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The objective of this study was to investigate the influence of contaminants on the tribological behavior of wheel–rail contact. Sand, phosphate, sulfur, and cement were the studied contaminants identified after a Tunisian railway expertise. All friction tests under different contaminants were conducted using pin-on-disk machine, maintaining the same sliding velocity and Hertzian pressure, respectively, at 0.1 m/s and 1000 MPa. All results were compared with reference of two configuration contacts: wheel tread-rail head (clean dry condition) and wheel flange-rail gauge (clean lubricated condition). The main findings of this study could be listed as follows. First, with reference to clean and dry condition tests, sand and cement showed a higher adhesion than phosphate and sulfur. Second, all contaminants increased the adhesion coefficient with reference to clean and lubricated conditions. Third, sulfur generated the lowest energy-wear coefficient yielding a mild wear. Fourth, sand, cement, and phosphate generated a higher energy-wear coefficient yielding an abrasive wear. Finally, the highest energy-wear coefficient was obtained with sand.

The tribological behaviour of anodic oxide layer formed on Al5754, used in automotive applications, was investigated against test parameters. The friction coefficient under different normal loads, sliding speeds, and oxide thicknesses was studied using a pin on disc tribometer. Results show that the increase of load and sliding speed increase the friction coefficient. The rise of contact pressure and temperature seems to cause changes in wear mechanism. Glow-discharge optical emission spectroscopy (GDOES) was used to investigate the chemical composition of the oxide layer. Morphology and composition of the wear tracks were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). On the basis of these characterization techniques, a wear mechanism was proposed. The observed mechanical properties can be related to the morphology and the chemical composition of the layer.

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Abstract:The objective of this study was to investigate the influence of the surface topography on the tribological behavior of the wheel/rail contact. Four different groove orientations forming the surface topographies-smooth surface, 0°, 45° and 90°-were manufactured by grinding and compared. All friction tests with different surface topographies were conducted using an alternative tribometer simulating the pure sliding process in the wheel-rail contact. The Hertzian pressure was maintained at 1,000 MPa with two levels of sliding velocity (20 mm/s and 80 mm/s). This study resulted in five main findings.First, the initial surface topographies seemed to have a significant effect on the friction coefficient independently of the speed. Second, the increase of the sliding velocity would decrease the friction coefficient. Third, especially when accompanied with a high sliding velocity, an initial rough surface would have a significant effect on the wear of the wheel. Fourth, the highest wear values were observed at groove orientations of 45° when accompanied with a high sliding velocity. Finally, the break-in duration seemed to depend on the initial surface topographies of the rail and the sliding velocity.