Interface - The Journal of Wheel/Rail Interaction

OUT OF ROUND WHEELS

Identifying Causes of Out-of-Round Wheels: Measuring Field Experience against Simulations (continued)

Results and Comparison
A large part of the deformations seen in railway operation are polygonizations and flats. Naturally, these effects are more pronounced in smaller-diameter wheels like those used for combined traffic, such as the "Rolling Highway," which is made up of specialized flatcars with small wheel diameters (380/360/335 mm) that are used to transport trucks by rail on some European railways (see opening photo) (5). The greater number of revolutions over the same distance (compared to a larger wheel), and the higher load per wheel, make this type of car ideal for this study. (Also, most of the available data originated from measurements of this type of combined traffic vehicles.)

Wear patterns that evolved for different bogie stiffness are shown in Figure 4. The behavior is highly nonlinear; a small change in the parameters can result in a very dissimilar wear pattern.

Due to the periodicity of the friction, as described above, along with the periodic motion itself, patterns evolve along the wheel surface. Depending on the choice of parameters, the patterns can also be extinguished again. This indicates that it is beneficial to introduce irregularities to break the periodic motion in order to prevent wear patterns from becoming too pronounced.

Another type of wear pattern, tread surface and circumferential cross section, is shown in Figure 5. This figure shows how an 8-mm flat spot spreads through polygonization over the entire surface of a wheel.

As a final example, the direct comparison between a simulated wheel (with an initial flat) and a measured wheel (see Figure 6) shows good correlation between the numerical results and real life (although, quantitatively, they do not agree completely).

Overall, the simulations in this study brought greater insight into the underlying mechanisms and causes of out-of-roundness. Together with field measurements they provided a promising tool to better predict wheels' lifecycles. The study and results also call attention, however, to the need for regularly scheduled, detailed measurements in order to predict wheel life and lifecycle costs. Frequent, detailed measurement also enables early detection of problems — an important factor in reducing defect-related costs, especially as heavier axle loads and higher speeds generate greater stresses on cars and track.

Acknowledgement
The research project "SIMOOR—Simulation of Out-Of-Roundness of Railway Wheels" was supported within the program "ISB – Innovatives System Bahn" by the Austrian Research Promotion Agency (FFG) under project # 811991.

References
(1) Frischmuth, K., “Rail-wheel contact, dynamical simulation and damage,” W. Kosinski, R. de Boer, and D. Sevcovic, editors, Problems of Environmental and Damage Mechanics, Warszawa, 1997. IPPT PAN.

(2) Nielsen, J., and Johansson, A., “Out-of-round railway wheels: a literature survey,” Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, volume 214, pp 79 - 91. Professional Engineering Publishing, 2000.

(3) Frischmuth, K., and Langemann, D., “Distributed numerical calculations of wear in the wheel-rail contact,” K. Popp and W. Schielen, editors, System Dynamics and Long-Term Behavior of Railway Vehicles, Track and Subgrade, volume 6 of Lecture Notes in Applied Mechanics, pp 85 - 100. Springer, 2003.

(4) Olofsson, U., and Lewis, R., Tribology of the Wheel–Rail Contact, Chapter 5, pp 121 - 141. CRC Press / Taylor and Francis, Boca Raton, FL, 2006.

(5) Wikipedia. “Rolling highway,” July 2008 (cited 2008-08-28), http://en.wikipedia.org/wiki/Rolling_highway.

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Bernhard Barkow, EURAIL-ING, Research & Development, Consultant was responsible for the "SIMOOR—Simulation of Out-Of-Roundness of Railway Wheels" research project at BAMM, 2006 - 2008.

Paul Mittermayr, EURAIL-ING, is Managing Director of BAMM, Research & Development, Scientific Consultant, Senior Lecturer (Vehicle dynamics) at UT Vienna, and primary research partner of Wiener Linien and Austrian Federal Railways (OBB) in the fields of contact geometry and profile optimization.