Chapter 5: Three-Dimensional Simulation of Single and Multiple Laser Shock Peening

5.1 Introduction

When a round laser spot is used for LSP, it may lead to a lack of compressive residual stress in the central area of the treated zone, as confirmed by experimental studies and simulation in the previous chapter. To avoid this drawback, a square laser spot can be used. The objective of this chapter is to evaluate the residual stress distribution in a metal alloy induced by single and multiple LSP with a square laser spot using the three-dimensional (3D) dynamic finite element method (FEM). The predicted residual stresses for single LSP are correlated with those from experiments and from an analytical model. The studies are focused on improving the understanding of dynamic stresses in the metal alloy during LSP as well as the effects of some essential factors on the residual stress field, such as laser spot size, pressure magnitude and duration, and number of LSP impacts.

5.2 Experimental

In the experiment of Ballard and his colleagues (Ballard et al., 1991), the surface of a metal specimen (35CD4 50HRC steel) was irradiated by a square laser spot of 5 5 mm with laser power density of 8 GW/cm ² and duration of 30 ns. The specimen surface was coated with black paint and the plasma was confined by a water overlay. The residual stress in the depth and on the surface of specimen was measured by means of X-ray diffraction, using successive electrolytic polishing.

For the purpose of evaluation, the material is assumed to be...