Correlation between Geometrically Nonlinear Elastoviscoplastic Constitutive Relations Formulated in Terms of the Actual and Unloaded Configurations for Crystallites

Abstract

A correct description of severe plastic deformation requires the use of nonlinear kinematic and constitutive relations. The relations should meet certain criteria, such as the frame-independence, closed stress cycles and the absence of energy dissipation under elastic cyclic loading. A most complicated issue in formulating these relations is the decomposition of motion into quasi-rigid and strain-induced motions, which is an extremely difficult problem with no unambiguous solution. For the majority of structural metals and alloys, this decomposition can be done in a physically justified way on the level of crystallites. Earlier, using a multilevel approach we introduced a corotational coordinate system for crystallites responsible for quasi-rigid motion. This allowed us to formulate frame-independent mesoscopic constitutive relations in the actual configuration and to perform test calculations to show that the above criteria are satisfied with high accuracy. A new way of motion decomposition was proposed which is a multiplicative representation of the deformation gradient with an explicit extraction of the corotational frame motion. Elastoviscoplastic constitutive relations satisfying the above criteria were formulated in terms of an unloaded "lattice" configuration. However, it is more preferable to formulate nonlinear boundary value problems in terms of the actual configuration in rates. This paper is aimed to study correlation between the earlier derived constitutive relations formulated in terms of the actual configuration and in terms of the unloaded "lattice" configuration. Example problems are solved to demonstrate the closeness of results obtained with these constitutive relations.