A general method for predicting temperature-dependent anisomorphic constant fatigue life diagram for a woven fabric carbon/epoxy laminate

The anisomorphic constant fatigue life (CFL) diagram approach to prediction of fatigue lives of composites, which was developed in an earlier study, is developed further into a more general methodology that can deal with the mean stress sensitivity in fatigue of composites at different temperatures. The temperature dependence of the anisomorphic CFL diagram for a given composite is characterized by the temperature dependence of the static strengths in tension and compression and of the reference S–N relationship for a critical stress ratio. The temperature dependence of the static strengths in tension and compression is first formulated to describe the temperature dependence of the critical stress ratio. To predict the reference S–N relationships at different temperatures, the change in the value of critical stress ratio with temperature as well as the effect of temperature on fatigue should be taken into account. To this end, a new and efficient engineering method is developed which is based on a grand master S–N curve built by means of a modified fatigue strength ratio and a life-temperature parameter of the Larson–Miller type. The generalized anisomorphic CFL diagram approach developed in this study succeeds in efficiently and adequately predicting the CFL diagrams for a woven fabric carbon/epoxy quasi-isotropic laminate at different temperatures and thus the mean stress dependence of the S–N relationships of the laminate at different temperatures.