CONTINUUM DAMAGE BASED CONSTITUTIVE-EQUATIONS FOR COPPER UNDER HIGH-TEMPERATURE CREEP AND CYCLIC PLASTICITY

Viscoplastic constitutive equations without damage for cast copper have been developed for cyclic mechanical and cyclic thermal loading over the temperature range 20-500-degrees-C (nominal composition: 99.99% Cu, 0.005% O2, B.S. 10355-1037). Model predictions have been compared with experimental cyclic plasticity tests. Good agreement has been achieved. Creep and cyclic plasticity damage evolution equations have been developed. The effect of cyclic hardening on creep damage evolution has been modelled by introducing an internal variable to represent the state of material hardening. A creep cyclic plasticity interaction law has been proposed, and with the creep and cyclic plasticity damage evolution equations, has been combined with the viscoplastic constitutive equations to establish a unified material model for copper over the temperature range 20-500-degrees-C. Predictions of lifetime and deformation history have been made for uni-axial test specimens subject to strain-controlled cyclic plasticity and ratchetting. Good agreement has been obtained with experimental results. The model has been validated for mechanical loading by predicting the response of uni-axial test specimens to strain-controlled cyclic plasticity with strain hold periods, and to combined strain-controlled cyclic plasticity tests with strain holds and ratchetting. The predictions compare well with experimental results. The model has been validated for cyclic thermal loading by predicting the response of uni-axial test specimens subjected to thermal loading cycles. Good comparisons have been achieved with experimental results.