Effect of Confinement Layer on Laser Ablation and Cavitation Bubble during Laser Shock Peening

Abstract

Laser shock peening (LSP) is one of surface treatments to induce residual compressive stresses near metal surface to improve the resistance of materials to surface-related failures, such as fatigue and stress corrosion cracking. In LSP process, short pulsed laser is focused and irradiated to the material covered by transparent overlay such as glass or water. This transparent overlay is also known as a confinement layer and has an important role to increase impact pressure during LSP process. When confinement layer is liquid, the characteristics of the layer such as temperature, viscosity, etc. affect the phenomena occurring during the peening process and undoubtedly influence the induced residual stress. In the present study, Acoustic Emission (AE) technique coupling with high speed camera was applied to study the effect of confinement layer on LSP process. The results were discussed using the impact force calculated by inverse analysis of detected AE waveforms and bubble parameters observed by high speed camera. The results showed that temperature, thickness and viscosity of confinement layer had strong influence on the generation and collapse of cavitation bubble. The optimization of process parameters could be obtained by AE technique.