Improved constitutive laws for finite strain inelastic deformation

The study of large strain inelastic deformation of metals forms an important class of mechanics of materials research. Many manufacturing operations involve large strain processes. An accurate material model for a workpiece in such a process is vital for life prediction in a subsequent application.Experimental research in large strain deformation has centered on compression and torsion experiments as well as tests simulating manufacturing processes. A large part of theoretical research in large strain has involved kinematical justification of the decomposition of the deformation into elastic and plastic constituents. With their strong link to the kinematics of the crystal lattice, crystal plasticity theories have proven valuable for correlation of preferred orientations (crystallographic textures) and have aided the development of models framed on the macro-scale using the current configuration. Little has been done to incorporate strain-hardening phenomena such as the nucleation and evolution of dislocation substructures into these micro-scale models, however. Macro-scale models for large strain, while having many kinematical issues largely resolved, have largely ignored the stress-state dependence of such hardening processes as well.Within the current research, the stress state dependence of hardening processes was investigated experimentally with the experimental information used to form a theoretical framework for large strain inelasticity. Large strain experiments involving compression, torsion, and sequences of compression followed by torsion and torsion followed by tension were conducted on 304L stainless steel. A transmission electron microscopy (TEM) investigation of the deformation substructure was conducted to ascertain the operable hardening processes as well as to address the stress state dependence of the evolution of the substructure. A macro-scale model framework was then constructed which incorporated the third invariant of overstress,...