True origin of the size effect in cold-welded metallic nanocrystals
True origin of the size effect in cold-welded metallic nanocrystals
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DOI：
10.1016/j.ijmecsci.2020.106102
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发表时间：
2020-12
影响因子：
7.3
通讯作者：
Yi Cui;Yuhki Toku;Y. Kimura;Y. Ju
中科院分区：
文献类型：
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作者：
Yi Cui;Yuhki Toku;Y. Kimura;Y. Ju
在我们之前的实验中，我们观察到了用于表面紧固件的冷焊接金属纳米线的尺寸效应。在这项工作中，一个大规模的分子动力学（MD）模拟和有限元（FE）模拟耦合的非奇异位错理论相结合，以探讨这种激烈的尺寸效应的真正起源。非常大的直径（高达200 nm）参与直接MD模拟，没有留下模拟和实验之间的差距。人们曾经认为，剧烈的尺寸效应来自于通过键合界面传递的货车德瓦尔斯力（vdW），这确实给出了数学上一致的标度律。然而，根据目前的模拟，建立了新的理解-剧烈的尺寸效应与位错发射有关，而不是vdW力。与单根纳米线相比，在纳米晶的键合角附近，由于存在巨大的应力集中，导致了外生应力的激增。因此，位错发射被触发。它也揭示了，压倒性的，位错发射应该是积极有利的冷焊纳米晶体。此外，多晶纳米晶体的MD模拟显示，随机取向效应和晶界效应都是次要的巨大的应力集中效应。在这种不太理想的情况下，位错发射仍然决定最大应力。
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.