The genesis of friction

Abstract

Abstract The genesis of friction is explained in terms of a new theory. Contrary to the postulates of the adhesion theory of friction, this theory postulates that the frictional force (and thus the friction coefficient μ) is affected by the sliding distance and the environment because of the changing contributions of three components of friction, i.e. that due to the deformation of surface asperities (denoted μd), that due to plowing by wear particles and hard asperities (denoted μp) and that due to the adhesion of the flat portions of the sliding surface (denoted μa). Therefore the coefficient of friction is not a simple material property. There are four or six stages of the friction regime depending on the sliding conditions. The initial friction coefficient μi can range from 0.1 to 0.2 for most machined surfaces. μi is largely independent of environmental conditions (including lubricants), materials and surface topography. μp varies from 0 to 1.0 and μa from 0 to 0.4. Only μa depends on the quality of surface adhesion. The history-dependent frictional behavior of materials is represented in the “friction space” diagram. According to this theory, the compatibility of sliding surfaces is dictated more by the mechanical properties of materials such as hardness than by their relative solubility at low temperatures.