A CUMULATIVE DAMAGE THEORY FOR FATIGUE LIFE PREDICTION

A cumulative damage theory is developed based on the concept of bounds on residual fatigue life in two-stage cycling. It is shown that such bounds follow from general properties of damage curves and involve only fatigue lifetimes and the endurance limit in single-stage cycling. It is then shown that such bounds can be narrowed by inclusion of additional information about the fatigue process, namely, crack-initiation and crack propagation lifetimes. The question of scatter in cumulative damage tests is considered and it is shown that the bounds can be optimized to bracket the entire test data scatter. As a result, it is found that the scatter in crack initiation cycles underlies the scatter observed in cumulative damage tests. © 1990.