A Study On Rolling Contact Fatigue Of High-Speed EMU Wheels

In recent years, rolling contact fatigue on wheel tread of high speed train is found in some passenger line. In order to eliminate the potential threat to the safety and economy of railway system, necessary measure should be taken, while the best strategy should be taken on the basis of well understanding of the initiation mechanism of rolling contact fatigue, this is the meaning of this thesis. The introduction of this thesis is brief as follows:Firstly, literature research of the classification and the cause of rolling contact fatigue is given, as well as a discussion about the factors which affect the rolling contact fatigue.Secondly, the results of general investigation in three high speed train using section about rolling contact fatigue of wheels are given.Essential information as location, angle and statistical analysis of rolling contact fatigue are recorded. And do some research about the relationship between rolling contact fatigue, running distance and wheel location. At the same time, make a classification and statistical analysis about other wheel damage. The results show that the rolling contact fatigue of high speed train wheel tread are related to curve passing behavior, and only happened on the inner side of curve which located between 15 to 30 mm outside of rolling circle. What is more, in order to support model building, hardness test and profile measure of wheel tread and rail head are conducted.In order to understand the cause of rolling contact fatigue through simulation model, vehicle multi-body dynamics model is established. Then introduce the shakedown map and damage function, and explain how to introduce the result of vehicle multi-body dynamics model to shakedown map and damage function which can predicate the rolling contact fatigue of wheel tread.Parameters of vehicle and railway and real profiles of wheel and rail are introduces into vehicle multi-body dynamics model and fatigue damage prediction model to and do some research about rolling contact fatigue initiation mechanism And do analysis on the force condition, hollow wear, radius difference, equivalent conicity and contact point pair of wheel tread with wheels of different running distance on curves of different radii. The results show that rolling contact fatigue cracks of wheel tread are mainly caused by wheel and rail interaction on inner curve, the most important factors are the changed rail head gauge profile of inner side on curve is too low, which is made by pre-grinding and wear, curve passing behavior on small radius curve (mainly a radius of 3500 m) and radius difference and negative equivalent conicity caused by hollow wear.A variation on vehicle parameters such as axle load, longitudinal stiffness of primary suspension, traction torque and braking torque and other parameters like rail cant and friction coefficient between wheel and rail are studied to find out their influence on rolling contact fatigue of wheel tread. The results showthat when the axle load is below 14 t, rolling contact fatigue damage is increasing with axle load slowly, while over 14 t, the damage is increasing quickly. The tread damage is higher with bigger longitudinal stiffness of primary suspension on curve, but low longitudinal stiffness of primary suspension lead a low critical speed, so there should be a balanced value, based on results, this paper recommends set longitudinal stiffness of primary suspension to 7.7 MN. Appropriate traction torque can counteract longitudinal creep force that have the opposite direction with running direction which is happened on the inner side rail on curve, this can alleviate rolling contact fatigue, while a big traction torque can also cause tread damage, the results show that traction torque is best around 0.05. Breaking torque has the opposite effect to traction torque. The rolling contact fatigue damage is more seriously with higher friction coefficient. In high speed railway system, rolling contact fatigue damage increases with rail cant, setting the rail cant to 1:40 is appropriate to minimise rolling contact fatigue damage. In addition, on the basis of results, some suggestions are proposed to relief rolling contact fatigue.Finally, conclusions are summed up, and research direction is put forward.