A Preliminary Investigation Into The Causes Of Rail Corrugation On Subway Track With Vanguard Fasteners

With the rapid expansion of subway networks over China,short-pitch rail corrugation has gradually become a wide spread problem of subways in recent years.Field investigations have shown that rail corrugation is very common and severe on section equipped with Vanguard fasteners(a type of vibration-absorbing fasteners with floating rail).Once coming into being,rail corrugations can cause severe vibrations of the vehicle-track system and emit noise.As the basis for better design of counter measures,the initiation mechanism of rail corrugation is studied in this work.Based on field surveys and numerical simulations,the following work has been conducted.(1)First,a survey on initiation mechanism of rail corrugation has been performed,based on which the significance and importance of this study are clarified.(2)A survey of rail corrugation on tracks equipped with Vanguard fasteners is conducted for a subway line in China.It is found that the corrugation is typically 30 to 40 mm in wavelength.Tests of track dynamic behavior and component vibrations have suggested that the corrugation is related to the dynamic characteristics of the track.(3)A 3D solid finite element model was established for the track equipped with Vanguard fasteners,with which modal analyses and dynamic responses under white noise excitations were analyzed.The results show that the vertical vibration of the track is easily excited in the range of 450~496 Hz and 543~638 Hz;the vertical bending modal frequencies of 480 Hz,560 Hz,and 630 Hz are close to the passing frequency of the corrugation.(4)A 3D wheel-rail transient rolling contact finite element model was established.In order to analyze the influence of the track's flexible characteristics on the formation of rail corrugation,a rigid wheelset is assumed in the model,and longitudinal and circumferential irregularities can be applied onto on the surfaces of the rail and the wheel,respectively.By comparing the static and dynamic wheel-rail contact solutions(such as rail displacement,wheel-rail force,wheel-rail contact stress,contact spot shape,stick-slip distribution work,etc.)of the track equipped with Vanguard fasteners and ordinary DTVI fasteners,it is found that the vertical displacement of the rail when the wheelset passes is 5 times larger in the track with Vanguard fasteners,and the rail flip angle is 2~3 times larger.This means that the stability of the wheel-rail contact over Vanguard fasteners is lower than that over DTVI ones,resulting in more severe wear of wheel and rail,and higher possibility of corrugation occurrence.(5)Using the 3D transient wheel-rail rolling contact FE model,the transient vertical wheel-rail force at longitudinal rail pit was calculated for the track with Vanguard fasteners.The effects of the pit lengths and rolling speed on the transient vertical forces were analyzed in the time domain,and then its frequency characteristics were further obtained using FFT.The results show that the vertical force,being in the range of 450-650 Hz,is related to the vertical bending modes of the track with Vanguard fasteners.This means that the short-wavelength corrugations with a wavelength of 30 to 40 mm is related to the vertical vibrations of the wheel-rail system at 450-650 Hz.The vertical bending modes at 480 Hz,560 Hz and 630 Hz are the reason of the short-pitch corrugation.(6)The wavelength,depth,velocity,and wheel-rail friction coefficient are varied to study their influences on the dynamic wheel-rail contact.The results show that they play an great role in the dynamic wheel-rail contact.For the short-pitch corrugation in subway lines,the wave depth should be strictly controlled to avoid severe vibration and noise problems.