Fatigue crack growth in a diverse range of materials

This paper generally examines long crack growth data for a range of aerospace and rail materials tested at a variety of R ratios. The results of this study revealed that, for the 22 materials studied, the crack growth rate, da/dN, could be represented by a variant of the Hartman and Schijve equation with da/dN being proportional to the quantity (Delta K - Delta K-th)(alpha) where alpha is approximately two. For cracking in 7050-T7451 it was also shown that this formulation holds for both long and small cracks, although a different value of Delta K-th was required for small cracks compared to that required for long cracks. A possible explanation for this discrepancy is proposed and a methodology to estimate the small crack behaviour based on long crack data is presented. As such these observations have the potential to simplify the prediction of fatigue crack growth lives. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.