Life Prediction Methodology for Composite Structures. Part II—Spectrum Fatigue

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Abstract
A previously developed model for predicting the life of composite structures under constant amplitude and two-stress level fatigue loadings is extended and applied to structures subjected to randomly-ordered loading spectra. The model is phenomenological and a limited amount of experimental data is required for its characterization. For uniaxially loaded laminates, this consists of static tension and compression strength distributions, S-N curves based on constant amplitude fatigue life distributions for two-to-three stress ratios, and a limited amount of two-stress level fatigue test results. The model is verified by comparing 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.