The effect of a tangential force on the contact of metallic bodies

Abstract When two solid bodies are brought together, they are usually very heavily deformed in their region of contact. Bowden marked breakdown occurs only when the tangential force is increased to a large fraction of that needed to cause sliding. It was found that the changes both in displacement and area of contact produced by tangential loading are essentially irreversible. A reversible (elastic) component of the displacements exists, but it is a small part of the total except when the tangential force is small. Release and even reversal of the tangential force produces no further irreversible changes until the force is increased again, in either direction, to a numerical value as high as the highest it has previously reached. It was further found that a lubricant does not essentially affect the deformation process for tangential forces less than those required to cause slip. The lubricant acts by weakening the surface-interaction, so that slip occurs for a smaller value of tangential force. Displacements corresponding to forces less than those required to cause sliding are approximately equal for lubricated and unlubricated specimens. The experiments provide quantitative data on the micro-displacements before sliding. The results can be interpreted in terms of the adhesion theory of friction. They confirm the analysis of combined stresses given by McFarlane & Tabor and extend its applicability.