Analysis of the Micro-Cantilever Size Effect
Recent discrete dislocation (DD) plasticity simulations of micro-cantilever bending will be used to provide an explanation for the observed strengthening with decreasing size of end-loaded single crystal micro-cantilevers milled from grains by focused ion beam. The micro-cantilever mechanism contrasts those of other “smaller is stronger” size effects. Simulations show that the micro-cantilever mechanism is related to the effect of the zero resolved shear stress isocontour, which does not generally coincide with the beam’s neutral axis, on the evolution of the dislocation structure; dislocations form “soft pile ups”, originating from sources closer to the cantilever surfaces where resolved shear stress is high. This specimen size effect differs from that of uniaxial tension, where DD simulations of sufficiently small single crystal samples reveal that a dislocation starvation mechanism due to the combined effect of a very small dislocation mean free path and a relative lack of sources can account for the observed strengthening of micro-pillars with decreasing size, although the latter does play a secondary role in the micro-cantilever size effect.