A cohesive zone model for predicting the initiation of Mode II delamination in composites under cyclic loading

A new approach for simulating delamination initiation under cyclic loading is proposed. This approach is based on the hysteresis cohesive zone modeling and the gradual degradation of interface properties. The initiation of delamination is predicted based on the monotonic traction–separation law of the interface. A damage criterion is proposed that depends on the bilinear traction–separation law and interlaminar stiffness is degraded by defining a damage parameter as a function of number of cycles and bilinear traction–separation law parameters. Numerical simulation is accomplished by implementing 2D finite element modeling for the case of double-notched specimen. Four-node zero-thickness interfacial cohesive elements are defined to capture the delamination behavior of midplane in the specimen. The results of numerical simulation are compared with available experimental data and a good agreement is observed. The main novelty of this research lies on assuming a cycle-by-cycle irreversible decrease in interlaminar stiffness prior to damage initiation and applying a damage criterion based on the bilinear traction–separation law in order to predict the number of cycles for initiation of delamination.