Effects of Tensile Overload on Crack Initiation Life and Fatigue Crack Growth in Notched Specimens

The high amplitude loads that are usually known as overload have different effects on fatigue behavior of the specimens. These effects depend on overload parameters, specimen geometry and applied time; whether crack exist or not. Single tensile overload was applied before crack initiation. Overloads with different ratios versus the applied load and constant amplitude loads were applied on the V-notched samples made by AA 2024-T3 to characterize the fatigue behavior. Crack growth rule and finite element analysis were employed to predict the sample behavior. Weight function methods were used to determine the effects of induced residual stress on effective range of stress intensity factor, Delta K-eff. There were good agreement between predicted and experimental results which proved the capability of the used method to predict the fatigue crack initiating from the notch root in presence of the residual stresses. Results revealed that the crack initiation life was improved considerably versus the overload ratio. Also, it was observed that the crack growth life increased by increasing the overload ratio. The improving effect of the overload on the crack initiation stage was found to be remarkably higher than its effect in growth stage.