A new test for sheet metal asperity flattening under varying subsurface strain conditions

Friction in sheet metal forming is largely determined by asperity flattening and the real contact area between sheet asperities and tool surface. This paper presents a new experimental test, which enables the investigation of asperity flattening under varying sub-surface strain ratios with or without the application of lubrication. The test is based on the Marciniak-Kuczynski test for inducing in-plane strains, while an asperity region in the centre is subjected to normal loading. The test was deployed to investigate model asperity flattening due to normal loading combined with controlled linear in-plane strain paths with and without the presence of liquid lubrication.