Thermally induced roughness of tread braked railway wheels

Roughness (corrugation, waviness) having circumferential wavelengths of 20 to 200 mm on the tread surface of a running railway wheel leads to vibrations in wheels, bogies and superstructure and also in rails, sleepers and roadbed. The vibrations radiate noise to the surroundings. The most efficient way to reduce the rolling noise would be to bring down the roughness on wheel tread and rail head. In the present work mechanisms causing wheel roughness are investigated. Results from full-scale tread braking experiments on an inertia dynamometer are presented. In these tests the influence of various parameters such as block material, wheel speed and braking force is investigated. The temperatures of the wheel tread and the temperatures and vibrations of the block are measured during braking. Tread surface temperatures are measured using IR techniques. The evolution of wheel tread roughness is measured after each braking cycle. Finally, the hardness of the tread is registered and the tread microstructure is determined by use of metallographic methods. In parallel to the experiments, a mathematical model of the interaction between brake block and wheel has been developed. Thermal loading, contact mechanics and surface wear are considered. A detailed understanding of the braking phenomena causing the growth of wheel roughness is aimed at. Countermeasures could then be developed.

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