Fatigue of Composite Materials—Damage Model and Life Prediction

Fatigue life prediction on composite materials is studied analytically using degradation and damage models, resultant strains, and fatigue modulus. Definition of fatigue modulus, new damage models using fatigue modulus and resultant strain, and prediction of fatigue life of composite materials using degradation and damage models are discussed. This approach can predict accurately the multi-stress level fatigue life as well as single-stress level fatigue life of composite materials. Fatigue life is predicted by the following procedures: (1) establish the fatigue modulus degradation model, (2) find fatigue life equation as a function of fatigue modulus, (3) calculate the fatigue life using strain failure criterion. Degradation models for composite damage are generalized; the three-parameter degradation model is found most suitable to predicting fatigue life of composites. Also the predicted two-stress level fatigue life using the proposed cumulative damage models is reasonably close to the experimental data.