Some notes on the adhesion and friction of non-metals

Abstract

The papers by Bowden, Young & Rowe and by Shooter show that the mechanism of friction of non-metals is similar to that of metals; strong adhesion occurs at the points of real contact and these regions must be sheared for sliding to take place. The reality of this strong adhesion is difficult to demonstrate directly, since, in general, the ‘junctions’ are broken by released elastic stresses as the load is removed. With a soft metal, such as indium, however, strong normal adhesive forces are readily observed (McFarlane & Tabor 1948; Parker & Hatch 1950). It is interesting to compare the frictional behaviour of non-metals with adhesion experiments using indium as one of the surfaces (Moore & Tabor 1952). With grease-free diamond surfaces the coefficient of adhesion σ (i. e. the adhesive force divided by the normal load) is about unity and is similar to that observed on metals. The junctions break at a short distance from the diamond interface, indicating that the adhesive bond is stronger than the bulk strength of indium. This is consistent with the suggestion that the adhesive forces at the diamond surface may be responsible for the frictional properties of diamond.