Constitutive law describing the strength degradation kinetics of fibre-reinforced composites subjected to constant amplitude cyclic loading

A two-parameter model based on strength degradation was developed and its predictive reliability was checked on a series of fatigue life and residual strength data available in the literature. The modelling approach explicitly accounts for the maximum cyclic stress, , and the stress ratio, , and requires a limited number of experimental fatigue life data to predict the cycle-by-cycle strength degradation kinetics until the "sudden drop" of strength before catastrophic failure. Different loading conditions were analysed for a large variety of composites, including short-glass-fibre-reinforced polycarbonate, glass/epoxy laminates, graphite/epoxy laminates, AS4 carbon/epoxy 3k/E7K8 plain weave fabric with [45/-45/90/45/-45/45/-45/0/45/-45](S) layup, and [CSM/fabric/(CSM/UD)2](S) glass/polyester laminate. The modelling approach indicates that the fatigue life and the residual strength are related to the statistical distribution of the static strength.