Gupta Nitant, Penev Evgeni S, Yakobson Boris I
Department of Materials Science and Nanoengineering, Rice University, Houston, TX 77005, USA.
Sci Adv. 2021 Dec 24;7(52):eabj6996. doi: 10.1126/sciadv.abj6996. Epub 2021 Dec 22.
Despite being one of the most consequential processes in the utilization of structural materials, fatigue at the nano- and mesoscale has been marginally explored or understood even for the most promising nanocarbon forms—nanotubes and graphene. By combining atomistic models with kinetic Monte Carlo simulations, we show that a pristine carbon nanotube under ambient working conditions is essentially indefatigable—accumulating no structural memory of prior load; over time, it probabilistically breaks, abruptly. In contrast, by using coarse-grained modeling, we demonstrate that any practical assemblies of nanotubes, e.g., bundles and fibers, display a clear gradual strength degradation in cyclic tensile loading due to recurrence and ratchet-up of slip at the tube-tube interfaces, not occurring under static load even of equal amplitude.
尽管在结构材料的使用中，疲劳是最重要的过程之一，但即使对于最有前景的纳米碳形式——纳米管和石墨烯，纳米和中尺度下的疲劳也只是得到了极少的研究或理解。通过将原子模型与动力学蒙特卡洛模拟相结合，我们发现，在环境工作条件下，原始碳纳米管基本上是不会疲劳的——不会积累先前载荷的结构记忆；随着时间的推移，它会突然地、概率性地断裂。相比之下，通过使用粗粒度模型，我们证明，纳米管的任何实际组件，例如管束和纤维束，在循环拉伸载荷下都会由于管 - 管界面处滑移的反复出现和棘轮效应而表现出明显的强度逐渐退化，即使在等幅静载下也不会出现这种情况。
