Constant and Variable Amplitude Fatigue Behavior and Modeling of an SRIM Polymer Matrix Composite

Strain-controlled fatigue behavior of smooth specimens of an SRIM polymer matrix composite under constant and variable amplitude loading was investigated, including the effects of mean stresses/strains. Significant degradation of the macroscopic stiffness was observed during cyclic loading, and SEM examination of the failed specimens revealed the degradation was due to a variety of damage mechanisms, including matrix cracking, fiber/matrix debonding, fiber fracture, and fiber buckling. Fatigue life predictions made using common strain-based models overestimated the experimental results for both constant amplitude and variable amplitude loading. An improved strain-based model for making life predictions using an effective strain amplitude was proposed which was in much closer agreement with experimental results.