Experimental and numerical investigation of the formability of an ultra-thin copper sheet

The aim of this study is to investigate the forming limits of an ultra-thin copper sheet (0.1mm thickness) that is used for connection applications. The first step consists in characterising the mechanical behaviour under different strain paths, up to necking and final rupture, such as uniaxial and biaxial tension, in order to investigate the largest range of triaxiality ratios for this material. Nakazima tests are performed on specific samples with a designed-on-purpose device in order to determine experimentally the onset of rupture. Strain distribution over the surface in tension is measured with digital image correlation technique. The forming limits are characterised experimentally for different strain paths and compared to predictions given by macroscopic fracture criteria. It is shown that when the macroscopic criterion involves a sufficient number of parameters, it is able to predict limit forming curves with a reasonable accuracy.