Operation of a 3D Frank–Read source in a stress gradient and implications for size-dependent plasticity
Operation of a 3D Frank–Read source in a stress gradient and implications for size-dependent plasticity
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DOI：
10.1016/j.actamat.2012.11.023
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发表时间：
2013-03
期刊：
影响因子：
9.4
通讯作者：
B. Szajewski;S. Chakravarthy;W. Curtin
中科院分区：
文献类型：
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作者：
B. Szajewski;S. Chakravarthy;W. Curtin
使用 3D 离散位错动力学 (DDD) 模拟和分析模型研究了存在空间应力梯度的情况下单个 Frank-Read (FR) 源的运行情况。在足够大的应力梯度下，FR源表现出由梯度应力场的低应力区域控制的新的稳定构型。源头的连续发射会产生越来越多的位错堆积，对源头施加越来越大的背应力，从而导致硬化。 FR 源在梯度场中的运行可以通过独特关键位置处的单个临界应力来很好地近似，从而可以开发源运行的分析模型。这些结果可用于合理化使用 DDD 模拟单晶梁弯曲和单晶悬臂梁弯曲实验中测量的强度尺寸尺度。这项工作表明，塑性的尺寸效应自然地从应力梯度内运行的位错源的力学中产生，在这种情况下，相关的材料长度尺度是FR源的长度。
The operation of a single Frank–Read (FR) source in the presence of a spatial stress gradient is studied using 3D discrete-dislocation dynamics (DDD) simulations and analytic models. Under a sufficiently large stress gradient, the FR source shows a new stable configuration controlled by the low-stress region of the graded stress field. Successive emissions from the source generate a growing dislocation pile-up that exerts an increasing back stress on the source, leading to hardening. The operation of the FR source in the gradient field can be well-approximated by a single critical stress at a unique critical location, allowing for the development of an analytic model of the source operation. These results are applied to rationalize the size-scaling of strength measured in simulations of single-crystal beam bending using DDD and in experiments on bending of single-crystal cantilever beams. This work demonstrates that size effects in plasticity emerge naturally from the mechanics of dislocation sources operating within a stress gradient, and in this case the relevant material length scale is the length of the FR source.