Rubber Structure and Coefficient of Friction

1. As a result of analysis of the formulas of friction of rubber and of a comparison with experimental data for steady-state friction on smooth solid surfaces it is demonstrated that the friction of vulcanized rubber is determined by three constants of the material, depending upon the type of rubber polymer and the structure of the vulcanizate. 2. The constant α characterizes the constant of the formation of the area of actual contact Sa under loading. This constant does not depend upon the rate of slip and the nature of the solid surface, but it does depend upon the stiffness of the vulcanizate, which is directly proportional to the crosslink density. 3. The tangential stress on the actual area of contact α=F/Sa depends upon the temperature, the rate of slip and the two constants of the material Sk and U. The first of these is the effective area of contact of a chain with the solid surface, depending upon the number of chains in the network of the vulcanizate, the second is the activation energy, depending upon the nature of the frictioning surfaces, in particular upon the structure of the polymer chain of rubber. 4. A method is proposed for calculating the area of actual contact of a vulcanizate from the number of chains per unit volume and from the number of chains which are in contact with the solid surface.