Research On The Formation And Effect Of Railway Wheel Out-Of-Roundness Due To Wheelset Eccentricity

Out-of-round(OOR)wheels of railway trains can lead to the periodic wheel-rail shock during operation,which not only reduces riding comfortableness,but also shortens the service life of the vehicles and track components,and affects the safety of train operation.The dissertation focused on wheel out-of-roundness of high-speed trains and subway trains,the typical characteristics of wheel out-of-roundness were elucidated by analyzing the field test results,and the formation mechanism and influence of wheel OOR wear were studied by numerical simulation.The main research contents and conclusions were as follows:(1)Based on the test results of the axlebox lateral acceleration of a trailer wheelset and the vehicle operating speed of an EMU train,the vibration caused by wheelset eccentricity was analyzed.A finite element model of the trailer wheelset-rails system was established,and the residual static unbalance values of wheels and brake discs were simulated by changing the material densities of specific areas on the wheelset.Using the transient dynamics simulation,the normal wheel-rail contact forces were obtained to analyze the uneven wear of the wheel tread.The effects of the vehicle speed,residual static unbalance values of wheels and brake discs as well as their phase difference on 1st order OOR wear of a wheel(wheel eccentric wear)were further studied.In addition,by recompiling the node coordinates in the finite element model to simulate the real wheel tread profile after eccentric wear,the development of the wheel eccentric wear was studied.The simulation results show that when the train runs at 237 km/h,the residual static unbalance values of wheels and brake discs can excite about24 Hz vibration of the wheel-rail system,which can lead to wheel eccentric wear.With the evolution of this wear,wheel-rail vibrations of about 48 Hz and 72 Hz are excited,which can induce the 2nd～3rd order wheel polygonal wear.When the maximum radius wear value of the worn wheel is greater than 0.15 mm,the vibration intensity of about frequency 72 Hz is greatest in the frequency range of 0 to 150 Hz,resulting in a rapid increase in the 3rd order wheel polygonal wear.Reducing the residual imbalance value and vehicle speed can suppress the formation of 1st order OOR wheels.(2)A rigid-flexible coupled finite element model of a high-speed railway wheelset-rails system was established,with wheelset geometric eccentricity as the only excitation of this model.Using the transient dynamics simulation,the changes of wheel-rail creep forces were calculated when the wheelset ran on the rails.The results show that when the train runs at a high speed of 237 km/h,a wheelset geometric eccentric value greater than 0.7 mm can lead to the longitudinal creep forces on the left and right wheels to periodically reach saturation during operation,causing wheel eccentric wear.The frictional self-excited vibrations of the wheelrail system under the influence of a saturated longitudinal creep force were predicted via the complex eigenvalue analysis.It was found that a vibration of about 605 Hz has the strongest occurrence trend,which could result in 24th～25th order wheel polygonal wear.The phase difference between the geometric eccentric directions of the left and right wheels of a wheelset can cause the phase difference between the saturation states of the creep forces on these wheels,resulting in the phase difference between the 1st and 24th～25th order OOR profiles of these wheels.The frictional self-excited vibration caused by a saturated wheel-rail creep force is one of the frequency-fixing mechanisms for the formation of high-order OOR wheels of highspeed trains.The corresponding phase-fixing mechanism is that the wheel geometric eccentricity causes the longitudinal creep force to reach saturation at a fixed position on the wheel tread in the circumferential direction.(3)Vibration frequencies excited by 24 th order wheel polygonalization were analysed by on-site tests of the axle box vertical vibration acceleration of a wheelset of a high-speed train.A finite element modelling method of OOR wheels was proposed,which was verified by comparing the field measurement with the dynamic simulation.The dynamic response of the fastener clip was simulated by using a rigid-flexible coupled model of the wheelset-track system.The effect of amplitudes as well as typical wavelengths of wheel out-of-roundness on the fracture of the clip was analysed based on the Miner fatigue damage accumulation ruler.The results show that when the wheelset runs at 237 km/h,and the amplitude of the 24 th order wheel polygonalization reaches 0.225 mm and above,excited vibrations of about 1172 Hz are transmitted from the wheelset-rails system to the fastener systems,thus reducing the service operating life of the clips.The decrease of Poisson’s ratio or the increase of Young’s modulus of the material could cause the increasing of the maximum Mises equivalent stress at the clip,which might induce cracks.(4)Based on the perspective that frictional self-excited oscillation causes wheel polygonal wear,a flexible metro wheelset-rails system was built.Using the complex eigenvalue analysis,the unstable vibrations of this system were predicted.Moreover,the influence factors on wheel polygonal wear were studied.The simulation results show that when a subway train runs on a tightly curved track at 50 km/h,the saturated creep forces upon two wheels of the leading wheelset are created.These forces can lead to unstable vibrations of about 51 Hz,60 Hz,and 69 Hz,which are capable of inducing 9th-order wheel polygonal wear.The unstable vibration intensity of the inner wheel-rail system is greater than that of the outer wheel-rail system,which leads to more serious uneven wear of the inner wheel.The length difference between the right-handed and left-handed curved tracks is the main reason for the different polygonal wear rates between the right and left wheels.Fastener failure can lead to a stronger occurrence tendency of wheel polygonal wear.The greater the friction coefficient between the wheel and the rail,the greater the incidence propensity of wheel corrugation.Reducing the fastener vertical stiffness is helpful in slowing down the formation of the metro polygon-shaped wheel,but wheel polygonal wear can be exacerbated when the lateral fastener stiffness is either too large or too small.Wheel polygonal wear easily occurs when the wheelset is located at the mid span of two sleepers rather than at the top of a sleeper.Installing the rail dampers on the track can suppress wheel polygonal wear.The track support structure has some effect on the wavelength of wheel polygonal wear.(5)To determine if the wheel-rail creep force was saturated,1:1 and 1:5 dynamics models of a metro vehicle-track system were established,respectively.Curve negotiations of these two models were simulated.Two finite element models of 1:1 and 1:5 wheelset-track-sleeper systems were established,whose wheel-rail contact parameters were from the dynamic simulation.Using the complex eigenvalue analysis,the stability of each wheelset-track system was studied.The simulation results show that the small-scale wheelset-track model has a good similarity with the full-scale model in the dynamic performance and the stability.Therefore,the small-scale model can be used to study the formation mechanism of wheel-rail uneven wear,both theoretically and experimentally.