Law of Friction for Surfaces in Elastic Contact

Abstract

Abstract In the elastic contact of two bodies, there corresponds to each value of the normal load N a definite area of actual contact S, the magnitude of which depends on the geometry of the surfaces and the stiffness of the contacting materials. In practice, friction of solid bodies in absolute elastic contact is not observed in the strict sense of the word. With metals in general there is formed a plastic contact, the magnitude of which is determined by the yield point of the softer metal of the friction couple; with plastics there is formed a nonelastic area of contact as a result of the property of plastics of developing quasi-residual deformation with loads above the limiting forced elasticity analogous to the yield point. Along with these materials there are others which give practically complete elastic contact with solid surfaces. These include rubbery network polymers (vulcanized rubbers). With the contact of vulcanized rubbers and metals, the actual area of touching is determined mainly by the properties of the rubber as a high elastic material with a modulus of elasticity about 104 times less than that of metals. There are at present a number of facts, which confirm that the law of friction, expressing the connection between the force of friction and the normal load, is determined by the load, to the extent that the load is capable of forming an actual area of contact. This postulate, formulated for pure metals and vulcanized rubbers is expressed by the formula: