Rubber friction variation with rate and temperature: some new observations

Abstract

Friction measurements are reported for the sliding of rubber over individual glass lenses, wavy-surface glass and abrasive paper. Two different apparatuses were employed to obtain friction data. All the experiments were made with the same vulcanised rubber compound moulded with smooth test surfaces to facilitate contact area observations. The measurements covered large ranges of sliding speed (0.001 to 10 mm s^-1), ambient temperature (-60 to +90 degrees C), normal load (0.01-57 N) and contact geometry (R=1-18 mm). Some results are given as a function of the sliding velocity by use of the WLF transform. It was found that, particularly for smooth surfaces, the friction varied only slightly with rate (WLF parameter). For the test arrangements employed the viscoelastic response of the rubber compound appeared to be of less importance than the geometry of contact, except when operating conditions were near to the glassy region of the rubber. A simple plot of friction coefficient as a function of the Hertz contact area brought together all the diverse measurements. In the course of experimentation the influence of the method of surface cleaning upon friction was investigated. New insight was also obtained concerning the nature and magnitude of the static friction of rubber.