Effect of Negative Stress Ratio on Fatigue Crack Propagation Behavior after Single Tensile Overload

It is well known that a single tensile overload applied during constant amplitude cycling at a positive stress ratio causes the crack growth retardation. In a case of a negative stress ratio R, however, the fatigue crack growth rate actually accelerated after a tensile overload. This crack propagation behavior is related to the local bulging of specimen thickness, the blunting behavior of crack tips and the residual stress distributions. When the crack tips were blunted during tensile overload and the succeeding compression stress with a high value was applied after the overload, the crack propagation rate got higher level than that before the overload application. In this case, a tensile residual stress was created in front of the crack. To investigate the effect of the negative stress ratio on the fatigue crack propagation, the fatigue tests under R=0, -1 and -1.5 applying the single tensile overload were performed using annealed 0.15% carbon steels. In the present study, a residual life after an overloading was specially investigated, and it was found that the transition phenomenon of the residual life was appeared in the case of the negative stress ratio