Evaluation of Fatigue Life Regression Models

Fatigue life regression models with constant and non-constant variance are evaluated and compared with a Random Fatigue Limit Model and a Probit model to estimate the fatigue strength and S-N relationship from fatigue test data. The Maximum Likelihood method is used to estimate parameters of the above models. Emphasis also is given to assessing the variation in fatigue strength and S-N relationships estimated from different models. Two different test data sets are selected for the evaluations: (1) a full S-N test data set with a large range of stresses and (2) a staircase test data set with a characteristically more narrow range of stresses. Model adequacies are evaluated from residuals and Anderson Darling measures of their fits. The Random Fatigue Limit Model is observed to best fit the test data, but its large number of parameters are under constrained with staircase test data and require care to get good results.