Technical Report on Atomistic and Dislocation Dynamic Modeling of Plasticity in Polycrystalline Metals

摘要

In this effort we have studied in atomic detail the structure / property relationship of geometrically realistic metallic nanowires. It has been shown that surface roughness can greatly affect defect nucleation as nucleation from the surface dominates. Twin boundaries were introduced and were found not to be favored as sites for defect nucleation but do lead to deformation hardening as they are efficient obstacles against dislocation propagation. The details of heterogeneous dislocation nucleation have been studied in depth showing the initial state of local stress determining the strength of the defect is very complex having many sometimes competing components. Three point bending tests performed by simulated nanoindentation experiments yield qualitative results very similar to recent atomic force microscopy investigations. Preliminary results subject to complex states of bending stress show the possible roles pressure may play in dislocation nucleation as well as propagation. Region of high hydrostatic stress appear to prohibit dislocation nucleation and propagation. Currently we are refining our simulation methods to include accurate force measurements from our simulated nanoindenter for direct comparison with current experimental efforts.