Welded Rail Joints Research Articles

Damage behaviour of rail flash-butt welding joints under controlled impact kinetic energy

Rail welded joints are a critical component of seamless railway tracks, and they are essential for maintaining the continuity and smoothness of the tracks. However, they also represent weak points in the entire track, which makes these areas susceptible to frequent damage and rail breaks. This study employs an impact wear testing platform with controlled energy to compare and analyse the impact wear characteristics of three different locations (i.e., weld zone, heat-affected zone and base material) on the U75VG flash-butt welding joint. Results indicate significant differences in material properties, such as hardness and microstructure, within different zones of the flash welded rail joints, which leads to varying impact damage behaviours. The heat-affected zones, which are located on both sides of the weld zone, exhibit the weakest ability to resist impact deformation. Thus, these areas are the most vulnerable in the entire welded rail joint and are prone to damages, such as squat. In general, damage in different zones of the welded joint gradually evolves from plastic deformation and local pitting into fatigue wear with delamination as the main failure mechanism, while the surface of the heat-affected zone tends to develop an oxide debris layer. The distinct damages observed in different zones of the welded joint pose challenges to the problem of track irregularities. This study offers a theoretical framework for predicting the evolution of damage in welded joints.

Experimental Study of Static and Dynamic Loading Effects on Guided Wave-Based Intelligent Monitoring of Welded Rail Joints

Experimental Study of Static and Dynamic Loading Effects on Guided Wave-Based Intelligent Monitoring of Welded Rail Joints

Structural condition assessment based strain-stress behaviour for railway welded rail joint using rosette fibre Bragg grating optical sensor

The rail provides a medium for trains to operate along and a support system for the cargo trains to carry. Proper caution should be exercised when handling the thermite welded rail, as it can be vulnerable to damage and failure if not properly maintained. The thermite welded rail joint experiences the greatest amount of train impact and has the least material rigidity. However, measuring the deformation or strain that occurs on a rail is difficult as limitation of the strain gauge itself and challenges to perform the measurement on site due to surroundings. A rectangular rosette Fibre Bragg Grating (FBG) sensor setup was mounted on the web surface of the rail to obtain three distinct strain directions, in order to measure and monitor the direct strain on the thermite welded rail joint. The location for the FBG sensor setup is determined by the presence of visible defects and the production of load sounds when the railway passes through specific locations on the rail track. The FBG sensor's wavelength signal displays three distinct patterns for each strain direction and is used to compare the results between the thermite welded joint and the smooth base rail structure. The wavelength signal exhibits tensional strain, compressional strain and tensional and compressional strain in combination. The principal strain and principal stress are examined between four different locations. The strain value obtained from FBG sensors show instability and variations, which can be attributed to factors such as the dynamic wheel-rail interaction and the condition of the rail structure. Therefore, the FBG sensors are proven to be acceptable in rail track condition assessment based on direct strain measurement for running rail track applications.

Improvement of the technology of resistance butt welding of rail strings for access railway lines

To ensure the quality of the welded rail joint, a study of the level of contamination with non-metallic inclusions of E76KhF rail steel (base metal and weld seam) was carried out. It was found that the predominant type of nonmetallic inclusions in welded joints in all studied samples are point oxides. It is shown that the modes of resistance butt welding do not affect the contamination of the samples.

Impact Wear of Flash- and Aluminothermic-Welded Hypereutectoid Steel Rail Joints

High-speed, high-load railway development has necessitated a deeper understanding of the wear behavior and mechanism of welded steel railway joints subjected to repeated impact. Under different simulated impact loads and impact cycles, the impact damage evolution and wear mechanism of flash- and aluminothermic-welded joints in the weld and heat-affected zones and base material were compared and analyzed. The results show that the impact wear severity increased with impact cycle and load. With increasing impact load and cycle, the impact wear in the welded rail joints progressed through plastic deformation, partial pitting failure, fatigue crack propagation, and spalling from the synergistic effect of fatigue and oxidation wear. The degree of impact wear increased in the order of the softening part of the heat-affected zone, welding seam, and base material. Comparison of the wear performance of the two kinds of welded joints showed that the fatigue resistance of the flash-welded joint was higher than that of the aluminothermic-welded joint under low impact loads and cycles. In contrast, under high impact loads and cycles, the wear degree of the flash-welded joint increased sharply upon reaching a critical value and was more severe than that of the aluminothermic-welded joint.

Structural fatigue investigation of thermite welded rail joints considering weld-induced residual stress and stress relaxation by cyclic load

This study developed a structural fatigue life prediction model of thermite welded rail joints taking account of the weld-induced residual stress and stress relaxation by external cyclic load. A three-dimensional finite element model including the sequentially coupled thermal–mechanical simulation and cyclic plasticity constitutive simulation was developed to investigate the welding process induced residual stress and the redistribution of the residual stresses due to cyclic bend fatigue loading, respectively. The numerical results of the finite element model were compared with experimental residual stress data to confirm the accuracy of the model developed. The fatigue crack propagation life prediction taking into account the as-welded residual stress and the stress redistribution was performed. The predicted life of weld-toe cracks at web-to-base location will be overestimated by at least 50% if residual stress and relaxation is not considered.

Investigation on material characteristics and fatigue crack behavior of thermite welded rail joint

This study investigates the material characteristics across the thermite welded joint and discusses the inherent correlation between the material properties and the mechanism of the fatigue cracking occurring at the fusion line. Various material regions across the welded joint are identified and the characterization of the mechanical and fatigue properties are conducted. The weld defects are investigated, and it is found that the defects lead to a reduction of fatigue limit and the local severe stress concentration which acts as potential crack initiation sites at the fusion line. The fatigue crack propagation behaviors were studied and the result reveals that the moderate material strength overmatch is detrimental for interfacial cracks propagation. The interfacial cracks, once initiated, grow towards the base rail metal and away from fusion line resulting in a shorter fatigue propagation life. It is concluded that the fatigue cracks occurred at the fusion line of the thermite welds are caused by the high density of weld defects and the mismatch of strength and fatigue properties.

Measurements of railway welded rail joints with a laser device

One of the methods of joining rails is welding with termite, which guarantees a secure and stable connection of two sections of the rail without the need to use additional connecting elements and supporting the welded place. After joining (making a weld), appropriate mechanical processing of the joint is required in order to obtain the given rail head profile. The quality and diligence of the connection made has a major impact on safety, noise emission during the journey (wheel rolling) and the comfort of travelers. This article describes selected methods of making railway rail joints and presents the results of measurements with a portable laser measuring device Calipri C40 of the rail head within the welded rail joint made by thermite welding. An attempt to use this device for measurements of welded rail joints is shown, advantages and disadvantages as well as conclusions from the performed measurements are described.

Fatigue Behavior of Rail Connections on Semi High Speed and High Speed Rail Networks

Rail joint is the most vulnerable and weakest part in the rail structure. Bolted rail joints and welded rail joints are the most predominantly used rail joints. In recent times, continuous welded rail joints are widely used. The literature study exhibits that the performance of welded rail joints are comparatively better than the bolted rail joints. This project mainly deals with the fatigue behavior of welded rail joints subjected to normal speed, semi-high speed and high speed rail networks with respect to rail joint location on the sleeper. The rail joint kept on two conditions, mainly rail joint on top of the sleeper and rail joint in between the sleepers. The model was created and the respective finite element analyses were made in ANSYS Workbench software. The rail joint was analyzed for the movement of wheel load on the rail for all speed conditions mentioned. The butt joint was given at the region of rail joint and the fatigue life results were obtained in the analyses made in ANSYS Workbench. The analyses methods covers the rail and wheel model creation, application of corresponding loads and supports and the simulation results were obtained. The simulation results portrays that when the continuous welded rail joint is located on the sleeper, the fatigue life of the rail joint in both the normal speed and semi-high speed conditions is higher when compared to the fatigue life of rail joint in high speed condition. And also when the welded rail joints are located in between two sleepers the rail joint in high speed rail networks provide increased fatigue life when compared with the rail joints located in normal and semi high speed conditions. This research provides a beneficiary effect and serves as a base for increasing the fatigue life of the rail networks.

Dynamics of Rolling Stock Wheels and Track Interaction in Areas of Welded Rail Joints Crush

Finite element models of a rail crushed in a welded joint area and fixed on an elastic damping foundation and a car wheel have been developed. An algorithm has been developed to calculate quasistatic and impact forces during a wheel rolling at different speeds. Experimental studies have been carried out to determine vertical forces in the crushed area of the welded joint at a depth of 1.8 mm using the strain measurement method on the rail web neutral axis.

Study of non-metallic inclusions composition in rail joints welded seams, obtained at their contact arc welding

The quality of welded rail joints depends on various factors, in particular, on the type and quantity of non-metallic inclusions, formed at their contact arc welding. To check a hypothesis of the cause-effect of welded joint mechanical properties decrease and composition of non-metallic inclusions in the welded seams, their chemical and metallographic analysis accomplished. To study the non-metallic inclusions, samples of 90×30×10 mm dimensions used, cut of Э76ХФ steel rail head. After contact butt welding at MC-2008 machine, the samples were cut by electro-erosion method perpendicularly to the welding seam into two parts. One part of the sample was used for tensile test, the other – for metallographic analysis for non-metallic inclusions and structure of the welded joint. The microstructure of the welded butts studied after milling and intensive etching in the 50% water solution of hydrochloric acid. The microstructure was studied at the optical microscope OLYMPUS GX71 in the light field at magnification 100–1000 folds after etching in an alcohol solution of nitric acid. The chemical composition of all the revealed inclusions were determined at the scanning electron microscope MIRA 3. It was established, that silicon and manganese oxides were the basic components of inclusions, revealed in the welded seam, as well as oxides of aluminum, iron, titanium, chrome – to a less amount. In the samples seam microstructure the ferrite net, typical for rail butts, was not discovered, which is probably stipulated by their accelerated heating due to the small section of the samples.

Influence of welding on microstructure and strength of rail steel

In this study, metallurgical and mechanical aspects of cold flash butt welded rail joints were investigated. The relationship between the material characteristics and the distance to the fusion line were evaluated. Significant changes observed in grain size as it ranges 2–8 according to ASTM E 112. Hardness tests conducted and the average results of the rail head, web, and foot were recorded. According to the results, three different zones were identified including the fusion line, recrystallization zone, and transition areas. Tensile properties and strength characteristics have been investigated for the specified zones separately. Obtained experimental values were used as input parameters for the developed finite element model (FEM) to calculate stress distribution. The welded rail was subjected to realistic wheel load and stress distributions in weld were evaluated. The developed model has also been validated by comparing the theoretically obtained stress values with the experimental ones under various loading conditions.

Testing Internal Mechanical Stresses in Flash-butt Welded Rail Joints

Testing Internal Mechanical Stresses in Flash-butt Welded Rail Joints

Irregularity model of welded rail joint and wheel-rail dynamic responses in heavy-haul railway

Due to the irregularity of excitation of welded rail joints (WRJs), the dynamic impacting force between the wheel and the rail would be obviously enhanced. According to measured irregularities of WRJs in heavy-haul railway, a modified excitation model is put forward to simulate the irregularity in this paper. Dynamic interactions excited by the irregularities are analysed, including the measured irregularity, the theoretical irregularities obtained from a traditional model and a modified model. Effects of parameters of the modified excitation model on dynamic interaction are discussed. Results show that, compared to the traditional model, the dynamic performances excited by the modified model present better consistency with those due to the excitation of the measured irregularity. Furthermore, with the growth of the depth, the wheel-rail dynamic indices will increase linearly, and they will decrease nonlinearly with the increase of the wavelength.

Dynamic responses of non-ballast track structures subjected to high-speed train loads at the welded rail joint

This paper presents a numerical study on the dynamic responses of the non-ballast track structures under the high-speed train load that is excited by the rail irregularity at the welded rail joint. In this study, a multi-body dynamics model with 10 degrees of freedom is built to model a high-speed vehicle and a finite element model is established to simulate the non-ballast track. A mathematical model is also given to characterize the geometry of the local rail irregularity at the welded rail joint. By coupling the high-speed vehicle model and the track model and taking the mathematical model of the welded rail joint as an input, the dynamic responses of the non-ballast track structures under a rail vehicle running at a high speed are simulated and discussed in this paper. The wheel/rail force and the rail and slab vibration acceleration are investigated to demonstrate the significant dynamic effects on the track structures due to the welded rail joint.

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.

Railway track geometry degradation due to differential settlement of ballast/subgrade – Numerical prediction by an iterative procedure

An iterative procedure for numerical prediction of long-term degradation of railway track geometry (longitudinal level) due to accumulated differential settlement of ballast/subgrade is presented. The procedure is based on a time-domain model of dynamic vehicle–track interaction to calculate the contact loads between sleepers and ballast in the short-term, which are then used in an empirical model to determine the settlement of ballast/subgrade below each sleeper in the long-term. The number of load cycles (wheel passages) accounted for in each iteration step is determined by an adaptive step length given by a maximum settlement increment. To reduce the computational effort for the simulations of dynamic vehicle–track interaction, complex-valued modal synthesis with a truncated modal set is applied for the linear subset of the discretely supported track model with non-proportional spatial distribution of viscous damping. Gravity loads and state-dependent vehicle, track and wheel–rail contact conditions are accounted for as external loads on the modal model, including situations involving loss of (and recovered) wheel–rail contact, impact between hanging sleeper and ballast, and/or a prescribed variation of non-linear track support stiffness properties along the track model. The procedure is demonstrated by calculating the degradation of longitudinal level over time as initiated by a prescribed initial local rail irregularity (dipped welded rail joint).

Исследование сварных соединений рельсов после механической обработки при различной послесварочной температуре

Исследование сварных соединений рельсов после механической обработки при различной послесварочной температуре

Determination of inspection intervals for welded rail joints on a regional network

One of the most frequent and dangerous failure modes in continuous welded rails is fatigue crack propagation terminated by brittle fracture. Due to the brittleness of the weld material and the scatter in its mechanical properties, a probabilistic approach is necessary. The paper deals with surface cracks at the foot base of aluminothermic welded rails, developing a probabilistic methodology for determining the day by day prospective failure probability. The model used is based on weld material characterization, simulation of fatigue crack growth and day-by-day failure probability calculation using the Monte Carlo method. The model is then adopted to assess the time dependent safety margin during fatigue crack propagation and to understand which variables are really influencing the failure probability. Finally, the results are compared to the standard rail classification method, considering the real traffic condition in several railway lines.

Исследование структуры и механических свойств алюминотермитных сварных соединений рельсов

Welded joints of rails are an integral part of continuous welded railway. However, they often do not have sufficient reliability during the operation. The paper presents the results of study of hardness and structure of aluminotermitic welded rail joints. It is found that the riding rail surface of welded joints has a reduced hardness compared to hardness of the rail metal, which can lead to the formation of soft sites with lower resistance to wear and crushing of the welded joints, particularly in the path curves. Hardness increases to 36-38 HRC on the boundary fusion line of the rail and welded metals. This is due to the harmful effects of overheating of the metal during welding process, which is confirmed by the results of microstructural analysis. Microstructural analysis also showed the differences in metal grain size in the welded zone and heat affected zone. The structure of welded metal zone is dendritic while the structure of heat affected zone is coarse-grained. Owing to the difference between structures of the welded joint zones, the probability of occurrence of brittle fracture on the boundary fusion line of the rail and welded metal is increased.