Contact between solid surfaces

Abstract

When two solid surfaces are loaded together there will always be some distortion of each of them. Deformations may be purely elastic or may involve some additional plastic, and so permanent, changes in shape. Such deflections and modifications in the surface profiles of the components can be viewed at two different scales. Consider, for example, the contact between a heavily loaded roller and the inner and outer races in a rolling element bearing. The degree of flattening of the rollers can be expressed as a proportion of their radii, i.e., at a relatively macroscopic scale. On the other hand, since on the microscale no real surface, such as those of either the roller or the race, can be truly smooth, it follows that when these two solid bodies are pushed into contact they will touch initially at a discrete number of points or asperities. Some deformation of the material occurs on a very small scale at, or very close to, these areas of true contact. It is within these regions that the stresses are generated whose total effect is just to balance the applied load. Classical contact mechanics assumes the deforming materials to be isotropic and homogeneous; in principle, its results can be applied both to global contacts and to those between interacting asperities.