Preprint #97-18
In a fatigue-limit model, test units tested below the fatigue limit
(also known as the threshold stress) theoretically will never fail. This
paper uses a random fatigue-limit model to describe: a) the dependence of
fatigue life on the stress level, b) the variation in fatigue life, and
c) the unit-to-unit variation in the fatigue limit. We fit the model to
actual fatigue data sets by maximum likelihood methods and study the fits
under different distributional assumptions. Small quantiles of the life
distribution are often of interest to designers. Lower confidence bounds
based on likelihood-ratio methods are obtained for such quantiles. To
assess the fits of the model, we construct diagnostic plots and perform
goodness-of-fit tests and residual analyses.
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University, Department of Statistics, Snedecor Hall, Ames, IA 50011-1210.