Calculating crack growth from small discontinuities in 7050-T7451 under combat aircraft spectra

This paper supplements previous work which showed that the crack growth rate in a large range of metallic materials fitted a variant of the Hartman-Schijve equation where da/dN is a function of (Delta K - Delta K-thr)(alpha), where Delta K-thr is a parameter that reflects the apparent fatigue stress intensity threshold of the material, and alpha is approximately 2. For the case of 7050-T7451 aluminium alloy the same equation is shown to fit both long and short crack growth data once the appropriate Delta K-thr is chosen for each specific data set. This equation is used here to produce accurate predictions of the fatigue crack growth in 7050-T7451 aluminium alloy specimens with both a low and high stress concentration subjected to two combat aircraft loading spectra. Thus, it is postulated that if long crack data are fitted to the variant of the Hartman-Schijve equation then accurate predictions can be made in the short crack regime for a wide range of materials. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.