TIME VARIANT FORMULATION FOR FATIGUE RELIABILITY

Methods for evaluating the time variant reliability of a component with deteriorating resistance and subjected to a stochastic load process are reviewed. An outcrossing formulation for fatigue degradation is presented, and an approximation, based on a time invariant model, is proposed. The approximation is simple, in concept and application, and is conservative. The formulations are extended to environmental load processes typical for marine structures, and the reliability is assessed in the presence of ergodic (e.g., seastate parameters) and nonergodic (e.g., crack growth parameters) random variables. The methods are verified by Monte Carlo time step simulation. It is demonstrated that a previously proposed method may be excessively conservative.