A combined model for initiation and propagation of damage under fatigue loading for cohesive interface elements

A model for the simulation of damage initiation and subsequent propagation under cyclic loading is proposed. The basis for the formulation is a cohesive law that combines phenomenological SN-curves for damage initiation with a fracture and damage mechanics approach for crack propagation. The evolution of the damage variable is expressed as a function of fatigue cycles. The model is independently calibrated for mode I and mode II loading using SN-curves and Paris-law coefficients obtained from simple coupon tests. The model was applied to three initiation-driven cases: Bending of 90° laminates, the Short Beam Shear test and the Double Notched Shear test. The predictions for the first two cases showed an excellent correlation with experimental data. Some modifications to the model were required when applying it to the Double Notched Shear test.