Effects of loading adjustment on the reliability degradation of composites

Abstract This paper defines two parameters to describe the effects of fatigue load adjustment on the reliability degradation of composites. The transition period, n _{2 a} , indicates the free failure time period from the instant of high-low adjustment until the residual strength distribution meets the low-level stress. The reliability drop, ∣Δ R ∣, is shown at the instant of low-high adjustment. Based on the strength-life equal rank assumption, a typical Yang model of the residual strength is considered to derive these two items by retrieving the residual strength distributions to the corresponding initials. The predicted parameters are verified to be in good agreement with the Monte Carlo simulation of fatigue failure. It is found that n _{2 a} increases dramatically as the reliability R _a at which the stress level changes, in the range of 1> R _a >0.95. The relationship between ∣Δ R ∣ and R _a exhibits a parabolic-like curve with a peak near the mean cycles to failure of the process at low-level stress.