Enhancement of fracture strain during abrupt orthogonal strain- path changes in ferrite/martensite dual phase steel

Abstract

Abstract In multistage press forming, the scrutiny of work-hardening behavior attributed to abrupt strain path changes in deformation paths has been pivotal in the context of press formability. However, applying this method to stretch flanging presents a formidable complexity. In such scenarios, substantial deformations resulting from shear-cut processing and subsequent stretch-flange formation significantly influence the local fracture strains, a critical determinant of process success. Therefore, our investigation examined the impact of deformation path variations on the fracture strain of dual-phase steel sheets. A crucial facet of our experimental approach involved manipulating the strain level during the initial tensile deformation. Tensile deformation was extended beyond the onset of necking, culminating in the emergence of microvoids within the material. Following this preliminary extensive strain, successive tensile tests were conducted on diminutive round-bar specimens, subject to a 90º change in the deformation path, to investigate their influence on work hardening and fracture strain. The outcomes of the diameter-measuring tensile tests unveiled a pronounced cross effect during the early stages of deformation, particularly concerning work-hardening behavior. However, as the deformation advanced, the results conformed to the stress-strain curve observed in the same direction of tension. Notably, the fracture strain exhibited an approximately 10% enhancement attributable to the abrupt strain path change, thereby having the potential to augment the practical stretch flangeability.