A study of fatigue damage and fatigue life of composite laminates

The fatigue damage and fatigue life of a batch of [+/- 45 degrees](2s) graphite/epoxy composite laminates are investigated in the present study. Residual stiffness is selected as a parameter to describe the degradation behavior of the composite laminates. In order to predict the fatigue life and residual stiffness of such laminates, a simple model which contains a residual stiffness degradation equation and the randomization of its parameters is proposed. A Markov chain model is also employed. Both models can be used to predict the probability distribution of the degraded stiffness at a specified loading cycle. The probability distribution of loading cycles for the residual stiffness to degrade to a certain amount can be predicted as well. Experimental data verify the applicability of both models to the studied composite laminates. According to the data, a simple relation between the ultimate strength and fatigue life of the laminates is also found. The relation provides us with quick estimation of the fatigue life of a component based on its ultimate strength which can usually be obtained very easily.