LIFE PREDICTION METHODOLOGY FOR COMPOSITE STRUCTURES .2. SPECTRUM FATIGUE

A previously developed model for predicting the life of composite stru ctures under constant amplitude and two-stress lever fatigue loadings is extended and applied to structures subjected to randomly-ordered lo ading spectra. The model is phenomenological and a limited amount of e xperimental data is required for its characterization. For uniaxially loaded laminates, this consists of static tension and compression stre ngth distributions, S-N curves based on constant amplitude fatigue lif e distributions for two-to-three stress ratios, and a limited amount o f two-stress level fatigue test results. The model is verified by comp aring predicted fatigue life distributions to experimentally observed fatigue life data for a variety of laminates and load spectrums. Good correlation between theory and experiment is obtained for all loadings and laminates studied.