The mechanical behavior of submicron body-centered cubic (BCC) micro-pillars is investigated by three-dimensional dislocation dynamics (DD) simulations to better understand the governing mechanisms for size dependent plasticity under uniaxial tension and pure torsion. A formula is developed to compute the incremental plastic twist due to dislocation motion in DD simulations. The DD simulations show that different dislocation microstructures are created depending on the loading conditions, which leads to different size dependent mechanical behavior. While in tension plasticity is mainly governed by the kinetics of dislocation motion controlled partly by the surface dislocation sources, plastic flow in torsion is controlled by dislocation pile-ups associated with strain gradients. The simulation results also reveal a Bauschinger effect and plastic recovery under cyclic twist, which have been observed in recent experiments.

通过三维位错动力学（DD）模拟研究了亚微米体心立方（BCC）微柱的力学行为，以更好地理解单轴拉伸和纯扭转下尺寸相关塑性的控制机制。在DD模拟中，开发了一个公式来计算由于位错运动引起的增量塑性扭曲。该DD仿真表明，根据加载条件会产生不同的位错微结构，从而导致不同的尺寸依赖性机械行为。拉伸时，塑性主要受位错运动的动力学控制，而位错运动部分受表面位错源控制，而扭转中的塑性流动受与应变梯度相关的位错堆积控制。仿真结果还揭示了在最近的实验中观察到的鲍辛格效应和循环扭曲下的塑性恢复。