The Friction and Lubrication of elastomers

This paper describes a study of the adhesion and friction of elastomers in dry and lubricated conditions under normal and tangential forces. Data are provided for the area of contact, in which the experiments were carried out between optically smooth concave elastomers and a glass substrate. Data for the corresponding frictional forces area also provided, in which the experiments were carried out between an optically smooth elastomeric strip and a glass indenter. The conclusion for the areas of contact is that adhesion plays a significant role in dry contacts under normal load as well as under a combined normal/tangential action, though the role of adhesion in the mechanism of surface separation upon the action of an imposed tangential force is still unclear. In lubricated conditions adhesion is greatly reduced and the classical theory of elasticity accounts for the areas of contact. Results for the corresponding frictional forces show a sharp decrease in the coefficient of friction in lubricated contacts, compared to its value for dry contacts, a trend which remained unaffected in all regimes of lubrication detected, namely “boundary”, hydrodynamic and elastohydrodynamic (EHL) lubrication. Finally, from the results of the areas of contact and the corresponding frictional forces, a first order calculation of the interfacial shear strength, s, of the elastomer was made and it was shown that s is a strong function of the sliding velocity and depends also on the normal load.