On Transient Rolling Contact Behavior Between Wheel And Rail At Higher Speeds In The Presence Of Short Wavelength Excitations

China railway high-speed is about to enter the era of 400 km/h,and no existing experience is present worldwild for such a high speed,suggesting great opportunities and huge challenges.The operation practice of existing high-speed railways has shown that short wavelength excitations may come into being on wheel and rail contact surfaces during service,deteriorating the wheel–rail rolling contact behavior,reducing the runing quality significantly,and even threatening the running safety of trains.Considering that short wavelength excitations may still occur at higher speeds,it is necessary to conduct thorough research on transient wheel–rail rolling contact behavior at higher speeds in the presence of short wavelength excitations,building a solid theoretical basis for designing railway at higher speeds.In light of such a background,this thesis carries out studies on the transient wheel–rail rolling contact over short wavelength excitations at higher speeds,providing a reference for management of short wavelength excitations of wheel–rail running at higher speeds.This thesis mainly involves researches on wheel–rail rolling contact theories,wheel–rail short wavelength irregularities and low adhesion of rail surface,etc.Therefore,firstly,a literature review of relevant researches is carried out,the problems and challenges faced at higher speeds are pointed out,and the necessity of analyzing the transient wheel–rail rolling contact behavior at higher speeds under short wavelength excitations is proposed.Given the final goal of research,this thesis establishes time domain numerical models that can solve the higher speeds wheel–rail rolling contact behavior,including a vehicle system dynamics model of EMU and a 3–D transient finite element model for wheel–rail rolling contact of the wheelset in the curve,among them,the dynamics model provides the key operating parameters of lateral shift,roll angle and yaw angle of the wheelset for the transient rolling contact model.The above models can introduce short-time low adhesion and short wavelength irregularities,two types of short wavelength excitations which are common in high-speed railways.The specific parameters of short-time low adhesion and short wavelength irregularities involved are obtained from the field tracking test results of in-service high-speed wheel–rail.Before analyzing the influences of short wavelength excitations on the transient wheel–rail rolling contact behavior at higher speeds,the quasi–steady wheel–rail rolling contact behavior without short wavelength excitations(smooth geometry and normal adhesion)are studied,revealing the influences of speeds(350～500 km/h),traction coefficients(0.05～0.3)and adhesion coefficients(0.15～0.45)on transient wheel–rail contact stress,adhesion–slip characteristics and wear,etc.The results shows that this model can realize the quasi–steady rolling of wheel–rail at higher speeds.Because of the quasi–steady state,the influences of speed on the wheel–rail contact solution are almost negligible,and the influences of traction coefficient and adhesion coefficient are the same as that predicted by traditional steady-state rolling contact theories.For example,with the increase of traction coefficient,the slip areas in contact spot increase gradually and the wear increases gradually;with the decrease of adhesion coefficient,the slip areas increase gradually,and the wear increases gradually.Taking the short-time low adhesion of one side rail in curve as an example,the influences of the length of low adhesion zones(0.2～1.0 m),the occurrence of rail side of low adhesion zones,speeds(350～500 km/h),traction coefficients(0.05～0.3)and adhesion coefficients(0.027～0.45)on the transient wheel–rail rolling contact behavior at higher speeds are studied.The results show that under typical parameters,the low adhesions on one side do not cause the whole wheelset to idle or slip with large creepage,that is,the normal adhesion side can balance the problem of insufficient creep force on the low adhesion side.When the low adhesion occurs only in the high rail;1)the low adhesion side will cause the uneven wear on the other side,and when the low adhesion zones are greater than or equal to 0.6 m,the uneven wear on the normal adhesion side will be more serious;2)when length of the low adhesion zones is longer than 0.6 m,the severity of uneven wear on both sides is basically unchanged;3)with the increase of speed,the peak value of wheel–rail force and creepage due to low adhesion decrease,and the degree of uneven wear of two wheels decreases slightly.The results of the low adhesion occurring in the low rail are similar,but the phenomenon is more slight.Therefore,more attention should be paid to the adhesion state of high rail in the field.Of course,if the adhesion level of the normal adhesion side is reduced to a certain extent,which is insufficient to meet the creep force demand of the whole wheelset,the low adhesion phenomenon of the whole wheelset will occur,and then the large creep phenomenon of the wheelset will occur.For example,for the condition with traction coefficient of 0.1,considering the dynamic load reduction effect,if the adhesion coefficient of the normal adhesion side is lower than 0.25,idling or slipping of the wheelset will easily occur.Taking the existence of asymmetric corrugations on both sides of the curve as an example,the influences of the occurrence of corrugations and the phase difference of corrugations occurring on both sides of corrugations occurs on the transient wheel–rail rolling contact behavior at higher speeds are studied.The results show that: 1)the high frequency vibration excited by the corrugations can be transmitted in the wheel–rail system,resulting in high frequency response on both sides,but there are significant differences in the amplitude and phase of the fluctuation between the two;2)the dynamic interaction between wheel and rail can be enhanced when the response caused by corrugations on both sides is superimposed at the same phase between wheel and rail on one side;3)based on the worst cases,that is,response with phase superposition,the lists of critical wave depth of wheel–rail contact loss are proposed under different speeds(350～500 km/h),wavelengths(30～210 mm),axle loads(10～15 t)and under consideration of low frequency vibrations(30% normal load reduction).