On predicting small fatigue crack growth and fatigue life from long crack data in 2024 aluminium alloy

Small fatigue crack growth data for cracks growing from constituent particles under constant amplitude loading are presented for the aluminium alloy 2024-T351. Confidence bounds are obtained for the small crack growth rate data. Fatigue crack growth and fatigue life are predicted using a stochastic choice of growth rate from within these bounds for successive increments of crack growth. A pragmatic approach is adopted to extend the analysis so that fatigue life prediction can be made from long crack growth data. Comparisons are made between fatigue lives reported in the literature for plane and notched samples and predictions obtained using the present analyses. Reasonably good agreement is obtained for both the shortest fatigue lives and for the spreads in fatigue lives.