Fatigue life prediction method for composite laminates based on equivalent life under time-varying loads

This article aims to investigate the fatigue life prediction methodologies of composite laminates and lay the groundwork for establishing fatigue life evaluation technology for composite structures. By extending the Hashin criterion to the fatigue failure criterion, an empirical equation for the fatigue life of unidirectional laminates with various fiber orientation is simply created. In view of the influence of the stiffness reduction coefficient of the failure layer, the failure sequence of each layer in the laminate is determined under time-varying loads. On the basis of the equivalence principle of fatigue damage, the equivalent life of the failure layer to the remaining layers in laminate is determined by considering the effects of load interaction, variable loading, and load cycles on damage. In combination with equivalent life, the fatigue life prediction model for composite laminates is constructed, and the proposed model agrees will with the test data.