Research On Occurrence Mechanisms Of Rail Corrugation Phenomena In Metros

With the rapid development of urban railway transportations,numerous problems of track degradation have been found.As a prominent track degradation in metros,rail corrugation not only influences the comfort of passengers,but also reduces the service life of structural components of vehicles and tracks.Furthermore,more serious rail corrugations can lead to derailment accidents.Rail corrugation has been investigated by worldwide scholars for more than a century,but some common and local phenomena of rail corrugation in metros have not been understood clearly so far.Therefore,some different theoretical models of rail corrugation have been proposed by numerous researchers,which are used to research the occurrence mechanism of these corrugation phenomena.In present thesis,based on the theoretical model of friction-induced oscillation causing rail corrugation,the research works on some phenomena of rail corrugation in metros have been performed.The mian conclusions can be summarized as follows.(1)Both the field measurement and numerical simulation are performed to comprehensively study the new viewpoint of friction-induced oscillation causing rail corrugation.In the field measurement,the surface profiles of the high incidence area of rail corrugation on a sharp curved track supported by rubber-booted short sleepers are measured and the vibration signals of rails at three different positions are collected when the vehicle runs across.In the numerical simulation,a finite element model of a leading wheelset-track system on the relevant track support structure is established.The unstable vibration modes and corresponding dynamic responses are calculated utilizing the complex eigenvalue analysis together with the transient dynamic analysis.The good agreement between the results of the field measurement and numerical simulation indicate that not all of wheel-rail vibration can lead to rail corrugation.The random vibration brings about the stochastic wear of a point on the rail working surface,which cannot lead to rail corrugation.However,the friction-induced vibration can bring about increasing wear of any investigated point,which can cause rail corrugation.(2)In the mechanism investigation on the typical corrugation phenomenon that almost all the low rails of the tight curved tracks suffer from corrugation but the high rails of the same curved tracks rarely do,based on the theoretical model of friction-induced oscillation causing rail corrugation,a finite element model of a leading wheelset-track system on the track supported by fixed-dual short sleepers is established and the friction-induced vibration of the system is researched.Then,the effect of the wheel-rail contact angle and the direction of the saturated creep force on rail corrugation are studied respectively.Parameter sensitivity analyses show that when the contact angle between the wheel and rail is larger than 8.41~o,no friction-induced vibration occurs on the relevant wheel-rail system even if the creep force between the wheel and rail is saturated.Therefore,no rail corrugation occurs on the corresponding rail.Besides,the saturated creep force in the lateral direction more easily produces rail corrugation than that in the longitudinal direction of the track does.The creep forces on the outer and inner wheels of the leading wheelset trend to be saturated when a vehicle passes through a sharp curved track.But because the contact angle between the outer wheel and rail of the leading wheelset is larger or equal to 15-20~o and that between the inner wheel and rail is equal to 1.5-2.5~o,it can be concluded that the unstable vibration of the wheelset-track system on a sharp curved track hardly generates on the high rail but easily occurs on the low rail,which means rail corrugation mostly appears on the low rail of a sharp curved track.(3)In the mechanism investigation on the common corrugation phenomenon that it generally arises when the curve radius is quite small,whereas it rarely occurs when the curve radius is larger or on a straight track,based on the theoretical model of friction-induced oscillationcausingrailcorrugation,differentfiniteelementmodelsof multiple-wheelset-track systems and multi-body models of the vehicle-track systems with track curve radius from 200 m to 800 m are established.The effect of the track curve radius on wheel-rail contact geometry,wheel-rail creep force,friction-induced oscillation of wheelset-track system and rail corrugation are synthetically studied.It can be found that when the track curve radius is less than 350 m,the creep forces on both the outer and inner wheels of the leading wheelset always trend to be saturated.Therefore,the occurrence probability of rail corrugations on these tight curved tracks is close to 100 percent.When the track curve radius is larger than 650-800 m,rail corrugations seldom occur on both low and high rails of these curved tracks due to the unsaturated creep force between the wheel and rail.(4)In the mechanism investigation on the local corrugation phenomenon of rail corrugation occurring on the tracks with Cologne-egg fasteners,based on the theoretical model of friction-induced oscillation causing rail corrugation,the finite element models of multiple-wheelset-track systems on a tangential track and sharp curved track with Cologne-egg type fasteners are established respectively.The simulation results show that a low rail support stiffness value is responsible for rail corrugation on the tangential track.When the Cologne-egg fasteners characterized by a lower stiffness value are replaced with the DTVI2 fasteners characterized by a higher stiffness value,rail corrugation on the tangential tracks disappears under the same conditions.However,rail corrugations on tight curved tracks cannot be suppressed using the same replacement.Furthermore,rail corrugation does not occur on all rails with Cologne-egg fasteners.If the creep force between the wheel and rail reaches or trends to saturated,rail corrugation may occur.(5)In the change interval of track support structure on an identical sharp curved track,the wavelength of rail corrugation in the Cologne egg sleeper section is obviously different from that in the fixed-dual short sleeper section.Based on the theoretical model of friction-induced oscillation causing rail corrugation,the friction-induced vibrations of the multiple-wheelset-track models on the three measuring positions are studied when a vehicle travels through the change interval of track support structure.The simulation results demonstrate that when a vehicle passes through the sharp curved track section composed of Cologne-egg fastener and fixed-dual short sleeper,the dominant unstable oscillation frequencies in the Cologne-egg fastener section and fixed-dual short sleeper section are noticeably different,which successfully reappears the occurrence of rail corrugation on the chance interval of track support structure.In summary,both the field measurement and numerical simulation are adopted to study the occurrence mechanism of common and local phenomena of rail corrugation in metros.The specific research route is listed as follows.Firstly,according to the field measurement and numerical simulation,the theoretical model of friction-induced oscillation causing rail corrugation can be verified.Then,based on the theoretical model,the occurrence mechanisms of the most typical and common phenomena of rail corrugation are investigated.Furthermore,the occurrence mechanisms of some local phenomena of rail corrugation are studied.Normally,the validation of a theoretical model of rail corrugation should include two parts,which are the validations of the most common corrugation phenomena and the local corrugation phenomena.According to the reappearance of several corrugation phenomena in actual lines,the theoretical model of friction-induced oscillation causing rail corrugation has been further verified.In the present thesis,researching on the occurrence mechanisms of different corrugation phenomena in metros not only has important reference significances and academic innovations on the investigation of rail corrugation,but also has important values in engineering application in solving the rail corrugation problems in actual metros.