An Improved Parallel Inverse Design Method of EMU Wheel Profile from Wheel Flange Wear Viewpoint

An improved parallel inverse design method is proposed for wheel profile optimization. The dominant merit of this method is the ability to automatically search the target performance curve and obtain the optimized profile without artificial experience. With the help of vehicle system dynamic theory, an EMU model has been established in Simpack, and the dynamic performance is calculated with two profiles, i.e., optimization profile and original profile. The contact and mechanical characters are analyzed by Hertz’s theory, Kalker global algorithm, and CONTACT program. It is found that the rolling radius difference (RRD) with the optimization profile is higher than the original one, especially when the lateral displacement is greater than 3 mm. The creep force density with the optimization profile is significant with a wheelset displacement of 6∼9 mm. Compared with the original one, the distribution of contact points with the optimization profile is more uniform, and the contact position is more biased towards the root of the wheel flange. It means the optimization profile can provide higher RRD value and creep force with large lateral displacement, which is beneficial for reducing wheel flange wear. The dynamic simulation indicates that the optimization profile can help reduce the wheel flange force and wheel flange wear in a sharp curve. Meanwhile, the dynamic behaviors and wheel tread wear on a tangent track or a large curved track are also favorable with the optimization profile.

Study on the Different Effects of Power and Trailer Wheelsets on Wheel Polygonal Wear

The wheels of power and trailer wheelset show different polygonal characteristics since their structures are obviously different. Therefore, the frictional self-excited vibration models of wheelset-track systems are established based on the viewpoint of the frictional self-excited vibration in reducing the wheel polygonal wear. Then, the motion stability of wheelset-track systems is studied by using the complex eigenvalue method. The results show that when the creep force between the wheel and rail is saturated, the unstable vibration frequency of the power wheelset is prone to induce 19-20th-order polygonal wear of the wheel, and the trailer wheelset is prone to induce 20-21th-order polygonal wear of the wheel. Meanwhile, the wheel polygonal wear can be effectively alleviated through changing the gearbox position of the power wheelset. And avoiding disc braking at high speeds can suppress the occurrence of wheel polygonal wear. In addition, the development tendency of wheel polygonal wear can be reduced by increasing the Young’s modulus of the brake pad, but Poisson’s ratio has little effect on the development tendency.

Contact and creep characteristics of wheel–rail system under harmonic corrugation excitation

To study the wheel–rail contact and creep characteristics and the evolution law of corrugation with different wavelengths, the wave-like wear is idealized as continuous harmonic excitations consisting of three wavelengths and wave depths, and the vehicle–track space coupled dynamic model is established for specific analysis. The results show that when the wavelength is fixed and the wave depth increases, the average values of rail/wheel vertical vibration acceleration and wheel–rail longitudinal creepage/creep force increase and the average value of transverse creepage/creep force decreases. But, when the wave depth is fixed and the wavelength increases, the average values of rail/wheel vertical vibration acceleration and longitudinal creepage/creep force decrease and the average value of transverse creepage/creep force increases. Both longitudinal and transverse creepages/creep forces contain the characteristic frequency consistent with the passing frequency of initial irregularity. The characteristic frequencies of longitudinal creepages/creep forces tend to develop in the high-frequency band with the increase of wave depth, whereas the characteristic frequencies of transverse creepages/creep forces concentrate in the low-frequency band and decrease with the increase of wave depth. Under the condition of the same wavelength, with the increase of operation times, the wear amount increases slightly in the low-frequency band but greatly in the middle- and high-frequency bands, which shows that rail corrugation will gradually develop toward short wavelength corrugation at the constant velocity. When rail corrugation is formed, its development speed will gradually slow down with the increase of vehicle running times, and the development speed of short wavelength corrugation is faster than that of long wavelength corrugation.

Rail Corrugation Characteristics of Cologne Egg Fastener Section in Small Radius Curve

By analyzing the measured data of rail corrugation in a small radius curve track with Cologne fasteners, the typical passing frequencies of corrugation were obtained. Then, according to actual line conditions, the vehicle-track coupled model and rail material friction and wear model were established and simulated, and rail corrugation characteristics of the curved section were studied. The results show that the variation amplitude of creep force on the inside of a guiding wheelset is large, and it coincides with that of the saturated creep force partially and the coincident part appears periodically. The variation amplitude of creep force on the outside of the guiding wheelset is small, and it is approximately equal to that of the saturated creep force. In addition, the variation range of the wear depth curve on inner rail is mainly changing from 0 μm to 0.0014 μm, showing periodic wavy wear, and when the creep force is equal to the saturated creep force, the wear depth reaches the peak. The variation range of the wear depth curve on outer rail is mainly changing from 0.0005 μm to 0.0008 μm, showing uniform wear. Combined with the predicted profile of rail wear, it can be seen that the inner rail mainly suffers from corrugation on the top of rail and the outer rail mainly suffers from uniform wear on the side, which results in serious corrugation on inner rail and slight corrugation on outer rail. The frequency characteristics analysis of wear shows that the inner rail wear has characteristic frequencies similar to the passing frequencies. Modal analysis results show that the vibration of inner rail at the characteristic frequencies is greater than that of outer rail, which lead to the corrugation of the corresponding frequencies more easily. The wear growth rates at the characteristic frequencies are relatively large, which indicates that the wear at the corresponding frequencies will continue to develop and eventually form corrugation.

Effects of Non-Hertzian Contact Models on Derailment Simulation

The derailment of trains is a complex phenomenon that requires an elaborate contact model in simulation to better understand its mechanism. The CONTACT program is a well-known reference for wheel-rail contact modeling due to its high accuracy. However, its low computational efficiency restricts its applications especially in the context of a multi-body simulation. Therefore, a high computational efficient, simplified and approximate non-Hertzian contact is preferred in derailment simulation. The aim of this research is to verify the efficiency of a recently developed non-Hertzian wheel-rail contact model in derailment simulation, which is a combination of the Kik-Piotrowski model and the KBTNH that is a fast creep force solver for non-Hertzian contacts. To assess the performance of the non-Hertzian model in derailment simulation, the derailment coefficient for steady-state and quasi-steady conditions, the wheel/rail contact forces during flange contact, and the dynamics behaviors of the wheelset prior to the derailment are compared with the state of the art contact methods representing different levels of modeling complexity, accuracy and efficiency, namely the classical approach (Hertz theory+FASTSIM algorithm) and the ‘exact’ solver CONTACT.

Friction-Induced Vibration of a Railway Wheelset-Track System and Its Effect on Rail Corrugation

In the present study, the effect of the radius of railway curved tracks on the slip of a wheel on a rail is studied. A 3D finite-element model of a wheelset-track system is established when the creep force between the wheel and rail is saturated. The occurrence propensity of the self-excited vibration of the wheelset-track system is predicted. It is concluded that the radius of curved tracks has a strong effect on the slip of wheels on rails. In the tightly curved tracks, the slip of the wheel of the leading wheelset on the rail always occurs. The wheelset-track system has a strong occurrence propensity for unstable vibrations on the tightly curved tracks. The accuracy of the rail corrugation prediction based on the unstable vibrations of wheelset-track systems is determined to be 85–90% or higher.