The relation between the friction and visco-elastic properties of rubber

Abstract

This paper describes a study of the friction of several types of rubber against hard surfaces over a wide range of temperatures and sliding velocities. The highest velocity did not exceed a few centimetres per second so that frictional heating was negligible. The results show that the friction increases with the sliding velocity to a maximum value and then falls. The application of the Williams, Landel & Ferry (1955) transform shows that the frictional behaviour of a rubber sliding at various velocities and temperatures on a given surface can entirely be described by a single ‘master curve’ and the glass transition temperature of the material. The master curve on a rough abrasive track shows, in general, two peaks—one of these occurs at a velocity related to the frequency with which the track asperities deform the rubber surface. This maximum is absent on a smooth track and thus reflects the deformation losses produced by the passage of the asperities over the rubber surface. The other peak occurs in general at much lower velocities; it coincides in position with the single maximum obtained on a smooth surface. Introduction of a fine powder (MgO) into the interface between the rubber and track eliminates this peak on both smooth and rough surfaces; it is therefore attributed to molecular adhesion. Comparison with the relaxation spectrum of the rubber gives a fundamental jump distance of the order of 60 Å. It appears therefore that friction arises from adhesion and deformation losses, and that both are directly related to the visco-elastic properties of the rubber.