Analysis of the extended stress-based forming limit curve considering the effects of strain path and through-thickness normal stress

• A modified M–K method for computation of extended stress-based FLC is proposed.
• The effect of strain path on the predicted extended stress-based FLC is reexamined.
• This new criterion is much less strain path dependent than the conventional FLC.
• Through-thickness compressive normal stress is also considered in analysis.

In this study, an approach based on the modified Marciniak–Kuczynski (M–K) method for computation of an extended stress-based forming limit curve (FLC) is presented. The extended stress-based FLC is built based on equivalent plastic stress versus mean stress. This curve has some advantages in comparison with the conventional FLC. This new criterion is much more strain path independent than the conventional FLC. The effect of strain path on the predicted extended stress-based FLC is reexamined. For this purpose, two types of pre-straining on the sheet metal have been loaded. Moreover, the plane stress state assumption is not adopted in the current study. The influence of a through-thickness compressive normal stress is also investigated theoretically. The verifications of the theoretical FLCs are performed by using some available published experimental data.