The forming limit diagram (FLD) is widely used to evaluate the formability of sheet metals. Past studies revealed that texture and work-hardening behavior of sheets play important roles in FLDs. However, few detailed comparative studies on the effect of texture and work-hardening behavior have been conducted using actual materials. Moreover, the underlying mechanisms have not yet been clarified. In this study, two 5000 series aluminum alloy sheets with similar textures and different work-hardening behaviors were used to experimentally and numerically investigate the effects of texture and work-hardening behavior on the FLDs. The FLDs were evaluated using the Nakajima test in the experiments and the Marciniak–Kuczyński (MK) approach combined with a crystal-plasticity (CP) model in the simulations. The experiments and simulations showed that the slope in the first quadrant of the FLDs was higher for the sheet with a smaller work hardening. To evaluate the effect of the work-hardening behavior on the FLD independently of the texture, numerical experiments using the virtual sheets were conducted. The results showed that the texture difference between the two sheets had negligible effects on the FLD, exhibiting that the work-hardening difference played significant roles in the differences in the FLDs in this case. Moreover, the influence of work-hardening behavior on the FLDs, particularly in the biaxial tension state, was examined using the forming limit stress criterion. • Slope in the first quadrant of FLD was steeper for sheet with lower work hardening. • Numerical experiments show a stronger effect of work hardening compared to texture. • Work hardening near limit strain was lower in biaxial tension than other states. • Lower work hardening requires larger strain for reaching forming limit stress.
SATO et al. (Sun,) studied this question.