Study on Improvement of Fatigue Strength Reliability in Machine and Structure by Laser Peening Treatment

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It is useful for the reducing of weight, energy, materials and the high efficiency to improve the fatigue strength reliability of machines and structures by giving high functional property. In the present research, the laser peening (LP) treatment is performed on machines and structural materials, and it is the porpose of the research to improve the fatigue strength reliability in the materials and to make clear the mechanism of the improvement The laser treatment of low energy YAG laser without protective coating is wsasused in water The materials used in the research a were austenitic stainless steels for nuclear plant structures, cast aluminum alloy for automobile parts and high strength tool steels.The main conclusions obtained in the research are as followings1. In all of the materials used in the research, it is confirmed to improve the fatigue strength by the LP treatment. And it is clear that the improvement effects were induced from compressive residual stress and the strain hardening in the surface layer of materials by the LP treatment.2. The restrained effects for fatigue crack propagation process were confirmed for the pre-cracked materials by the LP treatment And, the effects were induced from the compressive residual stress and the crack closure effect by plastic deformation near crack tip by the LP treatment.3.By the micro computed tomographic (μ CT) imaging technology with syncroton radiation equipment, surface fatigue cracks were successfully visualized non-destructively and three-dimensionally.