The Friction of Hard Sliders on Lubricated Rubber: The Importance of Deformation Losses

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Abstract
A study has been made of the friction of hard spheres and cones on a well lubricated rubber surface under conditions where relatively large deformations are produced. It is found that with spheres the sliding friction is almost the same as the rolling friction. Earlier work has shown that in the latter case the friction arises primarily from hysteresis losses in the rubber and it is concluded that, under the experimental conditions described, the main source of friction in lubricated sliding arises from the same cause. With conical sliders it is not possible to make a direct comparison with rolling experiments, but a simple calculation suggests that here again the friction is largely due to deformation losses in the rubber. For cones of small semi-angle there is a large increase in friction but this is associated with penetration of the lubricant film and tearing of the rubber. The friction results are in close agreement with measurements described by Miss Sabey for spheres and cones sliding on wet rubber at relatively high speeds (c. 6 ft sec−1). This suggests that in her experiments the water film provides very effective lubrication and that the friction arises largely from hysteresis losses in the rubber itself. As a general conclusion this study of the friction of lubricated rubber suggests that where interfacial adhesion is small and where relatively large local deformations occur the friction may well be dominated by deformation losses in the rubber. Under these conditions we may therefore expect the friction of hard spherical or conical sliders on rubber to be greater for rubbers of low Young's modulus and high hysteresis losses.

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