Service Life Of Rails Research Articles

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.

Effect of spherical and ballast dents on rolling contact fatigue of rail materials

Surface dents on railroad rails may be caused, for example, by the drop of freight goods or the impact of ballast rocks and may have a deep effect on the rail service life. To better understand this problem, this investigation aims at exploring the rolling contact fatigue behavior of the rail materials (as, for example, PD3 steel) after being impacted by two kinds of hard bodies: a simple spherical steel ball and a more realistic ballast rock. The results show that the residual tensile stress, which is distributed on the shoulders of the dent, decreases the rolling contact fatigue (RCF) resistance of the material around the dent. Moreover, the unbalanced wear behavior between the two shoulders of the dent makes the situation even worse on the side of the dent where the tangential force acts firstly. Finally, due to the higher martensite hardness with respect to the matrix material, the crack propagates faster around the dent in presence of white etching layer on the bottom of the dent itself.

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.

Optimal profile design for rail grinding based on wheel–rail contact, stability, and wear development in high-speed electric multiple units

High-speed electric multiple units have numerous advantages. However, a number of critical maintenance issues arise in the operation of high-speed electric multiple units. The previous researches about rail profile design usually take only a single type of wheel profile into account, which would cause some other problems such as severe increase of hollow wear on the wheels. This study systematically investigates the influence of rail grinding on running stability and wear development in high-speed electric multiple units and designs a new rail profile as reference for grinding that takes all types of vehicle wheels running on a specific line into account, in order to design a ground rail which could match the wheel profile and thus improve the running stability of electric multiple units. All types of wheel profiles used on the Wuhan–Guangzhou railway line are taken as the design reference. A wheel–rail wear simulation program is constructed based on CONTACT numerical simulation software and SIMPACK vehicle system dynamics software. The simulation results show that both the wheel–rail contact relationship and the running stability of high-speed electric multiple units improved after rail grinding. The results of the wheel wear analysis show that when the rail is ground to the target profile, after a running mileage of 200,000 km, the wear area of the new wheel profile LMA and the greatest hollow wear wheel profile LMA-25 decreases by 1.13 mm2 and 9.86 mm2, respectively. In addition, this method can prolong the wheel reprofiling interval. For the Wuhan–Guangzhou railway line, normally the grinding interval for the tangent track and large-radius curve is 2–3 years, and for the entering and exiting tunnel sections, the grinding interval should be set for 1–2 years, which could remove the damaged layer of the rail surface and could restore the designed profile of the rail and prolong the rail service life.

Comparative evaluation of corrosion resistance of wheel and rail steels in various media

In order to increase the service life of rolling stock parts and rails, it is necessary to know the value of the corrosion rate of alloys in various media. In this work, the corrosion resistance of various alloys, used in railway transport, was investigated. To determine the rate of corrosion, a polarization method with the use of the potentiostat-galvanostat “Pi 50-Pro” was used. The value of the corrosion rate was determined on the basis of processing of the polarization curves with the use of the graphical method. To control the obtained results, corrosion rate was determined by decrease of the mass of samples, made from the same alloys (gravimetric method). Obtained results showed high convergence. Studies were carried out in a simulated solution. Based on a comparison of the values of the corrosion rate, the most resistant steels were determined. Corrosion resistance increases in series: 09G2S, 110G13L, St3ps, 55G, 60G, M76T, E76KHSF12KH1, 12KH18N9T.

Small-amplitude hunting diagnosis method for high-speed trains based on the bogie frame’s lateral–longitudinal–vertical data fusion, independent mode function reconstruction and linear local tangent space alignment

Hunting stability is an important factor that influences the running safety of high-speed trains. Most of the existing hunting monitoring methods monitor only the standard hunting. The small-amplitude hunting, however, not only affects ride comfort but also aggravates the wheel–rail wear. Therefore, to extend the service life of wheels and rails and to improve the ride comfort, it is extremely important to monitor the small-amplitude hunting. Hunting motion is a coupled movement of lateral and yaw displacements of the wheelset. When the bogie is in an unstable state, instability will occur not only in the lateral side but also in the longitudinal and vertical sides of the bogie. To improve the robustness of the small-amplitude hunting monitoring methods, this study proposes an idea of the bogie frame’s lateral–longitudinal–vertical data fusion. In addition, the small-amplitude hunting signals have strong nonlinear characteristics, and their frequency and amplitude are unstable. Using only the amplitude or frequency to detect the small-amplitude hunting has obvious shortcomings. Therefore, a new feature extraction method based on the independent mode function reconstruction and linear local tangent space alignment (IMFR-LLTSA) is proposed. This method has been tested with three simulated signals. Finally, a method of combining the bogie frame’s lateral–longitudinal–vertical data fusion and IMFR-LLTSA is used to identify the small-amplitude hunting of high-speed trains. This method has been validated using the data of the CRH380a high-speed train running on the Shanghai–Hangzhou line, monitored by the authors’ research group. The results show that this method is superior to the single lateral diagnosis method.

Scratch test of pearlitic steels: Influence of normal load and number of passes on the sub-superficial layer formation

Abstract The formation of sub-superficial deformed layer in pearlitic steels under dry sliding conditions has been widely researched, especially for the rail/wheel system. The RCF defects are considerate the most important feature to be analyze on the rail service life determination, being common practices, the employ of rail grinding procedure to remove the surface defects. In this work, the multi-pass scratch was used as the laboratory test simulating the material removal mechanism under wear-controlled conditions, observed in maintenance procedures on heavy railways (which correspond to multi-pass abrasive wear events). It was analyzed the microstructural transformation beneath the scratched surface as a function of the numbers of passes (i.e. one-pass to five-passes) and the constant normal load (i.e. 4 N and 8 N). The material of interest consisted in samples of pearlitic steel without prior work hardening. The features of the grooves were characterized by Coherence Correlation Interferometry (CCI) and Scanning Electron Microscopy (SEM). The White Etching layer (WEL) formation was characterized by Focused Ion Beam (FIB-SEM) and the crystallographic orientation was determined by Electron Backscatter Diffraction (EBSD). The characterization of the grooves features shows a small difference in the friction coefficient between test conditions not correlated by the geometrical aspects (variation up to 30% in depth and width). The SEM and FIB-SEM micrographs revels the WEL formation, consisted in a sub-superficial and transitional layer, characterized by ultra-fine grains and mixture of deformed pearlite colonies with undeformed colonies, respectively. Crystallographic texture can be found in samples tested with the lower normal load (4 N) and its relationship with the number of passes was determined as a function of the reference plane selected. The crystallographic texture to scratch direction (RD) was found in the less severe condition of passes, while in the transversal direction (TD) as a reference plane, a high concentration of pearlite colonies oriented at {111} was determined.

Influence of the axial loads of rolling stock on the contact-fatigue life of rails

Analysis of operational data for defective and highly defective rails showed that up to 25 % is the contact-fatigue defects. In connection with the development of heavy haul traffic on the Russian railways, it is relevant to determine the influence of cars with increased axial loads of 25 and 27 tf on the contact fatigue life of rails. The solution of this problem is set forth in this article. The Brown-Miller model of multi-axial fatigue was used in the calculation. This model is integrated into the Fatigue software system, which is tied to the Marc calculation system through Pat-ran. Since under operating conditions the wheel moves (rolls) along the rail on meandering trajectory, in computer modeling weight coefficients were taken into account that characterize the percentage of wheels in the cross-sectional areas of the rail. Calculations of contact fatigue life took into account the variability of vertical loads from the impact on the track of trains formed from innovative open cars with axial loads of 23.5, 25 and 27 tf under operating conditions, loaded with real loading blocks. According to the analysis of calculated data with an increase in axial loads from 23.5 to 25 tf, it is necessary to expect a decrease in the service life of rails in contact fatigue resistance by 19 %, with a further increase in axle loads of up to 27 tf per 32 %. Considering that the share of freight cars with axial loads of 25 tf does not exceed 15...20 %, then on the routes of its use the service life of rails should be expected to decrease by 3...4 %. The method proposed by the authors for predicting the contact fatigue life of rails with increasing axial loads is advisable to improve in part of the experimental determination of the fatigue and strength characteristics of rail steel from the degree of hardening of the rolling surface, its probabilistic properties and the use of the integral distribution law for vertical forces, taking into account the structure of the freight traffic passing through the section. The work was carried out according to the RFBR project 17-20 01088.

A segmental evaluation model for determining residual rail service life based on a discrete-state conditional probabilistic method

Because steel rail is one of the most fundamental components of railway operations, the accurate estimation of residual rail service life is of great significance in ensuring the safe operation of railways. In addition, maintenance expenses must be minimized in a manner that allows limited railroad resources to be optimally allotted. In this study, the typical types of continuous rail segments on a rail line are classified into non-sharply curved rail segments and sharply curved rail segments. Using these classifications, a model for estimating the residual service lives of rail segments using a discrete-state conditional probability method is proposed based on an analysis of rail deterioration characteristics. The model considers several heterogeneous factors to determine their influence on the deterioration process and is shown to be capable of estimating the residual service lives of rail segments. Finally, the model is validated through a case study of the Beijing Metro, using inspection records of rail defects in conjunction with heterogeneous factor data to predict the service life of the rail, which is then compared with its actual service life. The model is found to show good agreement with the rail inspection and maintenance records of the Beijing Metro, indicating its appropriateness for use by railroad management in allocating future rail maintenance resources.

Determination of the level of separate rail failure using the indicator of their reliability

During the operation, the upper railway track structure constantly tends to age, which includes the increasing number of failures. This process is controlled by the track maintenance system, which provides for the current maintenance of the track in a certain railway section. As part of the current maintenance of the track, in particular, works are performed to eliminate defective elements of the upper railway track structure, which appeared during functioning of the track structure. The dependence of the operational cargo turnover on the amount of transported cargoes has been analyzed. It is directly related to the issues of organization of maintenance of the railway track structure taking into account the current track operation conditions. Regression analysis of the reported data allowed establishing a mathematical model of the dependence of the value of operational cargo turnover on the value of the transported cargo. The service life of rails (rail bars) in the track section has been established to be related to the indicator separate rail failure during the period of operation of the upper railway track structure by defects. The safety level of rails (rail bars) can be determined based on the value of this indicator.

Analytical modeling of grinding process in rail profile correction considering grinding pattern

An analytical introduction to rail grinding was presented in this paper where a newly-designed profile serves as the targeted ground profile to extend the rail's service life. A method for determining eliminated metal due to rail grinding is established as an initial consideration in the process of rail profile correction. The analytical model of material removal contains grinding wheel characteristics such as rotation speed, feeding speed, and applied pressure to the ground rail. The assumed coefficient in this model was fitted by a scratch test between a single abrasive grain and rail specimen. The sectional area s of removed metal can be used to estimate grinding capacity rather than the traditional grinding depth. An algorithm that generates personalized grinding patterns is proposed to arrange grinding wheel location and proper sequence. The whole procedure was indirectly validated in terms of grinding quality and rail profile error through rail grinding field data. A grinding pattern was generated by the proposed method that can effectively simulate the ground rail profile within a pre-determined tolerance. The area difference of predicted and target profiles was 13 mm2 (6.6%) and the experimental result was 12.2mm2 at rail cross-section.

Estimating railway rail service life: A rail-grid-based approach

Precise estimation of railway rail service life is of great significance for the efficient use of maintenance and replacement resources and the effective prevention of broken rails. Here, an innovative model for railway rail service life estimation is proposed. A railway line is divided into adjacent segments of the same specific length. Each segment is termed a “rail grid.” Employing the theory of Markov stochastic processes and hazard models, the service life of each rail grid is estimated and the degradation law of each rail grid is customized. The proposed model is verified using five-year rail inspection data for the Longhai Railway. Our evaluation demonstrates that the estimated rail service life is very close to the real rail service life and meets railway management requirements.

A design method for rail profiles based on the geometric characteristics of wheel–rail contact

Designing a proper rail profile carries more significance than designing a wheel profile because of the amount of work and cost involved in the maintenance of rails. A better rail profile will not only help to ensure achieving the desired dynamic performance of rail vehicles but it also extends the service life of rails. This paper presents a unique design method for the design of rail profiles based on the given geometric contact characteristics. The proposed method utilizes a given wheel profile and two typical functions respectively to set the main design targets. The first function is the rolling radii difference and the second one is the contact angle difference. Wheel–rail contact distribution is chosen as the secondary target to prevent stress concentration and the associated fatigue failure. With certain assumptions, the solution process becomes a reverse designed one, which can be solved by using proper discrete numerical methods. Two examples of rail profile designs have been discussed in detail for rigid and independent wheelsets.

An inverse design method for rail grinding profiles

ABSTRACTInspired by the optimisation design method for restoration of worn wheel profiles, an inverse design method based on optimal rail grinding profiles is presented in this paper. To improve grinding quality, vehicle dynamic performance is chosen as the main criteria and rolling radii difference function is selected as the key factor (also main target function) determining dynamic performance. Grinding material to be removed is chosen as the auxiliary target aimed at extending rail service life. Besides that, wheel–rail contact distribution is also taken into consideration as an auxiliary target preventing stress concentration and fatigue growth. By introducing certain presuppositions, all the design targets will form an inverse design problem. This problem can be solved using hybrid discrete numerical methods. Considering different grinding requirements, two examples of grinding profile design for straight and curved track will be discussed. Results show that the presented method is efficient and effective. Practical implementation has been carried out at several grinding sites in China.

Study on Rail Profile Optimization Based on the Nonlinear Relationship between Profile and Wear Rate

This paper proposes a rail profile optimization method that takes account of wear rate within design cycle so as to minimize rail wear at the curve in heavy haul railway and extend the service life of rail. Taking rail wear rate as the object function, the vertical coordinate of rail profile at range optimization as independent variable, and the geometric characteristics and grinding depth of rail profile as constraint conditions, the support vector machine regression theory was used to fit the nonlinear relationship between rail profile and its wear rate. Then, the profile optimization model was built. Based on the optimization principle of genetic algorithm, the profile optimization model was solved to achieve the optimal rail profile. A multibody dynamics model was used to check the dynamic performance of carriage running on optimal rail profile. The result showed that the average relative error of support vector machine regression model remained less than 10% after a number of training processes. The dynamic performance of carriage running on optimized rail profile met the requirements on safety index and stability. The wear rate of optimized profile was lower than that of standard profile by 5.8%; the allowable carrying gross weight increased by 12.7%.

A novel laser surface compositing by selective laser quenching to enhance railway service life

With the rapid development of high-speed and heavy-haul trains, it is challenging to improve the service life of rails. In order to ensure toughness and contact fatigue resistance (CFR) of rails, the present technical standards restrict the hardness of rails to be beneath HB400 and forbid the martensite structure in rails. In this study, a novel laser surface compositing (LSC) based on selective laser quenching is proposed to strengthen the rails. By designing the hardening area sizes and proportions rationally, the wear resistance of the rails is enhanced by 2.2–3.5 times without noticeably deteriorating their contact fatigue resistance (CFR). Furthermore, the wear and contact fatigue behaviours of the LSC rails were investigated systematically.

Fracture Mechanics Based Approach to the Significance of Certain Loads on the Service Life of Rails

In this paper, the fatigue design of rails in the transition from bridge to abutment is examined. The current fatigue design of rail systems is carried out with simplifying assumptions concerning the stresses in the rail. Thus, the determination of a fatigue endurance limit is done with stresses based on the Smith-Diagram. By applying this means of design, the assumption is made that there are mainly normal stresses in a rail. Those may originate from changes in temperature, accelerating or slowing down of the trains as well as bending stresses caused by the passing of trains. Horizontal components of the load (from the train's sine run, lateral shift of bridges or the cant of curves) are not considered in this design format.At the same time, specimens in fatigue tests with pulsing vertical loads regularly show unexpected and inexplicable cracks at the edge of the rail foot and a huge scatter of the results. In cases of rail breaks the location of the incipient crack is not necessarily in the cross section's area with the largest tensile stresses, but can be shifted to areas of smaller tensile stress (e.g. the edge of the rail foot).Obviously additional criteria such as the condition of the surface of the rail foot in combination with stresses from warping of the section (secondary bending) have more influence on the fatigue performance than estimated before.This paper presents an approach to evaluate the importance and priorities of the named influencing factors and criteria on the fatigue design of rails by means of fracture mechanics. The focus hereby lies on the rail foot, since in this region of the cross section there are no disturbing influences as contact problems or wear.

Wear and chattering characteristics of rail materials by ultrasonic nanocrystal surface modification

Stick-slip wear, sliding wear, rolling contact wear, fatigue failure and chattering are persistent problems of a wheel-rail interface, especially at corner track. Generally, high strength alloy and heat-treated rail were used at corner track in order to improve the service life and chattering level, but these targets still remain as unceasing challenge subject. Ultrasonic nanocrystal surface modification (UNSM) was applied to rail materials with the aim of replacing with heat treatment and/or improving the service life of rails. In this study, the mechanical and wear properties of the untreated and UNSM-treated specimens which were prepared from normal and heat treated rails. Friction and wear tests were performed to measure the friction coefficient and the amount of wear. Results revealed that the wear performance of the UNSM-treated specimens was improved due to the increased hardness and induced compressive residual stress after UNSM treatment. The wear mechanism of the UNSM-treated specimens was explained with the changes in surface properties of rail materials.

A Method of Determining Rail Grinding Parameters Based On Life-Cycle Cost

The factors affecting the economy efficiency of rail grinding and their interrelation are researched. Based on the management theory of life-cycle cost, the model of analyzing rail grinding parameters is established, the calculation method is determined, and minimizing the rail life-cycle cost is regarded as optimization objective for the optimal analysis of grinding factor. The results prove that with certain parameters (grinding interval and mental removal), the total present value of rail cost tends to decrease firstly and then increase with the increase of rail service life. With the increase of the grinding interval, the total present value of rail cost also tends to decrease firstly and then increase, and there is an extreme point in the variation tendency. In the economic cost of rail service life, rail replacement and waste of railway taking-up cost are two of the biggest parts. Therefore, reasonable rail maintenance strategy plays a significant role in reducing life-cycle cost.