Influence of non-proportional load paths and change in loading direction on the failure mode of sheet metals

Many studies have shown that failure following non-proportional load paths cannot be predicted by a linear Forming Limit Curve (FLC), as the deformation history and a change in loading direction influence the formability and failure mode. In this paper, the different failure modes due to different load paths are investigated, for the first time, by conducting Nakajima tests with pre-formed specimens. The main objective of the investigation is to better understand the influence of pre-forming and change in loading direction on the formability. To predict this behaviour, regardless of the failure mode, the Generalized Forming Limit Concept (GFLC) is extended.