Innovationsbericht 2010 21_09 Druckversion zur Archivierung

Innovationsbericht 2010 21_09 Druckversion zur Archivierung
Innovation Report
Innovation Report
2010
Institute of
Composite Structures and
Adaptive Systems
Contents
CFRP Repair.
2
Contents
Preface ......................................................................................................................4
Institute of Composite Structures and Adaptive Systems
..........................................5
Our Research Fields ...................................................................................................6
Nano - Micro - Macro
Nano to Macro: A Question of Interphases ................................................................7
Detection of Residual Stresses of CFRP by Using Magnetostrictive Nanoparticles .......8
Qualification Procedure for Carbon Nanotube Actuators ............................................9
Robust Primary Structure
Testing and Analysis of Composite Stringer De-Bonding ..........................................10
Innovative Repair Concepts for High Performance CFRP-Structures ..........................11
Pushing the Limits of Parallel Robots for Handling and Assembly .............................12
Compliant Aggregation of Functionalities
The Next Step in Elastomer Based Tooling
.............................................................13
Upper Wing Cover for Natural Laminar Flow
...........................................................4
Active Reduction of Turbulent Boundary Layer Induced Noise ..................................15
Self-Controlled Composite Processing
Smart Process Control for CFRP Production
Adapted Moulds for Microwave Curing
Prediction of Epoxy Curing Kinetics
.......................................................16
...............................................................17
........................................................................18
Autonomous Composite Structures
Mode Selective Lamb Wave Actuators for Structural Health Monitoring ...................19
On Realizing High Lift Structures for Green Aircraft Wings ......................................20
A Helical Antenna for AISat – Self-Deploying and Self-Aligning ...............................22
New Sound Transmission Loss Test Facility for Acoustic Evaluation
.........................24
Sustainable Production Processes
Advanced Automated Fibre Placement (AFP) Technology .........................................25
The Center of Lightweight Production Technology
.................................................26
The Development of our Institute ...........................................................................27
Multifunctional Materials ........................................................................................28
Structural Mechanics
..............................................................................................29
Composite Technology ............................................................................................30
Composite Design
Adaptronics
..................................................................................................31
............................................................................................................32
Publications and Patents 2009 - 2010 .....................................................................33
Imprint ....................................................................................................................35
3
Preface
Growth and sustainability drove our innovations in the last year, which we proudly
present in this now sixth innovation report. Our Institute has developed positively indicated by a growth of our staff. More than 25 young scientists joined us. Sustainable
mobility increases the attractiveness of our Institutes research in and beyond aviation.
The importance of cost-efficient, adaptive light-weight structures made from composites grows for the automotive industry as well as for other businesses like wind energy.
However, our main scientific focus remains on aerospace structures. We maintained
our cooperation network and especially strengthened it towards the OEMs suppliers.
Thus, our network of cooperation is steadily extended which in turn creates novel
research challenges.
In order to enable growth we reorganized our Institute in currently 5 departments
along the process chain of adaptive, light-weight composite structures. A sixth
department delving into the research on sustainable production processes for composite structures will be founded until the end of the year. Details of the department
competences are elucidated at the end of this report. Initiated by the reorganization of
our Institute was a comprehensive strategic discussion about our long term research
agenda in a bottom-up process. The amazing amount of new ideas was condensed to
six fields of innovation:
- Nano – Micro – Macro
- Robust Primary Structure
- Compliant Aggregation of Functionalities
- Self-controlled Composite Processing
- Autonomous Composite Structures
- Sustainable Composites Processes
These fields of innovation are explained in more detail on page 6, and they also serve
as your guideline through this report. Three exemplary research subjects are chosen for
each of the above mentioned fields of innovation.
We have dedicated our Day of Science 2010 to a main scientific focus of our Institute:
the investigation of the basics, the concepts and the technologies for multi-functional
and adaptive high-lift structures. The question of shape variability of composite structures for high-lift components is the topic of various national and European projects. We
currently completed the design and manufacturing of a common test demonstrator in
cooperation with EADS (Airbus, EADS-IW and EADS-MAS). You will find a contribution
about the related research in this innovation report on page 26.
Reorganization and growth for us also mean an actual extension of our working facilities and labs hosted by the novel building, the DLR’s Adaptronics and Transportation
Systems Centre. Please find brief information in the reports rear section.
Our thanks go to our partners with whom we have achieved the research results described in the following. Special thanks go to the authors of the report, who provided
you with the succeeding and inspiring pages. We are looking forward to future cooperation with you in the field of Composite Structures and Adaptive Systems.
Prof. Dr.-Ing. Martin Wiedemann
4
Prof. Dr.-Ing. Michael Sinapius
Institute of Composite Structures and Adaptive
Systems
High-Performance Structures
Adaptable – Efficient – Tolerant
We are experts for the design and realization of innovative lightweight systems.
Our research serves the improvement of:
- safety
- cost efficiency
- functionality
- comfort
- environment protection
We bridge the gap between fundamental research and industrial application.
The expertise of the Intitute of Composite Structures and Adaptive Systems in
- multifunctional materials
- structural mechanics
- functional lightweight structures
- composite technology and
- adaptronics
makes it the ideal partner for the industry, the DFG (German Research Foundation),
research establishments, ministries and civil aviation authorities in all issues regarding
development, design, computational prediction, manufacturing, experimental testing,
and qualification of lightweight structures used in aerospace and further applications.
The main objectives of the research and development work on material systems and
lightweight structures are
- increase of safety by improving stiffness, strength and durability of lightweight
structures with new material systems and improved structural analysis tools
- cost reduction in the production process and by optimizing design and the
fabrication procedure in order to strengthen the competitive edge
- increase of functionality of materials, structures and systems to improve their
performance; the active structural shape control replaces elaborate and costly
actuator systems
- increase of comfort in aerospace and on-ground transportation systems by means
of actively reducing noise and vibrations
- reduction of the environmental impact (especially resulting from fuel consumption)
and preservation of natural resources particularly due to reduced weight.
In order to deal with strength, stability and thermo-mechanical problems we operate
unique experimental facilities like thermo-mechanical test facilities, buckling facilities
with the special feature of dynamic loading. Manufacturing facilities like preforming,
filament winding, liquid composite moulding or microwave curing enable us to develop
novel manufacturing techniques und the realization of innovative composite structures.
We transfer our scientific and technical expertise in the field of design and
manufacture of lightweight composite structures and adaptronics as partners
in an international network of research and industry.
5
Institute of Composite Structures and Adaptive
Systems – Our Fields of Innovation
We work along the full process chain in the fields of multifunctional materials, simulation methods, lightweight functional design, production technologies, adaptronics and
in the near future up to entire production processes. This consideration of the full process chain is part of our strategy, and it is our conviction that successful research in the
field of functional CFRP structures is driven by collaborative work. How can research be
organized in such a broad field of scientific work, and how can each scientist preserve
attention for the work of the others? Innovation is the total of two steps: invention
and diffusion. Invention is where we start with our ideas. Diffusion is where at the end
we can present technical solutions to our customers. Innovation covers the full process
chain and this is why we have decided to organize six times a year meetings with all
scientists of our institute to discuss our long term strategic research topics.
Multi-phase materials like composites require the comprehensive understanding from
Nano – Micro – Macro -scale of the components interaction. This includes the effect
of nano-scaled additives to the resin as will as the effect of manufacturing defects
like pores on the mechanical properties of the structure. Moreover, carbon nanotubes
exhibit a significant actuation effect in an electrolytic environment. Understanding the
path from Nano to Macro means thorough research for our scientists looking for new
technical applications.
Reliable design methods for Robust Primary Structures are already mandatory, but
the challenge to ensure reliability (oder robustness) by adding additional functions into
the structure. We strongly believe in the potential of function integration within the
composite design, but there is the need to bring all of the elements of such a structure
to the same level of reliability. Our scientists keep this in mind while they are making
new inventions.
Compliant Aggregation of Functionalities aims for solutions, where integration
of additional functions does not degrade the original load carrying function of the
structure. To reach this goal the design principles must be adapted to the additional
functions. For example the active shape control of a structure may not lead to additional internal loads. Unconventional ideas from many people are required here to find
the right solutions.
Self controlled CFRP Processing is one of our most promising concepts for automation in the field of production of carbon fibre reinforced polymer (CFRP) structures, but
still in its infancy. With our competencies in ultrasonic NDT, process-simulation and in
the field of adaptronics as well as our long lasting experience in CFRP production technologies , our scientists can build on an unique combination of knowledge.
Building Autonomous CFRP Structures is our vision of function integration. Any
active system today requires external energy for control and actuation at least. The
omission of the wiring is one of the conditions for an increasing application of function
integration in structures. Our scientists know the vision and are looking for contributions to its realization.
Sustainable Composites Processes will finally become a very important topic in
the future for us. Not only the lightweight and multifunctional structure itself shell
support the idea of sustainability, but also the way, how this structure is produced. Our
scientist know about the need for further cost reduction but very soon this will be also
a demand for reduction of consumables in production and minimization of scrap. The
development of precise, effective and in-line quality automation along the production
processes will be a new research field for us.
6
Nano to Macro: A Question of Interphases
Carbon fibre reinforced plastics (CFRP) manufactured by injection technologies do still
not completely reach the performance of prepreg laminates. Beside of fibre ondulation,
the matrix causes deficits in the composites being mainly based on low stiffness and
high shrinkage of the polymer. Therefore, the Institute investigates comprehensively the
reinforcement of the polymer matrices with nanoscaled boehmite particles to increase
the performance of injection resins.
increasing particle content, interphase share and chain mobility
increasing network density
Particle-Polymer Interaction
Fig. 1:
Network pattern in dependency of particle
content.
Various types of boehmite nanoparticles have been homogenously dispersed into
epoxy resins aiming to achieve best results. After curing, the filled resins were investigated in terms of particle-polymer interaction, polymer network pattern, matrix
shrinkage and mechanical properties. Results showed not only an influence of particle
size and shape, but also of the surface modification. With a wisely chosen modification
not only a stable dispersion and a narrow particle size distribution can be achieved, but
also the resin-particle interactions can be adjusted in order to retain the injectability of
the resin. The altering of the interface enables the creation of materials with improved
properties.
30
properties changing [%]
25
20
15
10
5
0
Network Pattern
ILSS
+/-45°
+/-45°
shear
shear
strength modulus
bend.
strength
(4 pt)
compr.
strength
(RT)
Fig. 2:
Improved material properties of CFRP containing matrices with 15 wt.-% boehmite
nanoparticles.
A dependency of particle content on the mechanical properties can be observed for the
cured composites. Low filler contents create materials with a higher strain and lower
stiffness compared to the pure resin. With a higher solid fraction the effect is reversed
and the composite becomes more brittle. Analytical investigations explain this observation by sterical limitation of the cure by the nanoparticles. This way the tightness of the
network pattern decreases and the polymers become more flexible. With increasing
boehmite content the particles hinder the chain movement and the composite shows
a more ceramic-like character (Fig. 1). Besides the changes in the network pattern,
nanoparticles alter the fracture behaviour of the resin. Particularly small particle-particle
distances at high particle contents cause very effective crack deflection, -pinning and
-bridging.
Fig. 3:
Fibres and matrix relics after pull-out test;
Left: pure fibre and neat resin; Right: fibre
with adherent nanoparticles reinforced resin.
Reinforcing Mechanisms in CFRP
The resulting increased modulus and strength of boehmite nanocomposites can be
transferred to enhanced properties of CFRP. Specific matrix dominated characteristics,
such as, e.g., the compressive strength, the interlaminar fracture toughness, as well
as the resistance against impacts, and the related residual compressive strength were
investigated, and considerably upgraded materials have been observed (Fig. 2). Various
effects cause these observed improvement that result in a greater overall performance.
These are the enhanced mechanical properties, the lower shrinkage and thermal
Expansion as well as the higher thermal conductivity of the matrix material lead to less
residual stress, a decelerated crack propagation and delamination growth. Furthermore
fibre-matrix adhesion is significantly improved (Fig. 3). Our research shows the high ability of nanoparticles to improve the performance of carbon fibre reinforced composites.
>
G1C
(interl.)
Dipl.-Ing. Christine Arlt (M.Sc.) (right), Wibke Exner, (M.Sc.) (left)
7
compr.
strength
(HW)
CAI
(40J)
Detection of Residual Stresses of CFRP by
Using Magnetostrictive Nanoparticles
The Innovation
Currently fibre reinforced composites (CFRP) are predominantly manufactured in
Prepreg technology. Injection technologies (LRI) have been successfully established in
addition as cost efficient manufacturing techniques for CFRP. However, particularly in
the case of the LRI residual stresses are induced which have to be attributed to the volume shrinkage of the resin matrix during the curing step and the different coefficient
of thermal expansion (CTE) of the components. In consequence these effects lower the
maximum performance of the CFRP and reduce the dimensional stability of the CFRP
structure. Presently, residual stresses of CFRP can hardly be determined. A novel and
innovative way favours a non-destructive quantitative analysis of the residual stresses
by means of nanoparticles such as Terfenol. Here the direct magnetostrictive effect
of the Terfenol is used, i.e., in the case of any mechanical stress field (e.g. generated
by volume shrinkage) the magnetic properties of the nanoparticles vary. The induced
differences of the magnetic field (Néel Relaxation) can be three dimensionally detected
by a specific test set-up („Magnetic Particle Imaging“). After a preceding calibration,
a correlation is sought between the variations of the magnetic field and the internal
stress fields. The innovation addresses the following two objectives which should result
in better mechanical performance, higher durability and higher dimensional stability of
CFRP:
Fig. 1:
SEM image of aligned Terfenol particles
(20 wt%) in an epoxy resin.
- Determination of correlations between the measured residual stress and the macro
scopic material characteristics of the CFRP.
- Identification of beneficial manufacturing parameters for the preparation of stress
reduced CFRP by injection technologies.
Fig. 2:
Alignment of Terfenol particles in an epoxy
resin by the application of a magnetic field.
Initial Experimental Results
Initial experiments with preselected pure resins were successfully performed in order
to quantify the local stress condition. Here, Terfenol particles were dispersed in a first
step by means of a dissolver (0 - 300 m) and afterwards by a ball mill (20 wt.% Terfenol). This dispersion was cured in an external magnetic field (Fig. 1). Resulting in well
aligned domains of Terfenol particles which show improved magnetostrictive properties
(Fig. 2). These nanocomposites were observed in a tension test and the variations of
the magnetic flux density were measured by means of a Hall probe. This direct magnetostrictive effect is depicted in Fig. 3 and proves unambiguously the sensor effect of the
Terfenol particles in the polymeric matrix.
Fig. 3:
Variation of the magnetic flux density for a
Terfenol nanocomposite by tension load.
The detection of residual stresses in polymer matrices by means of magnetostrictive
nanoparticles has to be verified in subsequent experiments. In particular the impact of
the particle size and the particle concentration has to be analysed. Hence, the entire
process chain i.e. the production of suitable particle sizes, the dispersing technology as
well as the development of suitable dispersing agents and of a practical measurement
technology must be considered. The novel knowledge will be applied to CFRP and
thoroughly investigated thereafter.
>
8
Dipl.-Ing. Alexandra Fischer (l), Dr.rer.nat. Thorsten Mahrholz (r),
Prof. Dr.-Ing. Michael Sinapius
Qualification Procedure for Carbon Nanotube
Actuators
What’s Special about Carbon Nanotubes?
Carbon Nanotubes (CNTs) are cylinder-like furled monolayers of Graphene-sheets.
They have extraordinary properties, such as high stiffness and strength in combination
with a low density. Therefore they are already qualified as a future structural material.
Numerous research activities are ongoing to incorporate them into composites. Beside
that it was demonstrated that Carbon Nanotube structures, like CNT-mats (also called
Bucky-paper), can be actuated within an electric field and the presence of free ions.
The actuation principle is able to generate high strains of nearly 1 % at low frequencies, i.e. < 1 Hz, and low activation voltage (typically ± 3 V). These properties qualify
Carbon Nanotubes to become a material with great potential for adaptive systems.
Fig. 1:
In-plain test-rig for free-deflection-measuring.
How to Manufacture a Carbon
Nanotube Actuator (CNA)?
Young's modulus [MPa]
8000
Our research covers the whole process chain from the CNT-powder to the manufacturing and assembly of CNAs as well as comprehensive test procedures to measure
relevant properties. At the moment the work is focused on the optimization of two
main components of the CNAs, i.e. the microscopic structure of CNT materials and
the required electrolyte. In general CNT-based materials can be distinguished into
two structural classes. On the one hand mats of randomly oriented CNTs, consisting
of commercially available CNT-powders, which are processed using a high-pressure
filtration. Here it was possible to introduce materials with improved electro-mechanical
characteristics resulting in mats with higher conductivity and stiffness (Fig. 2). On the
other hand so called CNT-arrays are investigated. This configuration allows a more
efficient exploitation of the tube-deflection due to its anisotropic structure. CNT-arrays
are processed to flat slides of horizontally aligned CNTs with a clear main orientation.
SEM-micrographs and conductivity-tests confirm the alignment of the CNTs (Fig. 3).
The CNT-arrays are tested in an in-plain test-rig using a liquid electrolyte (NaCl-solution)
to identify the active potential of different materials in a symmetric actuator-build-up
(Fig. 1). The results confirm theoretical models of the actuation behaviour, which are
based on an electronic constant-phase-element. The work is carried out by the Institute
of Composite Structures and Adaptive Systems in cooperation with the Technical
University of Hamburg-Harburg, Institute of Polymer Composites and the Swiss Federal
Institute of Technology (ETH Zürich).
6000
5000
4000
3000
2000
1000
0
1
2
3
4
specimen-number
5
6
Fig. 2:
Process-induced optimisation of the mechanical BP-characteristics.
a)
b)
Fig. 3:
SEM-micrographs of Bucky Papers:
a): SEM-micrograph of a randomly oriented BP
b): SEM-micrograph of an aligned BP.
Next Steps towards Application
Some further steps are to be taken on the way from basic research into practical application:
- Improving the electro-mechanical characteristics of aligned CNT-structures.
- Investigations on the crucial CNT-actuation-mechanisms for CNA-optimisation.
- Identification of a time-stable solid electrolyte.
>
7000
Dipl.-Ing. Sebastian Geier
9
7
Testing and Analysis of Composite Stringer
De-Bonding
Lightweight structures of airplanes are built with frames, stringers and skins. Stringers
are attached to the skin to mainly prevent the skin from instability failure and destruction of structural integrity. Especially, the hat or omega stringer geometries became
popular for modern CFRP-fuselage structures in recent years and provide improved
weight to load carrying capabilities. In order to investigate the bondline strength of
composite stringers, a test setup has been developed at the institute to experimentally
analyse the skin-stringer de-bonding. A small bonding interface reduces significantly
the structural weight but affects the reliability and robustness of the bonding strength.
Furthermore, the manufacturing process of the bonding of components, e.g. integrated co-curing of uncured components or co-bonding of cured and uncured components influences the de-bonding behaviour.
Fig. 1:
Test setup to analyse the stringer-skininterface.
Testing of Stringer De-Bonding
The interface strength between the composite stringer feet and the skin is analysed by
pulling off the stringer from the composite skin with the test device shown in Fig. 1.
The loading direction of the specimen can vary between 0° and 45° orientations. The
behaviour of the stringer de-bonding is driven by different failure phenomena according to the fracture mechanics failure mode I for peel stress and mode II for transversal
stress. Tests under 0° loading direction cause mainly peel stresses according to mode I,
whereas tests under loading directions between 0° and 45° cause a combination of
peel and transversal shear stresses according to mode I and mode II.
Fig. 2:
FE-Model to determine the progressive damage between stringer and skin.
Non-Linear Failure Analysis
Finite element analyses (Fig. 2) reveal that the de-bonding is accompanied by different
failure processes. The de-bonding failure behaviour is analysed with cohesive zone
elements, the virtual crack closure technique and a novel three dimensional continuum
damage model for composites. It was found that the fracture mechanics approach,
driven by the interface failure, is not sufficient to predict the complete failure behaviour. A complete failure analysis requires both, the accurate description of the damage
propagation inside of the adhesive as well as the material damage growth. Although
the de-bonding of the interface can be analysed with traditional fracture mechanics
approaches, the material degradation requires an advanced material model.
The load displacement curves (Fig. 3) show results of the FE analysis from a cohesive
zone elements and the continuum damage model in comparison to the test results.
The cohesive zone model needs further improvement to predict reliably the onset of
damage, but is suitable to determine the progressive de-bonding behaviour. The 3-D
continuum damage approach adequately determines the onset of damage and final
failure load.
Fig. 3:
Load displacement curves from test and
FE-analyses.
>
10
Dr.-Ing. Daniel Hartung
Innovative Repair Concepts for
High Performance CFRP-Structures
The steady increase of CFRP-Structures in modern aircrafts has reached a new dimension by entry into service of the Boeing 787 Dreamliner. A decrease of maintenance
costs for the overall aircraft is expected due to an excellent corrosion and fatigue behaviour of CFRP. However, in the future an increased number of composite structures is
expected in maintenance requiring new repair methods.
State of the Art Repair of CFRP-Primary
Structures
Fig. 1:
Demonstrator of a hybrid RFI-infusionsrepair.
Primary structures are essential for the safe flight. Therefore, special rules are applied in
case of repair. The repair has to fully restore the load carrying capability of the original
structure by an equivalent level of safety. Two rival technologies exist which are capable
of recovering the full mechanical properties, bolted repairs and bonded scarf repair.
Nowadays only bolted repairs are certified for primary structures. For a bolted repair
the damage is drilled out and a titanium plate is bolted on top. The original load path
is bypassed by the bolts and the plate. The main disadvantage of the technology is that
the bolts require a minimum structural thickness which is a design and weight driver
for about 25 % of the primary structure. This does not apply for bonded repairs. The
surrounding healthy material is grinded away at a smooth angle and a cured CFRPpatch is bonded by film adhesive to the structure. It is the key challenge to verify the
repair success due to numerous environmental influences on the bond strength, e.g.
surface contaminations. Nowadays no non-destructive testing method (NDT) exists
which is capable to verify the bond strength or even rule out a slip bond (loss of bond
shear strength even though interfaces have contact). This is the reason why no structural bonded repair of a primary structure is yet certified for flight.
New Repair Concepts
In order to overcome this situation, three concepts are investigated in parallel. A repair
process with a high reproducibility ensures the required robustness. Therefore technologies for the automation of the bonded repair process are investigated. The work
focuses on replacing the manual grinding by a numerical controlled milling of the scarf.
Manual grinding can be imprecise and time consuming for structures with interleaved
lay-ups. The automated manufacturing of a repair scarf including an automated repair
design is available since the beginning of 2010. The second approach addresses a new
Non Destructive Testing method in order to detect slip bonds. Some experimental work
demonstrated the sensitivity of bond lines to the specific ultrasonic actuations. With
the well established know-how on Structural Health Monitoring (SHM) at the Institute,
future work is planned in this field. The third approach is a fail-safe approach. Small
steel z-pins in the scarf area are implemented connecting structure and patch in case
of a bond line failure. This generates a second load path. Experimental work on tensile
probes have been carried out, showing successfully the basic principle of the concept.
Long experience on innovative joining technologies of CFRP-structures have been effectively applied to the repair scenario. If one of these three concepts can be applied it will
be possible to overcome the philosophy of designing a primary structure for bolted
repair.
>
Fig. 2:
Detail of milled repair scarf.
Dipl.-Ing. Dirk Holzhüter (right)
11
Pushing the Limits of Parallel Robots
for Handling and Assembly
Parallel robots offer potential for improving the productivity in handling and assembly.
Due to lower moved masses compared to serial robots and higher stiffness, higher
dynamics can be achieved. This opens up the path to short cycle-times which is an essential benchmark in handling and assembly. Fig. 1 illustrates the comparison between
serial and parallel robots.
Aiming to research the field of parallel robots in handling and assembly, a DFG-funded
Collaborative Research Centre (SFB) “Robotic Systems for Handling and Assembly” is
established at TU Braunschweig with participation of DLR.
Fig. 1:
Comparison of serial and parallel robots.
Adaptive Systems for Improved Structural
Properties
Trajectories of robots with high accelerations and decelerations induce vibrations into
the structure of the robot. This leads to longer cycle-times as can be seen in Fig. 3,
where the actual cycle of a robot takes 0.5 seconds (shaded part) while the induced
vibration takes 4 seconds to decay as shown by the blue curve in Fig. 3.
Adaptive systems are able to change the structural properties of parallel robots actively,
making accessible the dynamic potential of these machines. Adaptive systems usually
consist of sensors, actuators or active components and suitable controllers. Proper
models of the robot’s properties were developed for motion-control of the parallel kinematics, design of active components for vibration suppression and controller design.
Typical components for active vibration suppression are active rods as shown in Fig. 2.
for the parallel robot TRIGLIDE. These rods are made of carbon fibre reinforced plastics
(CFRP) combined with piezo-patch-actuators. The combination of fibre materials with
piezo-actuators enables the optimization of actuation authority and the load-bearing
capabilities of active rods. The active components are able to induce vibrations and,
hence, actively counteract the disturbing vibrations.
Fig. 2:
Parallel robot TRIGLIDE with active rods
based on piezoactuators.
A prerequisite for suitable counteraction is a robust and high-performance control
algorithm, which takes the position-dependent structural properties of parallel robots
into account. An example of obtainable performance is given in Fig. 3, where the orange curve depicts vibration using an adaptive system resulting in a decay of vibration in
less than 0.5 seconds.
Summary
Fig. 3:
Vibration with and without use of an adaptive systems. The gray shading shows the
movement in a handling cycle.
Work in the Collaborative Research Centre leads to a better understanding of many aspects of parallel robot application for handling and assembly. Adaptive systems proved
to be a successful path to better structural properties of parallel robots enabling high
dynamic trajectories with short cycle-times.
>
12
Dipl.-Ing. Ralf Keimer (l), Dr.-Ing. Stephan Algermissen (r),
Dr. rer. nat. Michael Rose
The Next Step in Elastomer Based Tooling
State of the art manufacturing of fibre reinforced composites (FRCs) depends for many
applications on metal based tools. This tooling is well establish so far, but of course has
its weaknesses according to availability, costs and the construction methods required
for fibre reinforced composites. Because of this reason, the Institute of Composite
Structures and Adaptive Systems developed advanced tooling methods using elastomers. Moulding can be completed within days providing multiple purpose tools by
using elastomer materials.
Different Components Manufactured in
a Single Mould
Fig. 1:
Multiple curved frame manufactured by
elastomer tooling.
The development of tooling concepts requires a high flexibility for a design customisation and short period manufacturing. Metallic tools usually can’t fulfil these requirements. Stiffeners for aircraft structures for instance appear with different profiles (I-,
T- or Ω-section) and geometry. Both change during the structural dimensioning. By
elastomer tooling refitted tools are available in very short time and with significantly
less costs. Furthermore, one mould can be used for CFRP (carbon fibre reinforced
plastics) parts with different radii of curvature or changing geometric progression in
general. A longitudinal stiffener (stringer) and a radial stiffener (frame) with the same
cross section are producible in one single mould. Even more complex structures like the
multiple curved frame in Fig. 1 can easily be produced in combination with a fitting
base and/or additional utilities. Additional benefits are reduced weight, multifunctional
usage and simplified handling of the mould. A pressure-sealed design allows manufacturing without typical auxiliaries like sealent tape or vacuum bagging. The pre-process
shaping is easier and done in short time, by pre-heating the elastomer mould (Fig. 2).
Matching Future Requirements of
Complex Composite Structures
Quality assured manufacturing is of great importance today. Because of this reason
mould embedded sensors are a further research topic. Thermal sensors for instance
provide an overview over the heat distribution during the curing process which is very
important for the excellent mechanical properties of composites. Even more survey and
control of the manufacturing cycle will be gained by ultra sonic sensors. Sensors don’t
need a separate medium to couple the ultra sonic waves into the structure, connected with elastomers. Their implementation is simple. The sensors provide information
about the curing degree which leads to optimized processes (time of a curing cycle).
The thickness of the structure can be measured as well.
Fig. 2:
Preforming a W-stiffener in a silicone mould.
Future manufacturing of complex composite structures will increasingly depend on
sensors for process control und shall guide the way into automated process regulation
and optimisation. Highly cost efficient production of high-performance CFRP structures
is possible by using elestomer tooling.
>
Dipl.-Ing. Michael Kühn, Dipl.-Ing. Sebastian Malzahn,
Dipl.-Ing. Michael Hanke (photo f.l.t.r.)
13
Upper Wing Cover for Natural Laminar Flow Ultra-Precise Shape by Process Simulation
In the scope of developing efficient future aircraft, fuel saving becomes one of the
main issues. The idea of the project LaWiPro – Laminar Wing Production – is to develop
and manufacture a part of a wing upper cover fulfilling the aerodynamic requirement
of laminar flow.
The surface has to be much smoother compared to current wings. Waviness coming
from either manufacturing or load has to be kept in a much smaller tolerance band
than at current aircrafts. Also steps and gaps coming from assembly should be disregarded.
Fig. 1:
Global deformation of a wing under aerodynamic loads.
Two completely different ways may lead to fulfil these requirements:
- Either by stiffening: The structure can be stiffend until it will be within the requested
waviness. This could increase weight and therefore fuel use – for manufacturing as
well as travelling
- Or by the shape of the tool: It is adapted by predicting the local deformations caused
by the manufacturing process, like spring-in, warpage, and loads
Multi-Material, Multi-Functional Design
Fig. 2:
Loacal wing deformation.
A multi-material design is developed to eliminate steps and gaps using monolithic
carbon with integrated stiffeners for primary structures, glass sandwich for secondary
structures and metal-hybrid for load introduction areas. The multi-functional design
provides the opportunity to integrate anti-icing devices or connectors into the same
curing process.
Developing innovative process simulation methods gives the possibility to predict the
deformations caused by the manufacturing process. The required adaptation of the
tooling will be determined first time right, without today’s time and cost-consuming
iteration loops. The developed methods will be implemented into the Virtual Composite Platform (VCP). Comparing virtual results with real 3D optical measuring from tests
ensures the improvement of the methods.
Fig. 3:
Multi-material multi-functional demonstrator.
Automation is another key issue to produce a part with acceptable costs and quality for
the high production rate of single aisle aircrafts. Based on the first investigations done
for spring-in, warpage and pre-deformation, automation concepts will be developed to
produce the upper wing panel including part of the nose structure.
At the final stage of the project all ideas will be shown in a demonstrator manufactured automatically at the Institute‘s facility in Stade (ZLP Nord).
Eventually, the innovative simulation and integration of manufacturing discrepancies
and displacements under load on the Virtual Composite Platform might lead to an
environmental sensitive design for future aircraft designs.
>
14
Dipl.-Ing. Jens Bold
Active Reduction of Turbulent Boundary Layer
Induced Noise
The turbulent boundary layer (TBL) is one of the dominant noise sources in high subsonic aircrafts. Especially in modern aircrafts, where common materials for fuselages are
currently substituted by carbon-fiber-reinforced-plastics (CFRP), it is essential to avoid
a decrease of passenger comfort as a result of an inferior transmission loss of the new
materials. Increasing the transmission loss of CFRP panels, they can be equipped with
active structural acoustic control (ASAC) systems. These systems consist of a control
unit and surface mounted actuators and sensors. Structural vibrations of the panel are
measured by the sensors and filtered by the control unit to estimate the radiated sound
power in the far field. The transfer path from actuators over the structure to the sensors is called the controlled plant. Based on this information and a mathematical model
of the controlled plant, the controller calculates the signals for the actuators in order to
reduce the noise radiation.
Fig. 1:
Measurement of CFRP panel vibrations using
a laser scanning vibrometer.
Wind Tunnel Experiments
The Institute of Composite Structures and Adaptive Systems verified an ASAC system
in an experimental study in the aeroacoustic wind tunnel of DLR in Braunschweig. The
wind tunnel has an open test section and its nozzle has a cross-section of 1.2 x 0.8 m2.
The section is enclosed by an anechoic chamber to enable acoustic measurements.
For realization of TBL experiments, a closed test section has been designed and
built. The active controlled CFRP panel is mounted in the side wall of the section.
The TBL is growing steadily over the length of the closed test section until it reaches
the CFRP panel with a thickness of approximately 41 mm at Mach 0.16. The panel
(500 x 800 x 1.3 mm3) is stiffened with four stringers and equipped with five piezo-ceramic patch actuators and ten accelerometers. Actuator placement was accomplished
by an in-house ASAC pre-design tool. Panel fabrication as well as actuator application
were made by DLR. Active structural acoustic control has been used to reduce the
broadband TBL noise transmission in the bandwidth from 1 to 500 Hz. Robust H-infinity control algorithms were applied in the experiments and showed high performance
even in presence of plant uncertainties. The so-called generalized plant framework
of robust control is utilized to improve control results. By inclusion of 260 additional
surface velocity outputs identified from laser scanning vibrometer (LSV) measurements
(Fig. 1), an enhanced global observability has been established.
Fig. 2:
Radiated sound power measured with sound
intensity probe.
Broadband Noise Reduction
The experiments proved the possibilities of ASAC systems for thin-walled and stiffened CFRP structures. Though the structural excitation due to the TBL is spatially and
temporally weakly correlated, a broadband reduction of the transmitted noise in the
bandwidth from 1 to 500 Hz could be demonstrated. In third-octave bands reductions
of radiated sound power of up to 6 dB(A) were realized (Fig. 3). Future work will concentrate on the extraction of noise models for the TBL excitation to further improve the
control performance.
>
Fig. 3:
Reduction of radiated sound power.
Dr.-Ing. Stephan Algermissen (center), M.Sc. Malte Misol (right),
Dipl.-Ing. Oliver Unruh (left)
15
Smart Process Control for CFRP Production
Process Control for a Better Quality at
Lower Costs
Today’s autoclave and RTM processes for CFRP production strictly follow a given
temperature and pressure cycle which is optimized empirically by many iteration loops.
The structures quality inspection is performed after the process due to the “black
box” character of the autoclave and RTM tool. This makes it hard to perform process
parameter optimization and to find failure sources. High safety factors for the cycle
duration are used to assure reaching the right tool temperature, complete infiltration
and a high degree of cure. This, in turn, leads to excessive process time and costs. New
control technologies efficient CFRP production have to be developed to master the
challenges for automation. The new approach is to gather all information relevant for
the product quality by novel sensor technologies during the whole production process.
This information is used to control the process parameters with the support of real
time simulation tools. It allows direct control and setting of the desired part quality and
optimization of the process cycle duration at the same time.
Fig. 1:
Functional principle of ultrasonic thickness
measurement.
Sensors for Process Monitoring
Fig. 2:
Frame tool with vacuum assembly and
integrated sensors.
Ultrasonic measurement is one of the most important sensor technologies to directly
measure the laminate quality during the process. The resins acoustic properties change
during curing. Therefore, ultrasonic sensors can be applied into the mould and vacuum
bag, enabling degree of cure to monitor the during the process. This allows to look
inside the mould and react to the cure progress by applying temperature and pressure,
as function of the degree of cure and to demould the part at the optimal time. The
ultrasonic signal can also be used to measure the laminate thickness which can be set
by applying and adjusting differential pressure during the resin injection process. This
technology allows to achieve small laminate thickness tolerances of about 100 µm or
respectively to adjust the desired fiber volume content. This has already been tested
successfully by manual adjustment of the differential pressure, the next step will be
implementing an automatic differential pressure control connected to the ultrasound
system. The ultrasonic sensors can also be used to detect the resin injection line as
the sound waves can only pass through the laminate when infiltrated by the resin. An
advantage is that the sensors can be placed behind the inner surface additional of the
mould, so that they do not affect the quality of the structural surface.
Fig. 3:
Ultrasonic thickness measurement process
diagram.
The homogenous tool heating is a key factor for high quality parts since temperature
is one of the most important parameters for resin injection and curing . Especially
large and complex tools need a refined heating strategy. This can be accomplished by
simulation to localize critical points where additional heating elements are employed.
Especially for single moulds an interesting alternative to thermocouples is the thermal
imaging technology, where the temperature field of the part surface can be measured.
Therefore a protective housing is being developed to install a thermographic camera inside the autoclave which will be used to control the heat elements. This new approach
for CFRP process control allows short, flexible and efficient production cycles at a high
level of automation leading to low cost and significant reduction of scrap, which is an
important step towards a completely automated volume production of composites.
>
16
Dipl.-Ing. Nico Liebers
Adapted Moulds for Microwave Curing
Microwave driven dielectric heating of composites is evaluated to be a promising
method for curing polymers. To date, conventional metallic moulds are used in
combination with microwave driven heating, which does not allow for full capability
of the method.
Autoclave vessel
(heat sink)
Heat flux
Autoclave vessel
(heat sink)
Hot air
(heat source)
Mould (heat sink)
Composite material
(heat sink)
Significant improvements can be achieved by using moulds adapted specifically
to needs and requirements of dielectric heating. Fig. 1 shows the energy balance
of a convective (right) and a dielectric (left) heating process. While the convective
heating demands moulds with a high thermal conductivity, the microwave driven
dielectric heating requires tool materials with a low thermal conductivity and a high
transparency for high-frequent fields. Recently material screening took place in order
to identify suitable materials with good insulating properties and high transparency
for microwave fields. Especially ceramic materials and plastic foams seem to be very
promising for mould manufacturing. Additionally to their good thermal and electromagnetic properties, the machining and shaping of such materials is user-friendly.
However, new materials require innovative mould design, first iteration of which is
shown in Fig. 2.
Heat flux
to the
autoclave
vessel
Heat
flux
Heat flux
Cold air
(heat sink)
Mould (heat sink)
Composite material
(heat source)
Energy
transport by
microwave
field
Heat
flux
Heat loss to the
surrounding
Fig. 1:
Energy balance during convective and microwave driven heating.
microwave-transparent
mould sourface
Energy Saving is Possible by Using
Adapted Moulds
insulation
composite
First results show that microwave driven processes allow for high energy efficiency
and for locally variable heating. Innovative moulds (Fig. 2) would allow the highfrequent field to penetrate them and therefore double up the energy input into the
composite material to be heated. Accordingly to first trials, up to 30 % can be saved
by using microwave transparent moulds.
frame structure
The insulating layer within the mould is dedicated to the reduction of the outward
heat flux from the selectively heated composite. It was experimentally proven that
by modifying conventional metallic moulds with additionally applied insulating layers
made of ceramic wool the energy consumption can be reduced by another 40 %.
impedance
matching
Fig. 2:
Adapted microwave-transparent mould with
impedance matching.
As shown in Fig. 2, the energy input by the external microwave field can be adjusted
locally by the frame of a microwave-transparent mould. That might help to increase
or decrease the temperature at desired regions of the composite part.
Further work will focus on the design principles of microwave transparent moulds,
especially for curing of large-scale composite parts and the experimental verification
of estimations. Additionally to that, the economical impact of microwave assisted
dielectric heating and curing of composites on transparent and insulated moulds
will be assessed compared to the state-of-the-art convective heating and curing of
composites on conventional tools.
>
external
microwave field
Dipl.-Ing. Maksim Danilov
17
Prediction of Epoxy Curing Kinetics
One key challenge within the production process of carbon fiber reinforced plastics
(CFRP) is the reduction of residual stresses and deformations due to chemical and
thermal shrinkage during the curing process. Other goals are the reduction of cycle
times and energy consumption which is opposing the first target. Finding the optimum between both objectives is a complex task that can be supported by numerical
simulation of the curing process. Therefore the curing kinetics of epoxy resins must be
investigated properly and empirical curing models need to be determined. Such models
describe the curing behavior and contain a set of material parameters which have to be
validated with measurements.
Experimentally, the curing behavior of an epoxy resin is obtained using Differential
Scanning Calorimetry (DSC) measurements. This method provides the energetic behavior for arbitrary temperature profiles of epoxy resins. The desired heat flow due to the
exothermic chemical reaction is included as well as several other thermal influences,
e.g. phase transitions and the heat capacity as a function of temperature and degree
of cure.
Fig. 1:
Graphical user interface of CoPE.
Model Parameter Identification
Supporting tool generation, parameter determination and curing process simulation,
the software tool CoPE (Composite Parameter Estimation) was developed. Firstly a
noise reduction on the measured data is performed by filters in the time and frequency
domain. The heat flow can be extracted by setting a baseline within the region of the
characteristic reaction peak to approximate the magnitude of other thermal influences
(Fig. 1). Thus the area enclosed by the dashed baselines and continuous drawn sample
curves represent the enthalpy of the chemical reaction. For this sample background
correction, typical baseline functions are included in CoPE and enable calculating the
total reaction enthalpy and the reaction enthalpy rate for every sample point. Those
values are the basis for determining the degree of cure used within the curing models
defined in CoPE.
The determination of the model parameters is done by a curve fitting method. Hence,
the least square error as seen in Fig. 2 between sample data (continuous line) and model function (dashed line) provides the target function value to be minimized. Various
population based optimizers are available for this optimization task, ensuring robust
convergence towards the global optimum if the parameter space is not well known. In
the case that a reliable estimation of the optimum is available, a gradient based optimizer can be chosen to speed up the parameter identification.
Fig. 2:
Monitoring the sample data (continuous
lines) compared to the best fit (dashed lines)
during the parameter estimation.
Benefits of Curing Simulation
Having found valid curing model parameters, an ABAQUS user subroutine can be generated by CoPE in order to enable simulating the heat generation due to curing and,
thus, the transient temperature distribution within a finite element model. This can be
used to optimize a curing process with respect to the maximum valid curing temperature of the resin and process time. Additionally, the transient temperature distribution
of a structure is essential for simulating chemical and thermal shrinkage of arbitrary
geometries.
>
18
Dipl.-Ing. Sebastian Freund
Mode Selective Lamb Wave Actuators for SHM
Structural Health Monitoring
Structural health monitoring (SHM) is a novel technology using permanently attached
actuator and sensor networks, data acquisition and data evaluation systems to enable
in-service inspection of aerospace structures. The implementation of SHM systems
into aerospace applications enhances reliability, safety and maintenance performance
as well as economic aspects. In this context Lamb waves, a type of ultrasonic guided
waves, are a promising approach primarily because of their ability to propagate over
long distances in plate-like structures and their high sensitivity to a variety of structural damages. Lamb waves are excited and received using a network of piezoceramic
actuators and sensors. In case of damages, the excited Lamb wave propagation field
will be disturbed resulting in reflections, refraction, attenuation or mode conversion.
By analyzing the sensor signals this disturbance can be observed and the damages can
be detected and located. However, the presence of at least two Lamb wave modes
(symmetric, S0, S1, S2,…, and anti-symmetric, A0, A1, A2,…, modes) at any given
frequency, their dispersive characteristic and their interference with structural discontinuities produce complex wave propagation fields and sensor signals which are difficult
to interpret.
Fig. 1:
Mode selective Lamb wave actuators: (left)
interdigital transducer, (right) piezocomposite.
Design of Mode Selective Actuators
Fig. 2:
Sensor signal by driven the first strip of the
actuator (f = 40 kHz).
In order to reduce the complexity of the Lamb wave propagation field, DLR has developed mode selective actuators, which are able to generate a particular Lamb wave
mode. This is achieved by controlling the frequency as well as the wavelength of the
desired mode within the excitation. An appropriate technical solution is to use monolithic piezoceramic plates with applied interdigitated electrodes, so-called interdigital
transducers (Fig. 1, left). The electrode distance corresponds to the half-wavelength of
the desired Lamb mode. The bandwidth and the effectiveness of the actuator regarding mode selectivity can be enhanced by applying a weighting function (apodization)
to the electrodes during excitation. This is realized by varying the overlap length of the
electrode fingers. A promising alternative to conventional interdigital transducers is to
utilize the piezocomposite technology to increase the reliability of brittle piezoceramic
actuators (Fig. 1, right). To verify the mode selectivity performance of the actuators
experimental tests on quasi-isotropic CFRP plates with a surface bonded piezocomposite actuator, as shown in Fig. 1 (right), were carried out. This actuator is designed to
attenuate the S0 mode and thus to amplify the A0 mode at a frequency of 40 kHz. In
order to distinguish the S0 from the A0 mode, a collocated pair of circular piezoceramic sensors is bonded on the upper and lower plate surface. In a first setup only the
first strip of the actuator was driven by a rectangle burst signal at 40 kHz. The sensor
signals in Fig. 2 shows that the A0 and the S0 mode were excited in an amplitude ratio
of 100 % to 11 %. In a second setup all strips of the actuator were driven. An apodization of each strip was realized by individual signal adjustment. Fig. 3 shows that the
designed actuator can attenuate the amplitude of the S0 mode to 0,2 % compared
to the amplitude of the A0 mode of 100 %. In summary, it has been shown that the
interdigital transducer design is capable to excite a particular Lamb wave mode in CFRP
structures. Further research activities are focused on the development of finite element
and analytical models in order to design and optimize mode selective actuators for
different Lamb wave modes and excitation frequencies as well as for different lay-ups
and fibre orientations of CFRP structures.
>
Fig. 3:
Sensor signal by driven all strips of the actuator (f = 40 kHz).
Dipl. Ing. Daniel Schmidt
19
On Realizing High Lift Structures for Green
Aircraft Wings
Morphing as Enabler for Less Emissions
and Low Noise
Ambitious goals were defined in the well known VISION 2020 stating the need for
technologies to consequently reduce drag and airframe noise. The challenging recommendations of the ACARE group for the reduction of emissions per passenger kilometers are CO2 < 50 %, NOx < 80 % and noise < 50 % until 2020. Therefore, innovative
aircrafts and along with it new concepts for high lift device will have to manage the
transition from research into industrial products. Such novel systems have to comply
with the next generation aircraft requirements like high wing surface quality and a
very strict lightweight design. In conventional high lift configurations of today, devices
on leading and trailing edges open slots to achieve the additional lift. However, the
slots and especially slat gaps at the leading edge have been identified as the dominant
source of airframe noise in approach and are not employable for green laminar aircraft
wings. Eliminating these gaps and steps through morphing structures consequently
reduces airframe noise, flow resistance during low speed flight and functions as an
enabler for a fully laminar wing design. These are the components for green aircraft
wings.
Fig. 1:
Schematic illustration of a smart droop nose
concept consisting of an integrated outer
skin and internal driving mechanics.
Can a Composite Skin Handle it?
A morphing structure typically consists of a flexible outer skin and an internal driving
mechanism (Fig. 1). While many driving mechanisms where patented in the past, flexible skin structures that fulfil industrial requirements are still very scarce. One approach
to break through this barrier is to employ composite material systems. They generally
allow for tailoring the structural design to various applications and are widely available.
Nevertheless, a morphing high lift device in the shape of a seamless droop nose requires a skin that unites contradicting properties of flexibility and sufficient stiffness. From
the skin concept featuring a monolithic outer shell and internal spanwise stiffeners
result the detailed material requirements. It is desired that the skin is able to withstand
1 % strain and the omega stringers maintain integrity even during a load introduction
through the mechanical actuation inside the leading edge. Several structural tests of
flight-certified composite material systems have been performed allowing for a selection between carbon and glass fibre based systems. Fig. 2 illustrated carbon and glass
fibre specimen after bending tests, where CFRP (carbon fibre reinforced plastics) were
not able to provide the desired 1 % strain. The GFRP (glass fibre reinforced plastics)
skin on the other hand did not show significant performance degradation below the
given strain limit and in addition provided a significant security margin. So, composite
material systems are suitable for morphing and in our case GRFP was selected as material system for the smart droop nose structure to be manufactured for testing in the
national project SmartLED considering industrial requirements.
Fig. 2:
Exemplary GFRP (left) and CFRP (right) specimen after bending tests until fracture (top:
cross section, bottom: topview).
A Closer Look Inside our Structures
Fig. 3:
Stringer specimen manufacturing for testing
employing GFRP pre-preg and silicone
tooling.
Moving one step forward in the process chain for composite structures, the strength of
our omega stringer design (especially its binding to the skin) had to be benchmarked.
Numerical analysis and application of upstream damage models allowed for the classification of maximum loading and failure phenomenon.
20
On Realizing High Lift Structures for Green Aircraft Wings
Therefore, a representative stringer-skin substructure has been modelled and equipped with 3d continuum mechanics damage model to analyze the structures damage
at the expected large strains during morphing. The results from these finite-element
simulations provided confidence in our design. Nevertheless, we were striving for an
experimental validation and manufactured the analyzed substructures. Fig. 3 shows
such an omega stringer and morphing skin segment being build integrally employing a
silicone tooling and GFRP pre-preg. Its capability to handle morphing requirements was
impressively demonstrated (Fig. 4).
Fully Featured Virtual Testing
In the national project SmartLED, the test of a 2 m smart droop nose segment is being
performed in 2010. The smart droop nose segment had to be equipped with integrated kinematics that were developed in cooperation with EADS, where the entire
leading edge unit is mounted to a testing front spar suitable for a wing bending simulation. Such large scale tests require detailed preparation and, thus, the finite-element
modelling and simulation of the entire test setup was performed. The model in Fig. 5
included the composite morphing structure, the internal driving mechanics and the
front spar as well. An important goal for the analysis was to quantify the interaction of
the driving kinematics with composite structure and front spar in addition to the fully
featured virtual proof of function. We were able to refine the design of the composite
leading edge and the test stand. In a next step the test program was planned in detail
employing test stand simulation. Mainly three load cases are to be tested, which are
the 2.5 g case mimicking an interception manoeuvre, the 2.0 g case as gust load and
the 1.15 g case simulating the droop nose behaviour during landing.
Fig. 4:
Stringer specimen during testing until
fracture.
Fig. 5:
Finite-element model of droop nose test
stand.
Large Scale Test Hardware
The composite skin of the smart droop nose was manufactured integrally including
the omega stringers. Here, the previously selected GRFP pre-preg material has been
employed not just due to its proven strength but also to match the designed layup
sequence as close as possible and maintain low tooling costs. The tools and the integral manufacturing of the composite skin have been executed in cooperation with the
Invent GmbH of Braunschweig. First, a positive core with the contour of the leading
edge was milled out of tooling plastics and a CFRP tool was formed on this core such
that the resulting tool is able to resist the temperatures occurring during the GFRP
curing cycle. The pre-preg layers were positioned in the CFRP-tool and the pre-formed
but uncured omega stringers placed and locked in position. The manufacturing of
the entire composite structure in the so-called co-curing process allowed for a highly
loadable stringer-skin interface. Fig. 6 presents a side view of the resulting composite
structure for the smart droop nose to be tested in 2010.The smart droop nose test of
the integrated structure-kinematics concept will manifest the successful application of
the process chain in the Institute of Composite Structures and Adaptive Systems as well
as the institutes close cooperation with external partners. The work to transform ideas
into hardware was especially propelled forward by Sebastian Geier, Daniel Hartung,
Markus Kintscher und Thomas Wurl.
>
Fig. 6:
Large scale droop nose section (side view)
with marked high lift contour.
Dr. Olaf Heintze
21
A Helical Antenna for AISat –
Self-Deploying and Self-Aligning
DLR Nanosatellite to Monitor Maritime
Traffic
AISat is a suitcase-sized nanosatellite with a deployable fiber-composite antenna. The
antenna is stowed within a small volume for launch, only to extend to its operational dimensions once in orbit. Both the antenna and the AISat project as a whole are
ambitious undertakings – the DLR satellite will increase maritime safety and will precisely locate individual ships on busy sea routes. The ‘AIS’ in the mission name stands
for Automatic Identification System – a radio system designed for the exchange of
navigation, position and identification data from each and every vessel, to make global
maritime traffic safer and easier to control.
Fig. 1:
Adjusting the antenna.
Cooperating Partners
Two DLR institutes, the Bremen University of Applied Sciences, and two industrial partners are collaborating on the AISat project. DLR’s Institute of Space Systems in Bremen
developed the nanosatellite itself and performed the whole system engineering, while
the DLR Institute of Composite Structures and Adaptive Systems in Braunschweig took
the responsibility for the helical antenna, in particular for its experimental qualification
on a parabolic flight. The time schedule of the AISat project is tough, because the maiden flight of the first satellite is already planned for 2011. The satellite will be launched
on a Polar Satellite Launch Vehicle from the Satish Dhawan Space Centre on the Island
of Sriharikota, India.
Why a Helical Antenna?
Fig. 2:
Antenna in stowed configuration.
The mission objectives require an antenna with an excellent directionality, i.e. with a
comparatively narrow illumination radius. Otherwise, with a too large antenna footprint, the satellite would receive a huge amount of signals from a very large area. Moreover, many interfering signals which are present in adjacent frequency bands would
make it almost impossible to trace individual ships. High-gain helical antennas have the
required directionality – and they are able to receive not only the Class A VHF signals
from commercial shipping, but also Class B signals from non-commercial ships, as well
as Search And Rescue (SAR) transmitter signals sent from survival craft or distressed
vessels. Thus, the spiral form of the antenna was mandatory.
Acting Like a Spring
For the project team at DLR Braunschweig as well as for its partners at Schütze GmbH
& Co at Dorsten the task was to design the antenna core such that it would really
expand as a compression spring, once the hold-down mechanisms on the satellite base
plate would have been released. Since three hold-down mechanisms were needed (in
rotational symmetry, i.e. with an angular distance of 120° between them), the initial
friction of the antenna on each of them became a critical parameter with a strong
influence on the initial directionality of the expansion, i.e. on the generation of lateral
and torsional vibrations. In longitudinal direction the expansion was limited by fine
Fig. 3:
Test rack with stowed antenna on board the
NOVESPACE Zero-G aircraft.
22
A Helical Antenna for AISat – Self-Deploying and Self-Aligning
glass fiber threads, which act against the residual spring stiffness once the antenna has
achieved its final configuration. Four different types of fiber cores with varying stiffness
were built, containing combinations of carbon, glass, and aramide fibers. These antenna cores were coated with a thin metallic mesh, and only this covering is conductive
and acts electromagnetically as antenna. Mechanical and electrical functions of the
antenna are thus completely decoupled.
Deployment Tests in Weightlessness
It is obvious that such a slender structure as the 4 m long antenna helix could never
be tested on ground. In horizontal attitude the expanding helix would be immediately deflected downwards by its own weight, and in vertical (hanging) position the
antenna mass would concentrate itself at the bottom end, leaving the first coils below
the satellite under strong stress. Therefore the only chance to realistically prove the
deployment behaviour was a verification test under zero-g conditions – on occasion of
the 15th DLR Parabolic Flight Campaign in Bordeaux in March 2010. The test results
were impressive: The helix extends rapidly and in doing so, it moves the satellite body,
which is much smaller. Figuratively speaking, the tail really wags the dog! But soon the
vibrations become smaller and smaller; and once the satellite has achieved its final position, the configuration becomes operable. The tests were a large success; the results
were encouraging and will now be incorporated into the final design of the first AISat
flight unit.
>
Fig. 4:
Deployment tests on the 15th DLR Parabolic
Flight Campaign, March 2010.
Prof. Dr. Joachim Block
Fig. 5:
AISat in orbit (artists view).
23
New Sound Transmission Loss Test Facility for
Acoustic Evaluation of Smart Lightweight Panels
Reverberation
Chamber
Test
Opening
The sound transmission loss (STL) quantifies the propagation of incident acoustic
energy through a structure to a neighboring fluid. It is an important measure not only
in building acoustics but also in the aircraft, automotive, railway and marine industries
as it is directly linked to noise exposure and acoustic comfort of passengers. A low STL
permits a high transmission of acoustic energy through the structure resulting in high
noise levels, e.g. in the cabin of an aircraft. The growing use of stiff and lightweight
structures such as carbon-fiber-reinforced-plastics (CFRP) in the transportation sector
poses great acoustic challenges especially in the low-frequency domain (< 500 Hz)
where the STL typically drops. The urgent need of lightweight-compliant sound abatement methods promotes the development of smart structures with active structural
acoustic control (ASAC). The new sound transmission loss test facility makes it possible
to determine the STL of passive and active structures with method precision conforming to the relevant ISO standards.
Anechoic
Room
Characteristics and Functionality of the
Test Facility
The sound transmission loss test facility consists of a reverberation chamber and an
anechoic room. The rooms are connected by a test opening of 2.5 x 2.5 m2 which can
be used for the integration of flat or curved test structures such as aircraft panels. Additionally, both rooms can be used independently according to DIN EN ISO 3741/3745.
The lower cut-off frequency is 100 Hz for both rooms. If necessary, the test opening
can be closed by means of a highly sound absorbing double-panel construction with
surfaces compliant to each room. The reverberation room is typically used as the
sending room for STL measurements, providing a diffuse sound field excitation of the
test object. Furthermore, it facilitates quick sound power measurements based on the
temporal and spatial average sound pressure level (SPL). The anechoic room is typically
used as the receiving room for STL measurements providing semi-free field conditions
due to the sound-absorbing walls and ceiling. It moreover provides suitable conditions
for sound intensity probe and microphone array measurements, allowing a determination of the sound intensity distribution on the structural surface. Given the need of a
directional acoustic excitation of a structure for STL measurements, a sound source can
alternatively be placed in the semi-anechoic room. In this case, the transmitted sound
power has to be evaluated in the reverberation chamber.
Fig. 2:
Anechoic room of the test facility.
Incident Power
Lw1
Sound Source
Receiving Room
(anechoic)
Test Object
Sending Room
(reverberant)
Transmitted
Power Lw2
STL = Lw1 - Lw2
Application for Future Research in Active
Structural Acoustic Control
The activities of the Institute of Composite Structures and Adaptive Systems in the
field of ASAC are focused on the development of smart lightweight structures with
improved acoustic properties, especially in the challenging low-frequency domain. The
new test facility will provide the experimental conditions necessary for the investigation
and validation of numerically designed and optimized ASAC systems. A future research
topic will be to investigate the transmission of sound through double-panel structures
such as fuselage parts in order to derive more advanced actuator, sensor and signal
processing schemes for ASAC.
>
24
M.Sc. Malte Misol
Advanced Automated Fibre Placement (AFP)
Technology
The project GroFi develops advanced production processes for large-area, highly integral parts of fibre composite materials by using automated fibre placement technologies.
The aim is the development of a production platform of high productivity using both
fibre tapes and tows. Due to a simultaneous fibre lay up with coordinated robots a productivity of 150 kg per hour will be possible. Hence, the robots provide a high flexibility
for several tasks in the production process by an easy adaption of different tools. Three
key factors will increase the productivity of the fibre placement:
- Increasing the placement speed and the number of placement units
- Improving the system dynamics
- Integrating quality control and assurance into the production process
Fig. 1:
Using coordinated robots to produce large
area parts.
Specialised Automatic Fibre Placement
Heads
Besides the robot platforms, the technology used in the system includes a new generation of tow placement and tape laying heads. New online quality assurance techniques
will also be integrated to minimise the time required for downstream, non-destructive
testing processes or eliminate its need completely.
This highly flexible automated fibre placement system differs from today’s technology
by offering the following features:
Fig. 2:
Increasing the productivity by performing a
double-sided lay up.
- Coordinated, simultaneous deployment of several placement units
- Double-side lay up tools
- Integrating quality control and assurance into the production process
- Automating the vacuum evacuation and excavation
High Flexibility, High Efficiency and High
Precision
By using independent lay up units on movable platform the facility’s flexibility will be
increased in terms of the mix between AFP and ATP, a separate maintenance and several lay up heads. Due to that a high productivity will be guaranteed, since the specialised lay up techniques will be easily applied for different part shapes. The maximum lay
up rate will be achieved by a continuous lay up, where the lay up units move unidirectional around the tool and provide a double-sided lay up. With a smart data and sensor
management an interaction of the units make a high precision possible and production
defects will be avoided.
>
Fig. 3:
Producing different part shapes using moveable platforms on the circular rail system.
Dipl.-Ing. Ivonne Bartsch (center left),
Dipl.-Ing. Matthias Bock, (left)
Dipl.-Ing. Marcus Perner, (right)
Dipl.-Ing. Dirk Röstermundt (center right)
25
The Center for Lightweight-ProductionTechnology (ZLP)
The ZLP is a common approach of the Institute for Composite Structures and Adaptive systems and the Institute for Structures and Design with locations in Stade and
Augsburg. Its concept was designed to cover the complete process chain for composite
parts. ZLP is building upon the Institutes’ research portfolio consisting of materials
research, design, technology and assembly. With that, ZLP bridges the gap to the
industrial application in terms of technology. Close cooperation with industry is key
for a successful application. As an output, the technology in Stade has been identified
by considering both the interests of industry and research. Such examples include a
research autoclave with diameter of 5.8m and the fiber placement facility with a partlength of 20m. Hence, ZLP follows the interests of the manufacturing as well as the
machining industry, which is carrying out its know-how for the research platforms. This
acknowledges the aim for a quick use of research results within industry.
With the funding by the State of Lower Saxony, DLR has been given the opportunity to
do research in the fields of:
- Robot-based Automated Fiber Placement
- High production rates in resin transfer molding technology
- Online Quality Assurance for autoclave processes
- Tooling technologies
- Process simulation
ZLP is integrated in the CFK-Nord complex along with its industry and research partners. The technologies are driven by a future application for fuselages, frames and
wing covers. In Stade, DLR will develop three technology projects for robot based fiber
placement, high production rates in resin transfer moldings technology and online
quality assurance for autoclave processes. The projects are also used to build up the
research platforms. Within the project for robot based fiber placement the production of large scale parts is conducted through the development of the AFP-facilities,
as well as tooling technologies as described on the previous page 25. The project for
online quality assured autoclave processes aims to minimize the process time inside an
autoclave. The quality assured production inside the autoclave is based on fundamental
process understanding including elements described on page 16. Within the project for
high production rates in resin transfer molding technology the core process technology
has to be created first. Short cycles, automated handling and material development
are the focus of today’s demand. The project answers the question on how to produce
a high performance part 100.000 times a year. Therefore a multifunctional platform
will simulate several methods of application in terms of a fully automated process and
the full scale part. Thus, requirements from automotive and aeronautical industry are
taken into account. The basis of the technology development is given by the resintransfer-molding-process with its sub-processes. Within the project the whole process
chain is taken into consideration to demonstrate the cooperation between the several
sub-technologies.
As demonstrated by the three projects, ZLP in Stade provides the front end of the
process chain, which is completed by the approach in Augsburg. To cover a complete
process chain on an industrial scale will give a new perspective for applied science in
composite technologies.
>
26
Prof. Dr. Martin Wiedemann (r), Dr.-Ing. Matthias Meyer (l)
The Development of our Institute
Research results from adaptronics and from the area of transportation systems are
enjoying increasing demand from industry, leading to an increase in research activities
and scientists working in those fields.
The DLR in Braunschweig got the chance to enlarge its working facilities supported by
a states program recovery program. Therefore we decided to jointly establish together
with the Institute of Transportation Systems a new
Adaptronics and Transport Systems Centre
This building will create space for about 100 scientists coming partly from surrounding
buildings and partly as new young engineers to work on their PhD thesis in adaptronics
and transportation systems.
Together with new laboratories for lecture accompanying exercises and modern conference rooms the Adaptronics and Transportation Systems Centre – worth 9M€ - will
be a further step in strengthening the cooperation with the Technical University of
Braunschweig.
Furthermore we are engaged in the development of the joint organisation Campus
Research Airport, where today 13 institutes from DLR, from the Technical University
Braunschweig and Leibniz University Hannover are doing coordinated research. A renewal of the five years research strategy is just in development.
DLR and TU Braunschweig together have proposed a development plan for the area
surrounding the airport in Braunschweig, where small and medium enterprises together with the research institutes and the university can form an unique combination
of education, research and industrial application to find solutions for all the upcoming
challenges in the field of sustainable mobility.
As already presented on page 26 of this innovation report, the institute of Composite Structures and Adaptive Systems has recently inaugurated a new research centre
for composite structure production processes in Stade, where up to 40 scientists and
technicians will work. Together with our customer centre in Bremen housed in the materials and process department of Airbus with today 3 scientists we are developing the
institute towards a distributed organisation with offices close to cooperation partners.
This is a real challenge for our organisation as we have to find new ways to ensure and
maintain the intensive exchange and communication between our scientists.
But with our good, highly motivated and inventive scientists we have a strong foundation for implementation of all our new and future-oriented impulses. We hope that
after reading this innovation report you share our vision and our confidence and we
look forward to continuing to work with you in Braunschweig, Bremen, Stade, or any
other place.
27
Multifunctional Materials
Mission
From materials to intelligent composites!
The department of Multifunctional Materials is doing research on the development,
characterization and qualification of advanced fibre composite materials. New materials with superior properties are a prerequisite for technological innovations. Especially
the integration of new functionalities is the key to further enhance the competitiveness
and application range of composite materials. The collaborative research on composite
materials within interdisciplinary and international teams is focused on the following
areas:
- Integration of new functionalities
- Improvement of properties
- Advancement of processability
- Provision of reliable material data
- Qualification of new structural concepts
Based on our knowledge and experience in composite materials we explore new possibilities to enhance the properties and functionality of composites in many aspects. By
adding nano-scaled particles the mechanical properties, processibility and fire resistance
of composite materials are drastically enhanced. New bio-composite are developed
and characterized to offer sustainable and environmentally friendly material solutions.
Beyond that, new functional materials with sensing and actuation capabilities as
components for adaptive structures are investigated. Sensor and actuator networks are
embedded in materials to allow a continuous monitoring of fibre composite structures
during production and operation.
Competences
The department of Multifunctional Materials operates facilities for static and dynamic
testing of materials and structures. In combination with a well equipped thermo- analysis lab and a long experience in non destructive testing with ultrasound, new material
systems from coupon level and beyond can be evaluated. Our competence profile
comprises:
- Evaluation of new textile semi finished products
- Nano-technology in fibre composite materials (nano composites)
- Development and characterisation of bio composites
- Exploration of smart materials for adaptive structures
- Design and characterization of piezocomposites
- Development of structural health monitoring (SHM) systems
- Non destructive testing with ultrasound (NDT)
- Static and dynamic testing of materials and structures)
- Thermo-analysis and microscopy
>
28
Dr.-Ing. Peter Wierach
Structural Mechanics
Mission
From the phenomenon via modelling to simulation!
In order to fully exploit the high potentials of composite materials, efficient and qualified structural mechanical methods and tools are increasingly demanded. To cope with
this we develop, verify and validate computational and experimental methods integrated in robust development processes from the preliminary design up to the detailed
design phase. Within the scope of aerospace, aeronautical, automotive and railway
transportation applications our focus is laid upon:
- Fast and accurate design, simulation methods and tools
- Virtual testing for the entire life cycle
- Innovative experimental methods and test facility concepts
Competences
Supported by a highly qualified staff of scientific and technical employees, we bring
structural mechanical methods and tools to application for our customers within concurrent/integrated engineering concepts in the following areas:
- Strength Analysis (e.g. 3D reinforced composites, extended 2D methods)
- Structural Stability (e.g. postbuckling, imperfection, dynamic buckling, robust design)
- Damage Tolerance (e.g. failure criteria, impact, residual strength, degradation)
- Effects of Defects (EoD) (e.g. fibre waviness and porosity)
- “As Build/ Manufactured”-analysis (e.g. AFP feedback loop to account for
manufacturing deviations)
- Thermo-Mechanics (e.g. extended 2D methods, models for fibre metal laminates)
- Multi-Scale Analysis (e.g. global-local or submodelling concepts)
- Multidisciplinary Simulation (e.g. resin curing, spring-in, piezo-electric-thermal
coupling)
- Tool-Integration (e.g. fast, seamless and robust tool-chains for structural analysis and
life cycle assessment)
- Methods and tools for global aircraft analyis
- Test Facilities (e.g. strength, thermo-mechanics, structural stability)
An example is our contribution to the European large scale project MAAXIMUS (More
Affordable Aircraft structure through eXtended, Integrated, and Mature nUmerical
Sizing), where we hold the lead for the sub-project “Design” and give scientific contributions on the topics Effects of Defects (EoD), postbuckling and “As Build”-analysis of
advanced fibre placement methods development.
>
Dr.-Ing. Alexander Kling
29
Composite Design
Mission
Our design for your structures!
The department Composite Design offers a closed development chain from the first
sketch of composite structures, their sizing up to a design for an efficient production:
- Preliminary design: Herein, design concepts, an adequate selection of materials,
hybridisation, and further aspects specific to fibre composites are being addressed.
- Sizing: Design concepts are optimized and assessed by using low and high fidelity
simulation tools, which also take into account probabilistically distributed material
and manufacturing parameters.
- Detailed Design: In the end the detailed design is realized under consideration of
tolerance management, quality assurance and appropriate tool concepts.
Particular emphasis is placed on the design of multi-functional structures, which contain additional features like electrical conductivity, acoustic noise absorption, information transmission etc. besides their required structural mechanical properties.
Competences
From requirements via concepts to multi-functional structures
The department Composite Design proves itself as a strong link between research and
industrial application in the following topics:
- Door surround structures in future aircraft
- Composite-driven design of airframe structures
- CFRP-metal hybrid structures in aerospace applications
- Design considering relevant manufacturing aspects, e.g. spring-in effects
- Tools and facilities for efficient and economic CFRP-production
- Deployable structures in ultra-lightweight space applications
- Design of multi-functional lightweight terrestrial vehicles
The closed development chain and the design of multi-functional structures are subject
of continuous common research work with our partners.
>
30
Dr.-Ing. Christian Hühne
Composite Technology
Mission
The experts for the composite process chain!
In To fully exploit the potential of lightweight composite structures it is necessary to
have a detailed understanding of all physical and chemical parameters that have an
impact on the final component quality. Most of these parameters have to be adjusted
during the manufacturing procedure which means that there is a high potential for
process optimisation. On the other hand there is a significant risk because inaccurate
process parameters will inevitably lead to inacceptable results. To solve this problem
our approach is to directly control all crucial production parameters in a way that the
outcome of the production process is highly reproducible on the highest possible level.
In order to do this different sensors and adequate control strategies for geometrical
parameters like e.g. local fibre volume fractions and for structural parameters like e.g.
residual stresses are under development to realise smart and mature manufacturing
concepts.
Competences
- Development of quality assured process chains for specific production scenarios
- Development of production optimised mould concepts
- Development of production optimised manufacturing equipment
- Manufacturing of demonstrators and test components
- Evaluation of innovative fibre and matrix products under processing conditions
- Realisation of highly integrated multi-functional components
- Cost analyses and trouble shooting for production processes
Even though creating composite components simply means to embed load bearing
fibres in a polymer matrix the variety of technical approaches is nearly as multifarious
as the field of applications itself. Within the last 30 years all baseline manufacturing
processes like filament winding, prepreg lay-up, Liquid Resin Infusion and RTM processing have been considered and further developed in order to meet the demands of the
various research and development projects .
To ensure the highest possible productivity in terms of cycle times and reproducibility at
acceptable costs the actual focus is on the utilisation of industrial automation equipment for composite manufacturing strategies.
>
Dr.-Ing. Markus Kleineberg
31
Adaptronics
Mission
The adaptronics pionieers in Europe!
Since 1989 the department of Adaptronics works as one of the first European research
groups on solutions in the field of smart-structures technology. With their experience
adaptive systems comprising structural material, distributed actuators and sensors,
control strategies and power conditioning electronics across all lines of business can be
realised. Applications range from space systems to fixed-wing and rotary-wing aircraft,
automotive, optical systems, machine tools, medical systems and infrastructure.
An adaptive system has the capability to respond to changing environmental and
operational conditions (such as vibrations and shape change). Microprocessors analyse
the responses of the sensors and use integrated control algorithms to command the
actuators to apply localized strains/displacements/damping to alter the elasto-mechanical system response.
Within national and international interdisciplinary teams the department of
Adaptronics focusses the research on the following areas:
- active attenuation of vibrations (e.g. for parallel robots, antennas)
- active structural acoustic control (e.g. for CFRP fuselages, magnetic resonance
tomography)
- morphing structures (e.g. for high lift devices, rotor blades)
- Stand-alone systems (e.g. energy harvesting, shunted systems)
Competences
The department of Adatronics offers its competences to customers and project partners starting from consulting and system analysis up to the design of adaptive systems:
- Experimental methods for structural dynamical and vibro-acoustical system analysis
- Experimental deformation analysis of large structures
- Development of actuator and sensor systems
- Modelling and numerical simulation of complex adaptive systems
- Controller development and implementation
- System integration and validation
- Demonstration of adaptive systems and their components
>
32
Dr.-Ing. Hans Peter Monner
Publications and Patents 2009 - 2010
Selected Publications in Journals,
Books and Proceedings:
2010-01. 142 S. Dissertation, Technische
Universität Braunschweig, 2010.
16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Schweden, 2010.
Zemčik, R., Rolfes, R., Rose, M.,
Teßmer, J.: „High performance 4-node
shell element for the analysis of laminated structures with piezoelectric coupling.
Mechanics of Advanced Materials and
Structures“, 13 (5) , S. 393-401, 2009.
Lee, M.C.W., Kelly, D.W.,
Degenhardt, R., Thomson, R.: „A
study on the robustness of two stiffened
composite fuselage panels“. Composite Structures, 92 (2), Seiten 223-232.
Elsevier, 2009.
Monner, H. P., Misol, M.,
Algermissen, S., Unruh, O.: „Active
CFRP-Panels for Reduction of Low-Frequency Turbulent Boundary Layer Noise“.
AIAA/ASME/ASCE/AHS/ASC, Orlando,
USA, 2010.
Sickinger, Ch.: „Verifikation entfaltbarer
Composite-Booms für Gossamer-Raumfahrtsysteme“. Dissertation , Technische
Universität Braunschweig, 2009.
Orifici, A.C., Thomson, R.S.,
Degenhardt, R., Bisagni, C.,
Bayandor, J.: „A finite element methodology for analysing degradation
and collapse in postbuckling composite
aerospace structures“. J‘l of Composite
Materials , 43 (26), S. 3239-3263, 2009.
Kintscher, M.: „Method for the PreDesign of a Smart Droop Nose using
a Simplex Optimization Scheme“. SAE
Aerotech Congres, Seattle, USA, 2009.
Riemenschneider, J.: „Characterization
and modeling of CNT based actuators“.
Smart Materials and Structures, 18 (10),
S. 104003-104011, 2009.
Algermissen, S., Sinapius, M.,
Zornemann, M.: „Aktive Schwingungsunterdrückung bei Systemen mit veränderlichen dynamischen Eigenschaften“.
NAFEMS Magazin, 2009.
Wiedemann, M.: „CFRP - Status of
Application in Airframe Structures and
Future Development Process“. NAFEMS
World Congress, Kreta, 2009.
Kleineberg, M., Kühn, M., Friedrich, M.:
„Formwerkzeuge in der Faserverbundtechnologie, Möglichkeiten und Risiken“.
DGLR-Tagung, Aachen, 2009.
Fink, A.: „Lokale Metallhybridisierung
zur Effizienzsteigerung von Hochlastfügestellen in Faserverbundwerkstoffen“.
DLR-Forschungsbericht, 2010.
Degenhardt, R., Kling, A., Bethge, A.,
Orf, J., Kärger, L., Zimmermann, R.,
Rohwer, K., Calvi, A.: „Investigations on
imperfection sensitivity and deduction of
improved knock-down factors for unstiffened CFRP cylindrical shells“. Composite
Structures, 92 (8), Seiten 1939-1946.
Elsevier, 2010.
Kling, A.: „Contributions to Improved
Stability Analysis for Design of Thinwalled Composite Structures“. DLR-FB
Opitz, S., Riemenschneider, J.,
Monner, H. P.: „Modal Investigation of
an Active Twist Helicopter Rotor Blade“.
20th International Conference on Adaptive Structures and Technologies (ICAST),
Hong Kong, China, 2009.
Baaran, J., Waite, S., Kleine-Beek, W.:
Visual detectability of blunt Impact damage in a stringer-stiffened CFRP fuselage
panel. 14th European Conference on
Composite Materials, Budapest, 2010.
Keimer, R., Pavlovic, N.: „Design and
Tests of Adaptronic Joints with Quasistatic Clearance Adjustment in a Parallel
Robot“. ASME 2009 Conference on
Smart Materials, Adaptive Structures and
Intelligent Systems, Oxnard, USA, 2009.
Wetzel, A.: „Zur Restfestigkeit schlaggeschädigter Doppelschaler aus Faserverbundwerkstoffen“. DLR-FB 131-2009/17.
156 S. Dissertation, Technische Universität Braunschweig, 2009.
Hoffmann, F., Opitz, S.,
Riemenschneider, J.: „Validation of
Active Twist Modeling Based on Whirl
Tower Tests“. 65th Annual Forum of the
American Helicopter Society, Grapevine,
USA, 2009.
Khattab, I. A., Sinapius, M.,
Hartung, D.: „In-plane finite element
approach for analyzing manufacturing
defects in composite materials“. 16th
international conference MECHANICS OF
COMPOSITE MATERIALS , Riga, 2010.
Misol, M., Algermissen, S.,
Monner, H. P., Naake, A.: „Reduction of
Interior Noise in an Automobile Passenger Compartment by Means of Active
Structural Acoustic Control (ASAC)“.
NAG/DAGA, Rotterdam, 2009.
Rohwer, K.: „Simulation of Fiber Composites – An Assessment. In: CD, The
International Association for the Engineering Analysis Community, NAFEMS Nordic
Seminar: Simulating Composite Materials
and Structures, 110 S., Esbjerg, 2010.
Wiedemann, M.: „CFRP - Status of
Application in Airframe Structures and
Future Development Process“. NAFEMS
World Congress 2009, Kreta, 2009.
Danilov, M., Ströhlein, T.,
Niemann, S., Krzikalla, P., Hilmer, P.:
„Electromagnetic Assisted Preforming
and Curing of Carbon Fibre Reinforced
Plastics“. DGLR-Tagung, Aachen, 2009.
Siefert, M., Ewert, R., Heintze, O.,
Unruh, O.: „A synthetic wall pressure
model for the efficient simulation of
boundary layer induced cabin noise“.
Algermissen, S., Rose, M., Keimer, R.,
Sinapius, M.: „Robust Gain-Scheduling
for Smart-Structures in Parallel Robots“.
SPIE Smart Structures and Materials &
33
Publications and Patents 2009 - 2010
Patents:
Nondestructive Evaluation and Health
Monitoring 2009, San Diego, USA, 2009.
Algermissen, S.: „Regelungsverfahren und Regelungseinrichtung“,
GP 102010007560.4, 10.02.2010.
Kleineberg, M., Kühn, M., Friedrich, M.:
„Formwerkzeuge in der Faserverbundtechnologie, Möglichkeiten und Risiken“.
DGLR-Tagung, Aachen, 2009.
Hillger, W., Szewieczek, A.: „Verfahren
zum Optimieren eines Sensornetzwerkes“, GP 102009019243, 30.04.2009.
Kaps, R., Quappen, A., Wiedemann, M.:
„Simulation der Verteilung von Faservolumengehalten in der kombinierten
Prepreg- und Injektionstechnologie“.
DGLR-Tagung, Aachen, 2009.
Danilov, M., Meyer, M.: „Verfahren und
Vorrichtung zur Ausrichtung nichtmagnetischer, elektrisch leitfähiger Fasern“,
GP 102009002157.4-26, 2.4.2009.
Block, J., Straubel, M.,
Wiedemann, M.: „Ultralight Deployable
Booms for Solar Sails and Other Large
Gossamer Structures in Space“. 60th Int.
Astronautical Congress, Daejeon, 2009.
Heintze, O., Kintscher, M., Lorkowski, T.,
Monner, H. P., Riemenschneider, J.:
„Aerodynamisches Bauteil mit verformbarer Außenhaut“, EP 10163592.8,
21.05.2010.
Straubel, M., Sinapius, M.,
Langlois, S.: „On-Ground Rigidized, Deployable Masts for Large Gossamer Space
Structures“. 11th European Spacecraft
Structures, Materials and Mechanical
Testing Conference, Toulouse, 2009.
Krzikalla, P., Niemann, S., Ströhlein, T.:
„Verfahren und Einrichtung zur Kontrolle
des Feuchtigkeitsgehalts eines Bauteils“,
DP 102010022455, 02.06.2010.
Algermissen, S., Monner, H. P.,
Pohl, M., Wiedemann, M.: “Schienenfahrzeug-Rad“, GP 102010007116,
05.02.2010.
Straubel, M.: „Future Applications for
Lightweight Expandable Structures –
German/European Perspectives“. 50th
AIAA/ASME/ASCE/AHS/ASC Structures,
Structural Dynamics, and Materials Conference, Palm Springs, USA, 2009.
Heintze, O., Homann, S.: „Verfahren
und Vorrichtung zum Abmindern
von Schwingungen einer Struktur“,
GP 102010003400, 29.03.2010.
Kärger, L., Kling, A.: „Feedback Method
transferring manufacturing data of TFP
structures to as-build FE models“. ECCM
2010 (IV European Conference on Computational Mechanics), Paris, 2010.
Bartsch, I., Friedrich, M., Hühne, Ch.,
Nickel, J.: „Luftfrachtcontainer“,
GP 102009046409.3-22, 04.11.2009.
Hartung, D., Wiedemann, M.,
Teßmer, J.: „Experimental test and material model for three dimensional failure
analysis of Non Crimp Fabrics“. ETDCM99th Seminar on Experimental Techniques
and Design in Composite Materials,
Vicenza, Italien, 2009.
Fink, A., Hühne, Ch.: „Verbundwerkstoff aus mehreren Faserverbundschichten und einem Verstärkungsbereich“, GP 102010009769.1-16,
01.03.2010.
Hanke, M., Kühn, M., Malzahn, S.:
„Formwerkzeug zur Herstellung von
Faserverbundbauteilen und Verfahren
zur Herstellung von Faserverbundbauteilen mit einem solchen Formwerkzeug“,
GP 102010024986, 24.06.2010.
Wierach, P.: „Entwicklung von Piezokompositen für adaptive Systeme“.
DLR-Forschungsbericht. DLR-FB 2010-23.
102 S. Dissertation, 2010.
34
Danilov, M.: „Faserverbundbauteil
und Verfahren zu seiner Herstellung“,
GP 102010018518, 29.04.2010.
Borgwardt, H., Hühne, Ch.,
Kaps, R., Knote, A., Niemann, S.,
Ströhlein, T.: „Flugzeugrumpfbauteil“,
GP 102009056534, 03.12.2009.
Assing, H., Fink, A., Hühne, Ch.,
Niemann, S., Röstermundt, D.: „Rotornabe in Faserverbundbauweise für Windkraftanlagen“, DP 102010010283.0-15,
04.03.2010.
Bartsch, I., Ernst, G., Hühne, Ch.,
Krajenski, V., Nickel, J.: „Bemanntes
Luftfahrzeug“, GP 102010012414,
23.03.2010.
Homann, S., Nagel, B.,: „Schalldämpfer mit schraubenförmigem Gaskanal“,
GP 102010003595, 01.04.2010.
Assing, H., Fink, A., Hühne, Ch.,
Kolesnikov, B., Niemann, S.,
Ströhlein, T.: „Türrahmenanordnung und Tür, insbesondere fürLuft- und Raumfahrfahrzeuge“,
GP 102010014265.4-22, 08.04.2010.
Keimer, R., Opitz, S.,
Rose, M., Sinapius, M.: „Formvariables, rekonfigurierbares Strukturelement mit schaltbarer Steifigkeit“,
GP 102010029088, 18.05.2010.
Geier, S., Riemenschneider, J.: „Aktuator mit Nanotubes“, GP 102010030035
14.06.2010.
Kappel, E., Stefaniak, D.: „Modellieren
der Raumform eines einen Schichtaufbau
aufweisenden Faserverbundbauteils nach
dessen Aushärtung auf einem Formwerkzeug“, GP 102010030448, 23.06.2010.
Melcher, J., Templin, M.: „Sensor und
Aktuator, insbesondere für einen Rotationsfreiheitsgrad“, GP 102010029279,
25.05.2010.
Imprint
Published by
Deutsches Zentrum
für Luft- und Raumfahrt e.V.
German Aerospace Center
Institute of Composite Structures and Adaptive Systems
Titel Subject
Innovation topics of the Institute
of Composite Structures and Adaptive Systems
Adress
Lilienthalplatz 7
D-38108 Braunschweig
Tel. +49 531 295 2300
Editors
Prof. Dr. Martin Wiedemann
Prof. Dr. Michael Sinapius
Prof. Dr. Jörg Melcher
Brigitte Zell-Walczok
Printed by
on
Druckerei Thierbach
D-45478 Mühlheim an der Ruhr
September 2010
Reproduction in whole or in part or any
other use is subject to prior permission
from the German Aerospace Center (DLR).
www.DLR.de
35
DLR at a glance
DLR is Germany´s national research centre for aeronautics and
space. Its extensive research and development work in Aeronautics, Space, Energy, Transport and Security is integrated into national and international cooperative ventures. As Germany´s space
agency, DLR has been given responsibility for the forward planning
and the implementation of the German space programme by the
German federal government as well as for the international
representation of German interests. Furthermore, Germany’s
largest project-management agency is also part of DLR.
Approximately 6,500 people are employed at thirteen locations
in Germany: Koeln (headquarters), Berlin, Bonn, Braunschweig,
Bremen, Goettingen, Hamburg, Lampoldshausen, Neustrelitz,
Oberpfaffenhofen, Stuttgart, Trauen and Weilheim. DLR also
operates offices in Brussels, Paris, and Washington D.C.
DLR’s mission comprises the exploration of the Earth and the
Solar System, research for protecting the environment, for
environmentally-compatible technologies, and for promoting
mobility, communication, and security. DLR’s research portfolio
ranges from basic research to innovative applications and products
of tomorrow. In that way DLR contributes the scientific and
technical know-how that it has gained to enhancing Germany’s
industrial and technological reputation. DLR operates large-scale
research facilities for DLR’s own projects and as a service provider
for its clients and partners. It also promotes the next generation of
scientists, provides competent advisory services to government,
and is a driving force in the local regions of its field centers.
German Aerospace Center
Institute of Composite Structures and Adaptive Systems
Lilienthalplatz 7
38108 Braunschweig
www.DLR.de/fa
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