Ph.D. Thesis Defense by Robert McGinty
Monday, July 30, 2001

(Dr. David McDowell, advisor)

"Multiscale Representation of Polycrystalline Inelasticity"

Abstract

Metal inelasticity is of considerable technological importance in both commercial and military sectors, and has therefore received significant research attention in the forms of testing and model development.  Predominately framed at the macroscale, most internal state variable (ISV) models capture temperature, strain, and strain rate history effects.  In contrast, polycrystal plasticity models have focused on texture development and flow and strengthening mechanisms at the scale of grains.  It is common for each approach to neglect hardening and deformation mechanisms occurring at length scales other than the primary one addressed by the model.  However, deformation mechanisms evolve and interact over a range of length scales during inelastic deformation.

This work has focused on developing methods of simultaneously modeling multiscale hardening and deformation mechanisms.  Particular emphasis is placed on describing mechanisms that contribute to deformation-induced texture development and associated anisotropic plastic response at the macroscale.  The long-standing problem of determining active slip systems in rate independent crystal plasticity theory is addressed with a new algorithm that offers an order of magnitude reduction in the time required to perform most analyses.  The resulting framework makes it practical to incorporate other deformation mechanisms ranging from the development of dislocation substructure at the subgrain scale, to intergranular interactions and strengthening mechanisms occurring at the meso and macroscales.  The models are applied to the study of metal deformation processes including forming limit diagrams and high speed jet particulation.