Welded Track Research Articles

Analysis of the impact of rail head wear on railway superstructure stability

Continuous welded rail track (CWR) is a superstructure construction of the railway that withstands significant compressive forces from the longitudinal extension of the rails due to temperature changes, ensuring the safe railway operation. The applicable for the Bulgarian railway system methodology for determining the critical compressive force at which the CWR loses stability has been examined. Different types of rails with their respective design parameters, important for the force calculation, have been taken into consideration. The considered design parameters, as moment of inertia and sectional modulus of the rails, change during operation due to the rail head wear. The aim of the article is to examine specific examples of railway tracks on curves, analyzing the impact of the changed operational design parameters of the rail on the stability of the track. The operational and geometric parameters of the railway track have been considered.

Study of transitional phenomena in rail vehicle dynamics in relation to the reliability and operational state of the continuous welded rail track in terms of rail joints

This paper presents the results of experimental and numerical studies on reliability and monitoring issues of railway infrastructure in terms of safety and operation. The state of knowledge concerning methods of assessing track condition, in particular rail joints used in continuous welded rail track of railway lines is described. Experimental results of rail joints used in track transition zones and the results of numerical studies/tests of the rail vehicle-track model are outlined. It is demonstrated, basing on the analyses of the experimental results, that not only should the rail joints used in continuous welded rail track be diagnosed during their acceptance, but also during their operation. It is proven that the currently used methodology for testing welded rail joints applied during acceptance testing of contact track is not fully correct and leads to misinterpretation of the measurement results. Moreover, the results of numerical simulation tests presented in this paper confirm the possibility of diagnosing the condition of rail joints by any vehicle passing over such a track equipped with a suitable system.

System for determining state of continuous welded track

The article considers the main disadvantages of the existing method of examining the lashes of a jointless path, in which a pedestrian bypass of the sections of the canvas and their visual control is performed. A system for monitoring the temperature stresses of jointless rail lashes laid in the path is proposed, which allows monitoring the longitudinal displacement of the track throughout the entire life cycle: from the moment the rails are welded into long-length lashes, including their laying, and throughout further operation. The system makes it possible to monitor compliance with the optimal fixing temperature of rail lashes during their laying, welding and fixing, based on data obtained with the help of sensors, to determine the actual fixing temperature in the lashes of a jointless track; to control the optimal fixing temperature of rail lashes in areas of restoration of their integrity.

Review of factors affecting stress-free temperature in the continuous welded rail track

Railways have a significant role to play in sustainable transportation. Rail travel is currently the only mode of rapid, large-scale, long-distance transport for both freight and passengers that offers zero carbon dioxide emissions at the point of use. However, our railway infrastructure needs to be more robust and resilient to the combined effects of climate change, traffic growth and increases in vehicle loads and speed. Rail buckling is of increasing concern as environmental temperatures rise and traffic loads, speed and intensity of use increase. A key indicator and control of the propensity for track buckling is the stress-free temperature of the rails. However, determining the actual stress-free temperature of a given section of track is challenging. Knowledge of the factors affecting stress-free temperature will help in the identification of vulnerable sections of track and the development of an appropriate maintenance regime. This paper reviews and discusses the factors affecting stress-free temperature in ballasted railway track with continuous welded rails (CWR).

Numerical Analysis of Guided Wave Transmission Through a Long Defect in a Rail Track

Abstract Guided wave ultrasound has been used to continuously monitor welded rail track by transmitting guided wave ultrasound between alternate transmit and receive stations along the rail. A section of rail was encountered where transmission was not reliably achieved. It was found that there was considerable flank wear on the head of the rail, which varied in a sinusoidal pattern over approximately 10 m. The scattering due to the wear is investigated in this paper using numerical modeling. A 3D finite element (FE) model of the section of rail containing the wear defect was coupled to two semi-analytical finite element models of the incoming and outgoing waveguides. In the case of a 10 m long defect, which is over 100 wavelengths long, the 3D FE matrices were excessively large, and the global matrices could not be assembled nor solved. An approach of successively assembling layers of the mesh and reducing out internal degrees-of-freedom in the dynamic stiffness matrix was successfully adopted. The influence of the length of wear on the transmission loss was computed. It was found that short wear lengths generally cause more transmission loss although the relationship is not monotonic. It was found that the long-wear seen in the field does not cause transmission loss. In this case, where the change in cross section is gradual the incoming mode converted to a single mode in the smallest cross section and this mode converted back to the incoming mode in the second half of the wear section.

PROCESSES OF WELDED JOINT STRUCTURE FORMATION DURING ELECTRIC RESISTANCE WELDING OF RAILWAY RAILS

During operation of a continuous welded rail track, most of the fractures occur in welded joints. Welded joints failures take place due to various reasons including the presence of the hardened areas in the welded joint and increased local wear of the rolling surface. The paper presents the dilatometry results and the obtained continuous cooling transformation diagram of the supercooled austenite decomposition for R350LHT rail steel, which make it possible to define the critical cooling rate. It was determined that during welding in hard modes the welded joint cooling rate is lower than the critical one which leads to the martensite formation in the welded seam. The positions of critical points and phase equilibrium areas for the given rail steel were also modeled. It is proposed to use a new method for welding railroad rails based on the knowledge of dependences of the structural components dispersity and, first of all, pearlite and carbide particles formed in the process of obtaining welded joints of rails on the composition of steel and the conditions of their cooling.

Identification of Track Stability Model Parameters Based on Numerical Experiments

In the article, an identification method of railway track stability model parameters based on energy equilibrium is presented by the authors. A study of two parameters directly influencing the continuous welded track (CWR) stability is described by the authors, i.e., the rail-sleeper structure stiffness Bz is considered one beam, and the ballast lateral resistance r0. These parameters were estimated with the use of a numerical model for various railway track types. The adopted concept is based on the assumption that it is possible to determine substitute values for both parameters. Therefore, using one value of both of these parameters, we label them substitute parameters. The assumed numerical model forced lateral displacements of a track section, and, based on the obtained track section displacement results, energy equilibrium was determined. The equilibrium takes into account the work of external load and the bending work of rail-sleeper structure with the substitute stiffness Bz and the ballast deformation work, also with the substitute value of lateral resistance r0 with lateral displacement. The aim is to identify these substitute values to be used for analysing track stability with the semi-analytical model. These analyses are part of the studies related to the development of a method of assessing various methods of increasing track stability.

Research on the dynamic processes of vehicles and an arbitrary configuration rail track, influencing the side wear of the rail head and wheel flange contact surfaces at different values of friction coefficient between them

The paper studies the influence of the friction coefficient value between the rail heads and wheel flanges on the side wear between their surfaces, depending on the dynamic processes between the vehicles and the rail track of an arbitrary configuration. Research is aimed at reducing the rate of the side parts mutual wear of the rail heads and the wheel flanges of the vehicle running gears. It has been determined that a decrease in the friction coefficient in the range from 0.25 to 0.05 leads to a decrease in the indicators of side surfaces wear of the wheel flanges and rail heads by 3.5-4.5 times and an increase in the stability margin coefficient against wheel derailment of the moving vehicle running gear by 1.3-1.5 times. It has been revealed that the dynamic qualities of moving vehicles when using a continuous welded track and elongated rails, compared with the presence of butt joints on the track, decrease by 15-56%, and the stability and traffic safety indicators improve by 19-26%. The research results are provided for use in the underground, open-cut and rail transport to increase the operational life and traffic safety in transport.

Methodic for evaluating the performance of a continuous welded track according to the criterion of compliance of the actual rail fastening temperature with the standardized value

Problem of safety evaluation of continuous welded track operation is considered. A comparative analysis of the current assessment methods is carried out and a method is proposed for identifying dangerous track sections according to the criterion of compliance of the actual rail fastening temperature with the standardized one. Under the actual fxing temperature in the article, the temperature of the rail is taken at which, as a result of its thermal expansion or contraction, a zero value of the longitudinal force is formed in it. A method is presented for calculating the actual temperature of rail fastening using the dependence of the natural frequency of rail vibrations on the applied longitudinal force, which was obtained by the computational method using the fnite element model of the track section created by the authors by means of modal calculations for various values of the longitudinal force applied to the rail. Its verifcation was carried out using experimental data obtained as a result of testing at a specialized stand. The method of tests carried out on the stand and section of the continuous track of the Ozerskaya branch of the Moscow Railway is described, which consists in determining the natural frequency of the first mode of rail vibration at different values of the longitudinal force, and in the case of field tests at different values of the rail temperature. The calculation of the actual temperature of rail fastening is given on the example of a section of a continuous-welded track of the Ozerskaya branch of the Moscow railway. It was found that the temperature of rail fastening on the investigated section corresponds to the normative for the given region.

Features of the influence of intermediate rail fastenings on the operational durability of rails

Heat-strengthened rails of the R65 type are the main type of rails used on the railway network of Russian Railways. Reducing the number of cropped and acutely defective rails is possible due to the rational use of the design features of intermediate rail fasteners and their current content.The article presents study results of the stiffness influence of intermediate fasteners on the operational durability of rails. The general statistics of the use of various types of intermediate rail fastenings on the network of Russian railways is considered. The main results of previously published studies on the effect of the stiffness of intermediate rail fasteners on the accumulation of contact fatigue damage in rails are briefly presented.Calculations of the accumulation of contact-fatigue damages in rails, carried out by the authors, are based on the data on the vertical and horizontal transverse stiffness of intermediate rail fastenings obtained from the results of bench tests. Calculations of the accumulation of contact-fatigue damage were carried out using the “Universal Mechanism” software package. In the process of modeling, four types of intermediate rail fasteners were considered: ARS-4, ZhBR-65Sh, ZhBR-65PShM and W-30. Calculation results were obtained for a curve with a radius of 650 m on a continuous welded track section.

Improving the technology of aluminothermic rail welding based on software simulation

One of the modern methods of connecting railway rails when creating a continuous welded track is thermite welding. The gap between the rails, into which the metal is poured, is 25 mm. However, when repairing rails on the way, it may not be enough to eliminate the defective rail section. Therefore, an increase in the welding gap up to 50 mm is considered a promising direction in the development of thermite welding of rails. T his study presents the results of modeling the process of rail welding by the thermite method using the NovaFlow& Solid CV software package. The purpose of the study was to assess the change in the length of the weld zone and heat-affected zone with an increase in the welding gap from 25 to 50 mm. The results of the simulation are thermograms reflecting the distribution of heat from the weld zone into the rails. These thermograms were used to determine the boundaries of the welded seam and the heat-affected zone. It was found that the use of a welding gap of 50 mm, instead of 25 mm, leads to the increase in the length of the welded seam by 1.3—1.6 times.

Effective Method for Diagnosing Continuous Welded Track Condition Based on Experimental Research

The correct operation of the continuous welded track requires diagnosing its condition and preparation of track metrics requiring measurements of displacements of rail under operation. This is required as there are additional thermal stresses in the rails with values depending on the temperature changes of the rails. Therefore, the climatic conditions are important. This paper presents the original effective analytical method for diagnosing the condition of continuous welded track based on experimental research. The method allows for an appropriate repair or maintenance recommendation. In the experimental research, the authors considered track diagnostic conditions for two conditions: track under load and track without load. This paper presents empirical formulas for calculating rail temperature and longitudinal force based on ambient temperature, developed from long-term measurements. The formulas were developed for a track located on a straight section—both for a rail loaded and unloaded with a passing train under the following conditions: 60E1 rail, not on an engineering structure, conventional surface, wooden sleepers and very high train traffic load. The obtained results in the value of the correlation coefficient R2 ≥ 0.995 attest to very high accuracy of the calculations performed with the method proposed by the authors.

REQUIREMENT FOR THE TOP STRUCTURE OF THE ROADS ON HIGH SPEED RAILWAYS

Goal: Consider the issue of the requirement for the upper structure of the track on high-speed railways in the Republic of Uzbekistan. Methods: For reliable operation, the rails must be sufficiently strong, durable, wearresistant, hard and at the same time not fragile, since they perceive the shock-dynamic load. The material for the rails is high-strength carbon steel. Results: One of the main features of a continuous welded track is that wellfixed rail strings cannot change their length when the temperature rises or falls. Because of this, significant longitudinal tensile or compressive forces arise in them, which in hot weather can lead to the ejection of the path to the side, and in severe frost - to a fracture of the lash with the formation of a dangerous gap. Practical significance: An analysis from an experimental study shows the use of a continuous-welded track is especially effective on sections of high-speed train traffic, where increased requirements are imposed on the upper structure of the track. Particular attention is paid to the prevention and elimination of wavy wear of the rolling surface of the rails, which is eliminated by grinding them with special rail-grinding trains. The developed techniques can be recommended for practical use.

Procurement and technological innovations of India’s new dedicated freight railways

Indian Railways is investing INR 814.590 billion (£8.15 billion) in two new dedicated freight corridors to decongest its heavily used national railway network. Due for completion in 2022, the new 1839 km eastern corridor runs fro. DFCCIL, Delhi to Kolkata while the 1499 km western corridor, capable of carrying double-stack containers, link. DFCCIL, Delhi to Mumbai. This paper describes the procurement process and the new technologies being adopted on the project. These include the first use in India of 32.5 t axle loads, continuous welded track, twin 25 kV overhead electrification, and automatic signalling and centralised train control for 100 km/h line speeds. The project is expected to shift a significant amount of freight transport from road to rail, saving an estimated 455 Mt of carbon dioxide emissions over 30 years of operation.

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.

The influence of wave processes on the reinforcement of the base plate of a ballast-free railway track

Introduction. Since nowadays ballast-free track structures are most often used in combination with continuous welded track solutions for organizing a rail string, it should be emphasized that stresses arising in the rail string affect the stress-strain state of the entire construction of the track superstructure; therefore, it is necessary to monitor the current state of the continuous welded track. Nevertheless, kinks are formed and assembled rails and sleepers lose stability during the operational period of a continuous welded track, and methods are needed to determine the pre-failure conditions related to the temperature range of operation of a continuous track. Materials and methods. In this study, we propose a model of a flat structure made of a material having anisotropic properties, which makes it possible to take account of initiation and propagation of wave processes under the action of an external dynamic load. Results. The considered methods of simulating the propagation of elastic waves in a plate will make it possible to identify the points where direct and reflected waves of various orders converge; these waves can both increase and reduce the overall intensity of wave processes, leading to an increase or reduction in stresses and deformations in the characteristic points of a structure. Conclusions. The proposed solutions are most relevant for the structural elements of transport infrastructure facilities, since they are the ones that are exposed to alternating dynamic loads having varying intensity and time distribution of characteristic values.

Performance assessment of railway track under the impact of longitudinal forces during the implementation of maximum traction modes when using electric locomotives with an asynchronous traction drive

Strategic task of increasing carrying capacity of railways requires a constant increase in the mass of trains due to the passage of heavy and coupled trains. Development of heavy haul traffic is one of the most significant technological solutions aimed at increasing efficiency of using the infrastructure's capacity. In this case, capabilities of the track infrastructure become decisive. The article presents the results of experimental studies of the performance of a continuous welded track under the influence of longitudinal forces arising from the motion of modern locomotives with an asynchronous traction drive in the modes of maximum traction and electrodynamic braking. It is shown that it is necessary to take these forces into account when calculating continuous welded track for strength and stability. The object of testing was a railway track under the influence of increased longitudinal forces during the motion of the 2EV120 electric locomotive with the implementation of various traction modes and electrodynamic braking. Tests were carried out on three sections of the Test Center's track of the JSC VNIIZhT, the experimental joint was equipped with special strain gauge pads designed to measure longitudinal forces. According to the research results, it can be noted that the longitudinal forces in the rails caused by the implementation of the maximum traction forces and electrodynamic braking can reach up to 25 % of the maximum temperature forces. The real forces of resistance to the longitudinal displacement of rails in the nodes of intermediate fasteners when tightened with the force provided by the standards are about 3-4 kN, which is significantly lower than the standard values of 14-16 kN, and may be a consequence of the wear of the elements of intermediate fasteners and the state of friction surfaces. These phenomena can cause longitudinal displacement of both individual rail lines and the grid as a whole. The development of a set of measures to prevent this phenomenon requires a wide range of studies in real operating conditions, including optimization of traction and braking modes of driving heavy haul trains.

Simulating of the heat conduction processes and their impact on the stress-strain state of the continuously welded rail structure

One of the most important parameters when laying and maintaining of continuous welded rail track is the stress-free temperature of continuously welded rails at constant duty of operation, however the regulatory documents do not take into account the thermal stress occurring in continuously welded rails due to deformations on the solid subgrade. The expansion of continuously welded rails laying territory in the sections with complicated engineering and geological conditions requires to study this issue and to develop recommendations for further operation of the continuous welded rail track in the zone of permafrost sedimentary soils. The paper presents the results of simulating of thermoelastic processes due to uneven heating of special elements of the continuous welded rail track structure.

Modeling of the thermal stresses in the welded rails of the continuous welded track in the permafrost zone

The article focuses on the numerical methods that are used to solve heat conduction nonlinear problems with the help of the h-matrix to account for the relaxation of thermal stresses in continuously welded rails. A general mathematical model on the basis of the heat conduction nonlinear equation is presented to calculate the thermal field in an infinite unlimited plate. The developed mathematical model can be applied to choose the implementation modes of the continuously welded rails into the optimal thermal mode.

Development and Modeling of Differentially Heat-Strengthened Rail Welding: Welding and Local Heat Treatment Modeling

During the manufacturing of continuous welded rail track, the problem of the local hardened points in the welded joint during rail joint welding is resolved by using local heat treatment of the welded joint. As a result, the quenching structure formation is excluded. However, the appearance of new heat-affected zones with reduced hardness is possible. During operation, such rails are characterized by increased tread surface wear in these areas and rail flattening at the welded joint, which is the main reason for retiring the rails from service earlier than the guaranteed service life. A new technology based on the dependence of the structural component dispersion (primarily perlite and carbide particles formed in the process of rail butt welding) is proposed for the steel composition and cooling conditions. The cooling rate has a decisive influence on the dispersion degree of the ferrite-cementite structure formed during the austenite decomposition. During the welding rail process, the granular perlite formation is possible in a butt weld in areas with a temperature ranging within points Ac1 and Acm. To determine these critical temperatures, thermodynamic calculations were performed using the Thermo–Calc® software (TCFE database) allowing the chemical composition of the samples obtained by spectrometry. The iron–carbon state diagrams for rail steel 76KhSF with the minimum and maximum alloying element content according to GOST R 51685–2013 are modeled. To obtain the minimum number of sections with reduced hardness, it is possible to weld rails using shot discontinuous flash welding. In order to eliminate the formation of defective areas with a quenching structure, it is possible to control the cooling of the welded joint by contact heating. Temperature distribution measurement during welding according to given modes and controlled cooling confirms the theoretical conclusions.