Deceleration and acceleration of crack propagation after an overload under negative baseline stress ratio

In a previously reported study, it was found that the fatigue crack growth rate actually accelerated after a tensile overload under a negative value of baseline stress ratio R. This type of crack propagation behavior is related to the change in the compression residual stress to tensile residual stress distributed in the vicinity of the crack tip upon unloading to minimum load after an overload. In the present investigation, focused on the negative stress ratio, it was found that the deceleration and acceleration of crack propagation were associated with crack opening displacement at the overload point and the conditions of applied baseline cyclic stress. The fatigue crack growth rate decelerated after being overloaded at a positive R value. However, that rate accelerated rather than decelerated in some stress conditions at a negative R value. Therefore, the residual fatigue life after overloading became longer or shorter, depending on the overload level and baseline stress conditions.