Published: Jan 2007
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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 R = 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 R = 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 R = 0.1 but was found to be negligible at a high load ratio of R = 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 130–410 μm indicating the depth of the residual compressive stress layer developed for peening intensities of 0.004–0.016A, respectively.
fatigue, aluminum 7075-T7351, shot peening, residual stress, surface roughening
Senior Researcher, National Institute of Industrial Safety, Kiyose, Tokyo,
Professor, Department of Mechanical Engineering, University of Washington, Seattle, WA
Kobayashi, A. S.
Emeritus Professor, Department of Mechanical Engineering, University of Washington, Seattle, WA