Wear Theory.From Observation to Modelling of Transfert

The articles [TRI500][TRI501][TRI502] dealt with the generation of particles induced by relative motion between two solids (so-called first bodies), the focus of a scientific study of wear. Setting aside chemical corrosion and diffusion, we have seen that particles are emitted either as a result of a plastic cutting mechanism on a microscopic scale, or as a result of progressive damage to the surface material by the stresses and strains of repeated contact. This article deals with the consequences of this first stage. Particles may leave the contact and, for example, contaminate the lubricant; if the lubricant is insufficiently filtered, particles will then return to continue damaging the surfaces and accelerate wear. Other particles may remain in the contact:

• or because the geometry of the contact and/or the kinematics do not allow them to be expelled; for geometry, let us mention contact between two small kinematic surfaces such as an axisymmetric plane/plane contact, and for kinematics the case of fretting wear, or wear caused by small movements;

• or because these particles have adhered to the surface of one of the first two bodies.

Transfer is therefore manifested by the formation of a deposit of material from B on a part A rubbing against a part B. The surface of A is then transformed. The surface of A is then transformed, contact mechanisms can be upset and wear and friction can change dramatically. It is this last mechanism, "adhesive transfer", which is at the heart of this article.

This phenomenon can affect any type of contact. We shall see that the characteristics of the transfer layer, and the severity of its consequences, also depend on the nominal operating conditions of the tribological system: contact pressure, operating temperature, speeds, lubricant and lubrication system. At this point, we can distinguish between :

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