Fluid/Material Coupled Numerical Simulation of a Bubble Collapse Near a Wall for Laser Cavitation Peening

An impact of a bubble induced by a submerged pulsed laser is utilized for improvement of fatigue strength of metallic materials. As the bubble induced by the pulsed laser behaves like a cavitation bubble, the laser induced bubble is called as "laser cavitation". The mechanical surface treatment using the laser cavitation impact is named as "laser cavitation peening". At laser cavitation peening, the impact induced by laser cavitation collapse strongly depends on the bubble geometry. There are two typical mode at the bubble collapse. One mode is "microjet mode", at which bubble develops near the target and is collapsed with generating a microjet in the bubble. The other mode is "hemispherical mode", at which a hemispherical bubble develops on the target surface and is collapsed on the surface. As the bubble collapse of microjet mode is interesting phenomenon, a lot of researchers investigate "microjet mode". However, impact induced by "hemispherical mode" is significantly larger than that of "microjet mode". In the present paper, to optimize laser cavitation peening condition, a fluid/material coupled numerical simulation of a bubble collapse near a wall was carried out changing with standoff distance from wall. It was revealed that the equivalent stress induced by hemispherical mode was larger than that of microjet mode.