Effect of yield locus exponent on draw-in prediction during deep drawing of commercially pure titanium

Abstract

Abstract The Yld2000-2D yield locus is widely employed to model anisotropic plasticity in sheet metal forming. Its exponent, a , critically influences the shape of the yield surface and is typically assigned fixed values based on crystal structure–commonly $$a=6$$ for body-centered cubic (BCC) and $$a=8$$ for face-centered cubic (FCC) materials. However, no universally accepted value exists for hexagonal close-packed (HCP) metals such as commercially pure titanium, which exhibit pronounced anisotropy and complex hardening behavior. This study explores the influence of the value of a on accurately modeling the forming response of commercially pure titanium sheets. To examine the impact of the exponent value a comparison between finite element (FE) simulations and experimental draw-in profiles obtained from cup-drawing tests is performed. To account for evolving anisotropy during plastic deformation, the Yld2000-2D yield locus is further augmented with strain-dependent coefficients, while the loading asymmetry commonly present in HCP metals is neglected. The results show a clear preference for larger exponent values with $$a>9$$ giving the best results. This highlights the necessity of material-specific calibration for HCP alloys and provide actionable insights for improving the predictive fidelity of titanium sheet forming simulations.