Rail Temperature Research Articles

장대레일 좌굴 신뢰도에 기반한 국내 고속열차 운행속도 제한의 신뢰도 평가

혹서기에 궤도 좌굴을 방지하고 열차의 주행 안정성을 확보하기 위하여 국내 고속열차 구간에서는 2004년부터 고속철도 안전관리를 위해 레일온도에 따른 혹서기 열차 운행속도 제한을 시행하고 있다. 그러나 이에 대한 개념적, 이론적 배경이 불명확하다. 본 논문에서는 기존 본 연구진에 의해 개발된 장대레일 좌굴확률 평가프로그램에서 허용온도 계산 시 상한 및 하한좌굴온도를 고려하도록 개선하였으며, 국외 연구의 이론적 배경과 국내 선로조건이 고려된 좌굴확률을 근거로 국내 고속열차 운행속도 제한의 타당성과 신뢰성을 고찰하였다. In order to prevent the track buckling in the hot summer and ensure the safety of the running train, as a part of the safety control plan for high-speed railway, the train speed restriction according to the rail temperature was introduced in 2004. However, the conceptual and theoretical background of train-speed restriction is unclear. In this paper, the buckling probability evaluation program( ProCWR) developed by this researchers was improved to take maximum and minimum buckling temperature into account for the calculation of allowable temperature. From the theoretical background of the international research and the buckling probability considering domestic railroad conditions, the validity and reliability of Korean high-speed train speed reduction scheme were investigated.

Numerical Simulation of Temperature Field and Microstructure in the Quenching Process of Steel Rail

In this paper, the effect of rail head organization, cooling and quenching microstructure transformation time in different cooling speed are analyzed by the numerical simulation of the 60kg/m U75V, and study the change law of the rail temperature field and microstructure in the quenching process in the field.

Study of Pier Top Longitudinal Horizontal Rigidity on Rigid Frame Bridge Continuous Welded Rail

The pier longitudinal horizontal stiffness is the key technical parameter of rigid frame bridge and the continuous welded rail. Both the distribution of longitudinal force and the relative displacement between the beam and rail are rely on the longitudinal horizontal stiffness of the pier. This passage takes the symmetrical arrangement of different span rigid frame bridge in ballast track as an example to study the value of pier top longitudinal horizontal rigidity, using the finite element method. The analysis show that when the amplitude of rail temperature variation is less than 50 °C and the nominal temperature span within a certain range, the minimum value of pier longitudinal horizontal rigidity depends largely on the braking conditions. However, as the further increasing of the span, the pier longitudinal horizontal rigidity is restricted by the expansion conditions. Therefore, the small resistance fastening system should be taken into consideration. Especially, if the temperature of rail reaches above 50°C, laying rail expansion adjuster is needed in order to satisfy the requirement of the continuous welded rail temperature on bridge.

Development of a unified railway track stability management tool to enhance track safety

Track buckling is a serious problem for railways. High longitudinal rail stresses contribute to problems such as track buckling, rail joint failure, rail breakage and failure of turnouts. The direct and indirect costs of track buckling problems are very high. The influences of rail temperature, stress-free temperature (SFT) and lateral misalignment of track on track buckling need comprehensive investigation. In this paper, an experimental design comprising strain gauges, thermocouples and rail stress sensors has been implemented on the Queensland Rail heavy haul 60 kg/m rail network. A new creep measurement technique using internal rail stress has been developed. The changes in rail neutral temperature due to the variation of actual rail temperature and the occurrence of rail creep in straight and curved track is quantified. Modes of differences of SFT in the two rails at a location, and of SFT in straight track and in curved track are discussed. The relationship of SFT to rail temperature is also presented. Daily variation in rail temperature due to ambient air temperature is presented. Field trials showed that SFT can vary by 2–3 ℃ during the day. Based on this finding and the derivation of an equation for change of SFT, an improvement in utilising rail creep measurements for assessing track condition has resulted. This finding suggests that it is possible to determine the SFT throughout a day rather than just a single SFT value. This paper also presents a simple track stability management tool that is based on two major parameters, namely rail stress and track resistance. Each parameter in the tool has been given three levels of value to determine the required preventive measures. Overall, the tool decides the need for speed restriction during hot weather based on the quantified parameters from the field trials and rail standards.

Study on Mechanical Properties and Field Monitoring of Ballastless CWR on the Bridge in High-Speed Railway

In the design of long-span bridge , it is necessary to lay the expansion regulator in order to reduce the beam-track interaction. Take the Zhengzhou-Xi’an high-speed railway as an example, the paper created a CWR mechanical model on the bridge using the finite element software ANSYS, proposed the deformation law of the structure and its stress characteristics. Based on the fiber grating testing technology, many monitoring points were laid on the Weihe bridge, to make a long-term monitoring. Processed the monitoring data about rail temperature and temperature force of the regulator, the CWR service conditions were assessed. The study shows that the scheme laying a set of regulator on the longest span Weihe bridge has greatly decreased the beam-rail interaction. All of its design parameters are reasonable. The operation safety indexes can completely meet the need of limits.

System for in Situ Measurement of Neutral Temperature in Continuous-Welded Rail

Research has been focused on developing a system for in situ measurement of stress in continuous-welded rail to use as a basis for the determination of neutral temperature (NT). Continuous-welded rail is known to break in cold weather and buckle in hot weather because of thermally induced stresses. The need for a reliable technique for determination of NT (rail temperature with zero thermal stress) has been an ongoing challenge for railroads since the advent of continuous-welded rail more than 40 years ago. Railroads need to know the level of stress in the rail to schedule slow-order mandates properly and prevent derailments. A prototype (Rail-NT) was developed for wayside rail NT measurement based on nonlinear ultrasonic guided waves. Numerical models were first developed to identify optimum guided wave modes and frequencies for maximum sensitivity to the thermal stresses in the rail web, with minimal influence of the rail head and rail foot. Experiments indicated a rail NT measurement accuracy of a few degrees. The first field tests of the Rail-NT prototype were performed in June 2012 at the Transportation Technology Center in Pueblo, Colorado, in collaboration with the Burlington Northern Santa Fe Railway. The results of these field tests were encouraging; the tests indicated an accuracy for NT measurement of 5°F at worst on both wood and concrete ties. One of the issues that remains to be investigated is the effect of passing trains on the rail NT measurements.

Analysis on the influencing factors of mechanical characteristics of jointless turnout group in ballasted track of high-speed railway

Turnouts are in close proximity to each other in the stations of high-speed railway. The stress and deformation of those turnouts which are laid nearby are influenced mutually and therefore those turnouts should be considered together. On the basis of finite element method, according to No.18 jointless turnout with swing nose frog in the ballasted track of high-speed railway, a finite element calculating model of jointless turnout group coupling the longitudinal, lateral and vertical directions is established. The influencing factors, for instance the number of turnouts, connection form, length of intermediate straight line and ballast bed longitudinal resistance, on the mechanical characteristics of turnout, transverse deformation of switch rail and range of rail temperature for laying turnout are analyzed in this paper. The results show that more turnouts result in more obvious interaction between them when the lengths of intermediate straight line are the same; more significant influence between the turnouts with the connection form of head-to-head is produced compared to that of head-to-end; from the perspective of statics, influence between turnouts could be ignored basically if the intermediate straight line is over 50 m; bigger longitudinal resistance of ballast bed leads to less influence between the turnouts.

Modelling the Effect of Steady State Wheel Temperature on Rail Wear

A moving train subjects a rail cross section to many wheel passes and heat generation at the interface from bulk friction and microslip. Frictional heating at the interface causes the temperature of the contacting rail surface and wheel surface to rise. After the train has passed, the rail temperature drops to ambient till the next train arrives. Wheels, on the other hand, pick up the frictional heat input continuously and hence their steady state temperature could be much higher than that of the rail. A hot wheel provides an additional temperature rise at the rail surface. The accompanying thermal stresses and thermal softening may enhance the rail wear rate. This has been investigated in the present study. A ratchetting failure-based computer simulation has been employed to assess the wear rate of a pearlitic rail steel. It is found that the thermal stress effect on wear rate is only the modest, but thermal softening can enhance the wear rate by up to an order of magnitude for the conditions considered.

Theoretical Approach to Offer a Rational Speed Reduction Scheme in Korea Railway

In order to ensure the safety of running train against the track buckling in a sultry weather, a speed reduction scheme has been implemented in railway operating companies. However, this scheme is based on the limited knowledge on the buckling behavior of the CWR track. The rational speed reduction scheme based on the probabilistic method for the buckling of the CWR track is proposed to apply to Korea high and normal speed railway. Permissible level of the reduced speed according to the rule of restricted speed signal, accepted degree of the buckling probability, the practically managing degree of the variation of the rail temperature, and effects of the maintenance work on the track condition are reflected in the rational speed reduction scheme.

A reliability assessment of railway track buckling during an extreme heatwave

This paper presents a reliability assessment of railway track buckling during extreme heatwave events. Monte Carlo simulation is used to estimate the probability of track buckling. The effects of important predictor parameters such as the effective buckling length and buckling modes of the rails, as well as the rail temperatures at the time of their installation and during the heatwave are taken into account in the simulation. The results show that the probability of the buckling of tracks during an extreme heatwave similar to the event that took place in Melbourne in January 2009 is about 2/100,000 on average, which is a good estimate of the number of the track segments that were actually observed to have buckled in the Melbourne railway network. This assessment demonstrates a science-based approach to reliability assessment for track buckling during heatwaves.

Effect of temperature gradient on track-bridge interaction

Considerable longitudinal rail forces and displacements may develop in continuous welded rail (CWR) track on long-span bridges due to temperature variations. The track stability may be disturbed due to excessive relative displacements between the sleepers and ballast bed and the accompanied reduction in frictional resistance. For high-speed tracks, however, solving these problems by installing rail expansion devices in the track is not an attractive solution as these devices may cause a local disturbance of the vertical track stiffness and track geometry which will require intensive maintenance. With reference to temperature, two actions are considered by the bridge loading standards, the uniform variation in the rail and deck temperature and the temperature gradient in deck. Generally, the effect of temperature gradient has been disregarded in the interaction analysis. This paper mainly deals with the effect of temperature gradient on the track-bridge interaction with respect to the support reaction, rail stresses and stability. The study presented in this paper was not mentioned in the related codes so far.

Numerical Simulation of Heavy Rail Quenching Process

Heat-treatment i s emphasized for its important role to qualify the heavy rail. The temperature and stress field of U71Mn heavy rail during the quenching process were simulated by the FEM software and various kinds of factors that may influence temperature and stress field distribut ion were investigated . The result shows that the main factors influenc ing the temperature and stress field distribut ion were the heating and holding time, as well as the pressure of air blast during the coo l ing, whose values would directly influence the final performance of the heavy rail after the heat treatment. It is significantly valuable for the choice of relevant parameters for the heat treatment of U71Mn heavy rail.

Stable Analysis of CWR Track by its Vibration Characteristics

Stress contained in rails, mainly due to thermally-induced expansion and contraction, results in large longitudinal loads which lead to broken rails and track buckling. According to the beam bending theory of structural dynamics with a consideration of the influence of axial load, a CWR track model is developed in the present study to be used for extensive buckling analysis of CWR tracks. The model discusses CWR track vibration characteristics with a length of unsupported rail subjected to the longitudinal force due to fluctuation of temperature. From the result, it can be gotten that the critical point of the temperature which may cause the rail have the danger of unstable. This model would help to evaluated and measure the real temperature in rail by analyzing the dynamic response of CWR track.

Stable Analysis of CWR Track by its Vibration Characteristics

Stress contained in rails, mainly due to thermally-induced expansion and contraction, results in large longitudinal loads which lead to broken rails and track buckling. According to the beam bending theory of structural dynamics with a consideration of the influence of axial load, a CWR track model is developed in the present study to be used for extensive buckling analysis of CWR tracks. The model discusses CWR track vibration characteristics with a length of unsupported rail subjected to the longitudinal force due to fluctuation of temperature. From the result, it can be gotten that the critical point of the temperature which may cause the rail have the danger of unstable. This model would help to evaluated and measure the real temperature in rail by analyzing the dynamic response of CWR track.

Performance of Linear Motor Type Rail Brake Using Roller Rig Test Bench

Studies have been carried out on a rail brake applying linear induction motor technology, called LIM-type rail brake. This brake is capable of generating braking forces without contact. In addition, this method decreases the rise in rail temperature, and no onboard supply is required by using dynamic braking. It is necessary however to install this brake between front and rear wheels of the bogie. A prototype rail brake system was designed and built and its electromagnetic characteristics were examined on a test bench with a roller rig. These investigations revealed that the LIM-type rail brake could be applicable for practical use.

Multi-axial fatigue analysis of aluminothermic rail welds under high axle load conditions

Fatigue crack initiation analysis is performed at the edge of the weld collar of an aluminothermic weld, in order to examine one of the failure modes that occur in this weld type under high axle load conditions. Since the stress state is multi-axial and the stress history involves rotating principal stresses, a shear based multi-axial fatigue criterion based on the concept of critical plane is exploited. It is believed that the material distress as a result of wheel–rail contact, bending, residual and seasonally-dependent thermal stresses, as well as the geometrical features associated with the weld collar, would directly influence the location of fatigue crack initiation and the severity of damage. The fatigue assessment is performed using thermo-structural finite element analysis followed by the Dang Van multi-axial fatigue criterion implemented as a customized computer code. The method is applied to investigate the effect of operational parameters including the conditions of vehicle hunting or curving, residual stress, seasonally-dependent variations in rail temperature, and deficiencies in track support conditions in the vicinity of aluminothermic welds. The finite element simulation is validated through strain gauge measurements, and the results of fatigue analysis are compared with the locations of fatigue cracking and failure modes that occur in-service.

A methodology for developing high damping materials with application to noise reduction of railway track

A methodology is developed that allows a material to be formulated for a particular damping application where temperature-dependence has to be taken into account. This is applied to a tuned absorber system used for damping the vibration of a railway track. This is required to be effective over a temperature range -20 to 40 deg C. The time-temperature superposition principle is used to convert frequency-dependence to temperature-dependence for a notional material with constant loss factor. This is used in the prediction of decay rates and thereby noise reduction. In addition, a weighted noise reduction is studied by using measured rail temperature distributions. Two types of viscoelastic material, butyl and EPDM rubbers with various amount of fillers and plasticisers, are investigated. The properties of both rubbers have been measured over the range of temperatures for frequencies 300-3000 Hz. For butyl, the best combination of filler and plasticiser gives temperature weighted noise reductions up to 5.9 dB(A). The best EPDM compound gives a temperature-weighted noise reduction up to 6.2 dB(A). Comparing these two rubbers, EPDM is more suitable for low temperatures below 10 deg and butyl is more suitable for higher temperatures above 10 deg.

Predicting the effect of temperature on the performance of elastomer-based rail damping devices

Damping devices for railway tracks have been developed in recent years in which a tuned mass-spring absorber system is formed by an elastomeric material and embedded steel masses. The loss factor and stiffness of the elastomer are very important for the performance of the system but, unfortunately, both properties are sensitive to changes in the temperature. Although having a high loss factor gives good noise reduction, it also means greater variation of stiffness, and consequently tuning frequency, with temperature. Conversely, with lower loss factors the tuning frequency can be kept close to the target but a smaller noise reduction is achieved.To investigate the effect of the temperature on the performance of a generic rail absorber, a simple Timoshenko beam model of the track is used. To this is added a single-frequency continuous tuned absorber. The noise reduction at each frequency is estimated from the ratio of the track decay rates of treated and untreated rails.There is a physical link between the damping loss factor and the stiffness variation with temperature, of which account must be taken. The rate of change of stiffness with log frequency is established by assuming a constant value of loss factor. Using the time-temperature superposition principle, this is expressed in terms of temperature dependence. This is used in the prediction of decay rates and thereby noise reduction at different temperatures. This leads to an assessment of the relative importance of using a high damping loss factor or a temperature-independent stiffness.Finally, a method of weighting the noise reduction at different temperatures is investigated. A distribution of rail temperatures at a site in the UK is used to develop a weighting procedure. This is extended to account for temperature variations at other locations, where less data are available.

Basic Characteristics of Rail Brake Systems Using Linear Motor Technology

An eddy-current rail brake system is effective in stabilizing the braking ability of trains because its braking force does not depend on adhesion between the wheel and the rail. However, the use of the existing type equipped with DC electromagnets causes the rail temperature to increase, bringing the possibility of rail bending. Because of this, it is impractical for use in Japan. Accordingly, we applied an AC electromagnet (the same as those used in linear induction motors) to the rail brake system to reduce rail temperature rise, and investigated its basic characteristics using a rotary-type test machine.

Predicting crack growth and risks of rail breaks due to wheel flat impacts in heavy haul operations

The risk for rail breaks is investigated from mechanical and statistical points of view with particular focus on the influence of impact loads from flatted wheels. For a presumed rail head crack geometry and rail temperature, the stochastic relation between the crack position along the rail and the wheel flat impact position results in a risk of fracture. In addition to the analysis of the risk for final fracture, rail crack growth is also studied. In particular, the contribution of wheel flat impacts on crack growth rates is quantified. The study takes the form of a dynamic load analysis that evaluates rail bending moments due to wheel flat impact. Then, a fracture mechanics analysis is employed to establish stress intensity factors for rail head cracks under bending and temperature loading. These analyses are then combined to give risks of rail breaks and to quantify crack growth rates for varying operational conditions.