纳米接触过程中黏着规律的变化

本文应用大规模分子动力学方法, 模拟了两种具有不同粗糙形貌的、刚性球形探头与弹性平面基体之间的纳米尺度接触, 计算了探头与基体之间的拉离力和黏着功, 研究了接触过程中界面黏着力随载荷的变化规律, 分析了接触界面原子的法向应力分布. 研究发现, 原子级光滑接触的黏着力随着载荷的增大而线性增大, 而原子级粗糙接触的黏着力-载荷曲线分为以不同斜率增长的两个阶段. 相比于原子级光滑探头, 原子级粗糙探头与基体之间具有较小的拉离力和黏着功, 却在接触过程中形成了较大的黏着力. 因此, 拉离力和黏着功不能表征出纳米接触过程中原子吸引作用对界面法向力的贡献大小.

Variation of adhesive force in the nanoscale contact

Intermolecular attractive forces lead to the adhesion problem in M/NEMS. The Van der Waals formula for the interaction between macroscopic objects can be used only in the situation with no deformation. As to the adhesive contact between elastic bodies it is still unknown how the attractive force contributes to the normal force on the interface. In this paper large-scale molecular dynamics simulation is performed to study the adhesive contact between a rigid spherical tip and an elastic flat substrate. We study the effect of atomic-scale surface roughness on the adhesive properties, including pull-off force between tips and substrate, the variation of adhesive force with applied load, and the distribution of contact stress. The results show that the adhesive force varies linearly with the applied load for the atomic-scale smooth contact. But for the atomic-scale rough contact the variation of adhesive force with applied load can be divided into two phases, which are distinguished by different increasing slops. Compared with the smooth contact, the rough contact has a small pull-off force, but exhibits a large adhesive force during the contacting process. Our simulations indicate that the pull-off force cannot characterize the contribution of attractive interaction to the normal force on the interface in the case of an elastic adhesion contacting.