Fatigue Crack Initiation—Propagation Reliability Model

A model for translating fatigue (cycles to failure) data into a probabilistic model for strength, suitable for formal reliability analysis, is presented. The model explicitly includes both the crack initiation and crack propagation phases. The general strategy is to use a least‐squares analysis, modified by the equivalent prediction interval concept, to establish statistics of the parameters of a simple life law, NSm=A for both initiation and propagation. Thus, the model is thought to be most appropriate for fabricated structures, e.g., welds, where the initiation lives are expected to be relatively short. Features of the model include: (1) Ease of use; (2) accommodation of small sample sizes; (3) correlation between initiation and propagation phases; and (4) development of a probabilistic description of crack size given cycle life.