A statistical approach for predicting the crack retardation due to a single tensile overload

In this study, in order to investigate crack retardation behavior and the variability of retardation cycles, crack growth tests are conducted on 7075-T6 aluminum alloy under a single tensile overload. A retardation coefficient D is introduced herein as the ratio of the crack growth rate under constant amplitude loading and the crack growth rate after an overload. This coefficient D is separately formulated according to the retardation behavior composed of the delayed retardation part and the retardation part. To describe the variability of crack growth, the statistical crack growth equation was developed by modifying the Forman equation and adding a random variable Z to it in a previous study. By using the definition of the retardation coefficient and the statistical crack growth law, retardation cycles after an overload are predicted. The prediction by this method presents the representative retardation behavior and agrees with the experimental data. Especially, this method predicts the distribution of retardation cycles very well.