Abstract
In railway network, friction is an important factor to consider in terms of the service behaviors of wheel-rail system. The objective of this study was to investigate the effect of a solid friction modifier (FM) in a railway environment. This was achieved by studying the friction, wear, and rolling contact fatigue (RCF) damage on the wheel-rail materials at different slip ratios. The results showed that when a solid FM was applied, the friction coefficient decreased. After the solid FM was separated from the wheel-rail interface, the friction coefficient gradually increased to its original level. With the application of the solid FM, the wear rates of the wheel-rail decreased. In addition, the thickness and hardness of the plastic deformation layers of the wheel-rail materials were reduced. The worn surfaces of the wheel-rail were dominated by pits and RCF cracks. Without the FM, RCF cracks ranged from 84 to 120 µm, and subsurface cracks were generated. However, with the FM, RCF cracks ranged from 17 to 97 µm and no subsurface cracks were generated. These findings indicate possible methods of improving the performance of railway rolling stock by managing friction, and reducing wear and permanent RCF damage affecting both the wheels and rails.
Highlights
In railway network, an appropriate friction level can accelerate and decelerate a train
We found that the liquid friction modifier (FM) could decrease the friction coefficient, but they might lead to severe rolling contact fatigue (RCF) damage to the wheel-rail surfaces if improperly applied [37]
1) The friction coefficient was dependent on the slip ratio and solid FM
Summary
An appropriate friction level can accelerate and decelerate a train. A friction coefficient of the wheel-rail interface that is too low (less than 0.1) causes poor friction for trains during braking, which can result in safety issues by increasing the braking distance [7]. A high friction coefficient under dry conditions (0.5–0.8) could have a negative effect on train operations when braking and accelerating, or cause surface damage (RCF or wear) [8]. Friction modifiers (FMs) can be applied to the top surface of the rail to achieve intermediate friction coefficient (0.3–0.4) in the third body layer. This reduces wear and surface damage by reducing the traction forces without compromising the braking or friction functions. Friction control at the top of the rail has been used in Friction railway maintenance using liquid or solid FMs at the wheel-rail interface to reduce the friction coefficient, thereby reducing the wheel-rail wear, damage, and noise [9,10,11,12,13]
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