Novel Semi-Empirical Model for Forming Limit Prediction of Sheet Metal Material with Regard on Effects of Shear-Tension Loads

Abstract

The use of lightweight materials offers substantial strength and weight advantages in car body design. For characterization of capability of sheet material dedicated to deep drawing processes in the automotive industry, mainly Forming Limit Diagrams (FLD) are used. However, investigations conducted at the Institute for Metal Forming Technology using new specimen geometries have shown that formability of High Strength Steel Sheet Material changes by superposing shearing on in-plane tension loads. Hence, these mixed stress and strain conditions including shearing effects can occur in deep-drawing processes of complex car body parts. But these changes in materials formability nowadays cannot be described sufficiently by using conventional FLC-criterion. Considering such aspects in defining suitable failure criterions a new semi-empirical model has been developed considering the effect of shearing in sheet metals formability. This novel model is capable to separate shear and in-plane tension loads by using a special strain definition. For experimental calibration of so called Shear Forming Limit Curve (SFLC) several standardized and enhanced material testing procedures with novel specimen geometries are necessary. In this contribution firstly the need of enhanced material description and additionally the theory SFLC-Model is presented. For experimentally calibration required input parameters are determined by special specimen geometries.