| Deformation-induced anisotropy from initially isotropic polycrystalline metals is manifested through material responses and morphological changes. When a metal deforms, the complex interactions of the grain structure, lattice orientation, and dislocation substructure induce evolving elastic and plastic anisotropy. To construct a physically-based unified-creep-plasticity (UCP) constitutive framework, continuum slip polycrystal elastoviscoplasticity was used, which builds on the physical description at the scale of the grain. Physical realities are missing in both macroscale and mesoscale models; hence all possible anisotropic effects have not been included in constitutive frameworks represented by the two length scales.; This work elucidated and unified length scale issues in mesoscale polycrystalline and macroscale UCP models. A continuum slip polycrystal elastoviscoplasticity formulation, which includes scalar and second rank internal state variables, was developed and used to used to show better comparisons than the Taylor model for texture evolution and stress-strain behavior of OFHC Cu and 304L stainless steel at room temperature and quasistatic strain rates. Experiments considered include compression, torsion, and non-monotonic sequence tests. To understand which elements of the polycrystal elastoviscoplasticity theory were most influential in establishing guidelines for macroscale modeling, a statistical design of experiments study was performed. This study showed that slip level kinematic hardening and intergranular constraints had the strongest influence in affecting macroscale responses (effective stress, hardening rate, plastic spin, etc.). Strain path change experiments were performed to help constitutive developments better reflect the physics of hardening and flow, focusing on grain subdivision processes, generation of geometrically necessary boundaries, and the intermediate configuration and elasticity formulation. A thermoviscoplastic UCP model, which includes an internal state variable representing the effects of texture and dislocation substructures by use of the third invariant of overstress, was developed which characterized material response behavior differently than {dollar}Jsb2{dollar} theory. Guidelines were developed for incorporating an evolution equation for texture/substructure into a UCP model. The UCP model was implemented into the ABAQUS and PRONTO finite element programs and used to solve a complex, nonlinear boundary value problem (localization and failure as related to the forming limit diagram). |
