Investigation on the influence of combined shear loads on the forming limit for high strength steels

The knowledge of material behaviour under certain load conditions, occurring in metal-forming processes, urgently calls for the development of robust production processes. For characterisation of materials behaviour in metal forming processes in the automotive industry, Forming Limit Diagrams (FLD) are mainly used to characterise formability under certain in-plane load conditions . But in industrial forming processes not only in-plane- loads, but a mixture of in-plane, bending, pure-shear and combined shear-and tensions loads can occur. But today there is a lack in testing equipment for those combined load conditions because with conventional testing set-ups no superposed shear rates can be realized. For this purpose three novel sample geometries are presented in this article. Further first experimental results show the application of the specimen geometries. On the one hand maximal achievable strains under combined shear and tension loads are measured and on the other hand a first approach to get real stress-strain curves is shown.