Aspect ratio and stochastic effects in the plasticity of uniformly loaded micrometer-sized specimens

The mechanical properties of small-scale metallic structures change when their size is reduced to dimensions in the micrometer range. Experiments on micrometer-sized samples have shown increasing flow stresses with decreasing diameter and also with decreasing aspect ratio (AR). A three-dimensional discrete dislocation dynamics tool was used to simulate tension tests on micrometer- and sub-micrometer-sized samples in single-slip and multi-slip orientations. The simulations confirm experimental results of the size effect with respect to both size dependence of the flow stress and hardening behavior. The influence of the AR as well as the initial dislocation microstructure on the observed size effect is discussed. Furthermore, it is shown by a Weibull analysis that flow stresses in small single-slip-oriented samples follow weakest-link statistics.