Improvement on the modeling of rate-dependent plasticity and cyclic hardening by Bodner-Partom model

An additional isotropic internal variable is utilized to extend the Bodner-Partom unified viscoplastic constitutive model (original B-P) to improve the modeling of rate-dependent plasticity and cyclic hardening behaviors of metals. The extended model (new B-P) contains two isotropic internal variables: one plays the role of representing the fast hardening in smaller inelastic strain range, while the other evolutes at slower speed accompanied by larger accumulated inelastic deformation, such as cyclic hardening. To examine the validity of the extended constitutive model, the rate-dependent plasticity of a Ni-base superalloy Udimet 720Li at 650°C and 700°C are characterized using both models. Not only numerical simulations are conducted for various loading conditions by implementing both models into ABAQUS using a user material subroutine, also a systematic comparison between two models is completed. Numerical results show that the extended material constants in the new model provide more flexible capability in modeling the inelastic behavior of the material with sound accuracy.