Author:

Abstract:

The analysis of the clinch forming operation, commonly referred to as press-joining, with the aid of finite element techniques requires flow stress data and values of friction at the tool-sheet interface and between the combining metal sheets. As the forming involves severe local plastic deformation, up to plastic strains of the order 3, the stress-strain curve, obtained from standard tensile tests, has to be extrapolated by fitting a certain hardening law. The adopted extrapolation method strongly determines the error on the load-displacement curve during clinch forming simulation. On the other hand, the interface friction affects the material flow determining the final interlock, and, as a consequence, the strength of the connection. In this paper we present a punch compression test for sheet metal using circular specimens in combination with a gradient based optimization strategy. This test enables the identification of interface friction and material behaviour simultaneously. The flow curve is incrementally constructed using a multi-linear elasto-plastic material model, thereby eliminating the need for choosing the type of hardening a priori. ©2009 Society for Experimental Mechanics Inc.