Preliminary Study On The Cause Of Wheel Tread Shelling Of KKD Passenger CAR

In recent years, wheelset failure such as tread shelling, out-of-roundness and bearing cage breaking have been often observed on KKD wheels equipped in the air-conditioned passenger cars of25G after running certain time. The problems, which were reported on the networks of several Railway Bureaus, can cause fierce vibrations of the vehicles and lead to poor running quality, and even safety. This thesis investigated the cause of wheel tread shelling of KKD passenger car based on detailed analyses of the wheel-rail relationship. A simple introduction to the structure of this thesis is given in the following.(1) First of all, a literature review on wheel tread shelling is presented, in which significance of the research on wheel tread shelling is indicated.(Chapter1)(2) A wheel rolling contact fatigue (RCF) prediction model is developed on the basis of vehicle system dynamics, shakedown map and damage function, and is coded into a numerical program.(Chapter2)(3) Through field observation and testing, characteristics of the RCF occurred in KKD wheel treads are found out, e.g. their patterns and location. Most of RCF are located at positions about20-50mm outside of mean rolling circle. Meanwhile, wheel tread profiles, out-of-roundness, rail profiles and rail corrugation are measured to better take into account the wheel-rail interaction.(Chapter3)(4) With the developed model the influence of wear on wheel tread cracks and shelling is analyzed in detail, for which the vehicle-track negotiation is simulated for curves of different radii. The analyses cover the wheel-rail contact force, the contact point of the wheel, responses character of material and the magnitude and distribution of wheel damage. It is found that the wheel-rail interaction at sharp curves, especially those with a radius less than700m, is the main reason for the wheel tread cracks and shelling when the wheel and rail are wore.(Chapter4)(5) Vehicle structure parameters such as the longitudinal stiffness of the primary suspension and the axle load, coefficient of friction, rail cant, out-of-round wheels and strength of wheel material are also varied to study their influences on wheel RCF under the precondition of hunting stability of the vehicle. The results reveal that a lower longitudinal stiffness of the primary suspension or a lower axle load can slow down the initiation and development of wheel wear and tread cracks and shelling. Lubrication can reduces the occurrence of wheel RCF and wear, because it results in a lower coefficient of friction and further a smaller wheel-rail creep force. Out-of-round wheels can worsen the wheel-rail interaction, accelerating the formation of wheel tread cracks and shelling. The periodic wheel re-profile can improve the running quality of vehicles on one hand, and timely remove the fatigued material on the other hand to avoid deeply propagated cracks. Besides, higher yield strength of wheel material can reduce the accumulation of plastic deformation, so that it is also beneficial for reducing the occurrence of wheel tread cracks and shelling.(Chapter 5)...