Abstract A drastic size effect in cold-welded metallic nanowire for surface fasteners was observed in our previous experiment. In this work, a large-scale molecular dynamics (MD) simulation and a finite element (FE) simulation coupled with the nonsingular dislocation theory are combined to probe the true origin of this drastic size effect. Very large diameter (up to 200 nm) is involved in the direct MD simulation, leaving no gap between the simulation and the experiment. It was once believed that the drastic size effect comes from the Van der Waals (vdW) force transmitted through the bonding interface, which does give a mathematically agreeable scaling law. However, based on present simulations, new understanding is established―the drastic size effect is linked to dislocation emission, rather than vdW force. Compared with a single nanowire, the externally induced stress surges near the bonding corner of cold-welded nanocrystals due to the enormous stress concentration. The dislocation emission is hence triggered. It is also revealed that, overwhelmingly, dislocation emission should be energetically favorable in cold-welded nanocrystals. Additionally, MD simulations with polycrystalline nanocrystals reveal that both the random orientation effect and the grain boundary effect are secondary to the enormous stress concentration effect. Under such less ideal situation, dislocation emission still determines the maximum stress.

中文翻译：

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冷焊金属纳米晶体尺寸效应的真正起源

摘要 在我们之前的实验中观察到用于表面紧固件的冷焊金属纳米线的显着尺寸效应。在这项工作中，大规模分子动力学 (MD) 模拟和有限元 (FE) 模拟与非奇异位错理论相结合，以探索这种剧烈尺寸效应的真正起源。直接 MD 模拟涉及非常大的直径（高达 200 nm），模拟和实验之间没有间隙。曾经有人认为，剧烈的尺寸效应来自通过键合界面传输的范德华 (vdW) 力，这确实给出了数学上可接受的缩放定律。然而，基于目前的模拟，建立了新的理解——剧烈的尺寸效应与位错发射有关，而不是与 vdW 力有关。与单根纳米线相比，由于巨大的应力集中，在冷焊纳米晶体的结合角附近外部引起的应力激增。位错发射因此被​​触发。还表明，绝大多数情况下，冷焊纳米晶体中的位错发射在能量上应该是有利的。此外，多晶纳米晶体的 MD 模拟表明，随机取向效应和晶界效应都是巨大应力集中效应的次要效应。在这种不太理想的情况下，位错发射仍然决定了最大应力。在冷焊纳米晶体中，位错发射在能量上应该是有利的。此外，多晶纳米晶体的 MD 模拟表明，随机取向效应和晶界效应都是巨大应力集中效应的次要效应。在这种不太理想的情况下，位错发射仍然决定了最大应力。在冷焊纳米晶体中，位错发射在能量上应该是有利的。此外，多晶纳米晶体的 MD 模拟表明，随机取向效应和晶界效应都是巨大应力集中效应的次要效应。在这种不太理想的情况下，位错发射仍然决定了最大应力。