Atomistic locking and friction

Abstract

%'hen solid bodies contact and slide against each other, the frictional phenomenon occurs. The origin of the related frictional force is studied by assuming the existence of two clean crystal surfaces, which follows the current experimental trends. This study theoretically clarifies the atomistic origin of the frictional force intrinsically generated by the molecular interactions between the constituent atoms of solids, but not the force extrinsically generated by surface asperities, the existence of foreign atoms, etc. Furthermore, this study assumes that the constituent atoms of the two contacting surfaces interact with each other due to the interaction potential. This study found that there are two origins: atomistic locking and dynamic locking. Atomistic locking occurs when the configuration of the atoms on a contact surface continuously changes with the sliding distance and when the interatomic potentials have an arbitrary strength. In contrast, dynamic locking occurs when the configuration discontinuously changes due to the dynamic process and if the interatomic potential is stronger than a specific given value. A criterion is derived for the occurrence of dynamic locking. From studying various systems, it can be seen that dynamic locking is unlikely to occur in realistic systems. The frictional forces due to atomistic locking are calculated for a-iron. One other important finding prior to the experiments is that certain unique cases exist where the frictional force exactly vanishes if completely clean solid surfaces are prepared.

Simulations of atomic-scale sliding friction

“…28 Qualitatively, the conclusions agree with those of the simpler models. However, based on numerical calculations for ␣-iron, the authors conclude that nonadiabatic motion is unlikely to occur even in metallic systems.…”

“…23,27,28 The possibility has been suggested that two incommensurate surfaces can slide over one another without any friction. 23,27,28 Some studies predict that this could happen even in metallic systems. 28 In order to investigate the effect of interfacial mismatch on the frictional properties, a series of simulations have been performed for a system like the one in Fig.…”

Adhesion and friction of a multiwalled carbon nanotube sliding against single-walled carbon nanotube

“…[24][25][26][27][28][29][30] The interlayer interaction is known to be predominantly van der Waals. 1 Similar to the sliding between graphite in dry contact, 31 interlayer sliding inside multiwalled carbon nanotubes ͑MWNTs͒ exhibited superlubricity due to the socalled incommensurate contact, 32 bringing down the shear strength to as low as 0.05 MPa when the shell structure was defect-free. 24,26 The major energy dissipation mechanism was believed to arise from the interaction of the open end of outer tubes ͑where dangling bonds and defects were present͒ with the inner shells.…”

Friction between solids

“…When two incommensurate surfaces are in sliding contact, superlubricity or a state of extraordinarily low friction can occur. Hirano & Shinjo (1990) were the first to suggest that the interaction potential between two surfaces, V AB , could be reduced by making the surfaces incommensurate. Subsequent experiments examined the friction between muscovite mica sheets as a function of lattice misfit angle revealed that the friction was anisotropic and displayed periodicity consistent with the hexagonal symmetry of mica (Hirano et al 1991).…”