EXPERIMENTAL PARAMETER-ESTIMATION FOR NONPROPORTIONAL CYCLIC VISCOPLASTICITY - NONLINEAR KINEMATIC HARDENING RULES FOR 2 WASPALOY MICROSTRUCTURES AT 650-DEGREES-C

An earlier reported approach for estimating backstress from uninterrup ted, biaxial strain-controlled, nonproportional tests is applied to tw o different heat treatments of Waspaloy at 650-degrees-C. These result s are then used to compute backstress histories from cyclic proportion al tests. Information regarding the appropriate number of nonlinear ki nematic hardening rules for use in viscoplasticity models as well as e stimates of the values of the parameters in the kinematic hardening ru les are obtained from direct analysis of the experimental data. Comple te sets of isothermal model parameters are presented for both heat tre atments, and model results are compared with experimental results for several nonproportional, cyclic, strain-controlled test histories. It is shown that the nonlinear kinematic hardening rules determined using the presented methods allow a faithful description of the subtle diff erences in stress space response paths for the two different heat trea tments. Isotropic hardening for the two heat treatments under the expe rimental conditions is also discussed.