Welded Rail Research Articles

An analytical calculation method for displacement and force on continuous welded rails in temperature-transition zone

Abstract The rails at the transition between a bridge or subgrade and a tunnel tend to creep longitudinally because of a temperature gradient on the rail, which can cause irregularity in the track. The longitudinal temperature distribution along the rail and the longitudinal resistance of the fasteners are the main influences on rail creep. In this paper, the linear and nonlinear models of longitudinal temperature distribution on rails and the longitudinal resistance of fasteners are tested for their accuracy in predicting rail creep. By researching the rail at the temperature-transition zone, differential equations for the longitudinal displacement and force of the rail are established. To predict the changes that a rail will experience in a temperature-transition zone, expressions for the longitudinal displacement and force are derived from these differential equations. The derived calculation scheme is tested for three conditions: linear models of both rail temperature and longitudinal resistance, linear rail temperature and nonlinear resistance, and nonlinear models of both rail temperature and displacement. The maximum longitudinal rail displacement and the maximum longitudinal additional force in all three conditions are compared to reveal the influence of the maximum temperature force gradient multiple and the maximum fastener resistance on longitudinal displacement.

Experimental and numerical investigation of the characteristics of flash-butt joints used in continuously welded rails

Continuously welded rails are widely used in the Iran railway network, which are generally built using the flash-butt welding process. To accurately model the flash-butt welding process, thermal analysis, and prediction of the welding residual stresses, the influence of upsetting force on the total electrical resistance and a material model with consideration of the influence of temperature on the material properties are included in the numerical modeling. In this paper, numerical and experimental studies, including the finite element method, thermography, metallography, and hardness testing are performed to determine the characteristics of the welded UIC60 rail. By studying the fractured flash-butt welded UIC60 rails, it is shown that the location of the crack initiation and the rail failure in the web and heat affected zone of the welded rails was similar as compared to the maximum tensile residual stress calculated by numerical simulation. According to the numerical and experimental results, it is shown that four key parameters – such as the maximum temperature during the welding process, the total welding time, the upsetting time, and the upsetting force – control the size, microstructure, and the hardness profile of the heat affected zone which directly affects the characteristics and quality of welding.

Installation of CWR on Long-Span Bridges of Ballastless Tracks

In Korea, ballastless track bridges have been built since the early 1900s and are one of the most popular railway bridges. However, because the self-weight of the upper structure is relatively lightweight compared to the train, severe noise and vibration occur, and it is difficult to increase the train speed, owing to a 20-50 m long rail being connected by the seam plate. To overcome these problems, welded rails for ballastless track bridges are urgently required. This study preliminarily investigates the installation of continuous welded rails (CWR) for ballastless tracks in order to analyze the effects of and issues due to the track-bridge interaction in this configuration and determine solutions. Keywords: Ballastless Track, Continuous Welded Rail, Additional Axial Stress

Kalman Filter Based Load Monitoring in Beam Like Structures Using Fibre-Optic Strain Sensors.

The paper presents a proof of concept of a new methodology for the load estimation in beam-like structures under complex loading. The paper customizes a Kalman Filter (KF) based estimation technique which is shown to be robust to the presence of measurement noise as well as the changing condition of the beam for estimation of loads in beam-like structures. The methodology was validated using numerical as well as experimental data. The initial studies indicate that the proposed methodology has promise for applications where monitoring and classification of the strains is necessary, such as those in continuous welded rails.

Comparative analysis of structural state of welded joints rails using method of Barkhausen effect and ultrasound

To identify the imperfection of technological processes during smelting of rail steel and the subsequent production of rails in modern conditions, traditional methods of research are not enough. Implementation of Barkhausen effect amplitude measurement, residual stresses for defect detection, material structure analysis with the purpose of improving production technology is proposed. Thus, combination of traditional metallographic, mechanical and new research methods that complement and ascertain the requirements of GOST R 51685-2013 can allow conducting fast and accurate analyzes of the conformity of rail steels to GOSTs, and will also determine the causes of rail failure, inconsistencies in technological processes.

Effects of initial up-warp deformation on the stability of the CRTS II slab track at high temperatures

Initial up-warp deformation is one of the key factors that affect the stability of the China Railway Track System type II (CRTS II) slab track. Through modeling analysis, we studied the effects of different initial up-warp conditions on the deformation and stability of a slab track at high temperatures. Based on the theory of ‘variable span length’ in continuous welded rail (CWR), a vertical stability analysis model of the CRTS II slab track was established using the finite element method (FEM), and a scale model test was conducted. The effects of initial up-warp deformation features, such as rise displacement, span length, and line type on the stability of track slabs at high temperatures were studied through simulation. Results showed that the trends of vertical displacement were almost the same based on the FEM, analytical method, and on-site testing, but there was a better agreement between results from the FEM and the analytical method. When the span length was 6.5 m and the rise displacement of the initial up-warp reached 15 mm, compressional destruction was most likely to occur on the concrete at the bottom of the apex. The rise-span ratio of the slab up-warp reached its maximum when the initial up-warp span was 6.5 m at high temperatures. It is easier for track slabs to maintain their original form at a high temperature when there is an angle at the apex or a smooth boundary. However, with a smooth boundary, the concrete at the bottom of the apex is more likely to suffer compressional destruction. Therefore, to ensure the stability of the CRTS II slab track, an initial up-warp with a span of 6.5 m and a rise of 15 mm should be avoided, and the effects of different line types of the initial up-warp also need to be considered.

Divorced Eutectoid on Heat-Affected Zone of Welded Pearlitic Rails

Welds in heavy haul rails are usually associated with accelerated wear and are a common source of defects, justifying a careful study of their characteristics. Heat-affected zones usually present hardness loss, corresponding to a spheroidized cementite region. The literature acknowledges that this is a consequence of the welding heat input but without further explanations. However, in order to control this loss, the mechanisms of microstructural changes need to be fully understood. This paper clarifies the mechanisms for the formation of the spheroidized region in the heat-affected zone of pearlitic welded rails, using as an example a flash butt-welded rail. The weld surroundings had its microstructure characterized and the correspondent hardness measured. Those microstructures were then simulated using a quenching dilatometer for three different rails. The results make it clear that the spheroidized microstructure is a consequence of the divorced eutectoid transformation, which is at a maximum at the end of the eutectoid gap.

Axial stress determination using highly nonlinear solitary waves.

This article presents a nondestructive evaluation (NDE) method to infer the neutral temperature and the axial stress in thick beams. The method relies on the propagation of highly nonlinear solitary waves generated at one end of a chain of spherical particles in a dry point contact with the beam to be evaluated. The waves are reflected back to the chain and the research hypothesis is that the axial stress, which influences the beam's stiffness, affects the amplitude and speed of the reflected waves. To verify this hypothesis a general finite element model of thermally stressed beams was developed and coupled to a discrete particle model able to predict the propagation of the waves along an L-shaped granular medium. The models were validated experimentally to quantify the repeatability of the setup, the sensitivity of the wave features on the thermal stress, and the independence of the wave features on the neutral temperature of the beam. The hypothesis was proven valid by both the numerical and the experimental results. In the future, these findings may be used to refine a NDE method to assess stress in columns, to infer the neutral temperature of continuous welded rails, and to prevent thermal buckling of critical structures.

Novel Adaptive Peak Detection Method for Track Circuits Based on Encoded Transmissions

Track detection systems based on ultrasonic guided waves (UGWs) for continuous welded rails have achieved a rapid development in recent years. Though these systems can work properly in normal track conditions, UGW signals cannot penetrate the gap caused by a track breakage. To overcome this issue, a novel track circuit system based on a previous UGW system has been proposed in this paper. The 63-bit Kasami codes have been applied to the transmission scheme. The auto- and cross-correlation properties from Kasami codes have allowed the transmission detection at the receiver end, even under adverse conditions, such as noise or high attenuation. Furthermore, in previous track circuits, the correct detection and identification of the corresponding transmissions at the receivers had become a key aspect for the suitable and reliable operation of such type of systems. In this way, in addition to describing a novel track circuit, this paper focuses on the proposal of a novel adaptive peak detection algorithm to discriminate the main lobes in the auto-correlation functions at the receiver, thus making possible to correctly determine the track status in future works. This algorithm is mainly based on the discrete wavelet transform, on a moving average filter, as well as on the Hilbert Transform. Through the usage of a simulation model for the proposed track circuit as well as some outdoor experimental tests, the accuracy and the stability of the adaptive peak detection algorithm for the novel track circuit have been verified.

NONLINEAR FINITE ELEMENT ANALYSIS OF CONTINUOUS WELDED RAIL–BRIDGE INTERACTION: MONITORING-BASED CALIBRATION

Continuous welded rail is of high interest to operators of railway infrastructure facilities because of the reduced maintenance work and better train driving dynamics it offers. However, the application of continuous welded rail, in particular associated with its interaction with the superstructures of e.g. bridges, requires special caution with regard to the rail stresses in the transition area between the structure and the free field. These stresses are not only influenced by thermal deformations of the bridges but also by the clamp systems between the rails and e.g. the bridge. In general, these connectors are represented by spring elements during modelling, which: (a) causes singularities in the stress distributions in the rails, and (b) cannot capture all the mechanical system changes occurring due to loading, thermal effects, etc. The target of this paper is to present an alternative way of modelling the connection between rails and bridge superstructure based on composite materials which can overcome the disadvantages of the spring model. In particular, a nonlinear model of the whole system was developed for ballasted and non-ballasted track. Special attention was paid to the calibration of rail–bridge interaction and boundary conditions using measured data and code specifications. The aim of this study was to use the results of in-situ measurements to analyse the admissible stress in rails due to their interaction with a bridge caused by temperature loading.

Improvement of aluminothermic welding on the basis of the experimentally-theoretical research of welding seam cooling process

The distinctive features of welding rails in the aluminothermic way are considered. Defects appearing in the process of operation of welded rail seams are indicated. A computer simulation of the aluminothermic welded rail connection cooling process using the LVMFlow software package was carried out. Thermograms were obtained showing the temperature distribution over the cross-section of the rail during cooling. To confirm the results of computer simulation, we conducted field experiments, based on the results of which time-temperature dependences of cooling of the rolling surface of an aluminothermic welded seam were constructed. The time of the surface cooling of the welded seam after welding has been determined to reach a temperature of 600 ° C, which is necessary for grinding.

Fatigue characteristics of continuous welded rails and the effect of residual stress on fatigue-ratchetting interaction

ABSTRACTThe importance of ratchetting-fatigue interaction is garnering interest due to complex failure mechanism of rail welds under cyclic loading. The objective of this paper is to investigate the fatigue characteristics of continuous welded rails (CWRs) and the effect of residual stress on fatigue-ratchetting interaction. For this purpose, UIC60 rails have been modeled using a three-dimensional finite element model, including a combination of nonlinear kinematic and isotropic hardening. In addition, the interaction between cyclic loading and the effect of residual stress on fatigue is taken into consideration. Finite element model is validated against representative experimental findings. Smith–Watson–Topper (SWT) method is utilized in order to estimate the fatigue life of rail welds under static and cyclic loading. Lower fatigue life is predicted with increasing load due to the contact between rails and wheels. Simulation results also show that failure in the form of ratchetting occurs during the 10,236th cycle, while failure corresponds to the 15,290th cycle and the 145,161st cycle based on the SWT and Coffin-Manson fatigue models, respectively. These findings suggest that investigations on ratchetting and fatigue should be carried out simultaneously to estimate the failure of the CWRs.

The Evaluation of Axial Stress in Continuous Welded Rails via Three-Dimensional Bridge–Track Interaction

The crucial differences between conventional rail with split-type connectors and continuous welded rails are axial stress in the longitudinal direction and stability, as well as other issues generated under the influence of loading effects. Longitudinal stresses generated in continuously welded rails on railway bridges are strongly influenced by the nonlinear behavior of the supporting system comprising sleepers and ballasts. Thus, the track structure interaction cannot be neglected. The rail-support system mentioned above has properties of non-uniform material distribution and uncertainty of construction quality. The linear elastic hypothesis therefore cannot correctly evaluate the stress distribution within the rails. The aim of this study is to apply the nonlinear finite element method using the nonlinear coupling interface between the track and structural model and to illustrate the welded rail behavior under the loading effect and uncertain factors of the ballast. Numerical results of nonlinear finite analysis with a three-dimensional solid and frame element model are presented for a typical track–bridge system. A composite plate girder, modeled by solid and shell elements, is also analyzed to consider the behavior of the welded rail. The analysis result showed buckling under the independent calculations of load cases, including ‘temperature change’, ‘bending of the supporting structure’, and ‘braking’ of the railway vehicle. A parametric study of the load combination method and the loading sequence is also included in this analysis.

Non-Contact Smartphone-Based Monitoring of Thermally Stressed Structures.

The in-situ measurement of thermal stress in beams or continuous welded rails may prevent structural anomalies such as buckling. This study proposed a non-contact monitoring/inspection approach based on the use of a smartphone and a computer vision algorithm to estimate the vibrating characteristics of beams subjected to thermal stress. It is hypothesized that the vibration of a beam can be captured using a smartphone operating at frame rates higher than conventional 30 Hz, and the first few natural frequencies of the beam can be extracted using a computer vision algorithm. In this study, the first mode of vibration was considered and compared to the information obtained with a conventional accelerometer attached to the two structures investigated, namely a thin beam and a thick beam. The results show excellent agreement between the conventional contact method and the non-contact sensing approach proposed here. In the future, these findings may be used to develop a monitoring/inspection smartphone application to assess the axial stress of slender structures, to predict the neutral temperature of continuous welded rails, or to prevent thermal buckling.

Fatigue life evaluation of continuous welded rails on concrete slab track in Korea high-speed railway

There is a rapidly increasing demand for continuous welded rails. Continuous welded rails provide a more suitable installation on concrete slab tracks and more rapid and smooth movement and reduce overall maintenance cost. During the relatively short period in which concrete slab tracks have been used in Korea, there has been no documented case of rail fracture caused by repeated loading. This makes the evaluation of rail fatigue life using field data more difficult. In this study, the rail bending stress developed during high-speed train operation is obtained through analysis of vehicle–track interaction, and the correlation is analyzed by performing multiple regression analysis on train speed and rail surface irregularities. Equations for predicting the rail bending stress with regard to train speed and rail surface irregularity were derived. The effects of vehicle speed, track support stiffness, and fracture probability on the fatigue life of continuous welded rails on a concrete slab track in Korea high-speed railway were analyzed.

Investigations on Vehicle Interaction with CWR Tracks Considering Some Aspects of Rail Support Modulus

One of the important parameters for controlling the behavior of continuous welded rail (CWR) in railway tracks is rail support modulus. Reviewing the technical literature reveals some elapsed points in this regard such as continuous or discrete supports, V-shaped rail irregularity and geometrical stiffness which can considerably affect on the vehicle-track dynamic interaction. So, the present study was allocated to numerical investigating the effects of aforementioned parameters on the vehicle-track dynamic interaction. In this matter, the finite element model of ballasted railway track in conjunction with multi-body dynamics model of vehicle was developed and they simultaneously solved numerically. This preliminary model was verified through comparison of the results with published works in this area. Consequently the model was promoted considering continuous and discrete support condition, implementing the V-shaped irregularity and geometrical stiffness. In each step, the results of the extended models were completely presented in the form track structure response.

Increasing the operational stability of running surfaces of aluminothermiс welded rail joints by hot grinding

Welded joints have traditionally been a weak point in a design of continuous welded rail (CWR) tracks. Grinding can be used as a resource-saving technology. The purpose of this paper is to study the grinding technology for welded rail joints at different temperatures. The temperature in the weld grinding zone varied from 560 to 850 °С. Using methods of microstructural analysis and hardness measurement, it has been established that different temperature conditions for weld grinding lead to the creation of non-identical mechanical properties of metal and a surface structure of the rail head in the weld zone. As a result of the research, an optimum temperature range, 600 ... 560 °C, was determined. This range is recommended for grinding aluminothermic welded joints.

Longitudinal rail restraint of inexpensive continuous welded rail

Longitudinal rail restraint of inexpensive continuous welded rail

Upravljanje naponima u šinama na železničkim mostovima

This paper analyses the stresses in continuous welded rails on bridges including the aspect of fatigue of rail steel. Furthermore, it examines the possibility to avoid rail expansion joints, while simultaneously exploiting the permissible stress capacity of the rail profile 60E1. Accordingly, general application of permissible values of pressure and tensilestresses prescribed in the current European standards was critically analysed. Paper includes specific application aspects of the prescribed stress values for railway bridges in Serbia. General algorithm for reducing the stresses due to the vehicle/track/bridge interaction, which is presented in this paper, was developed by the authors. This algorithm includes all essential parameters of the bridge structure and railway superstructure, as well as the influence of climate conditions and railway route design.

Бализа как способ контроля за напряженным состоянием бесстыкового пути и движением поездов

Бализа как способ контроля за напряженным состоянием бесстыкового пути и движением поездов