Viscoplastic deformation analysis for spheroidal graphite cast iron by subloading-overstress model

Abstract

The time-dependent elastoplastic deformation behavior, i.e. viscoplastic deformation behavior, is observed in solids and structures subjected to high temperature under monotonic and cyclic loadings. Then, the deformation analysis is required by incorporating the rigorous viscoplastic constitutive equations capable of describing cyclic loading behavior at high temperature. There are two types of viscoplastic models, i.e. the overstress model and the creep model. The former is pertinent as the mechanical deformation behavior is reduced to that of the ordinary elastoplastic constitutive equation in the quasi-static deformation process, but the latter is impertinent as it is irrelevant to the ordinary one. Unfortunately, however, the existing overstress model is incapable of describing the cyclic loading behavior because the interior of the yield surface is assumed to be a purely-elastic domain. On the other hand, the subloading-overstress model possesses the basic structure capable of describing the viscoplastic deformation behavior under cyclic loadings, but the applicability to the prediction of real material behavior has not been verified hitherto. The mechanical tests of the spheroidal graphite cast iron under monotonic and cyclic loadings at high temperature and various strain rates are performed. The simulations of the test results are performed by the subloading-overstress model and the existing overstress model. Consequently, it is verified that the subloading-overstress model is capable of simulating the test results accurately.