Phonon modes involved in triggering threshold phenomenon characterising sliding-velocity dependence of wearless nanofriction.

Wearless nanofriction between nonmetallic solids is investigated in terms of molecular dynamics (MD). The results of this study concern wearless-nanofrictional characteristics of the MD models in which the thermal-buffer zone is located far enough from the sliding interface so as not to disturb the heat generation mechanism. An enormous number of simulation runs and frequent validation of their results were carried out so that the pressure and the interfacial temperature, which directly affect the heat generation processes, were made common at different sliding velocities even under the above constraint. Sliding-velocity dependence of the ensemble-averaged frictional force density under the steady sliding condition is characterised by the threshold phenomenon. The dramatic increase in rate of the frictional-heat generation at sliding speeds above the threshold is triggered by resonant coherent excitation of certain phonon modes. Spatiotemporal patterns of such elastic waves hidden in random thermal motion of atoms near the sliding interface were clarified by the sampling and averaging. Features of these patterns are discussed in relation to the threshold characteristics of wearless nanofriction. [ABSTRACT FROM AUTHOR]