Although difficult to highlight, a layer of third body one fifteenth of micrometer thick was present on the wheels and rails. In the case of the contact, these two layers joined to become a single layer. Initially composed of particles stemming from wheels and rails, this third body flows into the contact to accommodate the sliding between wheel and rail. These flows require that expertises of running surfaces of wheels and rails must distinguish contact fatigue cracks from the flow fronts of third body layers. The exchange flows of third body between wheel and rail are capable of progressively absorbing and digesting certain solid (sand) and fluid (oil) contaminants. This digestion considerably reduces the risks of cracking caused by indentations made by solid contaminants. Local wheel-rail contact behaviour tests must take this third body into account. Although the parameter of friction produced by the third body may be sufficient for models of railway dynamics, contact mechanics must progressively take into account the third body in order to improve the precision of calculations of stress gradients and deformations at micrometric scale, since this is the scale of mechanical rnodels of the initiation of degradation. The third body digests a large number of contaminants and has a complex rheology. This is why it can lead to very different friction values as a function of contact conditions (sliding, pressure, etc.). The study of flow fronts and the local distribution of the third body permits returning to in-situ contact conditions. The third body can therefore be used as a tracer of contact conditions and thus offset the difficulty of instrumenting a contact in-situ. Lastly, without the presence of this third body, the wheel-rail contact would be far less reliable and its life duration considerably shortened.
Presence and role of the 3rd body in a wheel-rail contact
2003
10 Seiten, 19 Bilder, 1 Tabelle, 31 Quellen
Aufsatz (Konferenz)
Englisch
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