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Effect of Shot Peening on Fatigue Crack Growth in 7075-T7351 Pages: 14 Published: Jan 2007
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View License Agreement Source: STP1497-EB Abstract The effects of shot peening on fatigue crack growth in 7075-T735 single-edged notch bend (SENB) and three point bend (TPB) specimens are discussed. Fifty-one total fatigue tests were conducted with SENB and TPB specimens, which were machined from an 8.1 mm thick 7075-T7351 aluminum stock plate. All specimens were tested in the as-received or shot peened conditions, with crack perpendicular to the rolling direction, i.e., in the L-T direction. Fatigue tests of SENB specimens were conducted at a constant maximum load, stress ratios of = 0.1 or 0.8, and to a pre-determined fatigue cycle or to failure. Crack growth rate was determined from the tunneling crack profile or by fractography. Peened surface roughness, subsurface microstructure, and micro-hardness profiles were also examined to evaluate their effect on crack growth rate. The TPB specimens were fatigued to failure at stress ratios of = 0.1 or 0.8 and a S-N diagram constructed. Both the SENB and the TPB test results showed that severe shot peening (0.016A) slightly increased the fatigue life at low stress ratio of = 0.1 but was found to be negligible at a high load ratio of = 0.8. The stress concentration factor due to dimples generated by severe shot peening was estimated to be 1.14 and had negligible effect on the fatigue life. Grain distortion was observed to a depth range of 130410 m indicating the depth of the residual compressive stress layer developed for peening intensities of 0.0040.016A, respectively.
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