High-speed Turnout Research Articles

Numerical characterization and formation process study of rail light bands in high-speed turnout areas

Numerical characterization and formation process study of rail light bands in high-speed turnout areas

Dynamic wheel-rail interaction of a train crossing a turnout under traction/braking behaviour and research on rail wear of the turnout

In order to study the dynamic behaviour of a vehicle passing through turnouts under traction and braking conditions, as well as its influence on the wear of turnout rails, a high-speed vehicle-turnout rigid-flexible coupling dynamic model is established based on the coupling dynamic theory of vehicle and turnout, using China’s No. 18 high-speed turnout and CRH380 high-speed EMU as prototypes. The model is used to analyse wheel-rail creep characteristics, wheel-rail contact mechanics, and wheel-rail wear under traction and braking conditions. The results indicate that when a high-speed train passes through a turnout under traction or braking conditions, the longitudinal creepage of the wheel-rail will change due to the rotative speed difference generated by traction or braking. Furthermore, due to the existence of the lead curve, the longitudinal creep rate of the wheel-rail becomes even more complex when passing through the turnout in the diverging route. The calculations reveal that the traction behaviour of the train leads to a significant increase in wear at the front of the switch rail and nose rail, while the wear number of the switch rail in the heel of the frog after 6m increases significantly under braking conditions. The different impact characteristics of vehicle traction and braking conditions on turnout rail wear obtained in this study can provide guidance for optimizing and grinding the profiles of turnout rails at the throat of railway stations.

The influence of elastic pads deterioration in the fastening system on the dynamic characteristics of the vehicle-turnout system

The deterioration of the elastic pads in the fastening system in high-speed turnout areas increases longitudinal stiffness irregularities along the track, posing potential hazards to wheel-rail impact and train running safety. This paper takes the frog area of No. 18 turnout as an example and constructs a vehicle-turnout rigid-flexible coupling model considering the detailed structure of the fastener elastic pads. By increasing the stiffness of the rubber pad under the tie plate to simulate the deterioration of the elastic pads in the turnout area, the study investigates the effects of deterioration location, degree, and number on the dynamic characteristics of the vehicle-turnout system, providing theoretical guidance for stiffness optimization and maintenance of the turnout area. The results indicate that: 1) the deterioration of the elastic pads significantly affects wheel-rail interaction and safety indicators, while having a minor effect on vehicle running stability; 2) the 95th sleeper (point rail with a top width of 60 mm) is identified as the most critical location for the deterioration of elastic pads; 3) comprehensively considering, the stiffness replacement limit for elastic pads in ballastless turnout areas can be set to twice the design stiffness, which is 50 kN/mm.

Positioning method of track irregularities in high-speed turnout area based on multi-resolution analysis

The assessment and evaluation of complex track geometry parameters (TGP) in turnout areas present challenges for track recording cars due to uncertainties in their positioning on short sections. To obtain precise and reliable measured TGP in the turnout area, a multi-resolution technology based on maximal overlap discrete wavelet transform (MODWT) is used to perform multi-layer decomposition of the longitudinal level. By utilizing the zero-phase characteristic of MODWT, the TGP can be determined by aligning the decomposed weld spacings with their corresponding theoretical lengths. The positioning error is assessed through statistical analysis of measured TGP and numerical simulation using a virtual track inspection method. Finally, a 70 m length of TGP, including the entire turnout section, was extracted with a positioning error of no more than 1.5 m.

Research on ultrasonic guided wave-based high-speed turnout switch rail base flaw detection

Turnout switch rail fracture detection is currently a serious issue in the field of railway transportation. Guided wave detection, a non-destructive testing method, is a good way of studying this issue and looking for a suitable solution. For this paper, a guided wave mode and an excitation position were selected based on the phase velocity dispersion curve and the wave structure. After this, a model was devised for the turnout switch area using the finite element (FE) method. This model considered the straight switch rail, curved stock rail, bolt hole, spacer block, and sub-rail foundation, and verifies the validity of the simulation model through the experiment. The propagation characteristics of guided waves in the switch rail were then simulated in different fracturing states by means of a 30-kHz excitation applied vertically to the rail base. The results showed that a single mode of the guided wave could be generated by this excitation method, showing that it could be used as an effective means for fracture detection. The growth rate of the root-mean-square (RMS) value of the time-domain acceleration signal could then be analysed to identify the state of fracture in the straight switch rail. This discrimination method is suitable for finding fractures parallel to the rail cross-section with a width of 5 mm or more at the bottom of the straight switch rail.

Numerical investigation of wheel-rail rolling contact characteristics and damage in a high-speed turnout switch panel under a large ramp

The damage pattern on a railway line under large ramp is more complicated than that of a standard railway line. In order to investigate the influence of the complex wheel-rail contact evolution in the turnout area on the service characteristics of the switch panel under a large ramp, this paper establishes an explicit FE model of the wheel-rail rolling contact on a 40‰ slope. The performance of a train crossing the turnout and the change in mesoscopic contact behavior is then analyzed under different operating conditions. The distribution rule for wear and fatigue damage to the switch rail under a large ramp is studied, with a regulation strategy proposed for improving the service performance of the switch rail based on the results. These show that there is an obvious cyclical incremental phenomenon on the mechanical behavior at the front end of the switch rail, with uneven abrasion distributed throughout the region. The increase in axle weight, speed and friction coefficient increases the stress concentration of the switch rail and exacerbates the damage. As the train passes through the switch panel, the service life of the switch rail can be significantly improved by reducing the traction.

Evenness improvement method for high-speed turnout crossing areas

In this study, an evenness improvement method for new high-speed turnout crossing areas is proposed for the development of high-speed turnout and amplification of the wheel–rail dynamic impact in the crossing areas. A dynamic analysis model of the vehicle–turnout coupling system is established. In this model, the stock and switch rails as well as the wing and point rails are independent units. These independent units are connected using spring–damper units with variable parameters to accurately simulate the wheel-load transition process and the dynamic characteristics of the turnout. On this basis, an optimized scheme is developed for point rail–wing rail matching based on the center-of-mass oscillation compensation of wheelsets, and the rationality of the optimization method is verified via dynamic simulation evaluation at a high speed. Finally, the proposed method is validated through indoor actual-scale tests. The following are the results of this study. (1) As the vehicle passed over the crossing under the existing design scheme, the center-of-mass oscillation reached an oscillation length of 1.16–1.52 mm such that lifting the wing rail alone failed to eliminate the center-of-mass oscillation of the wheelsets. This is because the point and wing rails were incorrectly matched, leading to a backward shift in the wheel-load transition, thus causing a sharp drop of the wheelsets. Together with wing rail lifting, the longitudinal slope matching of the point rail effectively retained the wheel-load transition characteristics under the existing design scheme and eliminated the center-of-mass oscillation of the wheelsets. (2) As the train passed through the turnout crossing at a high speed, the optimized scheme substantially reduced the center-of-mass oscillation of the wheelsets, wheel–rail dynamic impact, and axle-box vibration while ensuring consistency of the wheel-load transition characteristics with the existing design scheme. (3) The maximum deflection change rate of the wing rail in the assembled crossing was only 1.67 mm/m, which could not meet the requirement of the theoretical longitudinal curve, and would cause the problem of turnout sleeper lifting, affecting the precision of laying turnouts on-site. Computer numerical control machining should be used to achieve the longitudinal curve requirement of the wing rail. The iron plate thickness should be increased gradually to 0.5 mm from the #82 sleeper to the #86 sleeper. Accordingly, the amount of machining of the wing rail should be increased from 0 mm to 2 mm. At the #92–#95 sleepers, this amount of machining should be decreased from 2 mm to 0.6 mm and then increased to 2 mm. This process would accurately realize the theoretical longitudinal slope curve.

An optimised grinding target profile considering long-term service performance: A case study of no. 18 high-speed turnout

The design of rail grinding profiles for turnout has always been a significant subject of research. This paper proposes a rail grinding target profile design method that can improve the serviceability of turnout. Firstly, the high-speed turnout rail profile was parameterised by non-uniform rational B-spline (NURBS), with the amount of key section control point grinding used as a design variable. Secondly, considering the evolution mechanism of turnout dynamics performance and rail wear, a turnout long-term service performance prediction model is established based on deep feedforward network (DFN), with relevant evaluation indexes as the objective function. Non-dominated sorting genetic algorithm-Ⅱ (NSGA-Ⅱ) is used to solve this multi-objective optimisation problem. Finally, a comparative analysis of the performance of the turnout profile before and after optimisation is conducted. The computed outcomes demonstrate that after the turnout is ground, all the dynamic performance indicators have substantially improved in the short term. Additionally, the maximum wear on the straight switch rail has been reduced by 31.2 % and the position of the occurrence has shifted backward, which has improved the stressing of the weak rail elements to some extent. In long-term service conditions, the optimised turnout profile sustains a higher level of riding quality compared to the measured profile. Optimisation of the profile can effectively decelerate the rail wear rate and aid in prolonging the service life of the turnout.

High-speed turnout as part of the track

High-speed turnout as part of the track

Wear Prediction of Curved Switch Rail in High-Speed Turnout and Influence of Wheel and Rail Wear on Vehicle Dynamic Performance

Wear Prediction of Curved Switch Rail in High-Speed Turnout and Influence of Wheel and Rail Wear on Vehicle Dynamic Performance

Study on the optimization of high-speed turnout crossing structures based on actual elastic deformation of point and splice rails

In this paper, to address the shortcomings of the crossing structure design based on the elastic bending center method and the lack of related research, an optimization method for high-speed turnout crossing structures was proposed based on the actual elastic deformations of point and splice rails. Based on the finite element theory, the actual loading characteristics and spatial variable section characteristics of point and splice rails were fully considered, and a refined simulation analysis model of the switching system of point and splice rails in crossing areas was established. Moreover, the elastic deformation lines of point and splice rails in the nonworking state were obtained for the first time, which were consistent with actual situations. On this basis, system optimization was performed for the connecting parts of the crossing with a movable point in a high-speed turnout. In the crossing structure simulation model, the length adjustment values of the first–sixth spacer blocks between the branch line–wing and point rails and between the mail line–wing splice rails were ≤1 mm. Moreover, the lengths of the seventh–ninth spacer blocks decreased by gradually increasing amounts, and the length of the ninth spacer block decreased the most (∼6 mm). The length of the second spacer block between the point and splice rails slightly increased, but the length of the third spacer block significantly decreased by 6 mm. The length adjustment value of the distance block between the point and splice rails was smallest (0.7 mm). The calculated optimal lengths of the connecting parts of the crossing were found to be close to the empirical values used in actual manufacturing processes, and the dimension optimization patterns were completely consistent with actual situation, which validates the proposed optimization method. Thus, the proposed method can effectively improve the coordination between rails and connecting parts in crossing areas, substantially reduce internal stresses in crossing systems, and improve their assembly performance and service life. Moreover, the proposed optimization parameters can provide valuable references for the research on next-generation high-speed turnouts (400 km/h) and for improving the designs of existing high-speed turnouts.

Study on wear characteristics and authorized limits of switch rails of high-speed turnout

PurposeIt is quite universal for high-speed turnouts to be exposed to the wear of the stock rail of the switch rail during the service process. The wear will cause the change of railhead profile and the relative positions of the switch rail and the stock rail, which will directly affect the wheel–rail contact state and wheel load transition when a train passes the turnout and will further impose serious impacts on the safety and stability of train operation. The purpose of this paper is to provide suggestions for wear management of high-speed turnout.Design/methodology/approachThe actual wear characteristics of switch rails of high-speed turnouts in different guiding directions were studied based on the monitoring results on site; the authorized wear limits for the switch rails of high-speed turnout were studied through derailment risk analysis and switch rail strength analysis.FindingsThe results show that: the major factor for the service life of a curved switch rail is the lateral wear. The wear characteristics of the curved switch rail of a facing turnout are significantly different from those of a trailing turnout. To be specific, the lateral wear of the curved switch rail mainly occurs in the narrower section at its front end for a trailing turnout, but in the wider section at its rear end when for a facing turnout. The maximum lateral wear of a dismounted switch rail from a trailing turnout is found on the 15-mm wide section and is 3.9 mm, which does not reach the specified limit of 6 mm. For comparison, the lateral wear of a dismounted switch rail from a facing turnout is found from the 35-mm wide section to the full-width section and is greater than 7.5 mm, which exceeds the specified limit. Based on this, in addition to meeting the requirements of maintenance rules, the allowed wear of switch rails of high-speed turnout shall be so that the dangerous area with a tangent angle of wheel profile smaller than 43.6° will not contact the switch rail when the wheel is lifted by 2 mm. Accordingly, the lateral wear limit at the 5-mm wide section of the curved switch rail shall be reduced from 6 mm (as specified) to 3.5 mm.Originality/valueThe work in this paper is of reference significance to the research on the development law of rail wear in high-speed turnout area and the formulation of relevant standards.

Investigation of transient wheel-rail interaction and interface contact behaviour in movable-point crossing panel

The high-speed turnout is a key part of railway track infrastructure. A process of wheel-load transition and single-wheel/multi-track contact take place in the turnout area, causing significant wheel-rail interaction. Most high-speed turnouts include movable-point crossings. To investigate the wheel-rail transient rolling contact behaviour in movable-point crossings, a 3D finite element (FE) model of a wheelset rolling over a crossing was introduced. The actual geometrical profile of the wheel and the rails in turnouts, the nonlinear materials, the actual relative motion between the point/wing rail, and the moving postures of the wheelset were considered. The simulated mode shape was compared with the experimental mode shape to verify the wheel-rail coupling model. Precise frictional rolling contact solutions and dynamic response, including wheel-rail force, contact stress, equivalent stress, equivalent plastic strain, and stick-slip distribution of the contact patches, were all studied. After this, the parametric analysis of dynamic wheel-rail contact behaviour was carried out. The simulated results indicate that the proposed explicit finite element method can characterise wheel-rail coupled dynamic interaction and mesoscopic rolling contact behaviour well, and improve the understanding of wheel-rail contact behaviour in the movable-point crossing panel of the high-speed turnouts.

Experimental Research on the Load Transfer Mechanism of Tie Plates for 400 km/h High-Speed Turnouts

Based on the research and development demand of the 400 km/h high-speed turnout, a new type of elastic iron tie plate based on stiffness optimization is proposed. The new elastic iron tie plate is expected to reduce the stiffness unevenness and effectively solve the problems in the use of existing elastic iron tie plates. However, the new plate uses rubber bosses instead of rubber washers. There are certain differences in the force transmission mechanism from the original tie plate because of the change in structure of the new tie plate. In this paper, a series of experiments are designed to quantitatively compare and analyze the overall stiffness characteristics of different tie-plate structures and the differences in bolt force transmission and distribution laws. The main conclusions are as follows. The laws of vertical load transfer and distribution in the new tie plate are remarkably different from those for the original tie plate because of the differences in their structures. Under the rated bolt torque, the force transferred to the upper surface of the tie plate through the rubber boss in the new tie plate is less than that in the original tie-plate structure by 5.18 kN in the assembled state. Further, the new structure also has lower tie plate precompression; hence, the influence on the stiffness characteristics of the tie plate is less than that in the original structure. However, the steel sleeve deflection in the new tie plate is greater than that in the original tie plate; that is, a larger proportion of the bolt preload force is borne by the steel sleeve, thus making the vulcanized rubber under the steel sleeve more vulnerable to shear damage. If put into actual use, the tie plate bolt torque will be somewhat different from the rated torque; because of the difference in the torques coupled with the different vertical load transfer mechanisms between the new and the original tie-plate structures, the precompression and the proportion of the bolt preload force borne by the steel sleeves of the two tie plates will also show different degrees of deviation corresponding to different deviations of the tie plate bolt torque. Therefore, the new tie plate structure needs to be further optimized to make the transfer mechanism of preload force of bolt as consistent with the original tie plate as possible. In addition, the vibration and deformation characteristics and long-term service performance of the new type of plate under the condition of vehicle passing will be studied through a small-scale field trial and systematic dynamic tests.

Fatigue damage analysis of the straight switch rail considering complex random loads

It is of particular importance to be able to properly describe the complex alternating loads on a high-speed turnout, in order to accurately analyse fatigue damage and predict the fatigue life of the overall turnout structure. To this end, a vehicle-turnout rigid-flexible coupling dynamics model that considers the randomness of actual vehicle parameters and track conditions was built for this paper. The load-time history of turnout rails was traced under random conditions to systematically analyze the actual change in load characteristics on the straight switch rail. Finally, the fatigue damage and life of the straight switch rail were predicted based on the Multi-load step stress analysis, S-N curve and Miner’s principle of damage accumulation. The results showed that complex random excitation caused a change in load sequence on the straight switch rail, while the fatigue-sensitive area extended backwards to the cross-sections with a top width of 45-55 mm. The severest fatigue damage was observed on the cross-section of the straight switch rail with a top width of 50 mm. The result remains the same as the fatigue damage zone of the on-site straight switch rail, which verifies the accuracy of the calculation.

Study on the Factors Affecting the Wheel–Rail Lateral Impact of the Forepart of the Curved Switch Rail

In the switch rail section of a high-speed turnout, the wheel–rail lateral impact of the forepart of the curved switch rail is the most important factor affecting the passing performance. In order to reduce the lateral impact and improve the passing safety, a complete vehicle–track multi-body dynamics model is devised in this paper. The variation of the wheel–rail relationship when the train passes through is analyzed. The lateral force and derailment coefficient are calculated under different parameters, and the wear index is also calculated under some working conditions. The results show that properly reducing the lateral damping of the curved switch rail can effectively reduce the wheel–rail lateral force and derailment coefficient of this section, while keeping the track shape undamaged. The optimization of rail cant design plays an important role in alleviating lateral wheel–rail impact. Decreasing the height reduction of the switch rail is helpful to optimize the lateral force of the forepart of the curved switch rail. The selection of a suitable cutting mode for switch blade and reasonable control of the wheel–rail impact angle as well as passing speed have positive effects on controlling the lateral wheel–rail impact of the forepart of the curved switch rail.

A multi-objective optimisation method of rail combination profile in high-speed turnout switch panel

This paper presents a multi-objective optimisation method considering the switch and stock rail profiles in the switch panel. Based on the non-uniform rational B-spline (NURBS) theory, a parameterised model of the measured turnout profile is constructed to determine the variables. This study selects the vehicle dynamic performance and wheel-rail contact damage as the objective function to establish a multi-objective optimisation mathematical model that is solved using NSGA-II. Overall performances of the measured profile and the optimised profile are compared and evaluated for two aspects, dynamic performance and wheel-rail contact damage. The following are the conclusions: The maximum lateral vibration acceleration of the axle box is reduced from 2.64–2.09 m/s2, which has a 20.83% decrease. Concerning wheel-rail contact damage, the maximum wear index is reduced from 13.46–11.47 N, the reduction is 14.78%. At the same time, the cumulative surface rolling contact fatigue (RCF) is reduced from 8.29×10−5–7.38×10−5. This article can provide a profile repair method for worn turnouts, which can maximise the comprehensive performance of the turnout within a limited amount of grinding, and can reduce the wheel-rail contact damage of the turnout while taking into account driving stability.

Optimisation of turnout rail profiles based on equivalent conicity

This paper presents a method for the optimisation of wheel–rail profiles, and this is based on the relationships between the equivalent conicity, RRD curve and rail profile slope. This method can be used to improve the riding stability of trains when rolling across turnouts, and to optimise the equivalent conicity. The measured profile of a straight switch rail, i.e. a 60D40 rail laid in a high-speed turnout switch area, was taken as a sample for optimisation. The existing curve of equivalent conicity was lowered for reverse-reasoning calculation of the optimised profile. The optimised profile of the 60D40 rail was taken as the optimal design for an in-service straight switch rail. The effectiveness of the optimised design was then evaluated based on static wheel–rail contact and vehicle-turnout coupling dynamics. The conclusions show that, for an in-service straight switch rail, profile optimisation can effectively improve the wheel–rail relationship, thus enhancing the riding stability of trains in turnout switch areas.

Simulation analysis of high-speed turnout point rail switching force considering influence of external locking device

This study simulates the complete switching process of a turnout and presents an accurate method for calculating the turnout switching force. By establishing an analysis model for the turnout switching of high-speed turnout elastic flexible single-leg point rail No.18 while considering the effects of external locking devices, the actual switching force time-history curve is obtained. Simultaneously, the model is validated with experimental data from the field. Based on this model, the effects of different factors on the switching force of the point rail are calculated and analyzed. The research results show that the external locking device optimizes the stress state of the locking lever, and the switching force acting on the locking lever is much smaller than that on the point rail web. Foreign matter clearly increases the switching force, which is not conducive to the locking of the point rail. When the foreign matter size reaches 3 mm, the switching force of the point rail increases sharply, which causes the switching force to exceed the limit. Overall, the point rail switching force is proportional to the start time difference of each traction point; therefore, the maximum action time difference should be controlled within 0.7 s.

Development and application of a calculation method for the equivalent conicity in high-speed turnout Zones

ABSTRACT Equivalent conicity is an equivalent mean parameter for reflecting the effects of lateral wheel-rail forces on passenger comfort on trains. Based on the asymmetry of the variable cross-section rails in the turnout zone, this paper views the equivalent conicity of a wheelset in the turnout zone as an equivalent conicity of a wheelset in which the wheels match all constant-section asymmetrical rails. A calculation method is established for the equivalent conicity of the turnout zone according to the hunting motion wavelength formula of wheelsets; considering the Rolling Radius Difference (RRD) curve of several ‘zero-crossings’, the principle of minimum gravitational stiffness is used as reference for determining the point ye at which the equivalent conicity of a large lateral displacement is calculated. For fluctuating RRD, the equivalent conicity is calculated using the zoning method; the paper also proposes to evaluate wheel-rail contact geometry in the turnout zone based on the nominal equivalent conicity of the most probable lateral displacement of the wheelsets. Using the matching of wheelsets of different service lengths and the No.18 turnout switch zone as an example, this paper studies the effects of a changing wheel profile on the equivalent conicity of the turnout zone.