Fatigue Life Prediction for Complex Load Versus Time Histories

Fatigue life prediction for complex load versus time histories is considered from the viewpoint of separating the history into discrete events, or cycles, which may then be used with constant amplitude fatigue data in a cumulative damage type of analysis. Highly irregular histories require special attention, with minor load excursions being considered in cycle counting as temporary interruptions of larger load cycles. Local notch plasticity and mean stress effects are interrelated, and such effects are most rationally accounted for in terms of local notch stresses and strains. The paper describes and discusses a life prediction procedure for notched members which is based on modeling of the stresses and strains occurring locally at the notch.