Tribological Challenges at The Railway Wheel-Rail Interface Contact at the railway wheel-rail interface results in a fascinating array of problems and challenges to the Mechanical and Metallurgical Engineer.
A
ll of these challenges occur in an area typically as big as a South African R1 coin. Contact in this area can be classified as an open tribological system with a constantly changing environment and exposed to all kinds of contaminants. This is different from a closed system such as a sealed gearbox operating in a controlled environment that enables better control of friction, wear and applied lubrication.
the rolling-sliding contact. When the entire contact area is saturated with slip the adhesion coefficient approaches the Coulomb limit and gross sliding occurs in the contact patch. The dependency of the adhesion/traction coefficient on relative sliding (creepage) in the contact area is governed by an adhesion curve as shown.
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The creepage occurring at the wheel-rail interface
Creepage occurring at the wheel-rail interface is responsible for the vast majority of challenges Friction at the wheel-rail rolling-sliding contact provides the means of vehicle propulsion and braking as well as vehicle steering. Here the friction/creep/ traction force increases as the area in the contact patch associated with sliding (relative slip/creepage) increases compared to the area of adhesion for
Adhesion curve (Zakharov 2001)
Railhead corrugation
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THE SOUTH AFRICAN MECHANICAL ENGINEER
VOL 70 Mar/Apr 2020
