Analytical Model for Plowing Friction at Nanoscale

Existing analytical models for elastic-plastic friction, which have been developed for microscale single-asperity contacts, do not apply when the contact dimensions are reduced to the nanometer regime. We demonstrate that although the microscale models correctly describe elastic recovery behind a sliding nanoscale tip, they fail to predict the corresponding coefficient of friction. We show that the breakdown of microscale models can be attributed to the large contribution to friction from pileup. We propose an analytical model for plowing friction for single-asperity contacts, which includes the effects of both elastic recovery and pileup. Functional dependence of the average pileup height on elastic properties of the worn material and on the depth of cut is also proposed. Applicability of the new model is demonstrated in the examples of SiC and Cu.