Rail Life Research Articles

On the Issue of Determining Relative Rail Rolling Contact Fatigue Damageability

Adoption of heavy haul traffic on many railroads, comprising Russian railways, has highlighted the relevance of assessing the effect of increased axial loads on the contact fatigue life of rails.The article describes a set of theoretical studies carried out to create a scientifically substantiated method for predicting the contact fatigue life of rails depending on the values of axial loads. The stress-strain state of the contact area has been determined using the finite element model of wheel rolling on a rail. It has been found that the wheel-rail rolling contact area undergoes complex multiaxial loading with the simultaneous action of normal and shear strains. Based on the analysis of models describing multiaxial fatigue damage, the Brown–Miller model was chosen, which considers the simultaneous action of normal strains at the contact area and of maximum shear strains, which most fully describes the stress-strain state of the wheel-rail rolling contact area. To apply the Brown–Miller model, fatigue stress-strain curves for rail steel have been identified. Based on the analysis of methods for determining the parameters of stress-strain curves carried out by V. A. Troschenko, a modified Roessle– Fatemi hardness method has been applied. Based on the experimentally determined values of hardness on the rolling surface, the parameters of the curves of elastic and plastic fatigue have been revealed by calculation and experiment. To establish the damaging effect of the load from wheel rolling on a rail, the concept of relative damage per rolling cycle had been assumed which is the value inverse to the number of cycles preceding formation of a contact-fatigue crack at a given value of the axial load.Calculations of the relative damage rate of the rolling surface of rails caused by contact fatigue defects were carried out with the Fatigue software package considering mean values of the indicators of the degree of fatigue strength and plasticity of rail steel and the calculated stresses in the wheel-rail contact area, as well as the plasticity correction using Neuber method. The polynomial dependence of relative damageability of the rolling surface of rails is obtained. The established functional dependence of relative damageability of the rolling surface of rails on the values of vertical forces can be used as the basis for the developed methodology for predicting the contact fatigue life of rails.

Estimation of rail renewal period in small radius Curves: A data and mechanics integrated approach

This paper presents a data and mechanics integrated approach (DMIA) to analyze small-radius rail life caused by both severe rail defects and excessive rail wear. First, the Archard wear model, as a mechanics-based model, is adopted to calculate the wear growth chart under different radii. Second, based on the growth chart, the observed over-threshold rail lifetime is adjusted to estimate the lifetime when it reaches the wear threshold. Third, considering the influence of different curve radii and the segment length, an accelerated failure time (AFT) model, as a data-driven model, is used to analyze the heterogeneity of the corrected measurement data. A survival probability is obtained with increasing gross tonnage for different curve radii. Finally, the expected MGT is calculated for rail defect & rail wear-based renewal for curves with different radii, and the obtained values are compared with the corresponding values in the existing standard.

Investigation on the Rolling Contact Fatigue Behaviors of Different Laser Cladding Materials on the Damaged Rail

Abstract Surface damages on rail became severe with the increase in the axle load and speed. Laser cladding was used to repair the local damages on rail surfaces to ensure the service performance and prolong the life of rails. In the present study, five types of cladding materials (304, 314, 2Cr13, 316L, and 434L) were clad at a small part (trapezoidal shape) of the rail disc to simulate the defected rail in the field. Vickers hardness tester, optical microscopy (OM), scanning electron microscopy (SEM), and electron-dispersive X-ray spectroscopy (EDS) were employed to investigate the service properties of the repaired rail discs. Results indicated that all these five clad rail discs had lower wear-rates than the unclad rail disc. The wear-rates decreased with the increase in the initial hardness of the clad layer. Cracks with large angles mainly propagated along the boundary at the front edge, while at the rear edge, the crack morphology was closely related to the hardness of clad layer. 434L would induce the minimum wear loss and the modest rolling contact fatigue (RCF) of the repaired rail disc, which could be the potential cladding material for repairing the damaged rail.

Produljenje uporabljivosti tračnica u slučajevima oštećenja njihove glave

Rails are subjected to the processes of wear, corrosion and contact and bending fatigue during their lifecycle. As a result of these processes, various types of damage and defects are formed in rails. The residual life of rails depends on the size, position, and orientation of defects. Maximum permissible crack-size values are calculated in this paper using the finite element method. The crack plane orientation relative to the contact surface plane is analysed. The dependence of the stress intensity factor on the crack area is established. This allows continued use of defective rails and safe operation on low-activity railways.

A Review on Microstructural Features and Mechanical Properties of Wheels/Rails Cladded by Laser Cladding.

The service life of rails would be remarkably reduced owing to the increase of axle load, which can induce the occurrence of damages such as cracks, collapse, fat edges, etc. Laser cladding, which can enhance the mechanical properties of the rail by creating a coating, has received great attention in the area of the rails due to the attractive advantages such as low input heat, small heat-affected zone, and small deformation. In this paper, recent developments in the microstructural characteristics and mechanical properties of a cladded layer on the rail are reviewed. The method of process optimization for enhancing the properties of a cladded layer are discussed. Finally, the trend of future development is forecasted.

<b>New Rail Replacement Period Reflecting Results of Bending Fatigue Tests in High-cycle Region</b>

To estimate the service life of rails, it is necessary to clarify the relationship between the stress and the number of loading cycles needed to reach breaking point through bending fatigue tests. In the previous studies, bending fatigue tests were conducted under high stress levels exceeding the stress generated on real tracks. In this study, bending fatigue tests were carried out under lower stress level conditions, and the service life of rails was estimated reflecting the results obtained in high cycle regions. Based on the results of these tests, this paper suggests it may be possible to extend the period between rail replacements.

Effect of easement geometry on rail end fillet stress at bolted rail joints for transit track

Continuously welded rail (CWR) has become more popular than bolted joints because of the advantages of continuous geometry and stiffness and the resulting maintenance savings. Due to a variety of reasons, a considerable number of bolted joints are still in service in rail transit systems. With the high frequency of impact loads, rail at bolted joints are vulnerable to defects, such as cracking and head-web separation that could lead to more drastic failures and consequences (i.e. derailments, etc.). To prolong the service life of joint bars and rails, rail-end easements in the center of the bar were proposed and became standard in some freight rail companies. However, the effectiveness of a joint bar easement largely depends on the geometry of the easement. Therefore, the easement designed for freight track may not be effective for rail transit infrastructure. Further, the effect of easement geometry has not been thoroughly investigated and documented. Therefore, this study investigates the stress distribution at the rail end bolt-hole and upper fillet areas for joint bars with different easement geometries through a parametric analysis performed with Finite Element (FE) modeling. The FE model used in this study was developed specifically to study rail joints and was validated through full-scale laboratory testing. Results from this study show that a deeper easement yields lower contact stresses, while a longer easement does not necessarily reduce the contact stresses with the studied combination of rails and bolted joints for transit track. An easement may reduce the service life of the joint if the geometry of the easement is not properly engineered.

Prediction of rail damage using a combination of Shakedown Map and wheel-rail contact energy

Rolling contact fatigue and wear are two key damage mechanisms that govern rail life. Although there are several different mechanisms affecting both their initiation and propagation, the trade-off between them is important and their accurate predictions can provide significant benefits when planning rail maintenance activities. Through integration with vehicle dynamics simulations, damage models based on the wheel-rail contact energy (Tγ) and Shakedown theory have often been used to predict damage. In this paper, the findings from previous studies were reviewed to identify their limitations. To assess the accuracy of the predictions, their input parameters were compared for sites with and without reported RCF defects from two lines on the London Underground network. The results indicated certain variations and hence, a new wear and RCF damage prediction method was developed using a combined Shakedown Map and Tγ approach. While the wear model predictions were validated by comparison with measured rail wear, the availability of field crack depth measurements enabled the validation of the new RCF crack depth prediction model. Reasonable predictions of crack depth and wear over consecutive intervals have been achieved on various sites which increases the confidence of the models to support future optimisation of maintenance planning.

Инновационные технологии рельсообработки высокоскоростных железных дорог

Drawbacks in existing methods for rail grinding are analyzed. The innovation technologies for rail tread machining allowing the increase of rail life and rail machining capacity are shown. There are presented basic parameters and indices of the considered working methods taking into account a speed of a rail-working train.

Establishing a pattern in the influence of two-layer greasing on the wear resistance of rails

This paper reports the results of an experimental study into the influence of two-layer greasing, formed from the graphite powder and base molecules of industrial oil, on the durability of the side surface of a rail head. Thus, increasing the concentration of graphite powder in oil from 0 to 3 % under a load of 363‒646 N decreases a wear rate by 42‒29.7 %, respectively. The study procedure implied modeling the process of rolling friction at slippage using rollers at the SMC-2 friction machine. This particular type of friction occurs in the tribosystem wheel flange the side surface of a rail head in the curved track sections. The supply of oil applying an aerosol technique was also implied. Two independent factors were varied: the concentration of graphite powder in the industrial oil I-12A and an external load. The constant factors were the roller rotation frequency, which enabled stable slippage at the level of 20 %, and oil temperature, and the duration of each test. The results of the experiment have made it possible to derive a regression equation, which describes the wear pattern of a roller in the friction pair «roller‒roller» depending on the selected factors. At the final stage of this work, we calculated a rail resource in the curved track section. The results of calculating a railroad rail resource under conditions of increasing the concentration of graphite powder from 0 to 3 % at external loads from 363 to 646 N have demonstrated an increase in the rail resource from 40 to 61 %. The calculation was based on the obtained experimental data, which characterize the friction process between the side surface of a rail head and the wheel flange in a curved track section under the conditions of two-layer greasing at various loads. The two-layer greasing was formed through the aerosol application of oil onto the friction surface with a different concentration of graphite. The data obtained make it possible to predict the service life of rails in the curved track sections under conditions of two-layer greasing

The effects of periodic overloads on fatigue crack growth in a pearlitic Grade 900A steel used in railway applications

The objective of this paper is to predict a three-dimensional fatigue crack growth (FCG) in a pearlitic Grade 900A steel used in railway applications in the presence of periodic overloads. Numerical and experimental methods are used to investigate the behavior of FCG in the rail specimens. A 3-D boundary element model, using the BES tool is used to estimate the stress intensity factor (SIF) using the crack opening displacement (COD) approach in rail specimens. Also, the crack growth rate is predicted utilizing the Forman–Newman–de Koning (FNK) model. Linear elastic fracture mechanics (LEFM) is used to predict the fatigue life developed from a two-stage fatigue loading cycle where both mechanical loads and periodic overloads are present. The maximum tangential stress (MTS) crack extension criterion is used to obtain the FCG paths. The results revealed that fatigue life is highly sensitive to periodic overloads. Therefore, this factor significantly affects the fatigue life of railway rails during service conditions. In the present investigation, the periodic overloads have remained constant and the effect of load ratio and the number of overloads on the fatigue life has been investigated.

DEVELOPMENT ANALYSIS OF MAIN DEFECTS AND THEORETICAL FORECAST OF RAIL SERVICE LIFE IN THE CONDITIONS OF LUBRICATION

Purpose. The study is aimed at identifying the patterns of the load influence on the rail and the parameters of the two-layer lubrication on the development of the main rail defects, namely, lateral wear in the curved track sections. Methodology. To establish the distribution of the main rail defects by type and sections of the track, expert estimates of the track service of the Azerbaijan Railway were used with respect to the results of measurements of defective parameters and rail service life on individual sections. To establish the load influence patterns and the parameters of the two-layer lubrication on the intensity of lateral wear of the rails and their service life in the curves, we used the main provisions of the contact interaction mechanics, as well as tribology and chemmotology. Findings. The authors proved: 1) the leading rail defects in the curved track sections are defects associated with low contact fatigue strength of steel, high contact stresses and friction forces along the lateral surface; 2) according to the obtained distribution, the main rail defects in the curves should include: lateral wear of the head, metal shelling along the lateral surface, transverse cracks in the head in the subsurface area; 3) the use of a two-layer lubrication leads to an increase in the actual contact area of the wheel and the rail, a decrease in the contact pressure on the rail, and in aggregate, to a decrease in lateral wear and an increase in the rail service life. Originality. The authors first systematized the results of measurements of the rail defects parameters in curves and, on this basis, obtained a distribution of the main defects depending on the curve radius. The authors improved the mathematical model for calculating the service life of rails in curves, which, unlike the existing ones, takes into account the thickness of the lubricating film and the concentration of the solid anti-friction additive in the oil when lubricating the lateral surface. Practical value. The obtained results allow us to perform predictive calculations of the rail service life in curved sections depending on the load from the wheel for different operating conditions, namely, with dry contact of the wheel with the rail and in the conditions of their two-layer lubrication. The implementation of two-layer lubrication in railway transport, taking into account the influence of the studied parameters, will lead to an increase in the rail service life in the curves by 55%, 50% and 45% with an estimated rolling stock mass of 60, 70 and 80 tons.

The life cycle assessment of the used rails according to the results of cyclic high-frequency tests

The article presents the results of the strength tests and the metallographic studies of used rails with the significant running surface wear. On the basis of the accelerated modeling of the continuously welded rail life cycle, an assessment system is proposed to evaluate the life cycle of the used continuously welded rails that are sent to the rail repairing depots.

Prediction of contact-fatigue damage to rails using computational-experimental methods

Analysis of the operational data related to rails failure showed that contact-fatigue defects consistently hold a prominent place. The goal of the study is to show the possibilities of using modern numerical methods in calculation assessment of the service life of rails before the onset of contact fatigue crack formation on a running surface depending on the values of axial load. To calculate a stress-strain state in the area of contact interaction between the wheel and rail a detailed finite-element model implemented in the MSC. Marc software package is used. The analysis revealed complex multiaxial and non-proportional nature of the stress-strain state. The Brown – Miller multiaxial fatigue model implemented in the MSC. Fatigue software package was taken to determine accumulation of the contact fatigue damages on a rail running surface. The model is based on the assumption that maximum fatigue damages in the metal occur in the area with the maximum shear stress. The impact of normal stresses in this area is also taken into account. The results of a comparative computational analysis of the rail life time confirm that the service life decreases with increasing axial loads, all other conditions being the same. With a share of 20% of freight trains with axle loads of 25 tonf in a daily pattern one should expect a decrease in the contact fatigue life of rails by 3 – 4 %. It is possible to improve the method for prediction of the contact fatigue life of rails in terms of experimental definition of the fatigue and strength characteristics of the rail steel depending on the degree of hardening of the running surface, their probabilistic properties and the use of a cumulative distribution of vertical forces taking into account the structure of the freight traffic passing through the section.

Kajian Umur Jalan Rel Berdasarkan Keausan dengan Metode dari AREA dan Perjana

Penentuan usia layan rel merupakan hal yang penting untuk dilakukan untuk menghindari terjadinya kerusakan rel yang fatal. Estimasi usia layan komponen rel dapat ditinjau berdasarkan faktor keausan. Tulisan ini mencoba menghitung dan membandingkan usia layan rel berdasarkan rumus perhitungan keausan rel dengan metode AREMA yang menggunakan formula empiris dari Hay dan menggunakan metode PT KAI. Hasil menunjukkan nilai yang bervariasi untuk berbagai koridor yang ada pada lintas wilayah operasi Madiun, sesuai dengan spesifikasi jalan rel, beban lintas, dan geometri jalan rel. Namun demikian, perbandingan terhadap kondisi eksisting jalan rel belum bisa dilakukan karena adanya keterbatasan data hasil pengujian terhadap jalan rel yang dioperasikan.

The Impact of Two-Layer Lubrication Parameters on the Service Life of Railway Rails

The prerequisites, basic hypotheses and sequence of creation of a mathematical model for estimation of service life of railway rails in conditions of two-layer lubrication are given in the article. The created mathematical model is presented in the final form. The model takes into account the geometry of the wheel-rail contact, the initial and constant surface roughness, actual loads on the rail, speed of the rolling stock, strength characteristics of steels and the antifriction additive, as well as the basic parameters of two-layer lubrication. The main parameters of lubrication include the concentration of solid antifriction additives in oil which is sufficient to fill irregularities of the contact surface; the boundary molecular oil film thickness. The results of calculations using the developed mathematical model are presented. The performed calculations reveal the positive effect of the parameters of a two-layer lubricant on the resource of rails. The anti-wear effect of the lubricant increases as the concentration of graphite in the oil increases and the weight of the carriage decreases. Based on the performed calculations, conclusions and recommendations were obtained regarding further experimental verification of the mathematical model, as well as the influence of the parameters of two-layer spray lubrication on wear and service life of transport rails.

Use of shakedown maps to assess plastic flow in railway curves

Plastic deformation of rails can occur on tight curves, which can significantly reduce the rail life. This paper investigated the phenomena of gross plastic deformation, or plastic flow, using multibody vehicle–track interaction and simplified finite element analysis. The focus is on understanding the contact conditions on the low rail of curves and how these differ from those in shakedown maps. To this end, two trial sites are simulated using multibody vehicle–track software. The contact conditions are then compared against several criteria assumed in the derivation of the shakedown maps. A further assumption implicit in the shakedown maps is also investigated by a non-linear finite element analysis. In this case, a more realistic Chaboche material model is used as opposed to the simple linear elastic–perfectly plastic model in the shakedown theory. The results of the finite element analysis are combined with a bespoke indicator of plastic flow to assess the influence of distance to shakedown limits on the likely plastic flow. Finally, a simple interpolation scheme is used to map the finite element results back to the trial sites. The interpolated results for the sites are used to evaluate the influence of running speed and different levels of wheel profile wear. Results suggest that the bespoke indicator defined in this work can be used as an effective measure of plastic flow; this measure is then used to quantify the influence of cant excess on the rates of plastic flow.

Predictive wheel–rail management in London Underground: Validation and verification

London Underground is facing the challenge of increasing timetables against spending cuts across renewals and maintenance in all assets. In order to meet this challenge, it is reviewing all maintenance practices to make sure that they are appropriate for the current asset conditions. Management of the wheel–rail interface is critical to maximising the life of wheels and rails through preventative maintenance regimes that ensure all activities offer value for money and safe operation. Detailed monitoring of the asset condition using novel non-destructive techniques has allowed the identification of the problems which currently occur at the wheel–rail interface on the London Underground network. These problems are discussed in this paper along with some of the solutions proposed to manage them. Site observations from a range of rail rolling contact fatigue monitoring sites have also been compared to the outputs from vehicle dynamic simulations. These outputs were post-processed using a circle plotting technique, which illustrates the location, direction and severity of the forces, and the Whole Life Rail Model to predict the susceptibility to rail damage for two rail steel grades. The outputs from these comparisons have helped to illustrate the wheel–rail contact conditions and forces which are driving the observed damage and potential future enhancements to improve the accuracy of the models for predicting the observed rolling contact fatigue damage.

Three-dimensional study of rolling contact fatigue using crystal plasticity and cohesive zone method

A three-dimensional (3D) finite element model that includes the microstructure of grains and grain boundaries is developed for studying the rolling contact fatigue (RCF) damage caused by a rolling steel wheel on a steel railway. The 3D model uses a crystal plasticity-based micromechanical framework for simulation of stress-strain behavior inside the grains, and cohesive elements with traction-separation law for modeling the intergranular fatigue damages. A combination of moving normal Hertzian load and tangential loads are employed to mimic the rolling contact conditions. The effect of various parameters such as friction coefficient, traction, partial slip contact and wheel load on RCF is studied. The results reveal that RCF cracks initiate slightly below the surface for large wheel loads and low tractions. The cracks migrate toward the surface as the wheel-rail traction increases. For high tractions, the cracks initiate at the rolling surface. Under partial slip contact condition, there is a large change in rail life for small normalized tractions. With a slight increase in the latter, the rail life significantly decreases. For moderate to large tractions, rail life remains relatively unchanged or slightly increases. The results of the study appear to agree with anecdotal observations by the U.S. railroads from revenue service operation.

Rail Quality Standards and Monitoring

Rail quality is essential to railroad safety. Therefore, it is of the utmost importance to establish the characteristics that affect rail life. The goal of the present work is to assess the expediency, necessity, and sufficiency of current quality requirements on rails. Prospective directions for research are suggested, with a view to improving the quality standards.