Strain path dependence of the FLC0 formability parameter in an interstitial free steel

This work aims at studying the influence of the strain path upon the FLC 0 formability parameter, the root of the forming limit curves (FLC). The investigation was conducted in an interstitial free (IF) quality steel. The FLC 0 parameter was evaluated in an intrinsic tensile test in near plane strain (NPS) condition, but following two strain paths. The first one being a uniaxial (proportional) path up to initial necking. The second (non-proportional) path corresponded to applying 15 % nominal plastic strain in one direction (near plane strain) followed by a second deformation applied in the orthogonal direction up to the rupture of the samples. A reduction in the limit strains corresponding to FLC 0 in the non-proportional test has been observed. The forming limit stress curves (FLSC) and the critical values FLSD 0 are also related to these trajectories. A simulation using finite element method (FEM) has been applied to analyze the evolution of stress and strain during the two paths, and the results have been found consistent for both proportional and non-proportional paths. Texture and surface roughness evolution of the sheet were also measured and related to the applied strain paths.