Mechanisms for the generation of railroad wheel squeal

Abstract

Railroad wheel squeal is associated with rail vehicles rounding curves of small radii, and it is regarded as one of the most intense and annoying noise mechanisms on rapid transit systems. This paper reviews a theory for the generation of wheel squeal and provides experimental data from laboratory and field measurements that are compared with the theoretical analysis. Squeal occurs when the railroad wheel slides laterally across the rail head, and the theoretical analysis shows that the friction forces generated by this sliding can cause squeal if the coefficient of friction decreases with increasing relative velocity between the wheel and rail. Laboratory measurements of the coefficient of friction (μ) versus the lateral creep of a railroad wheel are discussed that verify the decrease in μ with increasing wheel rail relative velocity. A series of field measurements on several rapid transit lines is described that determined the influence of the ratio of curve radius to truck wheelbase on the occurrence of squeal and provided good agreement with the theoretical prediction for the onset of wheel squeal. Methods of controlling squeal have involved special damped or resilient wheels. A recent survey of the loss factor data of specialized wheels, known to suppress squeal, indicates that less wheel damping is required than that predicted by the present theory. Reasons for this discrepancy are discussed.