Delamination between plies is the most common failure mode in composite laminates that can cause fiber breakage and reduction in life of the composite. Currently Mode-I interlaminar fracture toughness or critical energy release rate of a composite is measured using double cantilever beam (DCB) with unidirectional composites (ASTM D5528). Unlike metals, the energy plot of a DCB specimen shows increase in energy release rate with increase in crack length. Also during testing the steady state energy release rate from each of the samples of the same batch shows a lot of variation due to fiber cross-over bridging that occurs only in unidirectional composites. In this study, a probabilistic Cohesive Zone Model (CZM) is developed to capture steady state energy release rate variations of 51 mm crack size DCB specimens based on unidirectional composite (IM7/977-3) test data. Then using the probabilistic CZM, the energy release rate variations of 76.2 mm crack size DCB model are predicted and compared to the test results. The predictions showed good agreement with the experiments suggesting a probabilistic CZM is capable of simulating the strength scatter during the delamination process in unidirectional composites that were of interest in this research.
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