Laser shock processing of materials: characterization and application of the process

The main objective of this work was first to set-up the basic principles of LSP, then to characterize and control the laser-induced surface stress loadings and lastly, through different `material' applications, to evaluate its potential as competitive surface treatment. In a first part, all the general aspects about LSP are presented, from the physical shock wave generation mode in water confined regime to the mechanical modifications conventionally induced in metals like plastic strain and compressive stresses. In a second part we focused on an experimental characterization of the process to highlight the influence of several process aspects on the stress wave generation: with the use of a velocimeter system (VISAR) for measuring back free velocities behind thin targets, different parameters were investigated like coating effects, laser spot size effects or plastic flow limit determination at very high strain rate (106 s-1) for most of the materials investigated. THe next part of the paper concerns the mechanical changes induced within targets by LSP in water confinement regime. Experimental results are shown for residual stress fields, surface roughness or work-hardening level increases focusing on 55C1 steel. Based upon these results, general trends are drawn concerning the mechanical changes of surfaces with LSP as a function of shock parameters. Lastly, recent fatigue results obtained on 55C1 investigated under different shock conditions displayed some 30% increases on the bending fatigue limits at R equals 0.1. As a conclusion, the recent developments of LSP are discussed, mainly dealing with the use of new high cadency excimer lasers for shock processing which seem to provide the most convenient configuration for industrial applications.