Statistical model for fatigue crack growth under random loads including retardation effects

A model for the statistical analysis of crack growth under random loading that includes the loading sequence effect is presented. The model defines and incorporates an equivalent closure stress that is included in the fatigue crack growth law via the effective stress intensity factor. The equivalent closure stress for each loading process is obtained from the probability density function of peaks p(S) in the random loading process, the properties of the material and the specimen geometry. The model was applied to the analysis of crack growth life under random loading on sheets of two different aluminum alloys: 2024-T351 and 2219-T851. The crack-growth lifetimes thus obtained were consistent with experimental data and with the results obtained by using a cycle-by-cycle simulation scheme.