Yunrui Li, Wanlin Guo

International Journal of Fatigue   ，2026，109581

Abstract: The fatigue crack growth behavior in the near-threshold regime, which is typically characterized using load-reduction test methods, significantly influences the high-cycle fatigue life of engineering structures, but the effect of load-amplitude changes has often been overlooked. In this study, we analyze the fatigue crack growth rate da/dN versus the stress intensity factor range (ΔK) obtained from load-reduction tests using a three-dimensional variable-amplitude fatigue crack growth model. By explicitly modeling the evolution of crack closure during load-reduction histories and recalculating the effective ΔK (ΔKeff), a parametric model describing the crack closure ratio U (=ΔKeff/ΔK) and the percentage reduction of ΔK relative to its initial value at the start of load reduction is developed. This model enables convenient correction of the increases, at least, of the plasticity-induced crack closure caused by load reduction, and mitigates the fanning behavior commonly observed in near-threshold crack growth. The recommended percentage reduction ranges of ΔK for typical aerospace alloys under high stress ratios are finally proposed to make better use of the load-reduction method within ASTM Standard E647 for fatigue crack growth threshold determination.

Link: https://www.sciencedirect.com/science/article/pii/S0142112326001015