Rail Head Research Articles

Transformation of structural-phase states in rail head at extremely long-term operation

Quantitative transformations of the structure at a depth of 0, 2, 5, 10 mm along the central and symmetry axis of the fillet of long differentially quenched rails head after extremely long-term operation (passed tonnage of 1770 mln. gross tons) were identified at macro-, micro- and nanoscale levels by methods of optical, scanning and transmission electron diffraction microscopy. At a macroscale level, the numerous shallow parallel cracks of contact fatigue are detected on the surface of working fillet, and on the surface of inoperative fillet there are only small spallings. The lateral wear of the rail was 2.5 mm and the vertical wear was 2 mm. Microstructure of the rail head metal corresponds to the requirements of standards and specifications of the Russian Railways. At microscale level, the transformation of cementite plates was established by cutting it with moving dislocations and dissolving with the escape of carbon to the dislocation lines, low- and high-angle boundaries. A decrease in microstructure dispersion is noted with a distance from the tread surface. At the nanoscale level, subgrain structure formed in the surface layers (subgrain size 110 – 200 μm) contains nanosized cementite particles (25 – 60 nm) localized at the joints and along the subgrain boundaries. It is supposed that this type of structure is formed as a result of dynamic recrystallization under megaplastic deformation in the process of extremely long-term operation of rails. The content of subgrain structure in the fillet layer is five-fold higher than that in surface layer of the tread surface. It was established that during operation, the transformation of lamellar perlite along the central axis of the head proceeds more slowly than along the symmetry axis of the fillet.

Gradients of Structure, Phase Composition, and Dislocation Substructure of Rails under the Ultra Long-Term Operation

In this paper, the structure, phase composition, dislocation substructure, and carbon redistribution in differentially quenched 100-meter rails after the ultra long-term operation (passed gross tonnage since 2013 — 1770 mln. tons) are studied using modern materials science and engineering approaches. The regularities of main parameters variations, such as changes in a relative variety of different morphological structures, scalar and excessive dislocation density, volume fractions of cementite, and redistribution of carbon atoms, are identified at the rail head cross section along the central axis and fillet rounding radius at the distances of 0, 2, 10 mm from the surface. It is suggested that the decrease of volume fraction of carbide phase in head surface layer can be related to the decarburization and appearance of carbon atoms at the steel structure defects. It is noted that transformations along the central axis proceed slower in relation to changes of the rounding radius of the fillet.

Redistribution of carbon atoms in rails under ultra long-term operation

The article considers quantitative estimation of the relative carbon content in the structure elements of rail head after passed tonnage of 1411 and 1770 mln tons. In the initial state carbon is mainly located in cementite particles and after the operation the defects of crystal structure together with cementite are the places of carbon location. It is shown that the processes of carbon redistribution take place more intensive in surface layers up to 2 mm. Increase in passed tonnage is accompanied by intensive carbon movement on the defects of working fillet structure compared to the tread surface.

Analysis on asymmetrical RCF cracks characterisation using an ACFM sensor and the influence of the rail head profile

Rolling contact fatigue (RCF) cracks are one of the typical surface-breaking defects that impairs the rail service life. RCF cracks propagation can deviate from regular semi-ellipse shapes, turning into asymmetrical profiles. RCF crack measurements using the alternating current field measurement (ACFM) method are unable to accurately characterise asymmetrical cracks, as the sizing algorithm is developed based on regular crack shapes. In this paper, the development of modelling capability to consider asymmetrical RCF cracks and the influence of asymmetrical shapes on ACFM signals are presented. A novel grid scan method using ACFM probe sensor for characterizing asymmetrical crack shapes is proposed. The influences of rail head profile on crack sizing are studied and result shows that it gives maximum 2 mm underestimation in crack depth if the worn rail head profile is not considered in ACFM sizing algorithm.

Transformation of Structural-Phase States in the Rail Head after Extremely Long-Term Operation

Transformation of Structural-Phase States in the Rail Head after Extremely Long-Term Operation

A Filtering Method for Suppressing the Lift-Off Interference in Magnetic Flux Leakage Detection of Rail Head Surface Defect

Magnetic flux leakage (MFL) detection is a common nondestructive detection method which is usually used to detect the surface defects of steel pipes and rails. To suppress the interference of lift-off on the detection signal of the defects in rail head surfaces, a filtering method is proposed according to the distribution characteristics of the defect leakage magnetic field (LMF) in different directions. The sensor array is used to confirm the reference signal according to the difference between the signals in x and z directions. The installation mode of the sensors is deduced according to the distribution of the defect LMF. The experimental results show that this method can effectively suppress the lift-off interference in the MFL signal of the defects in the rail head surfaces.

Physical nature of rail surface hardening during long-term operation

A comparative quantitative analysis of the physical mechanisms of hardening of rails surface layers after extremely long­term operation has been performed. The method is based on previously established patterns of formation of structural-phase states and mechanical properties of differentially hardened long­length rails produced by JSC “EVRAZ ZSMK” at a depth of up to 10 mm in the cutting of rails along the central axis and cutting out after the missed tonnage of 1411 million tons. The calculations took into account the volume fractions and characteristics of a particular type of substructure. Increase in microhardness and hardness of the surface layers of the rails subjected to ultra­long operation on the experimental ring of the Russian Railways is multifactorial and is determined by superposition of a number of physical mechanisms. The contributions are estimated due to friction of the matrix lattice, internal phase boundaries, dislocation substructure, presence of carbide particles, internal stress fields, solid hardening, and pearlitic component of the steel structure. Regardless of the analysis direction (along the central axis of the head or along the axis of symmetry of the chip), strength of the rails metal depends on the distance to the surface: it increases as it approaches the top of the head. The most significant physical mechanisms have been established, which provide high strength properties of the metal of the rail head subjected to extremely long­term operation. In the subsurface layer (located at a depth of 2 – 10 mm) of the rail head, the most significant physical mechanisms are dislocation mechanism, due to the interaction of moving dislocations with stationary dislocations (dislocations of the “forest”); in the surface layer of the rail head, substructural mechanism, due to the interaction of dislocations with small­angle boundaries of fragments and subgrains of a nanometer–sized polygon. A comparison with the quantitative values of the rail hardening mechanisms after the missed tonnage of 691.8 million tons was carried out. It is shown that an increase in the missed tonnage in the range of 691.8 – 1411 million tons leads to a significant (1.5 – 2.0 times) increase in strength.

EFFECTS OF SLIP RATIO ON WEAR PERFORMANCE OF CLASS B WHEEL STEELS AGAINST SOFTER R260 RAIL STEELS USING THE TWIN DISC SETUP

A train experiences different slip ratios at the wheel/rail contact point as it moves along the rail track, which influences the rolling contact fatigue (RCF) and wear properties of wheel and rail materials. This variation in slip ratios is caused by a change in contact area between the wheel and rail head at curves, as the slip ratio increases compared with when a train is moving on a straight track. When the train is moving on a straight track, the wheel is found to be in contact with the rail head; but that changes when moving around curves, as the wheel flange will now be in contact with the gauge corner of the rail, affecting the severity of wear. Therefore, more research needs to be done to understand the role that slip ratio plays in the wear performance of wheel and rail materials in order to be able to develop models or systems that could be used to predict preventive maintenance. The aim of this work was to investigate the effect of the slip ratio on the wear performance of class B wheels against softer R260 rail steels under rolling and sliding conditions, using a twin-disc setup developed at the University of Pretoria. The results showed that the severity of wear was heavily dependent on the slip ratio – i.e., it increased with the slip ratio, with class B wheels performing better than the softer R260 rail.

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.

Суық жағдайда жанасу-шаршау ақаулары пайда болған кезде рельсті бұзу механикасын зерттеу

During operation in transit, rails are exposed to the combined effects of various loads (power, temperature, atmospheric), under the influence of which complex and usually interrelated processes occur in the rail metal: plastic deformation of metal, the development of various types of irregularities on the surface of the rolling head. The occurrence of surface injuries and their development, the development of internal defects of contact fatigue origin. All this leads to significant changes in the service properties of the rails. The article discusses the causes of elastic stresses at the crack tip in an infinite plate during the movement of rolling stock. As a result of the conducted research, there were identified methods of repairing defects in the rail heads, which allowed raising the issue of continuing operation of rails with defects.

Evolution of the phase state, microstructure and properties of differentially hardened 100-meter rails after extremely long service life. Message 5. Gradient Structural-Phase States along the radius of the Rail Head after extremely long service life

Evolution of the phase state, microstructure and properties of differentially hardened 100-meter rails after extremely long service life. Message 5. Gradient Structural-Phase States along the radius of the Rail Head after extremely long service life

Структура рельсов после экстремально длительной эксплуатации

Using the methods of transmission electron diffraction microscopy the structure phase state and defect substructure in head of differentially quenched 100-meter rails at different depth after ultra long-term operation (passed gross tonnage 1770 mln. tons) are studied. The investigations are carried out along the rail head central axis of symmetry and working fillet rounding radius at the distances 0, 2, 10 mm from the tread surface. Dislocation ferrite substructure is presented by chaotically distributed dislocations and nets. The scalar and excess dislocation density increase as they approach the head rail surface. The values of these parameters on the surface are more than twice the corresponding value at a depth of 10 mm. The value of excess dislocation density is lower than scalar dislocation density which indicates elastic character of crystal lattice curvature-torsion. The quantitative evaluation of mechanisms dislocation strengthening is carried out.

Evaluation of the Effect of Heat Input and Cooling Rate of Rail Flash-Butt Welding using Finite Element Method Simulation

Abstract Simulations using the finite element method (FEM) were done to understand the effects of heating/cooling rates on the distribution of residual stresses. Two material parameters from rails were used while the boundary conditions remained constant: heat-affected zone size, maximum temperature and heating extraction rate. To complement the analysis, a flash-butt weld of a Premium rail was done with welding parameters adjusted to obtain a narrow HAZ, without forced cooling, to examine the microstructure formed in the critical regions in the web and the edge of the rail foot. The results showed that there was a concentration of vertical residual stresses in the web region, while the presence of horizontal compression residual stresses was mostly superficial in the rail head region. The main result from the simulation sets was that when using two simulation parameters with similar materials (rails) substantially different results were obtained. Metallographic examinations showed that there was no presence of acicular microconstituents (martensite/bainite). In the rail web, proeutectoid ferrite was observed in the central region, cementite in a previous austenitic grain boundary, in the region that reached temperatures close to AC3, and almost complete spheroidization in the region of maximum spheroidization. In contrast, in the rail foot edge region, there was a completely pearlitic microstructure, in the central region and in the zone that reached temperatures close to AC3, and a lower volume of spheroidization in the region where maximum spheroidization is typically observed, probably due to the higher cooling rate in this region.

Heat deformation analysis using a finite element model on gas pressure welding for railway rail

We developed heat deformation analysis model based on that of steel bar using Gaussian distribution in order to quantitatively understand deformation behavior of gas pressure welding of rail. The validity of the developed analysis model was confirmed by the variation of temperature, transition of upset length and geometry of budge through gas pressure welding test of rail. Therefore, it was confirmed that this model could simulate that with high accuracy. We found that the deformation degree at the center of the rail base and the jaw part of the rail head are smaller than that of other parts from results of heat deformation analysis. It is estimated that the deformation degree depends on the shape of rail. This paper describes the developed heating deformation analysis model of gas pressure welding of rail, and its validation test results.

New approach to analysis of railway track dynamics – Rail head vibrations

Abstract The article presents an original approach to the analysis of railway track dynamics. The “beam-inside-beam” concept is introduced as a dynamic generalisation of the static head-on-web effect, based on the two-layer model of rail. Rail head is a distinguished element of the rail. The system of distributed moving loads excites rail head as a beam supported by the rail web being considered as a viscoelastic layer. Rail head vibration is a kinematic excitation of the whole rail profile, including the rail head. The whole rail is also considered as a beam on viscoelastic foundation with parameters used in typical analyses of railway track dynamics. Vibrations of the whole rail obtained from the analysis of the two-layer “beam-inside-beam” model are compared with vibrations of typical one-layer track model. It is known that the static head-on-web effect is very limited. The range of significant rail head displacements covers nearly 0.6 m of area centred around the wheel position. This observation is also valid in the case of moving constant load. In other words, the dynamic effect of rail head vibrations in the case without imperfections type of track-vehicle is practically the same as in the static head-on-web case. Nevertheless, the analysis of track imperfections impact with various factors influencing the system behaviour, like the axles load and configuration, the track elastic parameters, the length of imperfection, or the train speed, show that the head-on-web effect is significant and should be analysed in more detail. For this purpose, a new model “beam-inside-beam” is proposed. The Fourier series are used to solve the two considered models. The load and unknown functions in the models’ solutions are expanded in the arbitrarily assumed interval which practically covers non-zero track response for the analysed system of parameters (group of wheels). This solving method for equation of motion was experimentally validated in the paper by Czyczula et al. (2017). Validation of the “beam-inside-beam” model is considered as future work and the current article should be recognised as a preliminary study of the analysed effects under assumption of being purely theoretical investigation so far, although forming hierarchically organised building of more complex rail models is possible to partially verify in further steps of modelling process.

DETECTION OF MECHANICAL STRESS LIMITING EFFECTS OF CRANE STRUCTURE DEFORMATION

The paper presents a construction design and results of laboratory tests of so-called mechanical stress detectors, which can be used to detect the deformation of the steel structure of a crane and to amplify the mechanical signal from the effect of the so-called crane skewing, which is included among occasional loads acting on the crane. The values of the relative elongation of the detectors corresponding to the magnitude of the instantaneous tensile force were obtained by conducting experimental mechanical tests. Detectors of a known extent of deformation were installed on a two-girder overhead crane bridge, where they measured axial forces generated during the controlled deformation of the crane bridge. In practice, the instantaneous values of the axial forces recorded by the individual detectors make it possible to regulate the speed of the crane drive wheels and thus eliminate, in a relatively short time, the undesirable effects of deforming the crane bridge and friction of the crane wheels on the sides of the rail heads.

Study of formation of secondary structures of frictional transfer on surface of steel samples in implementation of metal-plating technology

The state of the surface condition of steel samples (rollers) after tribological tests with modifi cation of working surfaces by applying hard cladding materials on friction surfaces are studied. Metal-plating of the subsystems of the wheel-rail friction mechanical system reduce friction between the wheel ridge and the side surface of the rail head, preventing the wheel from rolling onto the rail head. Surface morphology was investigated using an interference microscope surface analysis system and a scanning (raster) electron microscope with an energy dispersion analyzer prefix.

Fine structure formation in rails under ultra long-term operation

By the methods of transmission electron microscopy (TEM) at micro- and nanoscale levels the quantitative transformations of structure at a depth of 0, 2, 5, 10 mm along central axis and symmetry axis of fillet head of lengthy differentially quenched rails after severe plastic deformation (passed tonnage of 1770 mln. gross tons) are revealed. At a microscale level the transformation of cementite plates by newly formed grain boundaries absorption of carbon atoms from bulk carbides is established. At a nanoscale level the subgrain structure, being formed in surface layers, contains cementite nanodimensional particles, localized in junctions and along subgrain boundaries. This type of structure was formed as a result of dynamic recrystallization under megaplastic deformation being realized in a process of extremely long-term service of rails. The formation of so-called ‘channels of deformation’ is determined. It is shown that scalar and excess dislocation density in ferrite constituent of steel structure increases as the rail head surface is approached.

A machine learning framework for guided wave-based damage detection of rail head using surface-bonded piezo-electric wafer transducers

Due to repeated heavy loads, environmental conditions and non-frequent monitoring, the rail is subjected to heavy damage resulting in sudden failure. Hence, a frequent, faster, and efficient monitoring strategy is required. This paper attempts to investigate the application of guided wave (GW) generated through surface-bonded piezo-electric wafer transducer (PWT) to detect damages in rail at high frequencies. Firstly, a combined experimental and simulation study is presented in an effort to understand the dispersion characteristics of guided wave and its interaction with head damages in a relatively small rail specimen. The numerical simulation results are validated with those obtained from the experiments showing a good agreement between them. Secondly, a framework based on the machine learning algorithm is proposed to efficiently detect damage in rail head. Numerous inseparable guided wave modes are observed at higher frequencies implying the inability to detect damage through specific mode. Therefore, a machine learning framework is trained using time, frequency, and time–frequency domain features of the signal. Total 672 numerical simulations of different types of damage with different severity and location in the rail head are carried out to train and validate the model. It is found that GW generated through surface bonded PWTs is able to detect minimum defect size of 5% of head area with 1 mm thickness. Finally, the proposed framework is tested using simulation and experiment results of arbitrary damage in the rail head. The error in estimating severity was found to be in the range from 2.00% to 16.67%.

On the numerical study of fatigue process in rail heads by means of an isotropic damage based high-cycle fatigue constitutive law

The fatigue phenomenon has been historically related to the railway industry. Nowadays, thanks to the high quality of the materials used, most of the recorded problems have been overcome although there are still degradation processes which are associated to fatigue and need to be considered for the definition of the maintenance campaigns and the general progress of the sector. In this paper, the latest improvements in the isotropic damage based high-cycle fatigue constitutive law proposed by Oller et al. (2005) are presented and the approach is used for the study of two regions of the railway path where fatigue mechanisms are experimentally detected: a straight section and a crossing element. The analysis of the affected areas is performed through a finite element simulation identifying the critical regions liable to the fatigue degradation when the structure interacts with high speed vehicles and predicting the initiation of the degradation at the rail head while capturing the physics of the problem. The potential of the methodology is shown through the case studies and the current shortcomings and the future lines of research are clearly stated.