Wheel Rail Research Articles

Matrix coupled model for the vehicle–track interaction analysis featured to the railway crossing

This paper presents a matrix coupled model for the vehicle–track interaction analysis with the crossing panel taken into account. In this model, the wheel–rail contact is assumed to be elastic and solved by the mathematical matrix formulations. Specifically, the determination of the two-point contact during the transition of the wheel load in the crossing panel is demonstrated. To improve the efficiency while ensuring the accuracy in the simulation, a time step size varying solution is applied in the model. The performance of the crossing is validated using field measurement results and simulation results from other numerical methods. The comparable results proved that the model is capable to catch the main features of the wheel–rail interaction in the crossing panel. Moreover, the effect of track irregularities on the vehicle–track interaction is analysed. The simulation results indicate that track irregularities mainly affect wheel–rail interaction in the regular track. In the crossing panel, the variation of the rail geometry plays a dominant role in the wheel–crossing interaction rather than the track irregularity. This study contributes to the perfection of the current model for the vehicle–track interaction analysis and will help to provide more comprehensive guidance for the design, construction and maintenance of the railway track.

A semi-analytical numerical method for modelling the normal wheel–rail contact

ABSTRACT A new semi-analytical boundary element method is proposed for determining the wheel–rail contact zone and the normal stress distribution within it. The potential contact area is discretised using strip elements, employing an iterative algorithm to satisfy the contact constraints. At each iteration, the length of the contact strips is updated using an analytical expression based on Hertz's theory. This simplified formulation provides good approximation of the pressure distribution, and consequently the contact area, in non-elliptic cases. The reduction in the number of system unknowns by using a semi-analytical methodology also enables fast computation speeds, an indispensable requirement in railway dynamics.

Adaptive slip ratio estimation for active braking control of high-speed trains

Active braking control systems in high-speed trains are vital to ensure safety and are intended to reduce brake distances and prevent the wheels from locking. The slip ratio, which represents the relative difference between the wheel speed and vehicle velocity, is crucial to the design and successful implementation of active braking control systems. Slip ratio estimation and active braking control are challenging owing to the uncertainties of wheel–rail adhesion and system nonlinearities. Therefore, this paper proposes a novel adaptive slip ratio estimation approach for the active braking control based on an improved extended state observer. The extended state observer is developed through the augmentation of the system state-space to estimate the unmeasured train states as well as the model uncertainty. The accurate slip ratio is estimated using the observed extended states. Furthermore, the adaptability of the observer is improved by introducing the beetle antennae search algorithm to determine the optimal observer parameters. Finally, a feedback linearization braking control law is established to stabilize the closed-loop system due to its potential in coping with nonlinearities, which benefits the proven theoretical bounded stability. Experimental results validate the effectiveness of the proposed method.

Research on the Propagation Characteristics of Fatigue Cracks on Rail Surfaces

To solve the problem of rail crack propagation, inadequate studies mainly use a two-dimensional (2D) model for macroscopic crack analysis owing to the failure of accurately reflecting the contact status between the wheel and rail. In this work, we use ANSYS software to establish a three-dimensional (3D) wheel–rail contact model to clarify the microcracks on the rail tread. The influence of the number of horizontal and vertical cyclic loads during the rail’s fatigue crack growth is analyzed. The results suggest that as the number of vertical and tangential cyclic loads increases, the length of the rail crack increases. Using experiments to verify the law between the number of cyclic loads and rail crack growth length, the experimental findings proved that the law of crack growth is basically consistent with the aforementioned simulation results and the outcome of the Paris expansion curve, verifying the validity of the simulation results.

Modelling of vehicle-track related dynamics: a development of multi-finite-element coupling method and multi-time-step solution method

ABSTRACT In this paper, modelling methods are developed to achieve dynamics exploration for the vehicle–track system and its substructures. First, a coupled model, with the satisfaction of wheel–rail displacement compatibility and force equilibrium within each time step, is constructed for the characterisation of vehicle–track interaction, where the vehicle is modelled as a multi-rigid-body system, the ballasted tracks are modelled as a combination of elasticity, damping and mass structures by finite-element method, and time-varying wheel–rail contacts in geometry, creep and force are depicted at the three-dimensional space. On the foundation of vehicle–track interactions, a multi-finite-element coupling method originated from the energy variation principle is presented to integrate multiple substructures, such as bridge and soil subgrade, into the vehicle–track coupled system. Due to the variation of dominant frequencies of the vehicle–track system and its substructures, a multi-time-step solution method is proposed to achieve a hybrid solution of fine and coarse time step size for the vehicle–track system and substructure system, respectively. Numerical examples are presented to show the accuracy and practicality of the proposed model and methods.

Study on the Applicability of Dynamic Stability Evaluation Criteria by Comparison of Trackside Measurement Results of Different Track Structures

Countries such as Korea adopt design codes, evaluation criteria and specifications from standards originating abroad; this leads to a lack of distinction of the separate applications of dynamic stability evaluation parameters between various track structures of different track moduli. This paper discusses the applicability of the dynamic stability evaluation method of railway track structures by assessing 10 different types of railway track sections of a newly constructed railway operation line (5 ballasted and 5 concrete type track structures) by field instrumentation testing. Parameters of track support stiffness (TSS), wheel load fluctuation, derailment coefficient, and rail displacement are measured. The respective results are first compared to the standard criteria (design specification) and comparisons between the different track types are presented as ratios. Findings show that while all of the tracks satisfy the design specification requirements, each track type measurement result varies by a noticeable degree, particularly when comparing between concrete and ballast type track structures. Results of the study demonstrate that using the same dynamic stability evaluation criteria can lead to an incorrect assessment of the track performance evaluation of track structure, and a separate evaluation parameter for ballasted and concrete track structures is required.

Dynamic finite element simulation of wheel–rail contact response for the straight track case

The dynamic effects, mainly including the inertia effect and strain-rate effect, on the dynamic wheel–rail contact behavior become more and more serious as the train speed increases. The inertia effect can be automatically taken into account in explicit finite element analysis codes, while the strain-rate effect needs to be considered via inputting the related material parameters. In the present paper, the influence of strain rate on the dynamic wheel–rail contact response for the straight track case was explored, based on a 3D wheel–rail rolling contact finite element model, via LS-DYNA/explicit algorithm. Effects of the axle load and train speed on typical dynamic wheel–rail responses were discussed, and the results indicate that the coupled train speed with strain rate has a non-negligible influence on dynamic contact responses. The strain rate hardening effect increases the maximum contact pressure and stress, and inhibits the plastic deformation of the wheel–rail system. A rate-sensitive factor (RSF) was then introduced to describe the strain rate hardening effect, confirming that the rail is more sensitive to strain rate compared to the wheel. Finally, an error analysis of the wheel–rail Hertz contact theory was conducted, which further verify the differences between elastic and elastic-plastic contact solutions.

Influence of surface roughness and contact temperature on the performance of a railway lubricant grease

An adequate railway lubrication strategy is an important maintenance procedure that leads to decrease friction and wear extending the service life of the wheel and rail materials, improving the wheel-rail contact, avoiding energy losses and therefore, decreasing costs. On the other hand, poor lubricantion practices lead to losses instead of savings. Moreover, there are many commercial railway lubricants, but there are not proper methodologies to test their performance under different contact conditions.This work aims to evaluate the effect of roughness and temperature on the friction coefficient of ER8 wheel and 115RE rail materials by applying different amounts of railway lubricant grease using a pin-on-disc tribometer and simulating a wheel-flange and rail-gauge contact pressure. For a well-lubricated contact, the results reveal that for the same contact pressure and sliding velocity, rougher surfaces yield a lower friction coefficient.

Comparison of wheel–rail contact models in the context of multibody system simulation: Hertzian versus non-Hertzian

The calculation of the wheel–rail contact forces is one of the most difficult yet time-consuming processes in multibody system (MBS) simulations for a vehicle-track interaction system. The classical combination of the Hertzian model with the FASTSIM algorithm is the most widely used model in MBS code for railway application and the ‘exact’ solver CONTACT is seldom used due to its high computational cost. A trade-off solution between accuracy and computational efficiency is the simplified and approximate non-Hertzian approach. This paper attempts to compare the influence on MBS simulation for rail vehicle system dynamics of the varied combinations of the classical contact models (i.e. Hertz model and FASTSIM), well-known simplified non-Hertzian model (Kik–Piotrowski model) recently developed improved simplified non-Hertzian models i.e. Extended Kik–Piotrowski and Kalker Book of Tables for Non-Hertzian contact (KBTNH), and the CONTACT algorithm. The results show that all non-Hertzian approaches deviate from the classical Hertzian solutions in both local contact and global dynamics and the KBTNH model provides better agreement with CONTACT than the FASTSIM algorithm for non-elliptic contact conditions considered in this study. A detailed analysis of the causes and influences of the difference due to varied contact models is presented.

Fuzzy control system design for wheel slip prevention and tracking of desired speed profile in electric trains

AbstractThis study proposes an anti‐slip control system for electric trains based on the fuzzy logic theory, which prevents the wheels from slipping during the acceleration and simultaneously tracks the desired speed profile. To improve the control performance, the train longitudinal velocity and the slip ratio are estimated. By using a field‐oriented control (FOC), the angular speed of the traction motor is controlled. The fuzzy control system determines the desired angular speed of the traction motor as the reference input of FOC to obtain the desired slip ratio and track the desired speed profile. Simulation results show the effectiveness of the control system in various wheel–rail surface conditions based on the real parameters of ER24PC locomotive.

A New Switch and Crossing Design: Introducing the Back to Back Bistable Switch

A new track swtich and crossing (S&C), the back to back bistable (B2B) switch, is proposed that has shown potential to significantly reduce the wheel/rail contact forces through the switch due to its more continuous wheel/rail contact interface and more uniform track stiffness arising from the elimination of the crossing nose. This offers a major reduction on maintenance cost of future S&Cs. The paper explains the concept and identifies the design guidelines for a current layout and uses vehicle/turnout dynamic modelling to predict wheel rail forces through a switch to identify performance improvements relative to a conventional S&C. Both multi-body simulation (MBS) and Finite Element (FE) model have been developed to account for dynamic and thermal analysis. The new design has shown improvements in lateral and vertical wheel-rail contact forces and less relative rail displacements due to thermal effect compared to the conventional S&C.

Dynamic performance evaluation of an inspection wagon for urban railway tracks

A new type of track inspection wagons (TIWs) for damage detection in urban rail transit systems is proposed to overcome the problems existing in traditional track inspection and ensure efficient and safe detection. Research on the dynamic testing and evaluation of TIWs is inadequate, which is not conducive to the design and improvement of similar products. Considering this, extensive dynamic performance tests and safety assessments under different running speeds were carried out on a new intelligent TIW. In this study, the rail misalignment and harmonic defects were designed to simulate the local irregularities in actual track lines. The accelerations of the axle-box, frames, vision modules, and wheel–rail forces were measured and analysed. Since the vision modules are the most critical components in the inspection system, the experiments focused on the evaluation of the safety of the visual module subjected to various track impacts. The experimental results indicate that the new intelligent TIW shows outstanding dynamic performance in the lab tests. Within the normal working range of the vision module, the vision modules of the wagon can withstand certain impacts from local rail local irregularities owing to its suspension design. Rail harmonic irregularity has a higher impact on wagon vibration than rail misalignment irregularity.

Moving Element Analysis of High-Speed Train-Slab Track System Considering Discrete Rail Pads

This paper presents a study of the dynamic behavior of a coupled train-slab track system considering discrete rail pads. The slab track is modeled as a three-layer Timoshenko beam. The study is carried out using the moving element method (MEM). By introducing a convected coordinate system moving at the same speed as the vehicle, the governing equations of motion of the slab track are formulated in a moving frame-of-reference. By adopting Galerkin’s method, the element stiffness, mass and damping matrices of a truncated slab track in the moving coordinate system are derived. The vehicle is modeled as a multi-body with 10 degrees of freedom. The nonlinear Hertz contact model is used to account for the wheel–rail interaction. The Newmark integration method, in conjunction with a global Newton–Raphson iteration algorithm, is employed to solve the nonlinear dynamic equations of motion of the vehicle–track coupled system. The proposed MEM model of the system is validated through comparison with available results in the literature. Further study is then made to investigate the vehicle–track system accounting for track irregularities modeled as short harmonic wave forms. Results showed that irregularities with short wavelengths have a significant effect on wheel–rail contact force and rail acceleration, and the dynamic response of the track structure does not increase monotonously with the increase of the vehicle speed.

Metal cladding of friction surfaces in liquid media

On the basis of the quantum-chemical method, the possibility of using a liquid lubricant containing a fine powder of the Al-Mg-Li system is considered. It provides a high-quality process of metal cladding of steel friction surfaces and, as a result, an increase in the resource of a single application of a liquid lubricant and the resource characteristics of the tribological system “wheel rail”.

Coefficient of stability against lift by longitudinal forces of freight cars in trains

The paper is devoted to a theoretical study of the car movement stability when exposed to longitudinal forces of a quasistatic nature. The authors obtained the expressions for calculating the resistance coefficient of the car lift by the longitudinal compressive force acting on the car as part of a freight train. The influence of some factor’s combination on the longitudinal forces, at which the car movement stability is still maintained, was analyzed using the analytical dependencies to assess the longitudinal loading of cars in trains. The study was carried out by analytical method for assessing the freight car stability when moving at different speeds along curved track sections. The calculations were made in a curve of small radius taking into account the inertia forces from the unbalanced acceleration. In a theoretical study, the influence of quasistatic longitudinal compressive forces depending on changes in speed and force value, as well as the influence of friction in the wheel flange and rail contact and the eccentricity of fastening the automatic coupler shank on the stability were considered. When applying the results obtained, the stability of freight rolling stock can be increased, which in turn will remove some existing restrictions on the permissible speeds and increase the technical speed of train movement. Using the described methodology for determining the lift resistance coefficient will make it possible to justify the cause of derailment, as well as to develop and put into practice technical measures to prevent the lift of carriages, thrusts and shears of the track.

Reduction of freight car wheel wear of 1520 mm gauge railways

A brief description is given of the comprehensive modernization of standard freight car trucks through the use of devices of American companies adapted for railways with a 1520 mm gauge and wheels with ITM-73 specially developed wear-resistant profile, which allows several times to increase the resource of problematic running gears. An approximate method is proposed for solving the wheel–rail interaction problem with determining the position and size of non-elliptic contact patches, including with conformal contact. Using this method, new profiles have been developed for turning worn wheels (ITM-73-01), as well as new wheels for cars with an axial load on rails of 23.5 tf (ITM-73-02) and 25 tf (ITM-73-03). The data of experimental studies showed that the average wear rate of the wheel flanges of freight cars with complex modernized trucks equipped with wheels with ITM-73-01 profile is 3.5-5 times lower than that of a standard car with a standard wheel profile. According to forecast estimates, the use of wheels with profiles ITM-73-02, ITM-73-03 will allow to achieve even greater increase in the resource indicators of wheelsets for wear of the flanges.

Optimization of Tribotechnical Characteristics of Wheel–Rail Friction Modifiers

Optimization of Tribotechnical Characteristics of Wheel–Rail Friction Modifiers

A Lubricant for Rotaprint Lubrication of the Wheel–Rail System

A Lubricant for Rotaprint Lubrication of the Wheel–Rail System

Detailed wheel/rail geometry processing with the conformal contact approach

This paper proposes a new way of considering wheel–rail contact in multibody systems simulation that goes beyond the traditional planar constraint and elastic approaches. In this approach, wheel–rail interaction is modelled as a force element with pressures and shear stresses distributed over a contact area that may be curved, supporting conformal contact situations. This by-passes the selection of the contact reference location and reference angle, which are delicate aspects of planar contact approaches.The idea is worked out introducing the curved reference surface as the new backbone for the computations, instead of the tangent plane used previously in planar contact approaches. The steps are described by which the curved reference is constructed in CONTACT, using generic facilities for markers, grids, and coordinate transformations, by which generic wheel/rail configurations can be analyzed in a fully automated way.Numerical results show the capabilities of the new method for measured, worn profiles, suppressing discontinuities in the forces when multiple contact patches split or merge. A further application concerns the evaluation of strategies used in planar contact approaches. There we find that the tangent plane’s inclination is of the biggest importance. This should be defined in an averaged way to achieve maximum correspondence to the more detailed curved contact approach.

Improvement of traction capacity of industrial railway transport in the Arctic and on the continental shelf

The Russian Arctic is extremely rich in minerals (hydrocarbons, various minerals, precious metals, etc.). In modern conditions, it is of particular importance to develop vast territories located beyond the Arctic Circle, due to their special socio-economic, geopolitical and defense significance. The rapid development of the Yamal field needs a reliable and modern trunk railway. The project called the Northern Latitudinal Railway has been included in the Strategy for the Development of Railway Transport until 2030. At the temperatures below minus 20 °C, the use of ordinary sand to improve adhesion usually has low effect due to a significant increase in the hardness of ice and ice crust. It should be noted that given sand is present at the contact of ice-glazed rails and wheels, their metal–metal interaction is interrupted by of this sandwiched sand interlayer, which leads to a decrease in the traction characteristics of locomotives. To increase the adhesion coefficient in winter, the author has proposed an engineering solution protected by patent No. 2504492, which consists in the feed of pre-heated, for example, using an induction heater, dry quartz sand to the rail–wheel contact zone. This invention allows increasing the coefficient of adhesion and, consequently, the traction force of locomotives on average up to 10%. Currently, we are carrying out studies to solve the problem of removing ice deposits from the working surface of rails using innovative “sandless” methods that eliminate the need of using ordinary sand. The solution to the problem of removing ice from rails will contribute to the creation of a terrestrial year-round communication between Chukotka and the Barents Sea, which duplicates the Northern Sea Route.