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 (ΔK-ΔKth)α(ΔK-ΔKth)α where α 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 ΔKth 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.