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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] 1 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 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 3 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 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 5 5th International Conference on Composites Testing and Model Simulation l=2nL Introduction Method Results & Discussion Conclusion 6 5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 7 5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 8 5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 9 5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 10 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 11 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 12 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 13 5th International Conference on Composites Testing and Model Simulation Wavelength shift versus time Introduction Method Results & Discussion Conclusion 14 5th International Conference on Composites Testing and Model Simulation Wavelength shift versus time Strain versus crack length Introduction Method Results & Discussion Conclusion 15 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 16 5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 17 5th International Conference on Composites Testing and Model Simulation Algorithms: Trust-region-reflective Levenberg-Marquardt Introduction Method Results & Discussion Conclusion 18 5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 19 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 20 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 21 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 22 5th International Conference on Composites Testing and Model Simulation Simulated load displacement curve No bridging in the cohesive law Introduction Method Results & Discussion Conclusion 23 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 24 5th International Conference on Composites Testing and Model Simulation Fibre end Introduction Method Results & Discussion Conclusion 25 5th International Conference on Composites Testing and Model Simulation Using crack length versus time measurements to eliminate time Introduction Method Results & Discussion Conclusion 26 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 27 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 28 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 29 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 30 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 31 5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 32 5th International Conference on Composites Testing and Model Simulation Introduction Method Results & Discussion Conclusion 33