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 st udy. Residual stiffness is selected as a parameter to describe the deg radation 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 rando mization of its parameters is proposed. A Markov chain model is also e mployed. Both models can be used to predict the probability distributi on of the degraded stiffness at a specified loading cycle. The probabi lity distribution of loading cycles for the residual stiffness to degr ade to a certain amount can be predicted as well. Experimental data ve rify the applicability of both models to the studied composite laminat es. According to the data, a simple relation between the ultimate stre ngth and fatigue life of the laminates is also found. The relation pro vides us with quick estimation of the fatigue life of a component base d on its ultimate strength which can usually be obtained very easily.