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5th International Conference on Composites Testing and Model Simulation Samuel Stutz Jol Cugnoni John Botsis 1 LMAF-STI, Ecole Polytechnique Fdrale de Lausanne (EPFL), CH-1015 Lausanne Switzerland E-mail: samuel.stutz@a3.epfl.ch

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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 2

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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 load- displacement curve 3 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 4

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5th International Conference on Composites Testing and Model Simulation Prepregs from Gurit SP TM (SE 70) [0 20 ] Introduction Method Results & Discussion Conclusion 5 Sensor fibre Crack Crack initiator

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5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 6 =2n

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5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 7

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5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 8

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5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 9

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5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 10

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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 11 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 12 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 13 Introduction Method Results & Discussion Conclusion

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5th International Conference on Composites Testing and Model Simulation Wavelength shift versus time 14 Introduction Method Results & Discussion Conclusion

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5th International Conference on Composites Testing and Model Simulation Wavelength shift versus time 15 Introduction Method Results & Discussion Conclusion Strain versus crack length

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5th International Conference on Composites Testing and Model Simulation Wavelength shift versus time 16 Introduction Method Results & Discussion Conclusion Strain versus crack length Using crack length versus time measurements to eliminate time

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5th International Conference on Composites Testing and Model Simulation 17 Introduction Method Results & Discussion Conclusion

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5th International Conference on Composites Testing and Model Simulation 18 Introduction Method Results & Discussion Conclusion Algorithms: Trust-region-reflective Levenberg-Marquardt

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5th International Conference on Composites Testing and Model Simulation 19 Introduction Method Results & Discussion Conclusion

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5th International Conference on Composites Testing and Model Simulation 20 Introduction Method Results & Discussion Conclusion Crack opening as a function of the distance from the crack tip (from simulation) (z*) and the identified bridging traction distribution (z*) were combined to obtain the bridging law ( )

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5th International Conference on Composites Testing and Model Simulation 21 Introduction Method Results & Discussion Conclusion Cohesive element properties: Thickness : 20 m Damage initiation : 20 MPa Cohesive stiffness : 9000GPa/mm G(a) = G i + G b (a)

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5th International Conference on Composites Testing and Model Simulation Experimental load- displacement curve Two initial crack lengths, 30 and 60 mm 22 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 23 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/m 2 24 Introduction Method Results & Discussion Conclusion

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5th International Conference on Composites Testing and Model Simulation 25 Introduction Method Results & Discussion Conclusion Fibre end

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5th International Conference on Composites Testing and Model Simulation 26 Introduction Method Results & Discussion Conclusion Using crack length versus time measurements to eliminate time

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5th International Conference on Composites Testing and Model Simulation 27 Introduction Method Results & Discussion Conclusion Identified energy release rate (cohesive elements) G II =1070 J/m 2 Identified crack initiation: max = 38.7 MPa Identified friction between the loading pins and the sample: =0.35 There was no sensitivity to friction between the fracture surfaces ( =0.1 0.4)

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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 28 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 29 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 30 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. 31 Introduction Method Results & Discussion Conclusion

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5th International Conference on Composites Testing and Model Simulation 32 Introduction Method Results & Discussion Conclusion

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5th International Conference on Composites Testing and Model Simulation 33 Introduction Method Results & Discussion Conclusion