A probabilistic investigation of fatigue life and cumulative cycle ratio

Abstract

Fatigue life data under three constant amplitudes (200 replications each) and under four conditions of high-low and low-high two-stage loading (50 replications each) are presented. The constant amplitude life data are examined with the aid of Weibull and log-normal probability paper and by means of B-Models. The cumulative cycle ratio and the empirical distribution function (EDFs) under two-stage loading were examined in a similar manner. The log-normal distribution provides a better fit to the constant amplitude life data and cumulative cycle ratio than does the two-parameter Weibull distribution. The cumulative distribution functions (CDFs) generated by stationary unit-jump B-models provide a more comprehensive description of the constant amplitude life data edf, indicating the cumulative damage process is essentially stationary and the specimens have little scatter in their initial damage states. A similar comparison of the EDFs of life data under two-stage loading indicates load interaction increases life in the high-low case and decreases life in the low-high case, the magnitude of this interaction being approximately the same.