The residual stress introduced by laser shock peening (LSP) is one of the most important factors in improving metallic fatigue life. The shock wave pressure has considerable influence on residual stress distribution, which is affected by the distribution of laser energy. In this work, a titanium alloy is treated by LSP with flat-top and Gaussian laser beams, and the effects of spatial energy distribution on residual stress are investigated. Firstly, a 3D finite element model (FEM) is developed to predict residual stress with different spatial energy distribution, and the predicted residual stress is validated by experimental data. Secondly, three kinds of pulse energies, 3 J, 4 J and 5 J, are chosen to study the difference of residual stress introduced by flat-top and Gaussian laser beams. Lastly, the effect mechanism of spatial energy distribution on residual stress is revealed.

In this paper, the effect of residual stress on the stress–life (S–N) curve and fracture morphology characteristics of Ti6Al4V titanium alloy after laser shock peening (LSP) without protective coating was experimentally investigated. The fatigue test and residual stress measurement were conducted on specimens before and after the LSP process. It was shown that LSP produced a high-amplitude compressive residual stress field on the surface of the specimen. After the LSP process, the fatigue life limit was increased by 16%, and the S–N curve shifted upward. Then, based on the theory of mean stress, the mechanism whereby the compressive residual stress improves the fatigue life of Ti6Al4V titanium alloy was analyzed. It indicated the improvement in fatigue life was because of the high-amplitude compressive residual stress on the surface and in depth induced by LSP to reduce the tensile stress produced by external loading. In addition, the scanning electron microscope (SEM) pattern of fatigue fracture demonstrated distinct differences in the fracture morphology before and after LSP. After LSP, the crack initiation sites of the samples moved to the subsurface where it was difficult for fatigue cracks initiating here. Moreover, after the LSP process, there were high density of fatigue striations and many secondary cracks on the fracture of the treated specimen.