Stretch-flangeability of twinning-induced plasticity steel-cored three-layer steel sheet

Abstract

In this study, the stretch-flangeability of twinning-induced plasticity (TWIP)-cored three-layer steel (TWCLS) sheet was evaluated, Although the mechanical properties of TWCLS sheet follow the force-based rule-of-mixtures (ROM), the experimental hole expansion ratio (HER) is less than the predicted HER values. The poor HER in TWCLS sheet originates from crack initiation at the fracture zone of the TWIP steel-core. The fracture initiation energy vs. HER in TWCLS sheet reveals that the layered material follows the behavior of the monolithic material when the sound interface is conserved. If the initial defects are removed by a reaming process in the hole, the HER of TWCLS sheet follows the force-based ROM. This result shows that the stretch-flangeability of the layered material can be controlled by managing the volume fraction of parent materials when the sources of extrinsic damage (i.e, interface delamination and defects) are removed.