CONSTANT AND VARIABLE AMPLITUDE FATIGUE BEHAVIOR AND MODELING OF AN SRIM POLYMER MATRIX COMPOSITE

Strain-controlled fatigue behavior of smooth specimens of an SRIM poly mer matrix composite under constant and variable amplitude loading was investigated, including the effects of mean stresses/strains. Signifi cant degradation of the macroscopic stiffness was observed during cycl ic loading, and SEM I examination of the failed specimens revealed the degradation was due to a variety of damage mechanisms, including matr ix cracking, fiber/matrix debonding, fiber fracture, and fiber bucklin g. Fatigue life predictions made using common strain-based models over estimated the experimental results for both constant amplitude and var iable amplitude loading. An improved strain-based model for making lif e predictions using an effective strain amplitude was proposed which w as in much closer agreement with experimental results.