The role and effects of the third body in the wheel-rail interaction

This paper focuses on the presence of the third body, a solid interfacial layer in the wheel-rail contact. This third body is studied from different viewpoints: its presence including composition, thickness and morphology; and its role with respect to its load-carrying capacity, shearing behaviour, transfer of material and finally global friction coefficient. The general approach is phenomenological and is carried out as closely as possible of the real tribological behaviour of this contact. This paper presents a synthesis of different studies coming from: analysis of specimens taken out periodically from rails and wheels in service, and thus under real contact conditions; and test laboratories, allowing us to impose rolling-sliding conditions with very high precision. From all these studies and results, a better understanding of the role of the third body and its influence on friction, adhesion and damage mechanisms (wear, pits, cracks...) is reached and this is the first step for including its effect in numerical models.