The Fundamentals of Sliding Contact Melting and Friction

This paper focuses on the phenomenon of melting and lubrication by the sliding contact between a phase-change material and a smooth flat slider. The first part of the study considers the limit in which the melting is due primarily to “direct heating,” that is, to the temperature difference between the solid slider and the melting point of the phase-change material. It is shown that in this limit the relative motion gap has a uniform thickness and that the friction factor decreases as both the normal force and the temperature difference increase. The second part considers the limit where the melting is caused mainly by the frictional heating of the liquid formed in the relative motion gap. This gap turns out to have a converging-diverging shape that varies with the parameters of the problem. As the normal force increases, a larger fraction of the melt is pushed out through the upstream opening of the relative motion gap. Means for calculating the melting speed, the friction factor, and the temperature rise along the slider surface are developed.