Rail Section Research Articles

Evaluation of the coefficient of friction of rail in the field and laboratory using several devices

ABSTRACTAccurate friction measurement is vital to apply appropriate friction management techniques to the wheel/rail interface. This work analyses different friction measurement techniques under a variety of conditions in the laboratory and the field. Tests have been carried out using a pendulum tester, hand-push tribometer, twin-disc machine and full-scale rig in the UK and Colombia for a variety of interfacial conditions and rail hardness. The pendulum has been found to be more sensitive to different conditions than the hand-push tribometer. This is due to the area that the pendulum sweeps being smaller, and so it can be more carefully controlled and therefore measure the surface condition being tested. This is in contrast to the push tribometer which needs a long section of rail to take a measurement. Twin-disc and full-scale rig creep curves show good agreement between each other.

“Test-site operations for the health monitoring of railway ballast using Ground-Penetrating Radar”

Effective maintenance of railway infrastructures requires a comprehensive knowledge of the actual condition of the involved construction materials. In this regard, Ground-Penetrating Radar (GPR) stands as a viable alternative to the invasive and time-consuming traditional techniques for railway inspections. This work reports the experimental activities carried out on a test-site area within a railway depot in Rome, Italy. Specifically, a 30 m-long railway stretch was divided into 10 sub-stretches reproducing different various physical and structural conditions of the track-bed. In particular, combinations of varying scenarios of fragmentation and fouling of the ballast were reproduced. The set-up was then investigated using different multi-frequency GPR horn antenna systems. These were towed along the rail sections by means of a dedicated railway cart. Main electromagnetic parameters of railway ballast were estimated for each scenario using time- and frequency-domain signal processing techniques. Interpretation of results has shown viability of the GPR method in detecting signs of decay at the network scale, thereby proving this technique to be worthy for implementation in asset management systems.

Transport system of Northern Bukovyna and Khotyn region in the interwar period

In the article the author describes the main tendencies of the development of the system of communication routes of Northern Bukovyna and Khotyn region in 1918 – 1940.
 In the interwar period, in addition to the improvement of traditional modes of transport, new ones were launched. A major impediment to the improvement of transport infrastructure was the devastation during the World War I. During 1918 – 1940 the damaged sections of rails, bridges and stations had to be rebuilt. Similar were the problems with highways, the condition of which was one of the worst in Romania.
 The progressive shifts should include the establishment of a permanent domestic and international air connection between Northern Bukovyna and Khotyn. Urban public transport has also undergone qualitative changes in the interwar period. There were regular bus routes between the main settlements of the region.
 Keywords: Northern Bukovyna, Khotyn region, transport, rail, roads, tram, trolleybus, bus.

Numerical assessment of the loading of rolling contact fatigue cracks close to rail surface irregularities

AbstractRolling contact fatigue damage of railway rails in the form of squats, characterised by local depressions and cracks located at the rail surface, has been linked to the occurrence of local rail surface irregularities. This study concerns rolling contact fatigue cracks in the vicinity of fairly smooth surface irregularities, here denoted dimples. The influence of factors such as dimple geometry, cluster effects, and crack size is evaluated. To this end, dynamic vehicle–track simulations featuring realistic wheel and rail profiles are employed to characterise the dynamic impact during a wheel passage. The contact load in the vicinity of the dimples is then mapped onto a 3D finite element model of a rail section containing a crack in the rail head. The crack loading is finally quantified by multimodal stress intensity factors. The analyses establish that also shallow dimples might have a significant impact on the crack loading. This effect is increased for larger or multiple irregularities but decreases as the crack grows.

Multiparametric Investigation of Thermal Limitations in a Rapid-Fire Multirail Railgun Powered by a Pulsed MHD Generator

The operation of rapid burst firing multi-rail railguns was analyzed by numerical simulation using coupled 2-D and 3-D nonstationary formulations. In the calculations, a Sakhalin-type pulsed magnetohydrodynamic generator is assumed as a power source for the launcher. Launchers with three and five pairs of parallel rails connected into a series electrical circuit are considered. The simulation was performed for different numbers of projectiles in a burst and for different projectile masses. It is established that a major factor limiting the operation of launchers in such modes is the heating of the rails. It is shown that the rate of rail heating is determined by the inhomogeneity of the current density distribution along the rail section due to the nonstationary diffusion of the magnetic field into the rails and by the velocity skin effect. It has been shown previously that the maximum heating of the rails occurs in regions located outside the launcher channel provided that the width of the outer rail extends beyond the section of the launcher channel. We investigated the possibilities of reducing the heating of rails in these regions using rails of different widths in the rail launcher channel, using rails of different materials and rails with inhomogeneous electrophysical properties, and using armatures of different materials. The calculations show that with an optimal choice of the material and structure of the rails and the armature material corresponding to this structure, multirail launchers 5–6-m long can provide a projectile velocity of 2–2.5 km/s in a burst of 10–16 projectiles with masses of up to 800 g at a firing rate of 200–300 shots per second with no melting of the rails in the launcher channel.

Development of continuously cooled low-carbon, low-alloy, high strength carbide-free bainitic rail steels

In the present work, attempts have been made to design and develop low-carbon, low-alloy, high strength carbide-free bainitic steels for application in heavy-haul rail tracks. The study starts with an analytical approach for understanding the effects of different alloying elements on the thermodynamic and kinetic aspects of bainite transformation and the resultant microstructure and mechanical properties. Based on the analysis, two steel compositions were designed for further investigation. The alloys were prepared by melting and casting and processed by hot-rolling and air cooling, which is the usual route for the industrial production of rail sections. Microstructures of the developed steels primarily consisted of plates of carbide-free bainitic ferrite, interspersed with fine films of retained austenite. These continuously cooled steels offer ultra-high strength levels with very good ductility which are far superior to existing pearlitic grade rail steels. Detailed characterization and quantification of microstructural constituents have been carried out and they are correlated with the tensile proprieties using semi-empirical formulations available in literature.

Dynamic optimization of the rail-crown geometry in the rigid frog area by controlling the position of the wheel-load transition

To improve the stability of a train and reduce its influence on the nose rail when passing a rigid frog, the optimization of the rail-crown geometry in the rigid frog area is proposed in this study by controlling the transition range of the wheel load on the nose-rail head and evaluating it by a wheel–rail dynamic coupling model. The method was verified by studying a Chinese CN60-350-1:12 turnout. Results show that if the wing-rail heightening and nose-rail reduction are small, then the transition section of the wheel load on the nose rail may be close to or smaller than the minimum load-bearing cross section, which will cause damage to the weaker section of the front of the nose rail due to excessive load. If the wing-rail heightening and nose-rail reduction are large, the wheel-load transition section of the nose rail may exceed the extreme transition cross section, which will cause the wheel to hit the nose-rail head or make it difficult to climb the wing rail when the wheel passes through the rigid frog. During the optimization process of the rail-crown geometry in the rigid frog, the reasonable transition range of the nose-rail head can be determined by adjusting the wing-rail heightening and nose-rail reduction, and combined with the wheel–rail dynamics evaluation method, the optimal scheme can be selected to protect the nose rail and improve the running stability of the train.

Experimental study on the longitudinal resistance of WJ-8 fasteners subjected to torque and vertical loading in continuously welded rails

The key functions of the fastener system are to hold the rail against the sleepers and to restrain the rail from all forms of movements that could lead to loss of geometry and stability of the track. Thus, fastener resistance is an important parameter in the continuously welded rail technology. This study investigates the characteristics of the longitudinal resistance of WJ-8 fasteners subjected to varying torques and vertical loadings. The vertical loading was applied to the rail section through a reaction frame, while the torque was applied using a digital torque wrench. Two types of fasteners, conventional-resistance and small-resistance fasteners, were tested in this study. The study shows that: (1) The growth rate of the longitudinal resistance of the fastener is independent of the vertical loading until the fastener slips. (2) The slip resistance of fasteners increases as the torque and vertical loading are increased. (3) The relationship between the longitudinal resistance and the displacement of fasteners at varying torques and vertical loadings fits a power index function. (4) The relationship between the longitudinal resistance and the displacement of the fastener exhibits hysteresis. The study serves as a reference for verifying and improving future calculation methods for the longitudinal resistance of fasteners in continuously welded rails.

Force and deformation mechanism of great pipe shed advanced support in subway tunnel

Taking the construction of a certain section of Guiyang rail transit as an example, the theoretical analysis of the stress conditions and constraints of the pipe shed during tunnel excavation is carried out for the support parameters of the large pipe shed. By analyzing the force of the micro-segment of the pipe shed, bringing the Bernoulli-Euler beam theory formula into the equilibrium equation of the micro-segment, the governing differential equations of the pipe shed at the vault and the non-arch is obtained. Two types of pipe sheds are designed, and the numerical simulation of the tunnel with two structural forms of tunnel with advanced support of large pipe shed is carried out by using MIDAS/GTS NX finite element software, and the displacement and stress of the pipe shed are obtained and the theoretical verification is carried out. By comparing the displacement and vertical stress of the large tubular awning in plan 1 and plan 2, it is concluded that plan 2 is more reasonable and has better bearing capacity.

Development of Advanced Calibrations for Point and Wing Rails in a Universal Rail and Structural Steel Mill

We presented the results of scientific and practical investigations of the technology of rolling of asymmetric rail sections, namely, of point and wing rails, performed on a universal rail and structural steel mill. The detected disadvantages are described according to the initial calibration and the causes of formation of the surface defects in the course of rolling of these profiles are established. The results of the performed analysis made it possible to develop calibrations for the analyzed asymmetric rail sections with evaluation of the stressed state of the metal in the course of rolling.

Study of the stress-strain state of the wheel pair of a freight car during braking

Objective: study of the stress-strain state of the wheel pair of a freight car in the process braking. Methods: to determine the stress-strain state of the wheel pairs of a freight car. Results: A volumetric finite element model of a wheel pair with rail sections was created using a finite element of the ten knot tetrahedron type, and maximum shear stresses and maximum equivalent stresses were determined according to the Mises and Dang Wan theory. Practical significance: It is shown that the maximum tangential stresses are observed at a point located at a depth of 4.5-5.3 mm below the rolling surface of the wheel. In case of emergency (short) braking, maximum stresses occur on the rolling surface of the wheel. During prolonged braking (movement of the train along a prolonged descent), maximum stresses occur at the point of transition from the disk to the rim on the inner side of the wheel, and the magnitude of these stresses is 2.5 times higher than in the emergency braking mode.

Measurements of transverse section wear of rails in tracks of tram-loop

In article the problems of classical methods of transverse section wear of rails replacement with new techniques based on electronic devices was concerned. Reasons of rails shape section changes were defined. Principles of rails waste inspection resulting from regulations were reminded. Review of practical measurement methods and devices were made. Shapes of nominal sections of rails used in tram tracks were analyzed. Realization of measurements executed with mechanical-electronic profile gauge and mechanical track gauge on tram-loop Sępolno in Wrocław were described. Proposal of graphic manner analysis of rail wear measurements in connection with track width measurements were proposed. In summary conclusions from effected investigations were formulated.

Using the geometric wheel-rail contact algorithms for fault detection in turnout areas based on the variable section characteristics of rails

This paper presents a geometric wheel–rail contact algorithm suitable for fault detection in a railway turnout. It employs a dynamic profile sampling method based on the characteristics of the variable section rails in the turnout regions. This algorithm provides a fast and accurate method to identify the wheel–rail contact points in turnouts under different degrees of lateral shift and yaw angles. This method determines the contact point based on the minimum distance and can be applied quickly through the use of a moving window to scale the potential contact boundary within the rail width. The wheel–rail contact points and the geometric contact parameters in the internal rail that matched with the LMa and 60 N were virtually identical in both methods, which verifies the accuracy of the dynamic profile sampling model. A comparison of the different wheel–rail contact points and geometric parameters under different wheelset yaw angles in turnouts using the trace line and dynamic profile sampling methods shows that a trace method based on the assumption of equal rail sections is not applicable to turnouts, thus demonstrating the necessity of calculating the wheel–rail contact geometry in turnouts using the dynamic profile sampling method, which takes the characteristics of the variable sections into account.

The role of risk and assumption in the engineering geology of Crossrail

The Crossrail project is a new underground railway running east–west through the heart of London. It will connect with 110 km of new or upgraded sections of surface rail to Reading, Shenfield and Abbey Wood. Crossrail co-ordinated ground investigations for the central tunnelled sections began during the 1990s and continued to 2011 according to a strategy that was based on a review of other major tunnelling projects and best practice. The level of detail in the investigations varied according to local geological complexity and design requirements. However, the state of knowledge on the geological structure is hampered by London's long history, leading to assumptions on the level of complexity or simplicity. Drift-filled hollows and Lambeth Group sand channels were known features presenting risks to excavations but relationships with faulting were unknown or unproved. The emerging geological knowledge was developed through multiphase investigations and collation of third-party data to allow far-field considerations. The risk profile for tunnel boring machine tunnels is lower than that for sprayed concrete lined tunnels but the risk for both increases with increasing proximity to pre-existing infrastructure. Ground movement assessments become critical and mitigation of movements can be significantly affected by unexpected variations in ground conditions.

Experimental study of the vibration characteristics of the floating slab track in metro turnout zones

In railway turnout areas, vertical and horizontal structure irregularities, including geometry and stiffness, result in vibration amplification during the passage of trains. These vibrations can then spread to the surrounding environment. A steel spring floating slab track may be used to control such vibrations, especially in metro-type urban railways. An experimental study was conducted to investigate the vibration-mitigating effects of the floating slab track in turnout areas, and the results were compared with the performance of a regular slab track. Four test cases (consisting of six test sections) were selected: a floating slab track in the turnout zone (consisting of a switch rail section and a nose rail section), a floating slab track in the plain line, a slab track in the turnout zone (consisting of a switch rail section and a nose rail section), and a slab track in the plain line. The vibration characteristics of the floating slab track in the plain line and in the turnout were calculated to explain the test results. The test results indicate that when trains pass across the floating slab track in the turnout zone, the vertical vibration response is close to the horizontal response on the switch rail sections. The use of floating slab track can effectively reduce this vertical vibration. However, the vertical vibration response is much larger than the horizontal response on the nose rail sections of the turnout zone. When the floating slab track is used in these turnout zones, the vertical vibration of the rail decreases while the horizontal vibration increases. Compared to sections using the regular slab track in the turnout zone, the vibration of the floating slab track segments in the turnout zone is shown to be exacerbated, although the vibration level at the adjacent tunnel wall is effectively reduced.

Evolution of rail surface degradation in the tunnel: The role of water on squat growth under service conditions

Squats on open tracks, as opposed to track inside tunnels, have been reported by railway networks across the world. Theoretical research hypothesised that the hydraulic entrapment of water is critical to crack propagation associated with squat growth. The requirement for a fluid to enable crack propagation provides a rational to why squats vanish as soon as the railway enters a tunnel. However, the metallurgical evidence from the ex-service rails damaged by the presence of water at wheel and rail contact interface is lacking. In the current work, a localised section of rail was found to suffer severe surface damage associated with water dropping from an air-conditioning system located in a tunnel roof. This section of rail represented an ideal controlled location for detailed metallurgical investigation to examine the formation of white etching layers (WELs) under both dry and wet conditions. The location allowed to determine the relationship between WELs and squat initiation; and also to investigate mechanics of water on crack propagation and squat growth of ex-service rail.It was found that the presence of water on the rail surface is not an important condition for WEL formation. White etching layer in dry rails was observed to be associated with a distinguished sub-layer; called brown etching layer (BEL). Brown etching layer is thought to be a development stage of white etching layer. Crack initiation on rails inside the tunnel was confirmed to be caused by ratchetting (severe plastic deformation of the surface layer), with the requirement of the rail top surface to contain WEL. Crack propagation was manly influenced by the presence of water. The metallurgical analysis revealed significant amount of oxides existed along the crack faces. The presence of oxides associated with an absence of shear deformation on the cracks faces revealed that crack growth was driven by Mode I loading (tensile opening) associated with the mechanism of hydraulic entrapment of water. Furthermore, both fracture behaviour of some cracks, and confirmation of the presence of corrosive products inside the cracks by EDS analysis, represent strong evidence that stress corrosion cracking was involved in both crack growth and the observed formation of secondary cracks.

Development of the decision-making algorithm for railway maneuverer park equipment with independent controllers

Automation of non-centralised shunting area of a railway station calls for a deep and thorough analysis of conditions of train traffic safety. When choosing a method of centralised points, signals, rail sections (or circuits), one needs to look at a possibility to use programmable logic controller (PLC) to switch and control the points and to control signals and rail sections. It also allows reducing time spent on route setting and locking thanks to created state matrix of objects of railway automation.

Use of fiber optic sensing to measure distributed rail strains and determine rail seat forces under a moving train

Rayleigh backscatter fiber optic sensing permits dynamic strains to be measured along an optical fiber with a gauge spacing and temporal resolution sufficient for rail applications. However, this sensing technology is highly sensitive to vibration. A 7.5 m long section of rail was instrumented with optical fiber and strain measurements were recorded during passage of a freight train slowed to 8–11 km/h. This strategy to minimize rail vibration was successful in permitting distributed dynamic rail strains to be measured under freight car loading. The measured rail strains were used to determine the rail shear forces, which were then used with the static wheel loads to determine the rail seat load for 14 consecutive sleepers as the train passed over the field monitoring site. These data were then combined with measurements of dynamic rail displacement captured using digital image correlation to infer the rail seat load–deflection relationships for individual sleepers. These relationships were observed to provide significantly more detailed information about unsupported voids and the sleeper contact stiffnesses than the traditional consideration of the relationship between applied load and rail deflection and highlights how track behavior at a monitored location can be dependent on the conditions and behavior of neighbouring sleeper.

Degradation of railway track geometry – Correlation between track stiffness gradient and differential settlement

Based on the track geometry car recordings performed from 1999 to 2016 on a section of the Swedish heavy haul line Malmbanan, the vertical track geometry degradation is analysed for wavelengths in the interval 1–25 m. The upper layer of the subgrade on parts of the rail section is peat (depths of up to 2 m), while it is moraine on others leading to a significant longitudinal variation in substructure stiffness. The degradation rates of irregularities in the longitudinal level and the influence of track maintenance (tamping) on the track geometry are studied. In parallel, a method for continuous measurement of track vertical stiffness along the line, allowing for the detection of track sections with poor support conditions, is described and demonstrated. Synchronised measurements of the longitudinal level and the track vertical stiffness are evaluated to determine whether there is a correlation between a high stiffness gradient due to variations in substructure stiffness and a high growth rate of local track geometry irregularities. It is shown that recurrent severe local track geometry irregularities often occur on track sections where there is a combination of a low magnitude and a high gradient in the substructure stiffness. In such cases, tamping may not be a cost-efficient long-term solution to the problem. Instead, upgrading of ballast and subgrade layers should be considered as an option. It is concluded that measurement of track vertical stiffness is an efficient method for the maintenance planning of a more robust railway track, which also minimises the life cycle cost and environmental footprint.

On the Question of Monitoring Residual Stresses in Selectively Heat-Strengthened Rails

The question is considered of the relationship between the divergence of a longitudinal (400 mm) groove in the rail web, used as an indirect residual-stress–based rejection criterion, with internal stresses measured by acoustic strain gaging across the rail section. The internal stresses have also been evaluated in individual rail elements after cutting. A finite element simulation in the COMSOL Multiphysics software environment has been performed in order to establish connection between groove divergence and stresses. Results are presented for experimental measurements over 49 sections of different rails. The relationship is demonstrated between the stress level in rail elements and the level of stresses measured by an electromagnetic-acoustic structuroscope in an experiment on the side of the railhead. Based on the modeling and experimental results, an acoustoelastic technique is proposed for monitoring residual stresses in rails as an expert method with a rejection level of 80 MPa when sounding a rail section on the side of its head.