Fatigue of surfaces

Industrial mechanisms use parts in relative motion, usually linked by hydrostatic or hydrodynamic bearings, ball or roller bearings, gears, or cams and plungers. While the performance of these mechanisms depends on global concepts such as dynamics and elasticity, their operation and reliability depend on local concepts of tribology or contact mechanics. Indeed, the stresses generated by contact between elements in relative motion induce stress and temperature fields in the "skin" of these elements which, when compared with the permissible limits for materials, can be the cause of damage. The aim of this article is to define the criteria for analyzing the severity of contact operation and the risk of surface damage. This is an important issue, both from an industrial and a scientific point of view. Indeed, most mechanisms use contacts in their connections, and damage to these contacts is still a major handicap to their reliability. Moreover, modeling their operation and degradation is a recent field whose multi-disciplinary aspects make it a very open sector.

The scope of this study is limited to elastohydrodynamic contacts, i.e. those in which the contact pressure is high, of the order of magnitude of the elastic behavior limits of materials. These include bearings, gears and cams, but exclude bearings.

First, the families of damage will be presented, then, based on mechanical concepts, the operating parameters of these contacts will be defined, and finally certain limits will be established.