Compressive residual stress generation process by laser peening without pre-coating

Abstract

Laser peening without pre-coating has been applied to water-immersed specimens of high tensile strength steel. In order to understand the generation process of compressive residual stress, specimens with various laser irradiation patterns, i.e., single spot, line scanning and area scanning, were prepared. Detailed distributions of residual stress on the specimens were measured using synchrotron radiation. Large tensile residual stresses, which might be caused by the thermal effect of the laser pulse, were observed in the center region on the single spot. It decreased towards the edge of the spot, and changed to compression around the spot. The compression became larger with the increasing pulse numbers irradiated on the same spot. In the line scanning, a tensile residual stress was observed in the final spot of the line, which decreased and changed to compression as the distance from the final spot increased. The residual stress on the area scanning was compression as a whole. It was estimated that the compressive residual stress in the area scanning would be generated from the overlapping effect of the compressive field made around each laser spot. The residual stress generated by laser peening without pre-coating is considered to be the superimposition of the tensile and the compressive components due to thermal effect and plastic deformation, respectively.