A fatigue damage model for composite materials

Abstract Composite materials using polymer resins as matrices possess viscoelastic properties such that the fatigue behavior of the composite could be changed by different stress levels, stress ratio, stress frequency, or temperature. Based on a physical phenomenon of damage growth, this work develops a fatigue damage model including the nonlinear effects of stress ratio and stress frequency on the damage processes for carbon/epoxy composites. A damage index is defined and used to confirm the damage evolution behavior, and a series of fatigue tests of unidirectional specimens under monotonous loading and two‐stress level loading are conducted to test the proposed fatigue damage model. The results reveal that the proposed model could reasonably predict the fatigue life of composite materials under complicated loading conditions and it also includes the sequence effect of cyclic block loadings. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers