The Generation Mechanism Of Short Pitch Corrugation On High Resilient Rail And The Measurement Of Rail Unevenness

Rail transit is widely used to undertake a country's main transport task due to its high speed,large carrying capacity,energy-saving and environmentally friendly property.However,accompanying with the convenience brought by its rapid development,railway vibration and noise interfere the regular work of people living beside the lines.In order to decrease the influence of metro system's vibration on environment,resilient fasteners were used to isolate transmission of track vibration to the infrastructure.Field observations,however,show that severe rail corrugation occurs at the tracks where resilient fasteners are used.This new type short pitch corrugation is not caused by so-called pinned-pinned resonance which was believed to be suppressed by rail fastener with low stiffness.Therefore,for better mitigation measures,the mechanism of the corrugation at resilient tracks should be investigated according to its characteristic observed from field study.Track irregularities and corrugation gives rise to severe wheel-rail interaction and thus the fatigue of vehicle and rail parts and railway noise,which makes it a key point of track maintenance.Considering the costs of maintenance work,accurate monitoring of track unevenness becomes very important.Measurement based on inertia sensor mounted on in-service vehicle has attracted the attention of worldwide researchers in recent years.The acceleration signal of bogie and axlebox is the compound result of rail unevenness and rail vibration,which is also related to the unevenness itself.To obtain a better understanding of the measurement result,we studied the dynamic displacement response of the bogies and axleboxes to rail unevenness excitation.The major contents of the thesis involve three aspects: the generation mechanism of the corrugation at resilient tracks;the mitigation measures;the measurement of rail irregularity and corrugation.Firstly,dynamic model for multiple wheel-rail interactions is established,based on which the dynamic property of wheel-rail contact forces is studied in frequency domain with moving irregularity excitation considered.Then the dynamic forces are combined with a two-dimensional longitudinal wear model to calculate the wear amount of rail surface under wheel passages.The characteristic frequency of the corrugation at resilient tracks can be clearly seen from the corrugation growth rate of initial corrugation with different wavelengths.Results show that the corrugation at resilient tracks is related to multiple wheels' coupling effect.Because of the low damp introduced by the high elastic fasteners,the rail vibration wave propagating along the track cannot be effectively decayed,reflecting between wheels and forming standing wave,and thus gives rise to severe dynamic interaction force and differential wear.Secondly,the influence on corrugation of the stiffness and damp of the fasteners is investigated;the effect of tuned rail damper on the dynamic property of wheel-rail interaction force and the decay rate of rail vibration is studied.From the corrugation growth rate calculated by the wear model presented in the first section,we found that tuned rail damper is able to effectively mitigate the corrugation at high resilient tracks.This is because tuned rail damper can decay the rail vibration propagating between wheels and suppress the formation of standing waves.Thirdly,on the basis of the dynamic response of bogies and axleboxes to rail unevenness excitation,we illustrate the measurability and limitation of onboard accelerometer for the measurement of rail corrugation.At low frequencies(corresponding to long wavelengths)away from the P2 resonance,the axlebox response follows the rail unevenness and thus the long wavelength unevenness is measurable and almost equal to the axlebox displacement.At high frequencies(corresponding to short wavelengths),however,the axlebox response is influenced by the standing waves of rail vibration and swiftly varies with frequency,which makes the measurement of short wavelength unevenness through axlebox acceleration difficult.Finally,a remote-controlled and electric trolley is developed for the measurement of short pitch corrugation.