Fatigue life prediction and failure mechanisms of composite materials

Fatigue life prediction and failure mechanisms of composite materials are studied based on the fatigue modulus concept and experimental results. Single-stress level fatigue life is predicted using generalized fatigue modulus degradation model and resultant strain failure criterion. Cumulative damage models defined by fatigue modulus and resultant strains are derived as functions of fatigue cycle and applied stress. This approach can predict accurately the multi-stress level fatigue life in addition to single-stress level fatigue life of composite materials. Fatigue modulus is measured by a cyclic stress-displacement behavior and resultant displacements data. The prediction is also made by the fatigue modulus degradation model and fatigue life prediction results. The comparison shows that the predicted values lie within the experimental scatter band. The relationship between physical damage accumulation and material property (such as fatigue modulus) degradation is induced qualitatively through fractography and phenomenological analysis.