Prediction of Forming Limit Diagram Using the Marciniak-Kuczynski Method for Ti-6Al-4V Using Different Material Models

Abstract

The forming limit diagram (FLD) is a widely used tool to assess the formability of a metal sheet [1]. The current study aims to investigate the influence of strain rate, material anisotropy and hardening on the FLD of Ti-6Al-4V predicted by the well-known Marciniak-Kuczynski (M-K) method. The tensile data of quasi-static (8 10-5 s-1), intermediate (0.5 s-1) and dynamic experiments (approximately 1000 s-1) on Ti-6Al-4V sheet are available at three different orientations, with respect to the rolling direction: 0°, 45° and 90°. Different hardening models are taken into account. Also, von Mises and Hill yield criterion are considered. The results show that the influence of the hardening law on FLD is significant. In particular, the most conservative limit strains are predicted by the Voce law because of its saturation characteristic. The yield criterion is found to only affect the right part of the FLD. Regarding the strain rate influence, the left part of the FLD is mainly dominated by the amount of uniform elongation, while the right part is strongly dependent on the yield function used. Therefore, for this region the effects of strain rate and yield function are difficult to distinguish. Finally, the effect of material anisotropy on the FLD is significant. Under quasi-static conditions, the Lankford coefficient seems to be the driving factor in uniaxial and equibiaxial deformation. However, in plane strain conditions the effect of the strain hardening exponent is dominant.