A methodology to compute cumulative probability distribution functions (CDF) of fatigue life for different ratios, r of applied stress to first ply failure strength have been developed and demonstrated. Degradation effects due to long term nature of the mechanical cyclic loads are considered in the simulation process. A unified time-stress dependent multi-factor interaction equation model developed at NASA Lewis Research center has been used to account for the degradation/aging of material properties due to cyclic loads. Fast probability integration method is used to perform probabilistic simulation of uncertainties. Sensitivity of fatigue life reliability to uncertainties in the primitive random variables are computed and their significance in the reliability based design for maximum life is discussed. The results show that for applied stress to first ply failure strength ratio of 0.6, the laminate has half the endurance limit life with a reliability of 0.999. Also, the fatigue life reliability has been found to be most sensitive to the ply thickness and matrix tensile strength.
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