Shot Peening and Fatigue Crack Growth in 7075-T7351 Aluminum

Abstract

Thirty three SENB and nine TPB specimens, which were machined from an 8.1mm thick 7075-T7351 aluminum stock plate, were fatigued in the as-received or shot peened conditions. The SENB specimens were then fractured by overload and were recorded. The crack growth rate of the tunneling crack profiles were measured by fractography at various life cycles. SN curves of the as received and shot peened TPB specimens were also constructed. Peened surface roughness, subsurface microstructure and micro-hardness profiles were examined. X-ray diffraction technique was used to measure the residual stresses in selected shot peened SENB and TPB specimens. The fatigue life under a severe shot peening intensity (Almen scale 0.016A) of the SENB specimens was slightly larger than that of the as received SENB specimens at low stress ratio of R = 0.1 but the difference was found to be smaller at R = 0.8. The SN curves of the as received and severely shot peened TPB specimens were nearly identical. Grain distortion due to peening was observed to a depth of 410µm and was correlated with the measured residual compressive stresses. The compressive residual stress had little effect on the crack growth rates in shot peened SENB and TPB specimens.