Study On The Fatigue Property Of Aluminum Alloy Treated By Laser Shock Processing

Laser shock processing (LSP) is an innovative surface treatment technique, which uses compressive residual stress to improve material performance. Aluminum alloys have high ratio of strength/density and are widely used in the fields of aircraft industry and other industries. Therefore, it has important significance to know the effects of LSP on fatigue property of them.In this paper, the residual stress field induced by LSP and its effect on fatigue property were systematically studied by experimental and analytical methods.A finite element model (FEM) was built to simulate the residual stress field of 7075-T651 by explicit nonlinear dynamic analysis. Some key problems were discussed in detail. The influence of peak pressure and the number of impact on residual stress field were investigated in order to optimize LSP parameters. Experimental validations were performed, and the results indicate this model could predict the residual stress field induced by LSP accurately.A methodology was developed on the basis of generation mechanism of residual stress to predict the residual stress resulting from LSP in specimen with common geometric feature. This methodology uses the pre-strain produced by LSP coupled with a FEM of the specimen geometry to predict residual stress. Verification of the model was performed on a simple rectangular block, the present model results agree well with available data. The model then was used to predict the residual stress generated in a specimen with a corner fillet, and it shows that the geometrical effects of the specimen greatly influenced residual stress field.LSP was performed on fatigue testing specimens with optimized parameters. The fatigue improvement with respect to the as-machined condition was discussed accounting for residual stress. In particular, the extent of the residual stress relaxation during loading was investigated. A model was proposed on the basis of crack growth analysis to predict fatigue life of shocked specimen, with considering a time varying residual stress function. The predicted results were found correlated well with experimental results.