The Coefficients of Adhesion of Rubber

Abstract

Abstract What conclusions can be drawn from all these experiments? Attempts to find a possible relation between the adhesion characteristics and other mechanical properties of rubber have been unsuccessful. Nevertheless, from a purely qualitative point of view alone, the coefficients of adhesion become progressively less sensitive to pressure as the rubber approaches more and more to the solid state. This seems to be a general rule to which there is no exception. The theoretical interpretation of this peculiar property of rubber cannot be discussed within the scope of the present paper; in fact it offers a complicated problem, for scientific data on the behavior of rigid solids in contact are extremely scarce. Theories advanced to explain the external friction of solids are numerous, but none gives a truly complete explanation of the phenomenon. However, it seems probable at least that the peculiar behavior is attributable to the characteristic state of materials with rubberlike properties, i.e., a state intermediate between that of liquids and of solids. There are numerous applications where advantage is taken of the high resistance to sliding of rubber on the surfaces of dry solid bodies. There would be no point in calculating a priori their coefficients of adhesion under service conditions from the results obtained in the present work, for conditions in service are generally of a very complex nature and, also are extremely variable. Pneumatic tires on automobiles are a very good example of such conditions. On the other hand, in applications such as transmission belts and autorail pneumatic tires, which operate under much more uniform conditions, there is reason for believing that systematic tests of this kind might be of some use.