Theory of Wear. Wear Mechanisms

Relative movement between two solids generates two inseparable phenomena: friction, i.e. mechanical resistance to this relative movement, and wear, i.e. loss of material from the opposing bodies. Unlike friction, which has both positive and negative consequences, the wear and tear of rubbing parts in mechanisms and manufacturing tools has only negative aspects and must be minimized. However, contact involves two antagonists, and it is often desirable to concentrate wear phenomena, a priori unavoidable, on one of the two parts, which is easier and less costly to change. On the other hand, in abrasive machining processes, material must be removed from the workpiece material at the highest possible speed, while minimizing damage and wear from abrasive agents. Since wear must be taken into account in the design of machines and manufacturing operations, the aim of this series of articles is to provide models for predicting the wear rate of rubbing parts and manufacturing tools, and thus controlling their service life.

After outlining the issues involved in controlling wear, the previous article [TRI 500] defines wear and describes measurement methods. It then reviews the main criteria for characterizing the modes of interaction between rubbing parts: the nature of the lubrication regime and the mode of deformation of micro-contacts. He presents the Preston-Archard law, which describes the effect of normal force and sliding length on wear, using the wear rate k. He then discusses the microscopic origin of this law and its experimental limitations. After specifying the orders of magnitude of the dry friction wear rate of various materials, he shows how this law enables the calculation of the wear of various tribological systems and the mechanical analysis of abrasive machining processes.

This article presents wear mechanisms of mechanical origin (abrasion, adhesion, mechanical fatigue, burr extrusion), thermomechanical origin (creep, thermal fatigue) and physico-chemical origin (diffusion, tribocorrosion). It emphasizes the interactions between these various wear mechanisms and specifies the orders of magnitude of the corresponding wear rates.

For a more in-depth look at more applied aspects, such as detailed descriptions of worn parts or the implementation of solutions such as the deposition of a protective film, the reader may wish to consult the "Wear of mechanical contacts" articles [BM 5 065]