Recent Work on Solid Friction at the Research Laboratory for the Physics and Chemistry of Solids

Abstract

This paper is a review of some of the recent work which has been done in the Research Laboratory for the Physics and Chemistry of Solids, University of Cambridge. Three main topics are discussed: (a) The friction and wear of materials at very high rates of sliding. When a ball, spinning at high velocity, is brought into contact with a flat surface of a material such as bismuth, very rapid wear occurs as a result of melting on a large scale. For this to occur, the material should have a low melting point and a low thermal conductivity, as these properties together influence the rate at which the melted zone penetrates the solid. (b) Elastic hysteresis losses and rolling friction. A cylinder rolling over the surface of rubber causes the material under the roller to be subjected to a complex deformation cycle, partly torsion and partly tension. Experiments to investigate the hysteresis losses in such complex cycles are described and used in the interpretation of rolling friction results. (c) The effect of combined stresses and contamination on the growth of junctions between metal surfaces. The simple theory of friction treats the mean yield pressure and the maximum shear stress as independent strength properties. Plasticity theory suggests that the yielding of a junction should occur as the result of their combined action. The theory has been confirmed by experiment and used to explain the fact that small traces of contamination can reduce the very high values of friction observed with outgassed metals to normal values of 1 or 2.