SLIDING WEAR BEHAVIOR OF GLASS FIBRE REINFORCED TiO FILLED EPOXY RESIN COMPOSITE

SLIDING WEAR BEHAVIOR OF GLASS FIBRE REINFORCED TiO FILLED EPOXY RESIN COMPOSITE
SLIDING WEAR BEHAVIOR OF GLASS FIBRE
REINFORCED TiO2 FILLED EPOXY RESIN COMPOSITE
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
Bachelor of Technology in Mechanical Engineering
BY
TARUN AGGARWAL
ROLL NO: 10503057
DEPARTMENT OF MECHANICAL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY
ROURKELA-769008
2009
SLIDING WEAR BEHAVIOR OF GLASS FIBRE
REINFORCED TiO2 FILLED EPOXY RESIN COMPOSITE
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
Bachelor of Technology in Mechanical Engineering
BY
TARUN AGGARWAL
ROLL NO: 10503057
Under the guidance of
Prof. Sandhyarani Biswas
DEPARTMENT OF MECHANICAL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY
ROURKELA-769008
2009
CERTIFICATE
This is to certify that the thesis entitled “Sliding Wear Behavior of Glass Fibre
Reinforced Tio2 Filled Epoxy Resin Composite” submitted by Tarun Aggarwal
(Roll No. 10503057) in partial fulfillment of the requirements for the award of
Bachelor of Technology in the department of Mechanical Engineering, National
Institute of Technology, Rourkela is an authentic work carried out under my
supervision and guidance.
To the best of my knowledge, the matter embodied in the thesis has not
been submitted to elsewhere for the award of any degree.
Place: Rourkela
Date:
Sandhyarani Biswas
Mechanical Engineering Department
National Institute of Technology
Rourkela-769008
ACKNOWLEDGEMENT
It gives me immense pleasure to express my deep sense of gratitude to my
supervisor Prof. Sandhyarani Biswas for her invaluable guidance, motivation,
constant inspiration and above all her ever co-operating attitude enabled me in
bringing up this thesis in present elegant form.
I am extremely thankful to Prof. R. K. Sahoo, Head, Department of Mechanical
Engineering and the faculty member of Mechanical Engineering Department for
providing all kinds of possible help and advice during the course of this work.
It is a great pleasure for me to acknowledge and express my gratitude to my
parents for their understanding, unstinted support and endless encouragement
during my study.
I am greatly thankful to all the staff members of the department and all my well
wishers, class mates and friends for their inspiration and help.
Lastly I sincerely thank to all those who have directly or indirectly helped for the
work reported herein.
TARUN AGGARWAL
ROLL NO: 10503057
Department of Mechanical Engineering
National Institute of Technology, Rourkela
ABSTRACT
Glass fiber reinforced polymer composites find widespread applications these days
in hostile environment due to their several advantages like high wear resistance,
strength-to-weight ratio and low cost. The performance of the composites can
further be improved by adding particulate fillers to them. To this end, this work
successfully uses TiO2 as a filler material in polymer. The present work includes
the processing, characterization and study of the sliding wear behaviour of a series
of such TiO2 filled short glass-epoxy composites. It further outlines a methodology
based on Taguchi’s experimental design approach to make a parametric analysis
of sliding wear behaviour. The systematic experimentation leads to determination
of significant process parameters and material variables that predominantly
influence the wear rate.
CONTENTS
Chapter No.
Chapter 1
Description
1. INTRODUCTION
Page No.
2-6
1.1. Overview of composites
1.2. Merits of Composites
1.3. Scope of the project
Chapter 2
2. LITERATURE SURVEY
8-10
2.1 Objectives of the Research Work
Chapter 3
3. MATERIALS AND METHODS
12-17
3.1. Introduction
3.2. Processing of the Composites
3.3. Characterization of the Composites
3.4. Sliding Wear Test
3.5. Experimental design
Chapter 4
4.COMPOSITE CHARACTERIZATION:
19-23
RESULTS AND DISCUSSION
4.1. Introduction
4.2. Composite Characterization
4.3. Design of experiments via Taguchi method
Chapter 5
5. RESULTS AND ANALYSIS
25-29
5.1. Wear characteristics analysis
5.2. ANOVA and the effects of factors
Chapter 6
6. CONCLUSIONS
31-31
6.1. Scope for Future Work
REFERENCES
33-35
Chapter 1
INTRODUCTION
1
CHAPTER 1
1. INTRODUCTION
1.1. Overview of composites
Composite materials (or composites for short) are engineering materials made
from two or more constituent materials that remain separate and distinct on a
macroscopic level while forming a single component. There are two categories
of constituent materials: matrix and reinforcement. At least one portion of each
type is required. The matrix material surrounds and supports the reinforcement
materials by maintaining their relative positions. The reinforcements impart
their special mechanical and physical properties to enhance the matrix
properties. The primary functions of the matrix are to transfer stresses between
the reinforcing fibers/particles and to protect them from mechanical and/or
environmental damage whereas the presence of fibers/particles in a composite
improves its mechanical properties such as strength, stiffness etc. A composite
is therefore a synergistic combination of two or more micro-constituents that
differ in physical form and chemical composition and which are insoluble in
each other. The objective is to take advantage of the superior properties of both
materials without compromising on the weakness of either. The synergism
produces material properties unavailable from the individual constituent
materials. Due to the wide variety of matrix and reinforcement materials
available, the design potentials are incredible.
Composite materials have successfully substituted the traditional materials in
several light weight and high strength applications. The reasons why
composites are selected for such applications are mainly their high strength-toweight ratio, high tensile strength at elevated temperatures, high creep
resistance and high toughness. Typically, in a composite, the reinforcing
materials are strong with low densities while the matrix is usually a ductile or
tough material. If the composite is designed and fabricated correctly it
combines the strength of the reinforcement with the toughness of the matrix to
achieve a combination of desirable properties not available in any single
2
conventional material. The strength of the composites depends primarily on the
amount, arrangement and type of fiber and /or particle reinforcement in the
resin.
1.2. Merits of Composites
Advantages of composites over their conventional counterparts are the ability
to meet diverse design requirements with significant weight savings as well as
strength-to-weight ratio. Some advantages of composite materials over
conventional ones are as follows:
Tensile strength of composites is four to six times greater than that of
steel or aluminium (depending on the reinforcements).
Improved torsional stiffness and impact properties.
Higher fatigue endurance limit (up to 60% of ultimate tensile strength).
30% - 40% lighter for example any particular aluminium structures
designed to the same functional requirements.
Lower embedded energy compared to other structural metallic materials
like steel, aluminium etc.
Composites are less noisy while in operation and provide lower
vibration transmission than metals.
Composites are more versatile than metals and can be tailored to meet
performance needs and complex design requirements.
Long life offer excellent fatigue, impact, environmental resistance and
reduce maintenance.
Composites enjoy reduced life cycle cost compared to metals.
Composites exhibit excellent corrosion resistance and fire retardancy.
Improved appearance with smooth surfaces and readily incorporable
integral decorative melamine are other characteristics of composites.
Composite parts can eliminate joints / fasteners, providing part
simplification and integrated design compared to conventional metallic
parts.
3
Broadly, composite materials can be classified into three groups on the basis of
matrix material. They are:
a) Metal Matrix Composites (MMC)
b) Ceramic Matrix Composites (CMC)
c) Polymer Matrix Composites (PMC)
a) Metal Matrix Composites
Metal Matrix Composites have many advantages over monolithic metals like
higher specific modulus, higher specific strength, better properties at elevated
temperatures, and lower coefficient of thermal expansion. Because of these
attributes metal matrix composites are under consideration for wide range of
applications viz. combustion chamber nozzle (in rocket, space shuttle),
housings, tubing, cables, heat exchangers, structural members etc.
b) Ceramic matrix Composites
One of the main objectives in producing ceramic matrix composites is to
increase the toughness. Naturally it is hoped and indeed often found that there
is a concomitant improvement in strength and stiffness of ceramic matrix
composites.
c) Polymer Matrix Composites
Most commonly used matrix materials are polymeric. The reason for this are
two fold. In general the mechanical properties of polymers are inadequate for
many structural purposes. In particular their strength and stiffness are low
compared to metals and ceramics. These difficulties are overcome by
reinforcing other materials with polymers. Secondly the processing of polymer
matrix composites need not involve high pressure and doesn‟t require high
temperature. Also equipments required for manufacturing polymer matrix
composites are simpler. For this reason polymer matrix composites developed
rapidly and soon became popular for structural applications.
Composites are used because overall properties of the composites are superior
to those of the individual components for example polymer/ceramic.
4
Composites have a greater modulus than the polymer component but aren‟t as
brittle as ceramics.
Two types of polymer composites are:
• Fiber reinforced polymer (FRP)
• Particle reinforced polymer (PRP)
Fiber Reinforced Polymer
Common fiber reinforced composites are composed of fibers and a matrix.
Fibers are the reinforcement and the main source of strength while matrix glues
all the fibers together in shape and transfers stresses between the reinforcing
fibers. The fibers carry the loads along their longitudinal directions.
Sometimes, filler might be added to smooth the manufacturing process, impact
special properties to the composites, and / or reduce the product cost.
Common fiber reinforcing agents include asbestos, carbon / graphite fibers,
beryllium, beryllium carbide, beryllium oxide, molybdenum, aluminium oxide,
glass fibers, polyamide, natural fibers etc. Similarly common matrix materials
include epoxy, phenolic, polyester, polyurethane, polyetherethrketone (PEEK),
vinyl ester etc. Among these resin materials, PEEK is most widely used.
Epoxy, which has higher adhesion and less shrinkage than PEEK, comes in
second for its high cost.
Particle Reinforced Polymer
Particles used for reinforcing include ceramics and glasses such as small
mineral particles, metal particles such as aluminium and amorphous materials,
including polymers and carbon black. Particles are used to increase the
modules of the matrix and to decrease the ductility of the matrix. Particles are
also used to reduce the cost of the composites. Reinforcements and matrices
can be common, inexpensive materials and are easily processed. Some of the
useful properties of ceramics and glasses include high melting temp., low
density, high strength, stiffness, wear resistance, and corrosion resistance.
Many ceramics are good electrical and thermal insulators. Some ceramics have
special properties; some ceramics are magnetic materials; some are
piezoelectric materials; and a few special ceramics are even superconductors at
5
very low temperatures. Ceramics and glasses have one major drawback: they
are brittle. An example of particle reinforced composites is an automobile tire,
which has carbon black particles in a matrix of poly-isobutylene elastomeric
polymer.
Polymer composite materials have generated wide interest in various
engineering fields, particularly in aerospace applications. Research is underway
worldwide to develop newer composites with varied combinations of fibers and
fillers so as to make them useable under different operational conditions.
Against this backdrop, the present work has been taken up to develop a series
of PEEK based composites with glass fiber reinforcement and with ceramic
fillers and to study their response to solid particle erosion.
1.3. Scope of the project
1. The basic aim of the present work is to develop and characterize a new
class of composites with a polymer called epoxy-filler as the matrix and
glass fiber as the reinforcing material.
2. Their physical and mechanical characterization is done. Attempt is made
to use TiO2 as filler in these fiber reinforced polymer matrix composites.
3. Wear behaviour of this new class of composites is investigated in this
project work. Dry sliding wear is performed on the composites.
4. This work is expected to introduce a new class of functional polymer
composites suitable for tribological applications.
*****
6
Chapter 2
LITERATURE SURVEY
7
CHAPTER 2
2. LITERATURE SURVEY
This chapter outlines some of the recent reports published in literature on
composites with special emphasis on erosion wear behavior of glass fiber
reinforced polymer composites.
Polymers have generated wide interest in various engineering fields including
tribological applications, in view of their good strength and low density as
compared to monolithic metal alloys. Being lightweight they are the most
suitable materials for weight sensitive uses, but their high cost sometimes
becomes the limiting factor for commercial applications. Use of low cost,
easily available fillers is therefore useful to bring down the cost of component.
Study of the effect of such filler addition is necessary to ensure that the
mechanical properties of the composites are not affected adversely by such
addition. Available references suggest a large number of materials to be used as
fillers in polymers [1]. The purpose of use of fillers can therefore be divided
into two basic categories; first, to improve the mechanical, thermal or
tribological properties and second, to reduce the cost of the component. There
have been various reports on use of materials such as minerals and inorganic
oxides, such as alumina and silica mixed into widely employed thermoplastic
polymers like polypropylene [2,3] and polyethylene [4,5]. But very few
attempts have indeed been made to utilize cheap materials like industrial
wastes in preparing particle-reinforced polymer composites.
A key feature of particulate reinforced polymer composites that makes them so
promising as engineering materials is the opportunity to tailor the materials
properties through the control of filler content and matrix combinations and the
selection of processing techniques. A judicious selection of matrix and the
reinforcing solid particulate phase can lead to a composite with a combination
of strength and modulus comparable to or even better than those of
conventional metallic materials [6]. Hard particulate fillers consisting of
ceramic or metal particles and fiber fillers made of glass are being used these
days to dramatically improve the wear resistance of composites, even up to
8
three orders of magnitude [7]. The improved performance of polymers and
their composites in industrial and structural applications by the addition of
particulate fillers has shown a great promise and so has lately been a subject of
considerable interest. Various kinds of polymers and polymer matrix
composites reinforced with metal particles have a wide range of industrial
applications such as heaters, electrodes [8], composites with thermal durability
at high temperature [9] etc. These engineering composites are desired due to
their low density, high corrosion resistance, ease of fabrication, and low cost
[10, 11]. Similarly, ceramic filled polymer composites have been the subject of
extensive research in last two decades.
A number of experiments have been performed using different ceramics such
as Al2O3, TiC, and SiC by varying the particle size and particle volume fraction
[12]. Polymer/TiO2 composites have been successfully synthesized in different
polymer matrixes such as silicone elastomer [13], polycarbonate [14],
polyamide 6 [15], epoxy [16], unsaturated polyester [17], polyacrylate [18],
poly(methyl methacrylate) [19], polyimide [20], polystyrene [21] and dental
composites [22]. Titanium dioxide pigment is a fine white powder is one of the
most important filler used for making composites for many engineering
applications. Against this background, the present research work has been
undertaken, with an objective to explore the potential of TiO2 as a filler
material in polymer composites and to investigate its effect on the dry sliding
wear performance of the composites and also study the mechanical
characterization of different filler contents of the composites.
To study the correlation between the wear properties and the characteristic
parameters, e.g. the composition of the composite and the operating conditions,
is of prime importance for designing proper composites in order to satisfy
various functional requirements. But visualization of impact of any individual
control factor in an interacting environment really becomes difficult. To this
end, an attempt has been made in this study, to analyze the impact of more than
one parameter on sliding wear of the polyester composite. It is important as in
actual practice, the resultant wear rate is the combined effect of more than one
9
interacting variables. An inexpensive and easy-to-operate experimental strategy
based on Taguchi‟s parameter design has been adopted to study effect of
various parameters and their interactions. This experimental procedure has
been successfully applied for parametric appraisal in wire electrical discharge
machining (WEDM) process, drilling of metal matrix composites, and erosion
behavior of polymer matrix composites [23, 24, 25].
2.1 Objectives of the Present Work
The objectives of the project are outlined below.
Fabrication of glass fibre reinforced epoxy based hybrid composite
with/without filler content.
Evaluation of mechanical properties (tensile strength, flexural, hardness,
impact strength etc.)
Dry sliding wear of composite samples under various operating
conditions
The study of effect of fibre and filler content on sliding wear analysis.
Besides the above all the objective is to develop new class of composites by
incorporating TiO2 reinforcing phases into a polymeric resin. Also this
work is expected to introduce a new class of polymer composite that might
find tribological applications.
******
10
Chapter 3
MATERIALS AND METHODS
11
CHAPTER 3
3. MATERIALS AND METHODS
3.1. Introduction
This chapter describes the details of processing of the composites and the
experimental procedures followed for their characterization and tribological
evaluation. The raw materials used in this work are
1. Short E-glass Fiber
2. TiO2
3. Epoxy resin
3.2. Processing of the Composites
Short E-glass fibers (360 roving taken from Saint Gobian) are reinforced with
Epoxy LY 556 resin, chemically belonging to the „epoxide‟ family is used as
the matrix material. Its common name is Bisphenol A Diglycidyl Ether. The
low temperature curing epoxy resin (Araldite LY 556) and corresponding
hardener (HY951) are mixed in a ratio of 10:1 by weight as recommended. The
epoxy resin and the hardener are supplied by Ciba Geigy India Ltd. E-glass
fiber and epoxy resin has modulus of 72.5 GPa and 3.42GPa respectively and
possess density of 2590 kg/m3 and 1100kg/m3 respectively. Composites of
three different compositions such as 0wt% filler, 10wt% and 20wt% TiO2 are
made and the fiber loading (weight fraction of glass fiber in the composite) is
kept at 50% for all the samples. The castings are put under load for about 24
hours for proper curing at room temperature. Specimens of suitable dimension
are cut using a diamond cutter for physical characterization and erosion test.
3.3. Characterization of the Composites
Density
The theoretical density of composite materials in terms of weight fraction can
easily be obtained as for the following equations given by Agarwal and
Broutman [26].
ρ ct
1
Wf /ρ f
Wm /ρ m
12
(1)
Where, W and ρ represent the weight fraction and density respectively. The
suffix f, m and ct stand for the fiber, matrix and the composite materials
respectively.
The composites under this investigation consists of three components namely
matrix, fiber and particulate filler. Hence the modified form of the expression
for the density of the composite can be written as
ρ ct
Wf /ρ f
1
Wm /ρ m
Wp /ρ p
(2)
Where, the suffix „p’ indicates the particulate filler materials.
The actual density ( ρ ce ) of the composite, however, can be determined
experimentally by simple water immersion technique. The volume fraction of
voids ( Vv ) in the composites is calculated using the following equation:
ρ ct
Vv
ρ ce
(3)
ρ ct
Micro-hardness measurement
Micro-hardness measurement is done using a Leitz micro-hardness tester. A
diamond indenter, in the form of a right pyramid with a square base and an
angle 1360 between opposite faces, is forced into the material under a load F.
The two diagonals X and Y of the indentation left on the surface of the material
after removal of the load are measured and their arithmetic mean L is
calculated. In the present study, the load considered F = 24.54N and Vickers
hardness number is calculated using the following equation.
HV
and L
0.1889
F
L2
(4)
X Y
2
Where F is the applied load (N), L is the diagonal of square impression (mm),
X is the horizontal length (mm) and Y is the vertical length (mm).
Tensile and flexural strength
The tensile test is generally performed on flat specimens. The commonly used
specimens for tensile test are the dog-bone type and the straight side type with
13
end tabs. During the test a uni-axial load is applied through both the ends of the
specimen. The ASTM standard test method for tensile properties of fiber resin
composites has the designation D 3039-76. The length of the test section
should be 200 mm. The tensile test is performed in the universal testing
machine (UTM) Instron 1195 and results are analyzed to calculate the tensile
strength of composite samples. The short beam shear (SBS) tests are performed
on the composite samples at room temperature to evaluate the value of flexural
strength (FS). It is a 3-point bend test, which generally promotes failure by
inter-laminar shear. The SBS test is conducted as per ASTM standard (D234484) using the same UTM. Span length of 40 mm and the cross head speed of 1
mm/min are maintained.
The flexural strength (F.S.) of any composite
specimen is determined using the following equation.
F.S
3PL
2bt 2
(5)
Where, L is the span length of the sample. P is the load applied; b and t are the
width and thickness of the specimen respectively.
3.4. Sliding Wear Test
To evaluate the performance of these composites under dry sliding condition,
wear tests are carried out in a pin-on-disc type friction and wear monitoring test
rig (supplied by DUCOM) as per ASTM G 99. The experimental set up is
shown in Figure 1. The counter body is a disc made of hardened ground steel
(EN-32, hardness 72 HRC, surface roughness 0.6
Ra). The specimen is held
stationary and the disc is rotated while a normal force is applied through a lever
mechanism. A series of test are conducted with three sliding velocities of 210,
261 and 314 cm/sec under three different normal loading of 10N, 20N and
30N. The material loss from the composite surface is measured using a
precision electronic balance with accuracy + 0.1 mg and the specific wear rate
(mm3/N-m) is then expressed on „volume loss‟ basis as
WS = m/ t VS.FN
(6)
14
where
m is the mass loss in the test duration (gm)
is the density of the composite (gm/mm3)
t is the test duration (sec).
Vs is the sliding velocity (m/sec)
FN is the average normal load (N).
The specific wear rate is defined as the volume loss of the specimen per unit
sliding distance per unit applied normal load.
Figure 1. Schematic diagram of a Pin-on-Disc set-up
3.5. Experimental design
Design of experiment is a powerful analysis tool for modeling and analyzing
the influence of control factors on performance output. The most important
stage in the design of experiment lies in the selection of the control factors.
Therefore, a number of factors are included so that non-significant variables
can be identified at earliest opportunity. The wear tests are carried out under
operating conditions given in Table 1. The tests are conducted at room
temperature as per experimental design given in Table 2. Three parameters viz.,
sliding velocity, normal load, filler content and sliding distance each at three
levels, are considered in this study in accordance with L27 (313 ) orthogonal
array design. In Table 2, each column represents a test parameter and a row
gives a test condition which is nothing but a combination of parameter levels.
15
The experimental observations are transformed into signal-to-noise (S/N)
ratios. There are several S/N ratios available depending on the type of
characteristics. The S/N ratio for minimum wear rate coming under smaller is
better characteristic, which can be calculated as logarithmic transformation of
the loss function as shown below.
Smaller is the better characteristic: S
N
10 log
1
n
(7)
y2
where n is the number of observations, and y is the observed data. “Lower is
better” (LB) characteristic, with the above S/N ratio transformation, is suitable
for minimization of wear rate. The standard linear graph, as shown in Fig. 2, is
used to assign the factors and interactions to various columns of the orthogonal
array [27].
Table 1. Control factors and levels used in the experiment
Control factor
Level
I
A: Sliding velocity
210
II
261
III
314
Units
cm/sec
B: Normal load
10
20
30
N
C: Filler content
0
10
20
%
D: Sliding distance
2
4
6
km
The plan of the experiments is as follows: the first column is assigned to sliding
velocity (A), the second column to normal load (B), the third column to filler
content (C) and forth column to sliding distance (D) and the third and fourth
column are assigned to (A B)1 and (A B)2, respectively to estimate
interaction between sliding velocity (A) and normal load (B), the sixth and
seventh column are assigned to (B C)1 and (B C)2 respectively, to estimate
interaction between the normal load (B) and filler content (C), the eighth and
eleventh column are assigned to (A C)1 and (A C)2 respectively, to estimate
interaction between the sliding velocity (A) and filler content (C).
remaining columns are assigned to error columns respectively.
16
The
B(2)
(3,4)
(6,7)
D(9)
(8,11)
A(1)
E(10)
(12)
(13)
C(5)
Figure 2. Linear graphs for L27 array
Table 2. Orthogonal array for L27 (313) Taguchi‟s Experimental Design
L27(313)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
1
A
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
2
B
1
1
1
2
2
2
3
3
3
1
1
1
2
2
2
3
3
3
1
1
1
2
2
2
3
3
3
3
(AxB)1
1
1
1
2
2
2
3
3
3
2
2
2
3
3
3
1
1
1
3
3
3
1
1
1
2
2
2
4
(AxB)2
1
1
1
2
2
2
3
3
3
3
3
3
1
1
1
2
2
2
2
2
2
3
3
3
1
1
1
5
C
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
6
(BxC)1
1
2
3
1
2
3
1
2
3
2
3
1
2
3
1
2
3
1
3
1
2
3
1
2
3
1
2
*****
17
7
(BxC)2
1
2
3
1
2
3
1
2
3
3
1
2
3
1
2
3
1
2
2
3
1
2
3
1
2
3
1
8
(AxC)1
1
2
3
2
3
1
3
1
2
1
2
3
2
3
1
3
1
2
1
2
3
2
3
1
3
1
2
9 10
11
12 13
D
(AxC)2
1 1
1
1 1
2 2
2
2 2
3 3
3
3 3
2 2
3
3 3
3 3
1
1 1
1 1
2
2 2
3 3
2
2 2
1 1
3
3 3
2 2
1
1 1
2 3
1
2 3
3 1
2
3 1
1 2
3
1 2
3 1
3
1 2
1 2
1
2 3
2 3
2
3 1
1 2
2
3 1
2 3
3
1 2
3 1
1
2 3
3 2
1
3 2
1 3
2
1 3
2 1
3
2 1
1 3
3
2 1
2 1
1
3 2
3 2
2
1 3
2 1
2
1 3
3 2
3
2 1
1 3
1
3 2
Chapter 4
COMPOSITE CHARACTERIZATION:
RESULTS & DISCUSSION
18
CHAPTER 4
4.COMPOSITE CHARACTERIZATION: RESULTS AND DISCUSSION
4.1 Introduction
This chapter presents the physical and mechanical characterization of the class
of polymer matrix composites developed for the present investigation. They are
Short glass fiber Reinforced epoxy resin composites.
Short glass fiber reinforced epoxy resin filled with different weight
percentage of TiO2.
Details of processing of these composites and the tests conducted on them have
been described in the previous chapter. The results of various characterization
tests are reported here. They include evaluation of tensile strength, flexural
strength, measurement of density and micro-hardness has been studied and
discussed.
4.2 Composite Characterization
Physical and mechanical properties
The theoretical and measured densities of all composite samples along with the
corresponding volume fraction of voids are presented in Table 3. It may be
noted that the composite density values calculated theoretically from weight
fractions using Eq. (2) are not in agreement with the experimentally determined
values. The difference is a measure of voids and pores present in the
composites.
Table 3. Theoretical and measured densities along with void fractions in
composites
Sample No.
Filler content
(wt%)
1
2
3
0
10
20
Theoretical
Density
(gm/cc)
1.1
1.124
1.149
19
Measured
Density
(gm/cc)
1.103
1.112
1.138
Void Fraction
(%)
0.27
1.06
0.95
It is clear from Table 3 that the percentage of voids in hardened neat epoxy is
negligibly small i.e. 0.27 % and this may be due to the absence of any filler.
With the addition of filler content more voids are found in the composites and
with 10 to 20 wt% of filler, the volume fraction of voids is also found to be at
about 1 %. Density of a composite depends on the relative proportion of matrix
and reinforcing materials and this is one of the most important factors
determining the properties of the composites. The void content is the cause for
the difference between the values of true density and the theoretically
calculated one. The voids significantly affect some of the mechanical
properties and even the performance of composites in the place of use. The
knowledge of void content is desirable for estimation of the quality of the
composites. It is understandable that a good composite should have fewer
voids. However, presence of void is unavoidable in composite making
particularly through hand-lay-up route. The composites under the present
investigation possess very less voids and can thus be termed as good
composites.
In this study, the reinforcement of TiO2 particulate in glass fiber reinforced
epoxy resin has not shown encouraging results in terms of mechanical
properties. The tensile strengths of the composites with 10 wt% and 20 wt% are
recorded as 263.65 MPa and 257.76 MPa respectively where as that of neat
epoxy with short glass fiber is about 370 MPa. There can be two reasons for
this decline in the strength properties of these filled composites compared to
the unfilled one as shown in Figure 3. One possibility is that the chemical
reaction at the interface between the filler and the matrix may be too weak to
transfer the tensile stress; the other is that the corner points of the irregular
shape of the particulate result in stress concentration in the epoxy matrix. These
two factors are responsible for reducing the tensile strengths of the composites
so significantly.
20
400
Tensile strength (MPa )
350
300
250
200
150
100
50
0
0
5
10
15
20
Filler content (%)
Figure 3. Variations of tensile strength of the composites
Figure 4 shows the comparison of flexural strengths of the composites obtained
experimentally from the bend tests. It is interesting to note that addition of
small amount (10 wt%) TiO2 improves the flexural strength of glass epoxy
composite structure. But further addition (20 wt%) lowers the strength value
drastically.
Flexural strenght (Mpa)
400
300
200
100
0
0
5
10
Filler content (wt%)
15
Figure 4. Variations of flexural strength of the composites
21
20
The hardness values of the composites with filler content of 10 wt% and 20
wt% are recorded as 47 Hv and 49.5 Hv respectively. For hardened of unfilled
composite, is found to be 41.75 Hv. It is thus seen that the hardness is
improved, though marginally, by the incorporation of TiO2 as shown in Figure
5. The reduction in tensile strength and the improvement in hardness with the
incorporation of filler can be explained as follows: under the action of a tensile
force the filler matrix interface is vulnerable to debonding, depending on
interfacial bond strength and this may lead to a break in the composite. But in
case of hardness test, a compression or pressing stress is in action. So the
matrix phase and the solid filler phase would be pressed together and touch
each other more tightly. Thus the interface can transfer pressure more
effectively although the interfacial bond may be poor. This results in
enhancement of hardness.
50
Micro-hardness (Hv )
49
48
47
46
45
44
43
42
41
0
5
10
15
20
Filler content (%)
Figure 5. Effect of filler content on micro-hardness of different composites
It shows that the resistance to impact loading of glass epoxy composites
improves with addition of particulate filler up to 10wt% but further increase in
filler content up to 20w% it is decreasing as shown in Figure 6. High strain
rates or impact loads may be expected in many engineering applications of
22
composite materials. The suitability of a composite for such applications
should therefore be determined not only by usual design parameters, but by its
impact or energy absorbing properties.
Impact energy (J)
1.6
1.2
0.8
0.4
0
0
5
10
15
20
Filler content (wt%)
Figure 6. Effect of filler content on impact energy of different composites
*****
23
Chapter 5
RESULTS & ANALYSIS
24
CHAPTER 5
5. RESULTS AND ANALYSIS
The experimental results are analyzed using Taguchi method and the
significant parameters affecting material erosion have been identified. The
results of the Taguchi analysis are also presented here.
5.1. Wear characteristics analysis
From Table 4, the overall mean for the S/N ratio of the wear rate is found to be
7.16 db. Figure 7 shows graphically the effect of the three control factors on
specific wear rate. The analyses are made using the popular software
specifically used for design of experiment applications known as MINITAB
14. Before any attempt is made to use this simple model as a predictor for the
measures of performance, the possible interactions between the control factors
must be considered. Thus factorial design incorporates a simple means of
testing for the presence of the interaction effects. The S/N ratio response are
given in Table 5, from which it can be concluded that among all the factors,
sliding velocity is most significant factor followed by fiber content and normal
load while the sliding distance has the least or almost no significance on wear
rate of the reinforced composite. Analysis of the results leads to the conclusion
that factor combination of A1, B2, C3 and D2 gives minimum specific wear rate.
The interaction graphs are shown in Figures 8-10. As for as minimization of
wear rate is concerned, factors A, B and C have significant effect whereas
factor D has least effect. It is observed from Fig. 6 that the interaction between
A B shows greater significant effect on wear rate. Similarly, interaction
between B C also having second highest significant effect on the output
performance as shown in Fig. 9.
25
Table 4. Test conditions with output results using L27 orthogonal array
Sl
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
Sliding
velocity
A
(cm/sec)
210
210
210
210
210
210
210
210
210
261
261
261
261
261
261
261
261
261
314
314
314
314
314
314
314
314
314
Normal
load
B
(N)
10
10
10
20
20
20
30
30
30
10
10
10
20
20
20
30
30
30
10
10
10
20
20
20
30
30
30
Fiber
content
C
(%)
0
10
20
0
10
20
0
10
20
0
10
20
0
10
20
0
10
20
0
10
20
0
10
20
0
10
20
Sliding
distance
D
(km)
2
4
6
4
6
2
6
2
4
4
6
2
6
2
4
2
4
6
6
2
4
2
4
6
4
6
2
Wear rate
Ws
3
(mm /N-km)
S/N
ratio
(db)
1.0685
0.2224
1.1701
0.1324
0.3339
0.1128
0.4361
0.1436
0.0694
0.1643
0.4234
0.1311
0.3729
0.2435
0.231
1.0231
1.0034
0.5487
1.1201
0.6382
0.4312
1.2137
0.8794
0.4378
1.3248
1.0675
0.8754
-0.57550
13.0573
-1.36450
17.5620
9.52770
18.9538
7.20830
16.8569
23.1728
15.6872
7.46500
17.6479
8.56820
12.2700
12.7278
-0.19840
-0.02950
5.21330
-0.98510
3.90090
7.30640
-1.68220
1.11630
7.17450
-2.44300
-0.56740
1.15590
Table 5. Response table for signal to noise ratios
Level
1
2
3
Delta
Rank
A
10.999
8.817
1.664
9.335
1
B
6.904
9.580
4.995
4.585
3
C
4.794
7.066
9.620
4.826
2
D
7.592
9.194
4.693
4.501
4
But the factors A and C individually have greater contribution on output
performance, and their combination of interaction with factor A and C is shown
26
in Fig. 8 have least effect on wear rate and from this analysis the factor D has
least effect on the specific wear rate and A C interaction also have least effect
on the output performance. Hence, factor D and interaction A C can be
neglected for further study. In order to justified/conform the insignificant factor
and insignificant interaction a further statistical analysis is necessary i.e
analysis of variance.
Main Effects Plot (data means) for SN ratios
A
B
10
8
Mean of SN ratios
6
4
2
210
261
C
314
10
20
D
30
0
10
20
2
4
6
10
8
6
4
2
Signal-to-noise: Smaller is better
Figure 7. Effect of control factors on wear rate
Interaction Plot (data means) for SN ratios
16
B
10
20
30
14
12
SN ratios
10
8
6
4
2
0
210
261
A
314
Signal-to-noise: Smaller is better
Figure 8. Interaction graph between A×B for wear rate
27
Interaction Plot (data means) for SN ratios
14
C
0
10
20
12
SN ratios
10
8
6
4
2
0
10
20
B
30
Signal-to-noise: Smaller is better
Figure 9. Interaction graph between B×C for wear rate
Interaction Plot (data means) for SN ratios
15
C
0
10
20
SN ratios
10
5
0
210
261
A
314
Signal-to-noise: Smaller is better
Figure 10. Interaction graph between A×C for wear rate
28
5.2. ANOVA and the effects of factors
In order to understand a concrete visualization of impact of various factors
effect on the output performance, it is desirable to develop analysis of variance
(ANOVA) table to find out the order of significant factors. Table 6 shows the
results of the ANOVA with the specific wear rate. This analysis is undertaken
for a level of confidence of significance of 5 %. The last column of the table
indicates the order of significance among factors and interactions.
From Table 6, one can observe that the sliding velocity (p = 0.011), fiber
content (p= 0.082) and normal load (p=0.111) have great influence on specific
wear rate and the factor like sliding distance has least effect on specific wear
rate. Therefore, the like fiber content can be neglected for further study.
However, the interaction between sliding velocity
and normal load
normal load (p=0. 0.032)
fiber content (p=0. 0.233) show significance of contribution
on the wear rate and the remaining interaction i.e sliding velocity
content (p=0.648) presents less significance of contribution on wear rate.
Table 6. ANOVA table for specific wear rate
Source
DF
A
2
B
Seq SS
Adj SS
F
P
Rank
1.21923 1.21923 0.60961
10.56
0.011
1
2
0.37497 0.37497 0.18749
3.25
0.111
3
C
2
0.45095 0.45095 0.22547
3.91
0.082
2
D
2
0.11179 0.11179 0.05589
0.97
0.432
4
A*B
4
1.28032 1.28032 0.32008
5.55
0.032
1
A*C
4
0.14987 0.14987 0.03747
0.65
0.648
3
B*C
4
0.43464 0.43464 0.10866
1.88
0.233
2
Error
6
0.34624 0.34624 0.05771
Total
26
4.36800
******
29
MS
fiber
Chapter
6
CONCLUSIONS
30
CHAPTER 6
6. CONCLUSIONS
 This analytical and experimental investigation into the erosion
behaviour of TiO2 filled glass-epoxy hybrid composites leads to the
following conclusions:
 This work shows that successful fabrication of a glass fiber reinforced
epoxy composites with and without filler by simple hand lay-up
technique.
 These composites using TiO2 have adequate potential for tribological
applications. With the reinforcement of filler, they exhibit significantly
improved sliding wear resistance.
 Dry sliding wear response of these composites under different loads and
sliding velocities can be successfully analyzed using Taguchi
experimental design scheme. Taguchi method provides a simple,
systematic and efficient methodology for the optimization of the control
factors. While sliding velocity emerges as the most significant factor
affecting wear rate of these composites, other factors like filler content
and normal load and their interactions have been found to play
significant role in determining wear magnitude.
6.1. Scope for Future Work
 This study leaves wide scope for future investigations. It can be
extended to newer composites using other reinforcing phases and the
resulting experimental findings can be similarly analyzed.
 Tribological evaluation of TiO2 filled short glass fiber reinforced epoxy
resin composite has been a much less studied area. There is a very wide
scope for future scholars to explore this area of research. Many other
aspects of this problem like effect of fiber orientation, loading pattern,
weight fraction of ceramic fillers on wear response of such composites
require further investigation.
******
31
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32
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******
35
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