A Review of Spectral Methods for Variable Amplitude Fatigue Prediction and New Results

A review of the available methods for estimating fatigue damage from variable amplitude loading is presented. The dependence of fatigue damage accumulation on power spectral density (psd) is investigated for stationary Gaussian random processes. Improvements to the Rayleigh approximation are examined by comparison to rainflow analysis of time histories simulated from psd functions representative of simple theoretical and real world applications. Spectral methods investigated include those by Wirsching and Light, Ortiz and Chen, the Dirlik formula, and the Single-Moment method, among other recent methods. Guidelines and limitations are given for using spectral methods to increase confidence in the damage estimate.