Discrete dislocation simulations of compression of tapered micropillars

The effect of taper on the plastic response of micropillars with a relatively high density of dislocation sources (1.5×1014m−2) is analyzed. The large number of dislocation sources and dislocations in the simulations rule out many of the mechanisms that govern size effects in pillars with a low dislocation source density. The mechanical response of compressed pillars with mean widths of W=0.4, 0.8, 1.6, 3.2 µm and taper angles of 0°, 2° and 5° is analyzed using 2.5D discrete dislocation plasticity. For all taper angles, large scatter is found in the stress strain response for the submicron, W=0.4 and 0.8 µm pillars, and relatively little scatter for the larger pillars. Taper leads to an increased average hardening rate for the submicron pillars, although this increase is within the scatter band of the stress strain response. Little sensitivity of the plastic response to taper is found for the larger pillars. The effect of size and taper on the stress strain response stems from the build up of geometrically necessary dislocations (GNDs). The reduced number of dislocation sources in the submicron pillars is identified as the origin of the large scatter in the predicted mechanical response.