Uncertainty in fatigue loading: Consequences on statistical evaluation of reliability in service

A design-by-reliability approach is ever more required and accurate design inputs are needed to meet reliability targets while reducing costs. Different models have been proposed in the literature to describe fatigue life variation with respect to the applied stress by assuming the applied stress as a deterministic independent variable and the fatigue life as a dependent random variable. In the paper also the applied stress is considered as a random variable with its own uncertainty and the procedure to valuate the error on the estimation of parameters usually adopted in service reliability assessment of structural components is shown. Exact equations are proposed for some special cases and an illustrative example showing the reliability errors originated by applying the ASTM recommendations is given.