Influence of fatigue-life data modelling on the estimated reliability of a structure subjected to a constant-amplitude loading

This article describes how a selected material's fatigue-life-curve model influences the calculated reliability of a structure subjected to a dynamic loading. A uni-axially loaded structural beam with a fully-reversal constant loading amplitude was considered. The reliability for a certain number of cycles-to-failure was calculated as a cross-section of the probability distributions representing the load-amplitude scatter and the scatter of the material's fatigue-life curve. The probability density function (PDF) of the loading amplitude was modelled by a uniform and a Gaussian PDF. The scattered fatigue-life curve was modelled by a conditional two-parametric Weibull's PDF. Its parameters were estimated using two procedures: (i) a two-phase procedure and (ii) a direct procedure. Following the two-phase procedure a conditional PDF of the number of cycles-to-failure was estimated first and then converted into a corresponding conditional PDF of the stress amplitudes. In the direct procedure the conditional PDF of the stress amplitudes was modelled directly from the fatigue-life data. The two procedures were tested on 12 sets of simulated fatigue-life data and a set of experimental fatigue-life data. The two fatigue-life-curve models for the experimental data set were applied for calculating the reliability for the selected structural beam.