Elastic Deformation and the Wear of Electrographite

Abstract

IT has recently been shown that when electro-graphite slides repeatedly over a copper surface, the worn surfaces eventually become extremely smooth¹; the mean angles of inclination of the irregularities on both surfaces are of the order of 2–5°. The maximum slope of an irregularity which can be deformed elastically into the general plane of a surface is inversely proportional to the modulus of elasticity of the material and may be calculated from criteria given by Halliday². For metals the slopes required are usually less than 1°; for carbon and graphitic materials, however, the moduli of elasticity are much lower and the maximum permissible slopes range from about 7° to about 15°. Thus, with carbons, the stresses produced by deformation of the surface irregularities during sliding are likely to be well below the elastic limit, as recently pointed out by Clark, Connolly and Hirst³. In these circumstances, it has been suggested that wear might occur by a ‘micro-fatigue’ process, resulting from repeated applications of elastic stress over the localized regions of real contact¹. This possibility is directly supported by the experiments described here.