Forming limit of hot-rolled high-strength steels considering sheet thickness effect

The forming limit curve (FLC) has been commonly used tool to predict the metal forming cracking in engineering. Whereas, based on the assumption of plane stress state, the formability prediction of thick sheet of hot-rolled high-strength steels is quite different from the experimental measurement. Finite element simulation was used to study the effect of sheet thickness. It is found that extra stress along thickness is introduced between inside and outside the instability region, which become larger increased. Additionally, the visco-plastic self-consistent (VPSC) model and the M-K model are combined to establish the VPSC-MK model for investigating the influence of thickness difference. With reasonable capture of thickness stress, accurate prediction of FLC under different sheet thickness of hot rolled high-strength steel (HR-HSS) is well realized via VPSC-MK model. That is, it is revealed that the sheet thickness effect for HR-HSS mainly origins from normal stress induced during necking process.