Investigation on the non-homogeneity of residual stress field induced by laser shock peening

Laser shock peening can impart compressive residual stresses in the target material, which is an innovative surface treatment technique similar to shot peening. But when laser intensity exceeds a threshold, the lower residual stress at the center of the laser shocked zone compared to those away from the center will be induced. This phenomenon is closely related to the rapid and complex response of target material during the treatment. A complete numerical model, as an effective way to investigate the shock-solid interaction, is conducted to simulate the process and is experimentally validated by the surface deformation of target material subjected to multiple impacts. Dynamic responses of target material including surface displacements, stresses and strains, are analyzed in detail based on the model. The residual stress drop at the center is found to be induced by the reverse plastic loading due to the boundary effect of laser shock. And adopting square laser spots should attenuate the simultaneous focalization of release waves and decrease the residual stress drop.