Relaxation process of residual stress induced by laser peening

Akita, Koichi; Miyashita, Daisuke*; Takeda, Kazuya*; Oya, Shinichi*; Shobu, Takahisa  ; Sano, Kenji*; Saito, Toshiyuki*

Relaxation process of surface compressive residual stress during tensile or compressive loading on a laser peened aluminum alloy was investigated. The residual stress was measured by X-ray, synchrotron and neutron diffractions and analyzed by a finite element method. The relaxation process clarified in this study was described as follows. When the tensile loading was increased, plastic deformation was occurred at the tensile residual stress region that existed inside of the material to be balanced with the surface compressive residual stress. On the other hand, when the compressive loading was applied, the plastic deformation was started at the maximum compressive residual stress region located just beneath the surface. Because the plastic deformation of the inside of the material induced the redistribution of the residual stress in the sample, the surface compressive residual stress was relaxed prior to the surface yielding.