Transcript Slide 1
5th International Conference on
Composites Testing and Model Simulation
Samuel Stutz
Joël Cugnoni
John Botsis
LMAF-STI, Ecole Polytechnique Fédérale de Lausanne (EPFL),
CH-1015 Lausanne Switzerland
E-mail: [email protected]
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5th International Conference on
Composites Testing and Model Simulation
Increasing use of composites
Layered structure
Delamination
Characterization of propagation
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Approach:
Measuring strain with optical
fibre sensors during crack
propagation
Identify relevant properties
with a parametric FE-model
Comparing the numerical and
experimental loaddisplacement curve
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Method
◦ Manufacturing
◦ Multiplexed Fiber Bragg grating (FBG) sensors
◦ Distributed strain measurements
Results & Discussion
◦ Mode I (DCB) tests
◦ Mode II (4ENF) tests
Conclusion
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Prepregs from Gurit SPTM (SE 70) [020]
Crack initiator
Sensor fibre
Crack
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
l=2nL
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
No strain at the FBG positions
Strain ahead of the crack tip
reaches the FBGs
All FBGs are in the bridging
zone
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
No strain at the FBG positions
Strain ahead of the crack tip
reaches the FBGs
All FBGs are in the bridging
zone
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
No strain at the FBG positions
Strain ahead of the crack tip
reaches the FBGs
All FBGs are in the bridging
zone
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Wavelength shift versus time
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Wavelength shift versus time
Strain versus crack length
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Wavelength shift versus time
Strain versus crack length
Using crack length versus time
measurements to eliminate
time
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Algorithms:
Trust-region-reflective
Levenberg-Marquardt
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Crack opening as a function
of the distance from the
crack tip (from simulation)
d(z*)
and the identified bridging
traction distribution
s(z*)
were combined to obtain the
bridging law
s(d)
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Cohesive element properties:
Thickness : 20 mm
Damage initiation : 20 MPa
Cohesive stiffness : 9000GPa/mm
G(a) = Gi + Gb(a)
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Experimental loaddisplacement curve
Two initial crack
lengths, 30 and 60
mm
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Simulated load displacement
curve
No bridging in
the cohesive law
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Simulated load displacement
curve
With bridging in
the cohesive law
Energy release
rate of the
bridging fibres:
350 J/m2
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Fibre end
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Using crack length versus time
measurements to eliminate
time
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Identified energy release rate
(cohesive elements)
GII =1070 J/m2
Identified crack initiation:
smax = 38.7 MPa
Identified friction between the
loading pins and the sample:
m =0.35
There was no sensitivity to
friction between the fracture
surfaces (m=0.1 – 0.4)
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Experimental
load-displacement
curves
The different
slopes are due to
different initial
crack lengths
Some unstable
crack propagation
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Results from the
numerical
simulation
Cohesive elements
with the identified
properties
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
The multiplexed FBG sensor array proved to be an excellent
embedded sensor to measure non-homogeneous strain in
mode I and mode II delamination
The measured strain distribution was successfully used for
identification of material parameters
o Bridging tractions in mode I
o The energy release rate in mode II
The experimental load displacement curves were entirely
reproduced
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
The authors acknowledge the financial support from the Swiss
National Science Foundation (SNF) under Grant
200020_124397.
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Introduction Method Results & Discussion Conclusion
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5th International Conference on
Composites Testing and Model Simulation
Introduction Method Results & Discussion Conclusion
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