Fatigue Model for Fiber-Reinforced Polymeric Composites

A fatigue model based on cumulative damage is developed for predicting the fatigue life of fiber-reinforced polymeric composites. This model incorporates applied maximum stress, stress amplitude, loading frequency, residual tensile modulus, and material constants as parameters. The model is verified with experimental fatigue data on a glass fiber/vinyl ester composite. While the specimens are exposed to air, freshwater, or seawater at 30°C, they are subjected to tension-tension stress at four levels of applied maximum tensile stress in each of two frequencies. Both the residual mechanical properties at specified loading cycles and the number of cycles at which the specimens fail are measured. The results show that, for the material used in this study, the loss in residual tensile strength and modulus in saltwater is approximately the same as that in freshwater and that the fatigue life in these aqueous environments is shorter than that in air. Numerical analysis is carried out to determine the material constants of the composite. The fatigue model agrees well with the experimental data. The model can be used to predict the fatigue life of the polymeric composites subjected to an applied load in different environments and to predict the residual tensile modulus after a number of cycles of service at a given load.