Effects of Deformation in the Vicinity of Crack Tips on Crack Propagation after Applying Overload -Acceleration of Crack Propagation after Applying Overload-
Chobin MAKABE, Anindito PURNOWIDODO and Arthur J. McEVILY
Abstract:It is well known that a tensile overload applied during constant amplitude cycling at a positive stress ratio R can lead to retardation in the rate of subsequent crack propagation. However, in a case of a negative stress ratio R, 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 confirm the relationship between the crack blunting behavior and the crack propagation behavior, the effect of two overloads' application (first one was tensile overload and second one was compression overload) on crack propagation was investigated. It was found from this that the acceleration of the crack propagation occurred when the range of crack tip opening displacement became large level during overload stage. Key Words:Fatigue crack propagation, Overload, Stress ratio, Retardation, Acceleration, Blunting of crack tips, Bulging, Residual stress