Corrections to B-models for fatigue life prediction of metals during crackpropagation

In this paper a new model for the prediction of the Cumulative Distribution Function (CDF) of fatigue life of structural elements during the crack pro pagation stage is described. This problem is considered as a cumulative dam age process following the probabilistic approach of Bogdanoff and Kozin [1] (B-models). The initial and final crack lengths, the crack propagation ang le, the material fracture and elastic parameters and the external loads may be considered as random variables. In this initial approach, a linear appr oximation of the random variable 'fatigue life' and a truncated uniform dis tribution for the crack length variable are considered. Two corrections to this model are discussed: a second-order approximation of the fatigue life to compute its variance, and a modification of the Probability Density Dist ribution (PDD) of the crack length, which is now derived from the truncated uniform distributions of the initial and final crack lengths. Some example s for mode I are compared to the ones obtained using a Monte Carlo scheme w ith 400 000 samples, showing a good agreement and a much better performance of the corrected version of the model, specially for big standard deviatio ns. Copyright (C) 1999 John Wiley & Sons, Ltd.