Relaxation behavior of laser-peening residual stress under tensile loading investigated by X-ray and neutron diffraction

Akita, Koichi; Hayashi, Kengo*; Takeda, Kazuya*; Sano, Yuji*; Suzuki, Hiroshi  ; Moriai, Atsushi; Oya, Shinichi*

Compressive residual stresses induced by peening techniques improve the strength properties of steels, such as fatigue and stress corrosion cracking. However, the compressive residual stress might be reduced owing to thermal and mechanical loading in-service. In this study, the behavior of surface and internal residual stresses of a laser-peened ferritic steel under quasi-static tensile loading was investigated by X-ray and neutron diffraction. The complementary use of these diffraction techniques provided decisive experimental evidence for elucidating the relaxation process. The critical applied stress of peened samples subjected to a tensile loading can be estimated from the von Misses yield criterion with the maximum tensile residual stress inside the sample.