Qu Cangyu, Shi Songlin, Ma Ming, Zheng Quanshui
Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China.
Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China.
Phys Rev Lett. 2019 Jun 21;122(24):246101. doi: 10.1103/PhysRevLett.122.246101.
Surface and interfacial energies play important roles in a number of instability phenomena in liquids and soft matter, but rarely have similar effects in solids. Here, a mechanical instability is reported which is controlled by surface and interfacial energies and is valid for a large class of materials, in particular two-dimensional layered materials. When sliding a top flake cleaved from a square microscale graphite mesa by using a probe acting on the flake through a point contact, it was observed that the flake moved unrotationally for a certain distance before it suddenly transferred to a rotating-moving state. The theoretical analysis was consistent with the experimental observation and revealed that this mechanical instability was an interesting effect of the structural superlubricity (a state of nearly zero friction). Further analysis showed that this type of instability was applicable generally for various sliding joints on different scales, as long as the friction was ultralow. Thus, the uncovered mechanism provides useful knowledge for manipulating and controlling these sliding joints, and can guide the design of future superlubricity-based devices.
表面能和界面能在液体和软物质的许多不稳定性现象中起着重要作用，但在固体中很少有类似的效应。在此，报道了一种由表面能和界面能控制的机械不稳定性，它对一大类材料有效，特别是二维层状材料。当使用通过点接触作用于薄片的探针滑动从方形微米级石墨台面上切割下来的顶部薄片时，观察到薄片在突然转变为旋转移动状态之前无旋转地移动了一定距离。理论分析与实验观察结果一致，并表明这种机械不稳定性是结构超润滑性（一种几乎零摩擦的状态）的有趣效应。进一步分析表明，只要摩擦力超低，这种类型的不稳定性通常适用于不同尺度的各种滑动接头。因此，所揭示的机制为操纵和控制这些滑动接头提供了有用的知识，并可指导未来基于超润滑性的装置的设计。
