Wheel-rail Impact Research Articles

Effect of wheel flat on dynamic wheel-rail impact in railway turnouts

Wheel flat is a form of wheel tread defect that reduces the service life and running safety of trains and tracks. Based on the multi-body system dynamics theory, a rigid-flexible vehicle-turnout dynamic coupling modelwas established, and the wheel diameter-varying flat simulation method used to create wheel flat models of different sizes. The most unfavourable phase of flats on the wheels of a vehicle crossing a turnout was studied by scanning and calculating the phase of the flats. The influence of flat size and vehicle speed on a vehicle with flats crossing a turnout was also analyzed. The results show that, compared with a normal wheel crossing a turnout and a wheel flat acting on the interval rail, a wheel flat acting on the wheel load transition of the frog area will excite greater vertical wheel-rail forces and vertical axle box vibration acceleration; in the turnout area, the main frequency band of the vertical vibration acceleration of the axle box is 550–800 Hz, which is rarely affected by the size of flats or the speed of the vehicle. The third-order bending mode of the wheel is excited when the wheel transits from the wing rail to the point rail.

Dynamic response feature of electromechanical coupled drive subsystem in a locomotive excited by wheel flat

As a form of wheel tread failure, a wheel flat becomes increasingly severe in a large axle-load heavy-haul locomotive due to emergency braking or skidding idling. The presence of a wheel flat will cause additional impact forces at the wheel-rail interface which is likely to cause a more rapid fatigue failure of locomotive and infrastructure components. Therefore, it is necessary to determine the dynamics effect of the wheel flat on the railway vehicle system so as to allow efficient monitoring and maintenance. In this paper, a co-simulation model which combines the electrical drive subsystem with a locomotive-track coupled dynamics model considering the complete mechanical transmission subsystem has been presented to analyze the dynamic responses of the locomotive under the effect of wheel flats of different sizes. The results show that the existence of a wheel flat will exacerbate the wheel-rail impact and the vibrations of the components in the locomotive. In addition, the frequency associated with the wheel flat and the gear transmission can be extracted from the frequency spectrum of the current signals in a traction motor, which makes it possible to identify the existence of wheel flats or other rotary component defects in time through analysis of the electrical signals without installing extra sensors.

Finite element model of wheel – Rail impact due to flat spot

Mechanics of wheel-rail interaction is one of the most important research topics in railway engineering. It helps in determining the wheel impact response, track vibration, and track safety. Recently, Dedicate Freight Corridor Corporation of Indian Ltd. (DFCCIL) has started laying out the Dedicated Freight Corridor (DFC), which has made it possible for the freight car axles to carry higher loads and travel at higher speeds than previously possible. It leads to high contact stress on the rail-wheel interface. Under these loads, any defect in the wheel structure leads to wheel-rail impact forces that can lead to significant losses for track owners through damage to rails and sleepers beneath. These imperfections can be wheel flats, irregular wheel profiles, rail corrugations, and differences in the heights of rails connected at a welded joint. Wheel-flats form due to unintentional locking of the wheel-set during emergency braking, which leads to the sliding of the wheel. It leads to the formation of a chord on the circumference of the wheel. A wheel flat can cause a sizeable dynamic impact force, as high as four times higher than regular wheels, and produce high-frequency vibrations, which can damage the track structure. Finite Element Method is an excellent tool for analysing contact stresses between complex geometries in wheel-rail interactions. In this paper, wheel-rail interaction dynamics for a flat wheel is modelled through a three-dimensional finite element (FE) method using Finite Element Analysis (FEA) software package ANSYS. Models used in the simulation are generated according to the Indian Railways standard. The impact force was studied thoroughly, to find the evolution of the contact patch of the wheel rail interface and effect of the impact force in the cross section of the wheel.

Damage tolerance of fractured rails on continuous welded rail track for high-speed railways

Broken gap is an extremely dangerous state in the service of high-speed rails, and the violent wheel–rail impact forces will be intensified when a vehicle passes the gap at high speeds, which may cause a secondary fracture to rail and threaten the running safety of the vehicle. To recognize the damage tolerance of rail fracture length, the implicit–explicit sequential approach is adopted to simulate the wheel–rail high-frequency impact, which considers the factors such as the coupling effect between frictional contact and structural vibration, nonlinear material and real geometric profile. The results demonstrate that the plastic deformation and stress are distributed in crescent shape during the impact at the back rail end, increasing with the rail fracture length. The axle box acceleration in the frequency domain displays two characteristic modes with frequencies around 1,637 and 404 Hz. The limit of the rail fracture length is 60 mm for high-speed railway at a speed of 250 km/h.

Dynamic behavior of resilient wheels at a rail weld joint

The aim of this paper is to investigate the dynamic response of the resilient wheel equipped on the intercity train at the rail weld. A vehicle-track coupling dynamics model with resilient wheels is developed. A rigid multi-body system with 55 degrees of freedom is utilized to model the vehicle system. The rubber layer of the resilient wheel is modeled as a three-directional spring-damper unit between the wheel rim and the wheel core. For the track sub-model, the rails were modelled as Euler Beam and supported by concrete sleepers modelled as mass block. The vehicle and track motion equations are represented as mass-stiffness-damping matrixes. The accuracy of this modeling method at low frequencies is verified via the comparison between the field measured data and numerical results. The dynamic results of the rigid wheel are compared with those of the resilient wheel. Results show that the dynamic wheel-rail force of the rigid wheel is slightly higher than that of the resilient wheel. Furthermore, the mass factor is introduced to investigate the effect of the rubber layer position on the tire acceleration and the wheel-rail impact force. The numerical simulation results are expected to provide references for resilient wheel application into the intercity train.

Numerical investigation of crack initiation on rail surfaces considering laminar plasma quenching technology

To recognize the crack initiation life of a corrugated rail surface after quenching, the explicit finite element model referring to real condition is developed for precise frictional rolling contact solutions considering selective quenching. This takes rail profile evolution and the nonlinear material model used for quenching effect into account. Then the simulation results combined with the fatigue model is integrated for the crack initiation life after quenching, the crack initiation on edge of quenching region is mainly caused by the wheel-rail impact induced by irregularities, which is formed by discontinuous material characteristic between quenching and matrix material. Based on this, the most critically susceptible position to crack and number of cycles are predicted, the simulated results are verified through comparison with quenching rail in service.

Dynamic Modeling and Analysis of a Freight Train Vertical Vibration Reduction System

Based on wheel-rail impact vibration and considering the body stiffness and natural damping, this paper builds a three-degree-of-freedom vibro-impact system model for freight train’s vertical vibration reduction system. The dynamic behavior of the system is analyzed. The Poincaré map of the system is determined by the analytic solution of the system derived from the motion differential equation of the multi-degree-of-freedom vibro-impact system combined with Newton’s second law. It is found that the fork bifurcation, Hopf bifurcation and other dynamical behavior leading to Chaos when the system parameters are changed. In the process diagram, fork bifurcation is easier to be observed by engineers than Hopf bifurcation and can be easily applied to the control strategy of semi-active suspension. The dynamic parameters of the train are optimized to avoid chaos in the train operation, reduce the vertical vibration of the train, improve the stability of the train operation, and provide the theoretical basis for the vibration reduction design of the train.

In-Service Detection and Quantification of Railway Wheel Flat by the Reflective Optical Position Sensor.

Railway wheel tread flat is one of the main faults of railway wheels, which brings great harm to the safety of vehicle operation. In order to detect wheel flats dynamically and quantitatively when trains are running at high speed, a new wheel flat detection system based on the self-developed reflective optical position sensor is demonstrated in this paper. In this system, two sensors were mounted along each rail to measure the wheel-rail impact force of the entire circumference by detecting the displacement of the collimated laser spot. In order to establish a quantitative relationship between the sensor signal and the wheel flat length, a vehicle-track coupling dynamics analysis model was developed using the finite element method and multi-body dynamics method. The effects of train speed, load, wheel flat lengths, as well as the impact positions on impact forces were simulated and evaluated, and the measured data can be normalized according to the simulation results. The system was assessed through simulation and laboratory investigation, and real field tests were conducted to certify its validity and correctness. The system can determine the position of the flat wheel and can realize the quantification of the detected wheel flat, which has extensive application prospects.

Numerical-experimental study of contact-impact forces in the vicinity of a rail breakage

Broken rails or welds are among the rail discontinuities that generate significant impact forces in the wheel-rail contact surface. These forces lead to contact loss and thus an increase in the derailment probability. In this paper, experimental and analytical data are employed to study the impact force as the wheel crosses over a broken rail. In the experimental tests, the wheel-rail impact forces were measured using a Wheatstone bridge circuit. Prior to the field tests, the calibration factor of the Wheatstone bridge was determined by lab experiments. A three-dimensional finite element model (3D FEM) of the wheel and rail was developed and verified using the experimental test results. Using the numerical model, the effects of the distance between the breakage location and the adjacent sleeper, temporary repair of broken rails, and sleeper spacing on the wheel-rail impact forces were studied. The developed numerical model provided acceptable estimations of wheel-rail impact loads, as the difference of estimated and measured impact load is limited to 17%. According to the results of the numerical model, if the rail breakage is positioned between the two adjacent sleepers, impact forces are almost half of that of when the rail breakage occurs close to a sleeper. Moreover, the wheel-rail contact is not lost for any crossing speed of the vehicle. Also, by increasing the sleeper spacing from 60 cm to 70 cm, the impact load increases by an average of 20%, while reducing the sleeper spacing from 60 cm to 50 cm can decrease the impact loads by an average of 13%.

Reinvestigation into railway wheel-track interaction and suspension damage

Without considering either velocity or acceleration effects, the current conventional method presented in literature applies the vertical deflection of a wheel centre caused by a flat defect to the Hertzian contact theory. This method has been numerically and theoretically proved to be inappropriate and can incorrectly predict a higher wheel-rail impact force for a low speed than a high speed. Therefore, under a hypothesis of no wheel bouncing and sliding, two new methods, the velocity-based and the acceleration-based have been proposed. The former method takes the wheel centre deflection change in each computational increment from the Hertzian contact theory while the latter applies the wheel centre acceleration caused by the flat in revolutions to the wheel as a force in dynamic simulation, which interprets the speed effects on impacts precisely. A sensitivity study proves that the velocity-based method is unreliable as opposed to the acceleration-based method. A beam/rigid FE model has also been developed to inspect the wheel-track interaction by performing dynamic analysis in the time domain. It has been found out that the impact responses predicted by the FE analysis and the velocity method are similar and the FE results heavily depend on the compute increment, which implies the FE modelling in ABAQUS may be unreliable for this issue with current applied increments. Finally, the results calculated using the acceleration method have been employed to study the suspension/damper torsional stress caused by a wheel flat. This indicates that a wheel flat may lead to potential fatigue damage if without proper maintenance management.

Train Hunting Related Fast Degradation of a Railway Crossing—Condition Monitoring and Numerical Verification

This paper presents the investigation of the root causes of the fast degradation of a railway crossing. The dynamic performance of the crossing was assessed using the sensor-based crossing instrumentation, and the measurement results were verified using the multi-body system (MBS) vehicle-crossing model. Together with the field inspections, the measurement and simulation results indicate that the fast crossing degradation was caused by the high wheel-rail impact forces related to the hunting motion of the passing trains. Additionally, it was shown that the train hunting was activated by the track geometry misalignment in front of the crossing. The obtained results have not only explained the extreme values in the measured responses, but also shown that crossing degradation is not always caused by the problems in the crossing itself, but can also be caused by problems in the adjacent track structures. The findings of this study were implemented in the condition monitoring system for railway crossings, using which timely and correctly aimed maintenance actions can be performed.

Numerical analysis for investigating wheel-rail impact contact in a flange bearing frog crossing

The transition of wheel-rail contact point between the wheel tread and wheel flange in a flange bearing frog crossing (FBFC) is more complex than in a common crossing, which causes severe frictional rolling contact behavior and wheel-rail dynamic impact. This paper presents an analysis of the transient wheel-rail frictional rolling impact contact using an explicit finite element model of the dynamic interaction between the wheel and FBFC. This study adopts measured wheel geometry and an elastic-plastic material model for the simulations to provide an comprehensive understanding of the transient contact behavior of wheel-FBFC impacts. Each simulation calculates the evolution of the wheel-rail contact force, the distribution of micro-slips, and the stress during the wheel-FBFC impact. Then the contact damage mechanism is investigated and evaluated with the Zobory frictional wear model and “Layer” rolling contact fatigue model. The simulation results show that the irregular structure of the flange bearing frog crossing causes significant wheel-rail dynamic interaction, with the maximum wheel-rail force occurring in the bearing flangeway. The ratio of the tangential contact force to the normal contact force can be exacerbated by the geometric discontinuity of the crossings during impact. The main failure mechanism for different sections in the flange bearing frog crossing is different.

A finite element analysis-based study on the dynamic wheel–rail contact behaviour caused by wheel polygonization

In this study, an explicit finite element analysis method was adopted to investigate the wheel–rail impact response generated by wheel polygonization, using a three-dimensional wheel–rail rolling contact finite element model. In this model, the infrastructure below the rails and the stiffness and damping of the sleeper supports were considered. Then, the characteristics of the wheel–rail contact zone, the stress/strain state and the wheel–rail impact force of the polygonal wheel–rail system were presented and discussed and were compared with those of the ideally perfect wheel–rail system. A parametrical study was then carried out to examine the influences of train speed and the polygonal order of the wheel on the wheel–rail impact response. The finite element analysis results revealed that the vertical wheel–rail impact force induced by wheel polygonization is related to the wheel radial deviation; the maximum contact force, stress and strain are all elevated with the increase of the order of the polygonal wheel, which suggested that the wheel should be repaired when it is in the initial lower order polygonal state. These findings can provide some theoretical and technical support for the optimal design of the wheel–rail system and the safe operation of high-speed trains.

Wayside testing methods for high-frequency vertical wheel-rail impact forces and its applicability

Methods for measuring high-frequency wheel–rail impact forces are indispensable in the study of railway vehicle dynamics. Although there have been many methods proposed for impact force measurement, not all of them are accurate at high-frequencies. Additionally, most of the proposed measurement methods are quasi-static methods that require static calibration. Therefore, the accuracy and applicability of different high-frequency wheel–rail force measurement methods need to be studied and validated dynamically. In this paper, a refined numerical track structure model is constructed to simulate wheel–rail impact behaviors. Under dynamic loading conditions, compare the ‘equivalent value’ and ‘actual value’ of wheel-rail impact forces using different wayside testing methods. The simulation results are then dynamically verified using full-scale indoor test results. The rules dictating effective strain gauge arrangement and the application scope of each measurement method are then obtained, and the relationship between the layout of the strain gauges and the effective measurement length is clarified. The results of this study indicate that the high-frequency wheel–rail impact force measured on site is generally underestimated, and because rail joint splints change the supporting conditions of the rail, the accuracies of all high-frequency wheel–rail impact force measurement methods decrease obviously at such rail joints.

Investigating the Effect of Some Train and Track Parameters on Contact-impact Forces in the Vicinity of a Rail Breakage

Broken rails or welds are the main causes of derailment in railway networks. Therefore, a wheel-rail interaction model, which precisely estimates contact-impact forces in the presence of broken rails, can have a significant effect on derailment risk reduction. This paper attempts to present contact-impact forces in the vicinity of broken rails by employing a detailed 3D finite element model. The model is verified using a field test carried out on a ballasted railway track. Effects of train speed, gap length, axle load and railpad and ballast characteristics are studied on rail-wheel contact forces as well as on railpad and ballast forces. Results suggest that increasing the train speed from 60 km/h to 110 km/h would increase dynamic impact force from 2.46 to 4.11. It is also observed that increasing axle load results in an increase in the wheel-rail impact forces and in railpad and ballast forces, while leading to a reduced dynamic impact factor. Furthermore, investigating the effect of the track parameters demonstrates that ballast stiffness is the most important characteristic of the track, which has a reverse effect on dynamic impact forces. Moreover, unloading length increase and consequently derailment risk increase is highly sensitive to increasing train speed.

Simulation of wheel–rail impact load and sleeper–ballast contact pressure in railway crossings using a Green's function approach

A method for the simulation of dynamic vehicle–track interaction and evaluation of measures to improve the design of railway crossings is presented. To accurately represent the high-frequency dynamics and non-linear contact conditions of the vehicle–track system, the vertical interaction between a wheelset and the crossing is simulated in the time domain using a Green's function approach based on extensive finite element models of track and wheelset in combination with an implementation of Kalker's variational method to solve the non-Hertzian, and potentially multiple, wheel–rail contact. Both wheels of the wheelset in simultaneous contact with the crossing rail and the outer rail are considered. Rigid and flexible wheelset models are compared. The sampled contact geometry of the crossing, including the discrete irregularity between the wing rail and the crossing nose, is used to determine a three-dimensional surface geometry between each pair of adjacent rail cross-sections. A parameter study is performed to investigate the influence of crossing design on the maximum vertical wheel–rail contact force and the contact pressure generated at the sleeper–ballast interface. It is concluded that a design with a combination of increased sleeper width, softer rail pads and implementation of under sleeper pads (USP) will reduce the track stiffness gradients in the crossing panel and mitigate the risk of differential track settlement by lowering the sleeper–ballast contact pressure.

Wheel flat can cause or exacerbate wheel polygonization

ABSTRACT Wheel flat is a common local defect occurring to railway wheels. The relevant standards have specified the operational limits for wheel flats in terms of the length. However, in the actual operation, wheel flats, the sizes of which are smaller than the specified criteria, often appear on wheels, and such flats are difficult to be completely erased by normal wheel-rail wear, resulting in a long-term cyclic wheel-rail impact with a followed damping oscillation. Besides, the mechanism of wheel polygonization has not been explained perfectly. Considering these two aspects, this paper aims to investigate whether wheel flats can cause or aggravate wheel polygonization as well as the influence of vehicle speeds and flat lengths on polygonal wear. Firstly, a parametric and automatic wear calculation model, which combines FaStrip and USFD wear function, is proposed. The simulation results prove that wheel flats can cause or exacerbate wheel polygonization, and vehicle speeds and flat lengths have a large influence on the polygonal wear. Furthermore, the conclusion that wheel flat can cause or exacerbate wheel polygonization is verified by a field test. It further states that those excitations or defects, which can cause long-term periodic wheel-rail impacts, may cause or aggravate wheel polygonization.

Wheel–rail impact loads and noise generated at railway crossings – Influence of vehicle speed and crossing dip angle

Wheel–rail impact loads and noise at railway crossings are calculated by applying a hybrid prediction model. It combines the simulation of non-linear vertical dynamic vehicle‒track interaction in the time domain and the prediction of sound pressure level using a linear frequency-domain model. The two models are coupled based on the concept of an equivalent roughness spectrum. The time-domain model uses moving Green's functions for the linear vehicle and track models, accounting for wheel structural flexibility and a discretely supported rail with spatially-varying beam properties, and a non-Hertzian wheel–rail contact model. Three-dimensional surface geometry of the wheel and crossing is accounted for in the solution of the wheel–rail contact. The hybrid model is compared against field measurements and is demonstrated by investigating the influence of vehicle speed and crossing geometry on the radiated impact noise. Based on simulation results, it is concluded that the impact loads and noise can be mitigated by reducing the effective dip angle at the crossing, which is determined by the vertical trajectory of the wheel when making the transition between wing rail and crossing nose.

A study of formation of high order wheel polygonalization

High frequency and high magnitude wheel-rail impact forces caused by high order wheel polygonalization have been associated with service failures of different structural components in high-speed rail vehicles. In this study, a long-term wear iterative scheme was developed to identify primary contributors of high order wheel polygonalization and its propagation over the service period. The wear model was formulated by integrating an Archard wear model to a coupled vehicle/track dynamic model of a high-speed railway car. The effects of different vehicle and track parameters such as the flexibilities of wheelset and rail, vehicle speed, wheelbase, and rail pad stiffness and damping on the wheel wear were further investigated. The bending vibration mode of the rail segment between two wheelsets, regarded as three half wavelength bending vibration mode near 650 Hz, was identified as the primary contributor to high magnitude wheel/rail contact force in the 500–800 Hz frequency range. This represented a nearly fixed-frequency loading condition. Variations in the vehicle speed and the track could help distribute wheel circumferential irregularities over a broader range of wavelength and thereby mitigate the growth rate of wheel polygonalization of a single order. It is further shown that the wheelset flexibility and higher rail pad stiffness accelerate the wheel wear and more likely contribute to the lower order wheel polygonalization. Increasing the rail pad damping could effectively reduce the rate of growth of high order wheel polygonalization.

Wheel-rail impact interaction on the high-speed railroad bridges

The paper describes interaction of high-speed rolling stock and railroad bridge deck and proves the importance of adequate model of wheel (mechanism) and rail (structure) interaction. The model must consist of a rail and slabs of the ballastless deck. The paper characterizes the results of computer simulation of perspective rolling stock passing through high speed railroad bridge, that contains the uniform bridge superstructure for Moscow – Kazan line. The paper shows that in case of resonant bridge superstructure vibration the risk of derailment is high because of the decline of the wheel-rail contact force down to zero, which means wheel uplift. Moreover, the impact of the wheel is the result of uplift and the impact value is similar to the impact from impossible damages of wheels or rail on high speed railroad in consequence of which rail breaking occur. This rail breaking is the most frequent reason of derailment. The impact forces are equivalent to the impact of the fresh flat of the wheel and may be more than 300 kN while static force is equal to 85 kN. The vertical contact force is rising from zero to maximum value for 0.002 to 0.004 s after uplift. The computer simulation results show that it is the bridge superstructure resonance, which leads to impact interaction. The rail fasteners rigidity decline causes vertical interaction force decrease during the impact but the derailment risk still exists during vibration of “bridge – track – train” system.