Experimental and numerical investigation of forming limit diagram of Al/Cu two-layer sheet in high strain rate forming process

The formability of a two-layer sheet in the electromagnetic forming (EMF) process is investigated through experimental and numerical methods. The Al/Cu two-layer sheet is fabricated by using an explosive joint in the EMF process. By using the diameter changes in surface grids of specimens with various widths the forming limit diagrams used in necking and fracture conditions are calculated. The acceleration of the major strain method is used to predict the necking time in the simulation. The J-C damage constants were calibrated by using the surface response method with a 95% model fit. The Al/Cu two-layer sheet has a higher formability in the EMF process than in a static condition. The Al/Cu two-layer sheet's formability increases when the Cu is in the outer layer. The Cu layer has a higher formability than the Al layer and has a protective role against necking. The fracture forming limit diagram is linear and has a negative slope. The fracture strain in the in-plane strain condition in the AC lay-up is 36% greater than the CA lay-up, due to Cu's better resistance to fracture in tensile stress.