An explanation of the different regimes of friction and wear using asperity deformation models

Abstract

A slip-line field analysis is given for the deformation of a soft asperity by a hard one and equations are derived for the corresponding coefficients of friction and wear rates. Three main models are proposed. For smooth surfaces the first model gives low coefficients of friction and shows how plastic deformation of the asperity can occur without removal of material. The second model shows how wear and high coefficients of friction can occur for such surfaces. For rougher surfaces a cutting model applies with a chip (wear particle) being produced. In this way an explanation is offered of why “lubrication” is observed to inhibit wear for smooth surfaces and to encourage it for rougher surfaces. A possible explanation is also given of why the actual wear for engineering surfaces under normal working conditions is many orders of magnitude less than that calculated by assuming that all of the plastically deformed material is removed.