Analysis of wheel-rail dynamic characteristics due to polygonal wheel passing through rail weld zone in high-speed railways

Abstract

Wheel polygonal wear and rail weld irregularity are important excitation sources of wheel-rail interface, which will intensify the wheel-rail dynamic interaction, posing threats to running safety. Most of the previous research is focused on wheel rail dynamic responses under a single excitation, while the research on the wheel rail dynamic characteristics caused by the superposition of two excitations is not sufficient considering polygonal wheels generally exist in rail weld zones. On the basis of this, a high-speed vehicle-slab track vertical coupled dynamic model was employed, in order to study the effect of polygonal wheels passing through the rail weld zone on the wheel-rail dynamic characteristics. The vehicle-track coupled dynamic model is divided into two subsystems based on the vehicle-track coupled dynamics theory, that is, vehicle subsystem and track subsystem. Originating from the multi-rigid-body dynamics theory, the vehicle is treated as a four-axle mass-spring-damper multi-rigid-body system by taking one car body, two bogies and four wheelsets into account. As a result, the total degrees of freedom of the vehicle are 10. The rail is simplified as a Bernoulli-Euler beam supported by rail pads. The interactions between the vehicle and rail are characterized by the wheel-rail contact. The dynamic equations of motion for the whole system are described by differential equations. In this dynamics simulation, the measured wheel polygonal wear and rail weld irregularity were used to reflect the real running conditions. It should be noted that the complex-wave rail weld irregularity occurring extensively in the rail weld zones was used. The basic feature of the complex-wave rail weld irregularity is that a main 1m wavelength cosine wave is superposed with a secondary short-wavelengthen wave. Moreover, the influences of the polygonal order and amplitude on wheel-rail dynamic responses were analyzed under the high-speed operation. In this matter, the simple harmonic model was applied to describe the wheel polygon of the single order. In addition, the superposition relationship of the wheel polygonal wear and rail weld irregularity was investigated. The results show that the maximum response occurs at the coincident point where the variation rates of the wheel polygon and the rail weld irregularity are both the maximum. When polygonal wheel passes through the rail weld zone, under the superposition of the wheel polygon and the rail weld irregularity, more obvious wheelrail impact effect is induced, and the high-frequency vibration caused by the measured polygonal wheel is generated. In the rail weld zone, due to the wheel polygonal wear, the wheel-rail vertical force, wheel load rate, wheelset vertical acceleration, fastener force and rail vertical acceleration increase significantly, while the car body vertical acceleration is hardly affected. Under the high-speed operation, the maximum values of the wheel-rail dynamic responses are significantly exacerbated by the increased polygon order and amplitude. In the low orders, the maximum values of the dynamic responses varies slightly with the increase of wave depth, while in the high orders, the maximum values of the dynamic responses increase dramatically with the increased wave depth, which may easily cause instantaneous wheel rail separation.