Experimental and numerical study on fragmentation mechanism of copper sheet in laser dynamic forming

Abstract

The fragmentation mechanism of copper sheet in laser dynamic forming (LDF) process is investigated. The investigation of the fragmentation mechanism in the moving sample is quite difficult, so finite element method is adopted to provide detailed information on the stress state during micro-forming. The shock loading was generated using laser-shock-rubber loading technique in which a layer of rubber is inserted to improve laser shock efficiency. When laser power density is 0.491 GW cm⁻², the obvious circular fragmentation is located at the center region of rear surface. When laser power density is 0.658 GW cm⁻², the diameter of the fragmentation region increased, and what's more, circumferential and radial cracks were formed in the fragmentation region. The void linkages and terrace-like pattern were also observed. Finite element model reveals that the fragmentation in the moving sheet is not caused by the initial rubber direct loading, but the deceleration at the last stage of forming. Because the curvature in the tip has the highest value at the stopping point, deceleration passes through its maximum value and then causes fragmentation at the last stage of forming. When laser power density is 0.658 GW cm⁻², the single layer fragmentation, multiple layer fragmentation, circumferential crack, and radial cracks occur in that sequence.