In this work, coarse-grained atomistic simulations via the concurrent atomistic-continuum (CAC) method are performed to investigate compressive deformation of nano-/submicron-sized pillars in body-centered cubic (BCC) tungsten. Two models with different surface roughness are considered. All pillars have the same height-to-diameter aspect ratio of 3, with the diameter ranging from 27.35 to 165.34 nm; as a result, the largest simulation cell contains 291,488 finite elements, compared to otherwise ≈ 687.82 million atoms in an equivalent full atomistic model. Results show that (i) a larger surface roughness leads to a lower yield stress and (ii) the yield stress of pillars with a large surface roughness scales nearly linearly with the diameter while that of pillars with smooth surfaces scales exponentially with the diameter, the latter of which agrees with experiments. The differences in the yield stress between the two models are attributed to their different plastic deformation mechanisms: in the case of large surface roughness, dislocation nucleation is largely localized near the ends of the pillars; and in pillars with smooth surfaces, dislocation avalanches in a more homogeneous manner are observed. This work, which is the first attempt to simulate BCC systems using the CAC method, highlights the significance of the surface roughness in uniaxial deformation of nano-/submicropillars.

中文翻译：

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模拟压缩下纳米/亚微米尺寸钨柱的塑性变形：粗粒度原子方法

在这项工作中，通过并发原子连续体 (CAC) 方法进行粗粒度原子模拟，以研究体心立方 (BCC) 钨中纳米/亚微米尺寸柱的压缩变形。考虑了具有不同表面粗糙度的两种模型。所有柱子具有相同的高径比为3，直径范围为27.35至165.34纳米；因此，最大的模拟单元包含 291,488 个有限元，相比之下，等效的全原子模型中的其他元素约为 6.8782 亿个原子。结果表明，(i) 较大的表面粗糙度导致较低的屈服应力；(ii) 具有大表面粗糙度的柱子的屈服应力与直径几乎呈线性关系，而具有光滑表面的柱子的屈服应力与直径呈指数关系，后者与实验相符。两种模型之间屈服应力的差异归因于它们不同的塑性变形机制：在表面粗糙度较大的情况下，位错形核主要集中在柱端附近；在表面光滑的柱子中，可以观察到更均匀的位错雪崩。这项工作是首次尝试使用 CAC 方法模拟 BCC 系统，突出了表面粗糙度在纳米/亚微柱单轴变形中的重要性。在表面光滑的柱子中，可以观察到更均匀的位错雪崩。这项工作是首次尝试使用 CAC 方法模拟 BCC 系统，突出了表面粗糙度在纳米/亚微柱单轴变形中的重要性。在表面光滑的柱子中，可以观察到更均匀的位错雪崩。这项工作是首次尝试使用 CAC 方法模拟 BCC 系统，突出了表面粗糙度在纳米/亚微柱单轴变形中的重要性。