Total Fatigue Life Prediction Methods

Two analytical methods of predicting the total fatigue life of a component such as weldment are compared: a relatively uncomplicated, two-stage, total-life-model known as the initiation-propagation or IP model; and a recently developed model termed the PICC-RICC crack growth model which integrates the effects of plasticity-induced crack closure (PICC) and roughness-induced crack closure (RICC). The PICC-RICC model is combined with estimates crack nucleation life to provide the second total life model herein termed the nucleation-propagation or NP model. The predictions of the IP and NP models are compared and found to be similar. The simpler IP model is then used to explore the potential influence of weld quality, weldment size, base metal strength, and residual stresses on the total fatigue life of weldments.