On the relationship between statistical distributions of defect size and fatigue life in 7050-T7451 thick plate and A356-T6 castings

The relationship between the distributions for the size of fatigue-initiating defects and fatigue life of 7050-T7451 thick plate and A356-T6 alloy castings reported previously in the literature were analyzed. Results showed that (i) the size of fatigue-initiating defects in all four datasets follow the Gumbel distribution, (ii) the fatigue life model based on the Paris-Erdoğan law for crack propagation provides respectable fits to fatigue life data, and (iii) the statistical distribution for fatigue life based on the Gumbel distribution of defect size and the fatigue life model provides excellent fits to all datasets, (iv) this statistical distribution for fatigue life performs better than the lognormal and Weibull distributions commonly used to model variability in fatigue life of aluminum alloys.