Bridging the Gap Between the Atomic-Scale and Macroscopic Modeling of Friction |
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Authors: | O M Braun |
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Affiliation: | (1) Institute of Physics, National Academy of Sciences of Ukraine, 46 Science Avenue, 03028 Kiev, Ukraine |
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Abstract: | A short survey of a modern view on the problem of friction from the physical viewpoint is presented. An atomically thin lubricant
film confined between two substrates in moving contact has been studied with the help of molecular dynamics (MD) based on
Langevin equations with coordinate- and velocity-dependent damping coefficient. Depending on model parameters, the system
may exhibit either the liquid sliding regime, when the lubricant film melts during sliding (the “melting-freezing” mechanism
of stick-slip motion), the “layer-over-layer” sliding regime, when the film keeps a layered structure at sliding, or the solid
sliding regime, which may provide an extremely low friction (“superlubricity”). Atomic-scale MD simulations of friction, however,
lead to a “viscosity” of the thin film, as well as to the critical velocity of the transition from stick-slip to smooth sliding,
which differ by many orders of magnitude from the values observed in macroscopic experiments. This contradiction can be resolved
with the help of the earthquakelike (EQ) model with a continuous distribution of static thresholds. The evolution of the EQ
model is reduced to a master equation which can be solved analytically. This approach describes stick-slip and smooth sliding
regimes of tribological systems within a framework which separates the calculation of the friction force from the atomic-scale
studies of contact properties. |
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