A novel plasticity model for characterizing Lode parameter dependence on the differential yielding and hardening behaviors of Ti6Al4V alloy over a wide range of stress states

This study investigates and models the effect of Lode angle on the yielding and hardening behaviors of a forged Ti6Al4V alloy across a wide range of stress states. The as-received material was firstly demonstrated to exhibit no orientation effect. Subsequently, a total of 14 specimen types, including uni-axial tension, compression, simple shear, three notched round bars, three grooved plates and five newly designed tension-shear coupling specimens, were tested under the equivalent strain rate of 0.001 s⁻¹. Utilizing an iterative inverse method, equivalent stress–strain curves of the material subject to 14 dissimilar stress states were obtained. The distributions of stress state characterized by the stress triaxiality and Lode angle on the specimens were analyzed through simulations, confirming the validity of 11 out of the 14 plastic curves. Results indicate negligible stress triaxiality dependence but significant Lode angle dependence on the plasticity of Ti6Al4V alloy. Such results led to the proposal of a novel plasticity model, which effectively incorporates the Lode angle effect on both yielding and hardening behaviors of materials. Further validation through numerical simulations conducted in ABAQUS/Explicit demonstrated the model's applicability and accuracy in predicting material plasticity under complex loading conditions. These findings offer valuable insights into the mechanical behavior of Ti6Al4V alloy and have implications for design and performance assessment in practical engineering applications.