Characterization and modeling of evolving asymmetric/anisotropic hardening of CP-Ti sheet under monotonic and reverse loading

Commercial pure titanium (CP-Ti) is attracting extensive applications in high-end manufacturing industries, because of its high strength-to-weight ratio, excellent corrosion and fatigue resistance. However, due to its hexagonal close-packed structure and multi-pass processing history, However, the hexagonal close-packed structure and multi-pass processing history jointly lead to CP-Ti sheet aexhibits significantstrong tension-compression (T-C) asymmetry, anisotropy and Bauschinger effect in plastic deformation. Especially, the coupling interaction of T-C asymmetry in proportional loading and Bauschinger effect in reverse loading makes the hardening effects and its evolutions behaviors of CP-Ti sheet drastically complicated and more difficult to model for in complex loading scenarios. Aiming at theis challenging issue, this study firstly designed the monotonic tension/compression experiments, tension-compression and compression-tension experiments have been performed to comprehensively explore the hardening responses and their evolution characteristics of CP-Ti sheet under various loading paths and their evolution characteristics. On this basis, a constitutive modeling framework is proposed to describe the evolving asymmetric/anisotropic hardening behaviors considering proportional and reverse loading paths. In this model, the hardening behaviors are classified into three modes, viz., monotonic loading (ML), reverse tension (RT) and reverse compression (RC), and a criterion is constructed to judginge and activate the corresponding loading modes in actual deformation. In addition, the Yoon (2014) yielding criterion is employed to describe the asymmetric/anisotropic subsequent yielding at different strain levels for each loading mode, and a discontinuous multi-surface approach associated with non-associated flow rule is used to model the distorted evolution of yield surfaces. Finally, the developed model is calibrated, verified and numerically implemented, and further applied in simulation of V-/U-type bending cases with an improved prediction accuracy of deformation behavior and springback.