Keywords: railway, vehicle dynamics, derailment, impact.

The impact between a wheel and a sleeper is one of the most important issues for analyzing derailed vehicle motion. The authors have developed a vehicle model that meets derailment conditions that includes wheel-sleeper impacts [1]. With regard to the relationship between a wheel and a sleeper, we modelled three cases based on full-scale running tests under derailment conditions: when the wheel damages the sleeper; when the wheel runs on the sleeper surface; and when the wheel jumps over the sleeper. In this model, the damage to the sleeper is simply represented by the spring and damper. We have modeled a nine degree of freedom half car model that includes wheel-sleeper impacts. The validity of this model has been evaluated by comparing the calculated results with the measured data. Using this model and the simple model which consists of one wheel and one sleeper, we analyzed the motion of a derailed wheel and bogie frame, especially in a vertical direction, and found following conclusions.

1. Through analysis using a simple model, we clarified that the difference between the initial position of the bottom of a wheel and the surface plane of a sleeper , and vehicle speed have a great impact on wheel running behavior. As the difference increases, the wheel tends to move upward. Under the same difference condition, as the vehicle speed increases, the kinetic energy of the vehicle increases and the wheel passes through the sleeper without reaching the surface plane.
2. During the running test, both sleeper-damage running and the sleeper-surface running were observed under low speed conditions. This is because when vehicle speed is low, the wheel easily falls in between sleepers thereby increasing the above defined difference . As the difference increases and vehicle speed decreases, the wheel easily moves upward and switches from sleeper-damage running to the sleeper-surface running.
3. The vertical displacement of a wheel tends to be smaller as vehicle speed increases. This is because when vehicle speed increases, it is difficult for the wheel to fall in between the sleepers and large kinetic energy makes the wheel pass through the sleeper without climbing to the surface of the sleeper. In addition, the bogie frame motion in the vertical direction also decreases with the increase in vehicle speed.

1

H. Sunami, Y. Terumichi, M. Adachi, "Multibody Modeling of a Derailed Vehicle Including Impacts between Wheels and Sleepers", Proceedings of the 14th Asia Pacific Vibration Conference, 3, 1243-1252, 2011.

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