Crystal Plasticity Modeling and Simulation of Nanotwinned Metals

Abstract

This thesis presents the continuum micromechanics of nt FCC metals. Nanotwinned copper is used as a model material system. We focus on formulating and modeling the mechanics to describe the following characteristics reported in this model microstructure: (i) enhancement of yield strength with reduction in twin thickness, (ii) reduction in yield strength with decreasing twin thickness below a critical twin thickness, and (iii) migration of TBs under applied loads. The theoretical setting is developed using single crystal plasticity as a basis wherein the plastic slip on each slip system in an FCC crystal structure is modeled as a visco-plastic constitutive law arising from glide of dislocation ensembles. To model TB migration and yield softening, a TB-affected-zone is introduced that is endowed with an additional visco-plastic slip-law. Detailed micromechanics simulations and discussion of the strengthening, softening and TB migration in single-grained and polycrystalline topologies are presented.