Dry Sliding Contact Between Rough Surfaces at the Atomistic Scale

Abstract

Although, a lot is known about the factors contributing to friction, a complete physical understanding of the origins of friction is still lacking. At the macroscale several laws have long since described the relation between load (Amontons, Coulomb), apparent and real area of contact (Bowden and Tabor), and frictional forces. But it is not yet completely understood if these laws of friction extend all the way down to the atomistic level. Some current research suggests that a linear dependence of friction on the real contact area is observed at the atomistic level, but only for specific cases (indentors and rigid substrates). Because continuum models are not applicable at the atomic scale, other modeling techniques (such as molecular dynamics simulations) are necessary to elucidate the physics of friction at the small scale. We use molecular dynamics simulations to model the friction of two rough deformable surfaces, while changing the surface roughness, the sliding speed, and the applied normal load. We find that friction increases with roughness. Also all sliding cases show considerable surface flattening, reducing the friction close to zero after repetitive sliding. This questions the current view of (static) roughness at the atomistic scale, and possibly indicates that the macroscopic laws of friction break down several orders of magnitude before reaching the atomic scale.

Multiscale modeling and simulation of rolling contact fatigue

“…rigid layers shown in (a), so that the lubricant is sheared. This sliding velocity conduction has been widely used in MD simulations of thin film lubrication as it enables the simulation to obtain a required sliding distance within a reasonable calculation time [37,38,52,54]. In addition, the constant velocity mode makes it easy to record the friction forces.…”

“…For example, the simple ideal springs [52,61] and sine-wave potentials are often used. Another potential function, the L-J potential [54,62], gives a realistic representation of typical inter-atomic interactions. The L-J potential is a two-body potential commonly used for non-bonded interactions between atoms or molecules.…”

“…The L-J potential for the interaction between the wall atoms and the lubricant molecules is acceptable as long as the parameters are chosen properly. Moreover, reasonable results can be gained by using the L-J potential for the atoms of surfaces when two surfaces are sliding against each other [54]. Another significant advantage of using this potential is the computational efficiency.…”

MD/FE Multiscale Modeling of Contact

“…MD simulations are used to investigate nanoscale mechanisms at the origin of adhesive and friction forces [7,[14][15][16][26][27][28][29][30][31][32][33][34]. Besides the refined mechanical description achieved by MD models, severe limitations should be noted.…”

Advances in atomic-scale tribological mechanisms of solid interfaces

“…Meanwhile, the unveiling of friction mechanism at atomic scale will provide the guiding for finding the new solid lubrication materials which have the better lubrication performance. Along with the developments of molecular dynamic, first-principle theories and the appearance of atomic force microscopy (AFM), scientists have made a great progress [26][27][28][29][30][31][32][33][34] on atomic-scale tribological mechanism involving these solid lubrication materials and metals interfaces. Therefore, this paper aims at reviewing the theoretical advances which are associated with atomic-scale friction of solid sheet in recent years, from the respects of first-principle calculation, molecular dynamic and AFM experiments.…”