Rolling friction on single crystals of copper in the plastic range

Abstract

Both rolling friction and track width were found to vary with crystallographic direction when a sapphire ball was rolled in various directions on the cube face of a copper crystal. For a 1 4 -in. ball under a 200 g load, the rolling resistance was found to increase 32 per cent in changing from the 〈100〉 direction to the 〈110〉 direction while the track width decreased 31 per cent. The topography of the deformed areas was studied by optical and interference microscopy and microhardness measurements were made in and around the ends of the tracks. These studies aided in developing an explanation for the observed anisotropies. The rolling friction and track width variations may be explained by the topography around the static indentation and by the way that the rolling motion affects this topography to give anisotropic build-up of surface ahead of the ball and anisotropic work-hardening of the contact area. The topography around these indentations is explained on the basis of the plastic flow that results from the arrangement of the slip planes in the applied stress field. A dislocation model is presented of the plastic flow and the work-hardening in static and rolling ball-indentations on the cube face of copper.