Wheel–rail Contact Characteristic Of Wheel-rail Rolling Contact Behavior Test Rig Based On Finite Element Method

Wheel-rail test rig is an important tool to study wheel-rail rolling contact and its damage behavior.The applicability of the test rig is determined by the similarities and differences between the wheel-rail contact behavior of the test rig and the actual railway site.The Wheel-Rail Rolling Contact Behavior Test Rig(WRRCBTR)recently developed at the State Key Laboratory of Traction Power of Souwest Jiaotong University can be classified as scaled wheel-ring rail simulator,of which the discrete support characteristic under rail can be considered compared with the traditional twin-disc test rigs.However,the simulation characteristics and application scope of the WRRCBTR are not clear yet,and its application is still in its infancy.Therefore,in this thesis,the wheel-rail contact characteristic of the WRRCBTR is studied using the finite element method,which provides a meaningful theoretical reference for the its further application.Firstly,it is pointed out that it is necessary to simulate the wheel-rail contact behavior of the WRRCBTR by the finite element method and analyze its simulation characteristics.Then,a literature review is carried out on the application status of wheel-rail test rig at home and abroad,the solution method of wheel-rail rolling contact,and the simulation performance analysis of the test rig.The finite element models of wheel-rail static and transient rolling contact are developed based on the design parameters of the WRRCBTR.The results of wheel-rail force,contact stress and creepage in time domain are obtained.The rail wear depth is further calculated using the Tγ wear model,where T is the tractive force(normal force multiplied by coefficient of friction),γ the slip(percentage difference in surface speeds between the wheel and rail or test specimens).Accordingly,the static contact and transient rolling contact finite element models of wheel-rail in field service are established to quantitatively analyze the wheel-rail simulation performance of the rig.The vertical load of the test wheel is determined by the maximum normal Hertzian contact stress criterion.The influences of the longitudinal position of the wheel,the angle of attack of wheel-rail,and the wheel lateral displacement on the static contact of the test wheel-rail are analyzed,which are compared with the in-service wheel-rail under the equivalent conditions.The results show that the test wheel-rail has the ability to accurately simulate the in-service wheel-rail static contact.The longitudinal position of wheel and the angle of attack have little influence on the static contact.Due to the difference of roll angle,the static contact characteristics such as contact stress,contact patch geometry and Von Mises equivalent stress should be reproduced quantitatively only when the wheel lateral displacement is controlled within-1.0-3.0 mm.Under the condition of smooth wheel-rail surface,the transient rolling contact of test wheel-rail under typical condition with the speed of 116.7 km/h,the traction coefficient of0.1,the adhesion coefficient of 0.5 is solved.The influence of the above factors on the transient rolling contact behavior is invesitgated.A quantitative comparison is made with a speed reduction ratio of 1:3 and in-service wheel-rail of 350 km/h.The results show that the test wheel-rail has higher lateral force,tangential contact stress,spin creepage and rail wear depth.More obvious contact force fluctuation is observed with the increase of the speed.The longitudinal force,tangential contact stress,longitudinal creep rate and rail wear depth significantly increase with the traction coefficient.The decrease of adhesion coefficient makes the longitudinal creep rate and rail wear depth increase and decrease significantly,respectively.For the test wheel-rail transient rolling contact simulation at high speed(350km/h),the solving effect of the model is optimized by considering the initial wheel-rail speed in the implicit integration.A single dent and corrugation are introduced into the rail surface of the trasient rolling contact model,the wheel-rail transient rolling contact behaviors under high-frequency excitations are accordingly solved.The influences of the length and depth of the dent,wavelength and wave depth of rail corrugaiton on the wheel-rail transient rolling contact behavior are invesitgated.The difference between the test wheel-rail and the in-service wheel-rail under typical working conditions is quantitatively conpared.The results show that,under the excitation of the dent,the vertical force and contact stress of test wheel-rail decrease and then increase,and the dent tends to become wider and shallower.When the dent length increases(>10 mm),the fluctuation of wheel-rail vertical force,thr contact stress and the maximum rail wear depth decrease.With the increase of dent depth,both the contact force fluctuation and stress increase,and the maximum rail wear depth generally increases.Under the excitation of rail curragtion,the contact force and stress of the test wheel-rail fluctuates periodically and lags behind the corrugation geometry,and the corrugation has the trend that the wavelength keeps constant and the longitudinal position gradually moves.With the increase of corrugation wavelength,the peak and fluctuation values of the vertical contact force and stress decrease significantly.The rail wear depth changes little when the wavelength exceeds 26.7 mm.When the wave depth increases,the fluctuations of contact force and stress increase linearly,and the rail wear depth decreases on the whole.Compared with the in-service wheel-rail excited by the same proportion of dent or corrugation,the test wheel-rail underestimates the fluctuation of contact force and stress,but overestimates the rail wear depth.As a supplement to the above time-domain results,the inherent characteristics of test wheel-rail and in-service wheel-rail are compared from the perspective of frequency domain.The results show that the vertical sensitive frequency bands of the test track and the in-service track are 2 222-2 901 Hz and 963-1 845 Hz,respectively,and the lateral sensitive frequencies are 1 904 Hz,2 699 Hz and 528 Hz,692 Hz,963 Hz,1 845 Hz respectively.The natural frequency of the test wheel is 2.30-5.05 times that of the in-service wheelset with the same vibration mode.The natural frequencies of the torsion and vertical bending of the test rail are about 4.5 times and 3.3 times those of the in-service rail,respectively.The natural frequency of P2 resonance of the whole test wheel-rail is 1.9 times that of the service wheel-rail.