Vikram Deshpande, University of Cambridge

A Coupled Framework For Climb-Assisted Glide In Discrete Dislocation Plasticity
When Jan 28, 2013
from 02:00 PM to 03:00 PM
Where LR8
Contact Name
Contact Phone 01865 283302
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It is now well established that the plastic deformation of crystalline solids is size dependent at the micron scale for a range of loading conditions. While there are many underlying reasons for these size effects, attention has been primarily focussed on situations where plastic strain gradients are generated. Models typically tend to over-predict the experimentally observed size effects as they neglect a range of dislocation relaxation mechanisms. These mechanisms include dislocation cross-slip and dislocation climb. Dislocation climb requires the diffusion of vacancies and hence significant amounts of dislocation climb only occur at temperatures above a third of the melting temperature - in these cases mass transport reduces the plastic strain gradients and thereby reducing the effect of specimen size. However, even at lower temperatures, dislocations can surmount small obstacles with the aid of small amounts of climb. This prevents the build-up of large dislocation pile-ups which consequently again relaxes stresses.

The coupling of vacancy diffusion with dislocation motion is a true "multi-scale" problem as vacancy/dislocation interaction is essentially a dislocation core effect. We present a two-dimensional discrete dislocation plasticity framework coupled with vacancy diffusion wherein dislocation motion occurs by both climb and glide. The effect of dislocation climb is explored for a range of problems including size effects in bending of crystals, metal-matrix composites and passivated films. Dislocation climb typically tends to reduce strength enhancements that occur with decreasing size but in some surprising cases can also result in strength increases.