Simulation and experimental validation of mixed mode delamination in multidirectional CF/PEEK laminates under fatigue loading

Cyclic mixed mode delamination in multidirectional composite laminates subjected to high cycle fatigue loading has been investigated by numerical simulations and cyclic mixed mode bending experiments. The numerical model includes lamina and interface elements. The description of the delamination crack growth rate is based on the cyclic degradation of bilinear interface elements linking the evolution of the damage variable with the delamination crack growth rate. The constitutive cyclic damage model is calibrated by means of mixed mode fatigue experiments and reproduces the experimental results successfully and with minor error. It is concluded that only with implementing a cyclic damage variable in the cohesive interface element the experimentally observed crack growth and stiffness degradation can be captured properly. Scanning electron microscopy of fracture surfaces after cyclic loading revealed that abrasion of crack bridging surface roughness is the main microscopical cause of weakening and degradation of the interface.