad Express. See www.mathcad.com for more information.
5 ⋅ qrep ⋅ L2
η ⋅ qrep ⋅ L2
w2 ≔ ―――――
+ ――――――= 1.962 mm
385 ⋅ Ex ⋅ Ixctot 8 ⋅ Gcore ⋅ Acore.deck
4
2
1
⋅ L2 = 5.51 mm
wallowable ≔ ―――
300 ⋅ γc
So w2 < wu
Abutment to abutment (cross-section)
117
So w2 < wu
So w2 < wu
118
Chapter 8 | Structural Calculation
Abutment to abutment (cross-section)
Abutment to abutment (cross-section)
8.9 Abutment to abutment calculation
Neutral axis definition
Neutral axis
axis definition
definition
Neutral
Distancesfrom
from
base
axis
Distances
base
axis
x xx
Distances
from
base
axis
tfacing.top
tfacing.top
yy1 ≔
―――
++
+ tcore
+ tfacing.out
= 1.104
m
hinh+ t+
tfacing.in
+ tcore
+ tfacing.out
= 1.104
m
1 ≔ ―――
in facing.in
22
hin
hin+ tfacing.in + tcore + tfacing.out = 0.6 m
y2 ≔ ――
y2 ≔ ――
2 + tfacing.in + tcore + tfacing.out = 0.6 m
2
tfacing.in
y3 ≔ ―――
tfacing.in+ tcore + tfacing.out = 0.097 m
2
y3 ≔ ―――
+ tcore + tfacing.out = 0.097 m
2
tcore
y4 ≔ ――
+t
= 0.05 m
t2core facing.out
y4 ≔ ――
+ tfacing.out = 0.05 m
2
tfacing.out
y5 ≔ ―――= 0.004 m
2
tfacing.out
y5 ≔ ―――= 0.004 m
2
∑ ⎛⎝yi ⋅ Ai⎞⎠
yc = ――――
∑ ⎛⎝yi ⋅ Ai⎞⎠
∑ Ai
yc = ――――
∑ Ai
y1 ⋅ 2 btop ⋅ tfacing.top + y2 ⋅ hin ⋅ 4 tfacing.side + y3 ⋅ bin ⋅ tfacing.in + y4 ⋅ tcore ⋅ 2 tfacing.side + y5 ⋅ bout ⋅ tfacing.out
yc ≔ ―――――――――――――――――――――――――――――――
= 0.337 m
2 btop ⋅ tfacing.top + hin ⋅ 4 tfacing.side + bin ⋅ tfacing.in + tcore ⋅ 2 tfacing.side + bout ⋅ tfacing.out
y1 ⋅ 2 btop ⋅ tfacing.top + y2 ⋅ hin ⋅ 4 tfacing.side + y3 ⋅ bin ⋅ tfacing.in + y4 ⋅ tcore ⋅ 2 tfacing.side + y5 ⋅ bout ⋅ tfacing.out
yc ≔ ―――――――――――――――――――――――――――――――
= 0.337 m
2 btop ⋅ tfacing.top + hin ⋅ 4 tfacing.side + bin ⋅ tfacing.in + tcore ⋅ 2 tfacing.side + bout ⋅ tfacing.out
Moment of Inertia about centroidal (neutral) axis
Moment8.9.1
of Inertia
about
(neutral)
axis (neutral) axis
Moment
ofcentroidal
Inertia about
centroidal
2
Ixci = Ii + dyi ⋅ Ai
Ixci = Ii + dyi ⋅ Ai
3
2
2 btop ⋅ tfacing.top
4
⎛⎝y1 − yc⎞⎠ ⋅ 2 btop ⋅ tfacing.top = 0.00098 m
Ixc1 ≔ Created
――――――
+Mathcad
with
PTC
Express.
See
www.mathcad.com
for more information.
3
12
2
2 btop ⋅ tfacing.top
4
⎛
⎞
Ixc1 ≔ ――――――
+ ⎝y1 − yc⎠ ⋅ 2 btop ⋅ tfacing.top = 0.00098 m
12 ⋅ h 3
2
4 tfacing.side
4
in
Ixc2 ≔ ――――――
+ ⎛⎝y2 − yc⎞⎠ ⋅ 4 tfacing.side ⋅ hin = 0.004 m
12 with3 PTC Mathcad
Created
Express.
See
www.mathcad.com
for more information.
2
4 tfacing.side ⋅ hin
4
Ixc2 ≔ ――――――
+ ⎛⎝y2 − yc⎞⎠ ⋅ 4 tfacing.side ⋅ hin = 0.004 m
12 3
2
bin ⋅ tfacing.in
4
Ixc3 ≔ ―――――
+ ⎛⎝y3 − yc⎞⎠ ⋅ bin ⋅ tfacing.in = 0.00083 m
3
12
2
bin ⋅ tfacing.in
4
Ixc3 ≔ ―――――
+ ⎛⎝y3 − yc⎞⎠ ⋅ bin ⋅ tfacing.in = 0.00083 m
3
12
2
2 tfacing.side ⋅ tcore
4
Ixc4 ≔ ――――――+ ⎛⎝y4 − yc⎞⎠ ⋅ 2 tfacing.side ⋅ tcore = 0.0001 m
btop
3
12
2
2 tfacing.side ⋅ tcore
tfacing.side
4
Ixc4 ≔ ――――――+ ⎛⎝y4 − yc⎞⎠ ⋅ 2 tfacing.side ⋅ tcore = 0.0001 m
3
12
2
bout ⋅ tfacing.out
4
Ixc5 ≔ ―――――+ ⎛⎝y5 − yc⎞⎠ ⋅ bout ⋅ tfacing.out = 0.002 m
3
12
2
bout ⋅ tfacing.out
4
Ixc5 ≔ ―――――+ ⎛⎝y5 − yc⎞⎠ ⋅ bout ⋅ tfacing.out = 0.002 m
12
4
Ixctot ≔ Ixc1 + Ixc2 + Ixc3 + Ixc4 + Ixc5 = 0.008 m
Ixctot ≔ Ixc1 + Ixc2 + Ixc3 + Ixc4 + Ixc5 = 0.008 m
Ultimate limit state
Ultimate limit state
qtot = γG ⋅ qG + γQ ⋅ qQ
4
bin
bout
tfacing.in
tcore
tfacing.out
hin
tfacing.top
2
2
bout ⋅ tfacing.out
4
Ixc5 ≔ ―――――+ ⎛⎝y5 − yc⎞⎠ ⋅ bout ⋅ tfacing.out = 0.002 m
12
119
Bio-basedI FRP≔structures:
bridge
in 4Schiphol Logistics Park
Ixc1 + Ixc2 + A
Ixc3pedestrian
+ Ixc4 + Ixc5 =
0.008 m
xctot
8.9.2
Ultimate
limit state
Ultimate
limit state
qtot = γG ⋅ qG + γQ ⋅ qQ
Dead load
qG = AFRP ⋅ pFRP + Acore ⋅ pcore
AFRP ≔ 2 btop ⋅ tfacing.top + hin ⋅ 4 tfacing.side + bin ⋅ tfacing.in + tcore ⋅ 2 tfacing.side + bout ⋅ tfacing.out = 0.061 m
Acore ≔ bout ⋅ tcore + 2 hin ⋅ tcore = 0.353 m
2
2
pFRP = pf ⋅ Vf + pm ⋅ Vm
but
Traffic load
Vf + Vm = 1
(NEN-EN 1991-2)
pFRP = pf ⋅ Vf + pm ⋅ ⎛⎝1 − Vf⎞⎠ = ⎛⎝pf − pm⎞⎠ ⋅ Vf + pImposed
m
load
kN
qG ≔ ⎛⎝AFRP ⋅ pFRP + Acore ⋅ pcore⎞⎠ ⋅ g = 1.661 ――
m
kN
qped ≔ 5 ――
2
m
kN
qQ ≔ qped ⋅ bout = 10 ――
m
kN
qtot ≔ γG ⋅ qG + γQ ⋅ qQ = 16.946 ――
m
kN
qped ≔ 5Bending
―― moment
2
m
2
1
Created with PTC Mathcad Express. See www.mathcad.com
more
Mmax ≔ ―qtot ⋅ L1 = for
135.6
kN ⋅information.
m
8
kN
Imposed load
qQ ≔ qped ⋅ bout = 10 ――
m
Stress
Traffic load
(NEN-EN 1991-2)
kN
qtot ≔ γG ⋅ qG + γQ ⋅ qQ = 16.946 ――
m
Bending moment
2
1
Mmax ≔ ―qtot ⋅ L1 = 135.6 kN ⋅ m
8
Stress
Mmax
σmax = ――
W
Iy
W = ―――
hout − yc
Ixctot
3
W ≔ ―――= 0.009 m
hout − yc
Mmax
σmax ≔ ――= 14.742 MPa
W
0.012 ⋅ Ex
σmax.allowable ≔ ―――= 122.008 MPa
γm ⋅ γc
Mmax
σmax = ――
W
Iy
W = ―――
hout − yc
Ixctot
3
W ≔ ―――= 0.009 m
hout − yc
Mmax
σmax ≔ ――= 14.742 MPa
W
(first moment of area)
0.012 ⋅ Ex
σmax.allowable ≔ ―――= 122.008 MPa
γm ⋅ γc
CUR 96 ;2003 recommends a stress criterion which limits the
CUR 96 ;2003 recommends a stress criterion which limits the maximum stress in the lamina
maximumtostress
in the laminate
according to the following:
according
the following
formula:
σmax
―――――
≤1
σmax.allowable
σmax
―――――
= 0.121 < 1
σmax.allowable
CUR 96 ;2003 recommends a stress criterion which limits the maximum stress in the laminate
according to the following formula:
σmax
―――――
≤1
(first moment of area)
1
―――
= 0.51
γm ⋅ γ c
120 Chapter 8 | Structural Calculation
8.9.3
Service
limit state
Service
limit state
Deflection
kN
qrep ≔ qG + qQ = 12.161 ――
m
(The loads without partial factors)
AFRP.parapet ≔ 4 ⋅ tfacing.side ⋅ hin = 0.029 m
2
5 ⋅ qrep ⋅ L1
η ⋅ qrep ⋅ L1
w1 ≔ ―――――
+ ――――――
= 4.483 mm
385 ⋅ Ex ⋅ Ixctot 8 ⋅ Gx ⋅ AFRP.parapet
4
2
1
⋅ L1 = 22.039 mm
wallowable ≔ ―――
300 ⋅ γc
So w1 < wu
Laminate Calulation
8.10 Optimization of the structure
The resulting stresses andmdeflections both from the parapet to parapet and the abutment to abutment check
f
Thicness of
tfabric
≔ ――
= 0.22
mm
proved
to fabric
be much
lower
than
the
allowable values. Consequently, the structure is unreasonably over-dimenpf
sioned, making excessive material use which leads to increased material costs. In order to reduce the margin
between the design and
tfabricthe allowable values the thickness of the laminate and the core are reduced. The
Thicness oftable
ply
tply ≔ ――
= 0.45 mm
following
shows
the influence
of dimensional changes on the mechanical performance of the structure.
Vf
The first data in the table are
the results from the calculations that have been already performed, while the next
two are results from calculations based on difference dimensions.
Thickness of QI laminate module (8 plies):
tQImod ≔ 8 ⋅ tply = 3.596 mm
Number of modules: Nmod ≔ 2
Table
8.7 Optimization of laminate and core thickness
Thickness
Parapet
parapet
tlam ≔ Nmod ⋅ tQImod
= 7.191tomm
[mm]
σmax/σallow < 1
n
tlam
≔ ――
= 16
Parapet to parapet
wmax
< wallow= 5.51mm
Abutment to abutment
σmax/σallow < 1
Abutment to abutment
wmax
< wallow= 22.04mm
ply
laminate=
tply 7.2
core= 86
0,05
1,96
0,12
4,48
_
_
laminate= 3.6
core= 56
0,15
8,75
0,26
9,30
+
laminate= 3.6
core= 78
0,11
4,74
0,25
8,94
It becomes clear that the most critical result is the deflection of the deck on the width of the bridge between
the parapets and not the deflection in the length (span) direction. However, the thickness of the laminate is
Created
with PTCtoMathcad
Express.
Seedimension.
www.mathcad.com
forlaminate
more information.
reduced
successfully
half of the
original
The 3.6mm
consists of the single 8-ply quasi isotropic module that was used for the original laminate calculation.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
121
Nevertheless, the structure could be further improved by optimising the properties of the laminate in critical parts. As it was mentioned previously, a quasi-isotropic laminate behaves structurally
in a similar way in all principal directions as the
fibre reinforcement is equally distributed within
the structure of the laminate. On the contrast an
orthotropic laminate shows higher properties in
specific directions that are reinforced with more
unidirectional plies. Thus, orthotropic laminates
are preferred in structures that demand better
performance in one main direction.
With deflection closely under the allowable for
the ‘‘parapet to parapet’’ structural check and
a big margin between the maximum and the allowable value in the ‘‘abutment to abutment’’
check it is obvious that the structure would benefit in terms of efficient material use, with the application of a laminate with orthotropic properties on the deck of the structure. As diagram 6.6
shows, the orthotropic laminate will have its highest mechanical properties oriented to the width
direction.
8.4 Optimum arrangement of fibre orientation in the laminates
Other critical areas are the two top edges of the parapets. Being the most distant areas from the neutral axis
they show the highest stress consentrations. Although, in terms of stress the values are much below the allowables, this stress could be reduced by increasing the thickness of these top flanges and orienting the fibres to the
longitudinal direction so that maximum stability is achieved.
0
+45
0
90
-45
-45
90
0
+45
0
8.5 Chosen fibre orientation for the Orthotropic laminate
of the deck
For the orthotropic laminate of the deck, the existing quasi isotropic structure was modified by
adding two extra layers with orientation angle
of 0 degrees. Thus the thickness of the laminate
was increased from 3,6mm to 4,5mm. With the
new layers the percentages of fibre orientation
change to 40% 0o, 20% 45o, 20% -45o and 20%
90o. The suggested structure is illustrated in the
scheme.
The properties of the laminate were calculated
again by the classical laminate theory while digital software Kolibri was a useful and efficient tool
that was used in order to avoid repeating the
procedure manually during the optimization process. The new resulted values for the orthotropic
laminate are shown in the table below.
Table 8.8 Orthotropic laminate properties
E-modulus longitudinal
25,9 GPa
E-modulus transverse
19,8 Gpa
Shear modulus
7,08 GPa
Poisson’s ratio longitudinal
0,33
Poisson’s ratio transverse
0,25
Chapter 8 | Structural Calculation
1
―――
= 0.51
γm ⋅ γ c
σmax
―――――
= 0.121 < 1
σmax.allowable
8,94
kN
qped ≔ 5 ――
2
m
0,194
(NEN-EN 1991-2)
5,35
Traffic load
0,097
0,18
Abutment to abutment
wmax
< wallow= 22.04mm
kN
qQ ≔ qped ⋅ bout = 10 ――
m
deck/flange= 4.5
parapet= 3.6
core= 56
2,94
0,25
(first moment of area)
_
_
0,07
4,746
Abutment to abutment
σmax/σallow < 1/
Imposed load
deck/flange= 4.5
parapet= 3.6
core= 78
1
―――
= 0.51
γm ⋅ γc
_
_
0,11
Iy
W = ―――
hout − yc
deck/flange= 3.6
parapet= 3.6
core= 78
Parapet to parapet
wmax
< wallow= 5.51mm
kN
qtot ≔ γG ⋅ qG + γQ ⋅ qQ = 16.946 ――
m
Parapet to parapet
σmax/σallow < 1
2
1
Mmax ≔ ―qtot ⋅ L1 = 135.6 kN ⋅ m
8
Thickness
[mm]
Bending moment
Stress
Table 8.9 Optimization of laminate and core thickness
Mmax
σmax = ――
W
Ixctot
3
W ≔ ―――= 0.009 m
hout − yc
Mmax
σmax ≔ ――= 14.742 MPa
W
0.012 ⋅ Ex
σmax.allowable ≔ ―――= 122.008 MPa
γm ⋅ γc
CUR 96 ;2003 recommends a stress criterion which limits the maximum stress in the laminate
according to the following formula:
σmax
―――――
≤1
σmax.allowable
σmax
―――――
= 0.121 < 1
σmax.allowable
Created with PTC Mathcad Express. See www.mathcad.com for more information.
122
8,37
8,73
8.11 Evaluation of flax, jute, glass and basalt fibre reinforced laminate
After having calculated the optimum thicknesses for the basalt fibre reinforced composite, the same optimized
structure with orthotropic laminate for the deck and the top flanges and quasi isotropic for the parapets will be
calculated again with flax, jute and glass fibres as reinforcement instead of basalt. Table 6.10 shows the laminate properties for an orthotropic and Quasi-isotropic laminate structure.
Table 8.10 Mechanical properties of Orthotropic and Quasi isotropic laminates
Basalt
Flax
Jute
Glass
Ortho
Q-Iso
Ortho
Q-Iso
Ortho
Q-Iso
Ortho
Q-Iso
E-modulus longitudinal [GPa]
25,9
21,3
18,3
15,3
13,8
12,0
21,4
17,6
E-modulus transverse [GPa]
19,8
21,3
13,8
15,3
11,0
12,0
15,7
17,6
Shear modulus [GPa]
7,08
7,98
5,51
5,98
4,43
4,68
6,22
6,87
Poisson’s ratio longitudinal
0,33
0,33
0,28
0,27
0,29
0,28
0,28
0,28
Poisson’s ratio transverse
0,25
0,33
0,21
0,27
0,23
0,28
0,20
0,28
As was also concluded from the research on natural fibres, the hydrophilic nature of lignocellulosic fibres allows for extensive moisture uptake while
compatibility with conventional resins in most of
the cases problematic. Moisture results in dimensional changes (swelling), mechanical performance changes (plasticisation and hence higher
strains to failure but lower moduli) and higher susceptibility to microbiological attack (Searle et al,
1999). Fibre treatment methods that have been
researched during the previous years, improve
at a certain degree the performance of the fibre
but they also increase its cost and environmental
impact. The result is a higher degree of reduction
in mechanical performance compared to glass
and basalt.
According to Shahzad, hemp fibre reinforced
composited showed a reduction of 40% in
strength and stiffness under accelerated weathering conditions. Another research (Joseph et. al)
proved that sisal fibre-reinforced polypropylene
composites showed almost 20% reduction in tensile strength only after 3day immersion into 28o C
warm water. Experiments done on untreated jute
fibre-reinforced composites resulted even in 90%
reduction of their initial properties.
600
400
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics
Park
200
Taking into consideration these results, calculating the structure with natural fibre reinforced laminates requires higher levels of safety by increased
factors regarding moisture and temperature. Increasing the conversion factors reduces the allowable values for strength and stiffness, resulting
in increased thicknesses. Graph 6.8 shows the increase of the weight of the structure according
to 30%, 50% and 80% end of life reduction of the
properties of jute and flax. With reduction above
50%, natural fibres “lose” their benefit of being
lightweight as their composites start to weight
more than glass and basalt fibre-reinforced composites.
[kg]
0
Total fibre weight
reduction
10-20%
30%per stiffness/strength
50%
80%
1200
Jute
800
In conclusion, considering the reasons above,
basalt proves to be the best option for fibre reinforcement compared to glass, flax and jute.
Basalt
Glass
Total fibre weight per stiffness/strength reduction
1200
600
1000
400
800
200
600
0
10-20%
10%-20%
400
8.6
However, cost was from the beginning another
critical factor for this project. Research of the
previous years, done on natural fibres, recognizes
them for their lower cost in comparison with conventional fibres. Nevertheless, approaching suppliers and requesting prices for specific products,
such as unidirectional technical textiles, proved
that some fibres could not be considered as a
cost efficient solution. Flax, for instance turned
out to be the less economic solution as its UD
textiles had an almost four times higher cost than
glass-fibre textiles. Glass fibre showed the lowest
price, closely lower from basalt. Diagram 6.10
compares the four fibres in terms of cost.
Jute
1000
200
with
Knowing the weight of the material needed, the
embodied energy of the total fibre amount can
be calculated by taking average values from the
findings of the LCA. Graph 6.9 shows that basalt is
the most competitive among all other fibres. Even
with a minimum reduction of 30% in the performance of natural fibres, jute has similar embodied energy with basalt while in the same category flax is the most efficient option.
123
0
30%30%
Jute
Jute
50%50%
Basalt
80%
80%
Glass
Weight of fibre required for the bridge in relation
reduction of mechanical properties
10-20%
30%
50%
80%
Energy consumption on fibre per stiffness/strength reduction
Jute
90000
Jute
Basalt
Glass
80000
70000
60000
50000
1200
40000
Total fibre weight per stiffness/strength reduction
30000
1000
20000
800
10000
0
600
10-20%
10%-20%
30%
30%
Jute
400
Flax
50%50%
Basalt
80%80%
Glass
8.7 Energy consumption of the required fibre in relation
with reduction of mechanical properties
200
0
10-20%
30%
50%
Total fibre cost per
stiffness/strength
reduction 80%
Jute
60000
Jute
Basalt
Glass
50000
40000
30000
20000
10000
0
10-20%
10%-20%
30%
30%
Jute
Flax
50%
50%
Basalt
Glass
80%80%
8.8 Cost of the required fibre in relation with reduction
of mechanical properties
124
Chapter 8 | Structural Calculation
Manufacture
&
Installation
126 Chapter 9 | Manufacture and Installation
9.1 Moldmaking and lamination
According to the research done on composite
shaping processes, the most appropriate production method for this bridge proved to be the vacuum assisted resin transfer molding, widely known
as resin infusion or resin injection. The reasons that
led to that technique were mainly the low butch
size, as the bridge would be a single product and
the budget limitations that directed the design to
inexpensive mold solutions.
The structure of the mold will consist of a bended steel plate and two side molds out of wood,
connected on the plate. After the mold is constructed the inner surfaces may be coated with
a release agent that eases demolding. The first
stage in laminating is the application of a gel
coat over the inner surfaces of the mold that protects the laminate. This coat is a non-fibrous pure
resin with less than 1mm thickness. Special resins,
with good hardness and impact resistance are
used for this coat.
9.1 Mold diagram. Bended steel plate and wooden
side parts for parapets
After the gel coat has been applied, the reinforcement fabrics of the laminate are laid, with
the first layer being usually a fine fleece that ensures a good surface finish. The process of layering the plies is repeated until the desired thickness
is achieved.
Arrangement of the individual unidirectional plies
is based on the outcome of the structural calculation. For the deck an orthotropic laminate that
consists of 10 plies was chosen. The plies are laid
symmetrically with a different angle on top of
each other, according to the following sequence
[0,+45,0,90,-45,-45,90,0,+45,0]. The dominant direction (0o) is oriented to the width direction as
this part proved to be the most critical by the
calculation of the structure. For the parapets, the
quasi-isotropic laminate chosen consists of 8 plies
symmetrically arranged according to the following sequence [0,+45,90,-45,-45,90,+45,0].
9.2, 9.3, 9.4 Mold constuction of a 21meter fibre-reinforced composite bridge. Similar to the bio-based brige
of this project, the process followed in that example is
also vacuum assisted resin injection.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
9.2 Construction of shear web
After finishing with the lay-up of the reinforcement
of the lower facing, the core is placed over the
fibre plies. In the case of making a shear web in
order to ensure a good bond between the core
and the facing, which is the case of this bridge,
the core obviously is not a continuous single unit.
The core is separated in linear pieces that are
placed repeatedly the one next to the other with
a ply of fabric in between them. In that way, during resin injection, the liquid matrix will flow from
the plies of the facings to the fabric between the
shear web plates, making them part of both the
lower and upper skin.
The detailed way the rectangular core beams
are arranged side by side together with the separating fabric is clearly shown in the following
schemes. The plies are repeatedly arranged with
one (gray) taking a Z turn, starting from the upper facing, turning down attached to the side
of the core and then continuing as a ply of the
down facing. Then the next fabric (blue) is laid
waiting for the next piece of core. The core pieces can also wrapped all around their surfaces
usually with a ply of a +45o, – 45o non-crimp fabric (green) before there are placed in the mold.
With this technique, both facings are connected
through these fabrics that after curing they consist a compact shear web within the sandwich
structure.
9.5 Detail of the shear web in the structure
9.6 Arrangement of unidirectional plies around the core pieces in order to build a shear web whithin the structure
127
128 Chapter 9 | Manufacture and Installation
9.3 Direction of the web plates
In web-core structures, the web plates run only in
one direction. In a similar way as spanning a rectangular concrete slab with beams, these plates
are normally arranged vertically to the span direction. By doing so, both the core beams and
the web plates have higher stiffness as due to
their short length (3.0m) deformation is less than if
spanning was in the long direction (8.0m).
In order to achieve a good concentration of web
plates that prevents separation between the two
facings the plates are usually spaced at a distance 10–100 times the thickness of the facing.
Thus, the distance of the web plates was chosen
to be 100mm, which means that core blocks of
this thickness have to be produced.
9.7 Arrangement of core elements for the achievement of the shear web
9.4 Injection and final operations
After injection and curing of the product the panel is released from the mold and the edges are
trimmed to the desired shape. Sawing the composite at the cutting edges removes the facing
plates from the cut sections leaving their surfaces uncovered with the core visible and exposed.
Thus, layers of pure resin, preferably the same
used for the entire structure, are applied manually afterwards over these surfaces in order to enclose again the core and achieve a smooth and
aesthetically better finish at the cut corners.
9.8 Construction method of the laminate
The final process in the manufacturing unit, before the bridge is transported to the site, is the
adjustment of the two cradles at the edges of
the deck. The role of the cradles is to prevent direct contact of the structure with the foundation
system. The cradle consists of a rubber material
that is placed on the structure and is hand laminated with the same combination of fibre and
resin used in the structure. After the addition has
cured the holes that will connect the structure
with the foundation are drilled.
9.9 Plastic cradles at the edges of the deck
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
129
9.5 Installation on site
Prior to the transportation of the structure on site,
the foundation is constructed. Due to the light
weight of the structure the foundation can be a
simple system. A common solution in such cases
is the use of concrete blocks as a foundation system with poles would be excesive. However, it
is suggested for the bridge of this projected the
concrete blocks to be replaced by glass-fibre
reinforced blocks that are used in FRP manufacturing companies as testing models. These blocks
normally have cubic shape with a volume of 1m3
and while their sturctural performance is still after
the test good, these cubes costist a waste material for all these companies. Thus, reusing this elements, avoids the added envionmental impact
and financial cost of a concrete supporting structure.
9.10 Soil compaction next to the foundation (concrete
block solution)
A problem that occurs in most bridges that use a foundation system similar to the concrete blocks is the soil
compaction through time. The ground that gradually moves causes the pavement to slide vertically together
with the ground resulting in a small step. To solve this, a steel plate is adjusted on the top surface of the concrete block and extendts under an algle into the ground. The soil that is placing compact soil above the steel
plate ensures that the pavement will remain straight and no slide will appear above the plate.
9.11 Foundation solution with glass-fibre reinforced plastic testing block and steel plate
Detail of the foundation
130
Chapter 9 | Manufacture and Installation
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
9.12, 9.13 Foundation solution with glass-fibre reinforced plastic testing block and steel plate
131
132
Chapter 9 | Manufacture and Installation
Conclusions
&
Recommendations
134
Chapter 10 | Conclusions and Recommendations
10.1 Conclusions
Considering the results from the LCA and the
structural calculation we can conclude that sustainability can be approached by many different
ways. It is finally the way a material is used or the
chosen application and not only its natural origin
that makes a product or structure sustainable.
Reducing extensively the end of life of a structure such as a bridge by using a non-durable but
sustainable material proves to be less efficient in
terms of sustainability than using a conventional
durable material.
Main drawback of natural fibre is their low durability due to various reasons, such as moisture
absorption, temperature and fibre-resin low compatibility. Resulting in bigger dimensions, more
material is required, which increases the environmental impact and embodied energy of the
structure. Development of sustainable fibre treatment methods that would be applied during textile manufacturing could become a future solution. Yet, more research and testing results are
required in order to be able to use natural fibres
in load-bearing applications without considering
serious mechanical performance reduction.
For the present level of development of natural
fibres as reinforcement in composites, their use in
non-loadbearing and less durability-demanding
applications with lower life-span is a more efficient
practice. For that reason, the automotive industry
was the ideal sector to introduce such bio-based
materials, test them and use to the maximum all
their advantages. It is no wonder that this sector
has high percentage in use of bio-plastics.
Another disadvantage of the two examined natural fibres was their high price that raised together the increase in material requirement. So even if
the environmental benefit by using natural fibres
in a load-bearing application was of significant
importance, the cost of the structure would be a
few times higher than it would be by using conventional fibres. All the above show that for this
specific project, in which durability is linked with
sustainability and cost is an influential factor,
conventional fibres prove to be a more sustainable and efficient solution.
Comparing glass fibre and basalt, as mentioned
in the LCA, the latter shows advantages in terms
environmental impact and embodied energy
compared to glass fibre. Easier recyclability, pure
consistency, non-toxicity and use of alternative
sources for the production of basalt are some
factors that reduce the impact of basalt. In addition, basalts higher durability and mechanical
performance compared to glass allows for less
material use. Specifically, from the calculation
it was found that having the minimum laminate
thickness of 4,5mm, basalt reinforcement allowed
for reduction of the core material to 56mm, as
the margin was still considerable. In contrast, the
4,5mm glass fibre reinforced laminate could not
achieve core thickness lower than 76mm.
Due to the reasons explained above, basalt fibre
was considered as the most efficient solution for
the bridge of this project in terms of sustainability, cost and feasibility of the real construction.
In any respect, opting for reinforcement with
non-renewable resource does not influence the
bio-based character of the bridge as for the core
a natural material (balsa wood) was chosen and
the matrix is the bio-based furan.
Bio-based FRP structures: A pedestrian bridge in Schiphol Logistics Park
10.2 Recommendations and points of improvement
Research regarding the durability of natural fibres
and their use as reinforcement in fibre-reinforced
composites, used in load-bearing application is
still at an early stage of development. Through
the present research, it became clear that accelerated reduction of the mechanical properties of plant fibres due to low durability is the main
reason prohibiting their use in such applications.
Thus, future research should be directed on exploring solutions for improving the durability of
these fibres either by fibre treatment methods or
long-lasting protection within the composite. In
any case, such an investigation requires material testings and experimentations on real testing
samples in order to draw conclusions.
Apart from the fibre, significant is also the contribution of the resin for the durability, environmental impact and strength of a composite. However, in this graduation project most of the research
is dedicated on natural fibre, rather than the resin
and the core material, which creates topics for
further development on these two elements.
Finally, the life-cycle analysis done on natural
fibres was an important step with interesting results regarding the embodied energy and the
environmental impact of the fibres. However, the
LCA focuses mainly on the production phase of
the fibre rather than on the use phase (maintenance, repair) and the end of life treatment (recycle, disposal, etc.). A complete extensive LCA
that would consider all phases could consist an
individual topic of research on the environmental
impact of load-bearing natural fibre-reinforced
plastics.
135
136
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