Effects of crystal microstructure on residual stress relaxation

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Peening techniques, such as shot-peening and laser-peening, introduce compressive residual stresses in the surface layer of metallic materials. The compressive residual stress is effective for preventing stress corrosion cracking and fatigue fracture, therefore the peening techniques have been applied to power plant structures. However, the compressive residual stress might decrease due to thermal and/or mechanical loading in service, and it reduces the benefit.In this study, the relaxation behavior of the compressive residual stress due to mechanical and thermal cyclic loading were investigated by in-situ neutron diffraction techniques. Also, the microstructures introduced by shot-peening and laser-peening were observed by an X-ray diffraction line profile analysis, and the relationships between the microstructures and the relaxation behavior of the compressive residual stress were discussed.