Viscoplastic constitutive modeling of inelastic deformation of Udimet 720 Li at high temperature

The mechanical deformation of a nickel-based superalloy Udimet 720 Li was modeled simultaneously by the Chaboche unified viscoplastic constitutive theory under tensile, cyclic and creep loading conditions at 700°C. To describe the phenomena of cyclic relaxation of mean stress under strain controlled cyclic loading and fast isotropic softening during unloading, the equations of internal variables of the theory were modified. A program code of parameter optimization was compiled with one-dimentional Chaboche model by Levenberg-Marquadt nonlinear algorithm. A global strategy for model parameters optimization was proposed, which produced good results. The numerical simulations show that this modified Chaboche model has sufficient capability of modeling various mechanical behaviors under complex loading conditions.