The proposed research focuses othe relationship between the atomic configuration of dislocation cores and macroscopic plastic flow. Our principal goals are 1. to develop physically based continuum constitutive relatins that account for complex phenomena arising form non-planar dislocaiton core structures and can be utilized, for example in finite element analyses and in hydrocode simulaitons. We will consider a range of technologically important materials from different crystal classes andunder conditions that arise in both deformation processes and the response of componenets subjected to mechanical loading. Common signatures of core effects are unexpected deformation modes and slip geometerics, stron and unusual dependence of flow stresses on crystal orientation and temperature, and most prevalently, a break-down of 'Schmid's law' due tothe dependence of slip on non-guide componenets of stresses. At the same time, these core effects may critically affect macroscopic flow of polycrystals, for example, significantly influcencing the physically based sontitutive models that incorporate effects of non-glide stresses on multiple-slip deformation is the focus of the proposal. To do that solely based upon experiments is difficult if not impossible, whereas atomistic simulations can directly reveal those characteristics of dislocations that are responsible for complex macroscopic behaviors. These in turn, depend on bothe the crystal structure and bonding characteristics of a given material. Strain localization has been shown to be quite sentitive to multiple-slip hardening and non-glide stress affects. We propose to investigate localized deformatin both because of its inherent importance provides a chalenging test of the new models.
