Anisomorphic constant fatigue life diagrams for quasi-isotropic woven fabric carbon/epoxy laminates under different hygro-thermal environments

The effect of absorbed moisture on the fatigue strength of a plain-weave roving fabric carbon/epoxy quasi-isotropic laminate under constant amplitude loading at different stress ratios has been examined. First, constant amplitude fatigue tests are performed at room and high temperatures (HT), respectively, on the specimens immersed in hot water until saturation as well as on the specimens kept in a dry place. The results indicate that the fatigue lives of wet specimens are shorter than those of dry specimens, regardless of stress ratio as well as test temperature. The fatigue strength is reduced by about 11% due to water absorption at room temperature (RT), regardless of stress ratio. A similar reduction in fatigue strength can be seen in wet specimens at HT as well. Then, the full shapes of constant fatigue life (CFL) diagrams for the woven carbon fiber-reinforced plastic (CFRP) laminate in dry and wet environments are identified using fatigue test data obtained at different stress ratios and at different test temperatures. The results show that the experimental CFL diagrams are asymmetric and nonlinear, and the shape of CFL envelope gradually changes. Finally, the CFL diagrams for the woven CFRP laminate under uniaxial fatigue loading in different hygro-thermal environments are predicted using the anisomorphic CFL diagram approach for composites that was developed in an earlier study. Comparison with experimental results demonstrates that the anisomorphic CFL diagram approach is a promising step in predicting the CFL diagram for the woven CFRP laminate not only in a dry environment but also in a wet environment, regardless of test temperature.