A nonlinear kinematic hardening theory for cyclic thermoplasticity and thermoviscoplasticity

Abstract

Abstract The multiple backstress nonlinear kinematic hardening model of Moosbrugger and McDowell [1990] is extended to thermomechanical cyclic loading conditions. The model employs a decomposition of the isotropic hardening between the yield surface and backstress saturation amplitudes, with certain components independent of the degree of isotropic hardening. General forms are presented for thermoplasticity and thermoviscoplasticity that include temperature rate terms in both the kinematic and isotropic hardening parameters. General forms are presented for temperature path history-dependent and -independent materials; it is shown that the latter case is an important feature in thermoplasticity, since the flow rule cannot exhibit the necessary degree of temperature dependence. In the thermoviscoplastic case, the rate-dependence is decomposed between the flow rule and backstress saturation amplitudes, a unique feature consistent with dislocation cross slip. Thermodynamical restrictions are discussed for both cases, and isothermal and nonisothermal cyclic loading experiments are correlated with both theories.