Applying a Physics-Based Description of Fatigue Variability Behavior to Probabilistic Life Prediction (Preprint)

摘要

We describe fatigue lifetime variability as the separation/overlap of a crack-growth-controlled life-limiting mechanism and a mean-lifetime dominating behavior. We implement this description through a bimodal probability density representing the superposition of the crack growth and the mean-lifetime dominating densities. With the help of an a+b titanium alloy it is shown that the effect of microstructure, temperature, and loading variables on lifetime variability can be realized in terms of the degree of influence of these variables on the two densities affecting their separation and therefore, the total variability. We suggest that this behavior may be related to the development of a range of heterogeneity levels in a material at any given loading condition, which appears to present some probability of a predominately crack-growth controlled mechanism. A procedure, based on the new description of fatigue variability, for predicting the probability of failure from relatively small number of experiments is discussed.