A cyclic resistance curve approach to estimating fatigue limit in the presence of over- and underloads

Tensile overloads (OL) and compressive underloads (UL) can have a significant effect on fatigue crack propagation and fatigue limit. This article provides a simple method for quantitatively estimating the fatigue limit in the presence of sporadic over- and underloads via a cyclic resistance curve (R-curve) analysis. Finite element modeling results show that both loading spikes can effectively reset the R-curve by removing crack closure. It is shown that recurrent application of either loading spike can significantly reduce the effective fatigue limit. The saturation value of the effective fatigue limit is governed by the intrinsic threshold ∆ K th,eff and the rate of saturation depends on the loading spike type.