Rail Rolling Contact Research Articles

Rail rolling contact fatigue on a Chinese heavy haul line: Observations, monitoring and simulations

Severe rail rolling contact fatigue (RCF) occurring on curves of a heavy haul line in China was studied by field observations, monitoring tests, failure analyses and numerical simulations. Visual appearance, worn profiles, surface hardness, crack dimensions and so on were measured in field for rails and typical running wheels, meanwhile other related information was also collected. Significant influences of the radius of curvature and loaded/empty trains were figured out. RCF cracks on R600 m curves was found to get initiated in days, propagated downward very quickly in the first 2 months, and then stabilized at a depth of about 2.5 mm until rail replacement owing to further propagation into un-flowed bulk material. Though the failure analyses, crack depths measured by an eddy current detector were verified. Considering measured/collected data, a numerical approach combining a train dynamic model and the damage function model (Tγ) has been developed to predict the rail RCF occurrence, in which the influence of trapped liquids was better modelled by introducing a critical angle of the resultant creep force. Typical simulations showed that numerical predictions could well explain the observed phenomena, providing a useful tool for further studies.

Development of a flexible arrayed eddy current sensor with three-phase excitation for inspection of rail rolling contact fatigue cracks

A Flexible Arrayed Eddy Current (FAEC) sensor can inspect a large area in a single probe pass, which is beneficial for customizing the profile of the inspected part. This paper presents the development of a flexible arrayed eddy current sensor with three-phase excitation for inspection of Rolling Contact Fatigue (RCF) cracks in rail. The excitation coils are driven by three-phase currents that are 120° apart in phase. The induced eddy current in the conductive rail sample shifts electrically along the phase variation direction of the excitation currents. The sensor measures a small background signal to determine if there is no defect in the rail sample. Therefore, the sensor has a high relative sensitivity to defects. We study the operating principle of the sensor using a 3D finite element method (FEM) model. The numerical results demonstrate the sensor's viability for fast inspection and characterization to detect RCF defects in conductive rail steel samples.

Research on the Influence of Wheel Tread Defects on Rolling Contact Fatigue

With the rapid development of high-speed trains, local rolling contact fatigue caused by special local defect damage forms has become more prominent. This article takes circular defects as the research object, adopts the Jiang Sehitoglu multi-axis fatigue damage criterion based on the critical plane method, establishes a finite element model of wheel tread circular defects, and studies the influence of wheel tread circular defects on wheel rail rolling contact fatigue. Based on finite element analysis to obtain fatigue damage parameters, an improved PSO-BP neural network was used to establish a neural network prediction model for fatigue damage parameters, and the feasibility of the model was demonstrated. The research results show that the main influencing factors on the rolling contact fatigue life of wheel tread defects are shear stress and shear strain; The fatigue damage parameter is maximum at the edge of the wheel tread defect; As the defect distribution moves from the center to both sides, the contact stress and damage parameters gradually decrease; As the depth of the defect increases to the size of the radius, the contact stress and damage parameters first increase and then decrease; As the diameter of the defect increases, the contact stress and damage parameters increase, but the amplitude change gradually tends to stabilize with the increase of the defect diameter. The neural network prediction results indicate that all predicted samples are within a reasonable range, and this neural network model can provide a reference for predicting fatigue damage of wheel tread.

An efficient 3D finite element procedure for simulating wheel–rail cyclic contact and ratcheting

Various models for simulating rail ratcheting behaviour were developed to study rolling contact fatigue (RCF) damage in rails. However, limitations remain in terms of the accuracy of wheel–rail contact modelling and computational efficiency of the cyclic loading simulation. This study developed an efficient 3D finite element (FE) procedure to simulate ratcheting in rails subjected to numerous load cycles. The procedure simulates a wheel rolling repeatedly over a rail section with updated stress–strain states, enabling automatically executed cyclic loading simulation given a predefined number of cycles. To ensure the accuracy of the contact modelling, the effect of meshing schemes on subsurface stress distribution was examined. In addition, the FE contact model with the selected meshing scheme, which balances accuracy and computational efficiency, was verified against the widely accepted CONTACT program. Subsequently, a non-linear kinematic hardening (NLKH) steel material was used in the FE model for ratcheting simulations with up to 100 wheel-loading cycles. The rail surface and subsurface stress states were replicated under partial-slip wheel–rail rolling contact conditions with traction coefficients of 0.10, 0.20 and 0.35, respectively. The ratcheting behaviour was extensively analysed in terms of plastic deformation, contact patch evolution, and ratcheting rates. The simulated plastic deformation was found to alter the contact geometry and thus contact stresses, which in turn affect further accumulation of plastic deformation and subsequent ratcheting strains. These findings highlighted the importance of considering the interplay between the rail ratcheting behaviour of the rail and evolving contact conditions for predicting ratcheting and RCF damage in rails.

Track Deterioration Model—State of the Art and Research Potentials

Track deterioration models (TDMs) help to allocate maintenance work (direct costs) to vehicle runs. Furthermore, these models demonstrate the impact of rolling stock properties on infrastructure. This paper review provides an overview of the state of the art in railway track deterioration modelling and outlines the research potential in this domain. The main focus lies on ballast degradation, rail surface wear and fatigue, and their description in an empiric analytic wear formula. The basis for discussion is the wear formula of the Graz University of Technology. While the TDM demonstrates effectiveness, enhancements are sought, particularly with regard to adjusting the track parameters that vary across railway networks. Further exploration aims to refine the description of rail surface wear and rolling contact fatigue (RCF), incorporating factors such as traction energy and short-wave effects and adapting mathematical functions such as the t-Gamma function. This review underscores the need for ongoing research to develop TDMs that are both simple and detailed enough to encourage track-friendly rolling stock design.

Effects of Lubricating Conditions on Wear Performance of U77MnCrH Rail

With the rapid development of railway towards being high speed and having heavy load capacity, the wheel–rail wear and rolling contact fatigue in the curve section with a small radius of freight have become the key problems in urban railways, which need to be solved urgently. The aims of this study were to compare the wear resistance with three different lubricating conditions on wheel–rail wear based on the wheel–rail rolling contact simulation tests. The wear loss, microhardness, and microstructure of the contacted surface of the rail were detected systematically. The results showed that the wear rates of rail were reduced by 71% for grease lubrication and 55% for solid lubrication, compared to those without lubrication. At the same time, the thickness of plastic deformation layer of rail samples were about 167 μm for the dry state, 138 μm for the solid lubrication state, and 128 μm for the oil lubrication state, respectively. It indicates that the thickness of the plastic deformation layer was significantly reduced under both grease and/or solid lubricating conditions. In addition, the microstructure of the deformation layer with two kinds of lubricated states was coarser and denser than that without lubricants. The average grain size of the deformation layer was approximately 0.22 μm under dry conditions and 0.32 μm under lubricated conditions. It also indicated that the changes in lubricants did not have a significant effect on the average grain size of the deformation layer. The results of the present study could provide theoretical reference for the development and design of lubricants used as rail materials.

Investigation of rail damage considering impact at a welded joint under wet condition

PurposeThe purpose of this study is to develop a transient wheel–rail rolling contact model to primarily investigate the rail damage under wet condition when the train passes through the welded joints.Design/methodology/approachThe impact force induced by welded joints is obtained through vehicle–track coupling dynamics. The normal and tangential wheel–rail contact pressures were solved by elastohydrodynamic lubrication (EHL) theory and simplified third-body layer theory, respectively. Then, the obtained tangential pressure and normal pressure were applied to the finite element model as moving loads, simulating cyclic loading. Finally, the shakedown map and critical plane method were used to predict rolling contact fatigue (RCF) and the initiation of fatigue cracks.FindingsThe results indicate that RCF will occur and fatigue cracks are more prone to appear on the subsurface of the rail, specifically around 2.7 mm below the rail surface in the vicinity of the welded joint and its heat-affected zone.Originality/valueThe cosimulation of numerical model and finite element model was implemented. The influence of surface roughness and fluids was considered. In this model, the normal and tangential wheel–rail contact pressure, the stress and strain and the rail fatigue cracks were obtained under a rail-welded joint excitation.

Numerical Investigation of Elastic Layer Effects in Wheel–Rail Rolling Contact

In railway systems, layered structures could be induced in wheel–rail contact interfaces due to several causes, such as head hardening, work hardening, plastic deformation, and mechanical or thermal excursion-induced phase transformation. This study proposes an explicit finite element (FE) method for investigating elastic layer effects in wheel–rail rolling contact. The proposed method is first validated by comparing its solution with that of Kalker’s boundary element method (BEM) when the layer is not present, with a focus on the tractive rolling contact. To investigate general layer effects, the rail is assumed to consist of two layers, i.e., the top layer and the matrix material. The top layer is assumed to have different elastic moduli from the matrix material and then the top elastic layer effects on contact characteristics such as contact stress, contact patch, and subsurface stress are investigated. Different layer thicknesses are also considered. It is observed that a harder layer tends to introduce larger contact pressure and surface shear stress, but a smaller contact patch. A harder layer also produces larger subsurface stresses. A thicker layer may intensify these effects. The results suggest that in engineering applications, the analysis of wheel–rail rolling contact consequences such as wear and rolling contact fatigue (RCF) may need to consider the layered structures using appropriate methods.

Nonlocal thermomechanical coupled modeling method for two-dimensional rolling contact using a peridynamic approach

The development of thermomechanical coupled simulations for rolling contacts is challenging when the adjacent material is temperature-dependent or when there are cracks or other discontinuities on the contact surface. This paper proposes a novel thermomechanical coupled modeling method for rolling contacts using a nonlocal peridynamic (PD) approach. Fully coupled, ordinary state-based PD thermomechanical equations for the plane strain and plane stress cases are derived based on the strain-energy density, including thermal coupling terms, and detailed information on each parameter is provided. Subsequently, an algorithm for rolling thermal contacts in PD is proposed based on the penalty method. This study further provides a detailed modeling process and an algorithm for the proposed method based on a multi-rate time-integration scheme for numerical implementation. A typical two-dimensional (2D) wheel–rail rolling contact model is established to evaluate the performance of the proposed contact modeling method in wheel–rail thermal contact and to analyze the influence of temperature-dependent material and rail-surface cracks on the thermomechanical response. It is found that the contact stress and rail-surface temperature rise in the case of small creepages and temperature-independent materials are in good agreement with the analytical solution. In the case of large creepages, the mechanical and temperature results of using temperature-dependent materials and temperature-independent materials are quite different, and the frictional heat generated can cause martensitic transformation of adjacent materials. Rail-surface cracks cause a sharp increase in the contact stress and temperature rise near the cracks, and the high temperature also promotes crack growth.

Microstructural investigation on a rail fracture failure associated with squat defects

Squats, observed in numerous railway networks worldwide, are a significant concern for rail track maintenance. This work presents a specific case study of a rail fracture failure associated with squat defects. A detailed microstructural analysis was conducted to investigate the causes of squat formation, subsequent crack propagation, transverse defects, and fracture. According to the findings, the initiation of squats can be attributed to the presence of White Etching Layers on the rail surface and rolling contact fatigue. After the initiation of Squats, the cracks extended downwards into the bulk rail at a shallow angle until reaching a sizeable martensitic island located in the subsurface of the rail along the path of crack propagation. The brittleness of the undesired martensitic structure triggered rapid crack development, facilitated transverse cracking, and ultimately resulted in rail fracture failure. Transmission electron microscopy examination confirmed that the abnormal defects are plate martensite with a twin substructure and high carbon content, which could be generated as a result of improper heat treatment during the manufacturing of rails.

Study on non-destructive testing of rail rolling contact fatigue crack based on magnetic barkhausen noise

Rail rolling contact fatigue (RCF) crack and other rail damage have great impact on the normal operation of the railway system. The detection and evaluation of RCF crack can effectively ensure the running safety of the train. Compared with the traditional non-destructive testing methods, the characteristics of Magnetic Barkhausen Noise (MBN) detection technology such as easier implementation, higher efficiency and faster inspection process etc., make it an ideal choice for non-destructive detection technology of rail RCF crack. Therefore, this paper studied the influence of plastic deformation layer and crack of rail roller on MBN signal. The detection equipment based on MBN signal was built and used to detect and characterize the rail PDL and cracks. The wheel-rail rolling-sliding tests were conducted on a twin-disc tribometer to prefabricate the rail RCF crack and PDL. Experimental results proved that MBN signal decreased with the increase in plastic deformation layer (PDL) thickness. Crack initiation would release the residual compressive stress (RCS) of material surface, resulting in the abnormal increase in MBN signal under the general trend of gradually weakening. The influence mechanism of cracks on MBN signals was analyzed and discussed.

Different responses of wheel–rail interface adhesion and wheel surface damage induced by an out–of–round wheel tread

The out–of–roundness of wheel treads are an inherent degradation characteristic of the wheels of railway vehicles, and the interface behaviour of the wheel and rail caused by out–of–roundness features has essential research value in high–speed train running safety and quality. Sliding–rolling contact wear testing was conducted to evaluate the effect of the out–of–round wheel on the wheel–rail damage behaviour, by using a twin–disc setup. The effects of four wheels, three wheels of different eccentricities and one normal wheel were taken as a control group. The characteristics of the wheel–rail interface adhesion, wheel surface damage and compressive residual stress (CRS) distribution were compared and analysed. The results showed a dramatic increase in the fluctuation amplitude of the wheel–rail vertical force of the eccentric wheels, and the adhesion coefficient of the wheel–rail interface significantly decreased. Furthermore, eccentric wheels dramatically accelerate the wear loss of the rail used as a counterpart during wheel–rail rolling contact. The surface damage behaviour of the eccentric wheels is obviously different along the circumferential direction, and non–uniform wear was observed. The damage mechanism of the worn surface presented varying characteristics, which could be divided into a severely damaged zone (located at the maximum of the rolling radius rmax) and a slightly damaged zone (located at the minimum of the rolling radius rmin). The surface contact stress of the severely damaged zone was high, this finding can be explained by the extremely rough worn surface caused by the severe fatigue delamination characteristics and the initiation and propagation of fatigue cracks in the severely damaged zone. Furthermore, the values of surface hardness and residual stress were relatively low. By contrary, an adhesion layer was observed on the worn surface of the slightly damaged zone. The adhesion layer protects worn surface in the slightly damaged zone was relatively flat, and the CRS was relatively high.

Effects of varying normal loads on the rail rolling contact fatigue behavior under various frequencies and creepages

Track irregularities caused by wheel and rail damage would lead to vibration at wheel-rail contact interfaces, resulting in the fluctuation of normal forces which would further increase the damage to both wheels and rails under operational freight train services. This study aims to investigate effects of varying normal loads on the rolling contact fatigue (RCF) behavior of rails under various creepages and vibration frequencies using a twin-disc test machine. Results indicated that tangential forces and wear rates both increased with the increase in creepages, while they decreased with the increase in vibration frequencies. In addition, surface and subsurface damage parameters, and characteristics of cracks in the railhead including average lengths, depths and angles first increased and then decreased with the increase in creepages, and they all decreased with the increase in vibration frequencies. Further, the sizes of wear debris particles decreased with the increase in both creepages and frequencies.

Effect of vibration amplitude and axle load on the rail rolling contact fatigue under water condition

Wheel-rail vibration could be caused by the surface irregularity of wheel-rail material, and the third body medium also played an important role in the evolution of rolling contact fatigue (RCF) under the vibration condition. This study aims to investigate the effect of vibration amplitude and axle load on the rail rolling contact fatigue (RCF) under water condition using a twin-disc test machine. Results indicated that the average friction coefficient and the plastic deformation depth decreased, while the surface hardness, wear rate, surface damage and the crack damage degree all increased with the increase in both the axle load and the vibration amplitude. Applying vibration into rollers interface would increase the entering water flow and accelerate the crack propagation, forming crack intersections which tended to generate material spalling, leading to the catastrophic increase in the wear rate and the proportion of crack propagating in transgranular manner.

Research Progress of High-Speed Wheel–Rail Relationship

The research on wheel–rail relationship includes the basic theoretical models and corresponding numerical methods of wheel–rail in rolling contact, geometric parameter matching and material matching of them, friction and wear, wheel–rail rolling contact fatigue, wheel–rail adhesion and noise. They are also key theoretical and technical problems of the high-speed train/track coupling system. The basic theoretical models of wheel–rail in rolling contact and the corresponding numerical methods are the basis and one of the basic means for solving other wheel–rail relationship problems. The other is the experimental means. Moreover, the modeling and analysis of coupling behavior of the train and track can only be realized by means of the wheel–rail rolling contact mechanics model and its corresponding numerical method. This paper mainly discusses some research work and achievements on high-speed wheel–rail relationship problems since China opened a high-speed railway system on a large scale. The discussions in this paper include the classic wheel–rail rolling contact theoretical models (analytical forms) and the modern wheel–rail rolling contact theories (numerical methods), their advantages and disadvantages, their application and future development direction of them. The reviewed research progress on the other wheel–rail relationships mainly expounds the thorny problems of the wheel–rail relationship encountered in the operation of China’s high-speed railway, how to adopt new theoretical analysis methods, test means and take effective measures to solve these problems. It also includes research results of similar important reference values performed by international peer experts in related fields. Challenging and unsolved problems in high-speed wheel–rail relationship research are also reviewed in the full text.

Optimisation of wheelset maintenance by using a reduced flange wear wheel profile

This paper investigates whether it is possible to develop a wheel profile design that will extend wheelset life compared to an existing commonly used Great Britain passenger wheel profile, the P8. The P8 wheel profile was originally developed in the late 1960s as an alternative to a 1:20 coned wheel profile (the P1). The P1 often required frequent turning as the conicity could increase quickly over time as the wheel wore in service. The P8 was designed based on an average worn shape of a P1 wheel. The P8 was found to stay closer to its original shape as it wore in service. However, new P8 wheels or newly profiled P8 wheels tend to experience a high initial flange wear rate in the first 20,000–30,000 miles, until the worn wheel shape reaches ‘dimensional stability’; after this, the flange width typically remains relatively constant. A ‘Reduced Flange Wear’ (RFW) wheel profile has been developed, based on the P8 profile but with a modified flange root geometry. The Wheel Profile Damage Model has been used to calculate how the proposed RFW wheel profile could reduce wear rates and therefore increase wheelset life. This paper presents results for a typical electric multiple unit train (EMU1) running on rural and suburban routes and a higher speed variant (EMU2) running on an inter-city route. The effect of the proposed RFW profile on rail rolling contact fatigue (RCF) has also been evaluated using the Whole Life Rail Model, for the same routes. The results suggest that the proposed RFW profile does reduce flange wear compared to a P8, with larger reductions achieved on routes that are more curvaceous. For wheel turning based purely on restoring wheel profile geometry, the RFW profile could half the amount of material removed at each turning (based on turning wheels at 250,000 miles). Furthermore, the results show that the RFW profile experiences slightly less wheel RCF damage than the P8. When new, the RFW profile appears to cause slightly higher rail RCF than a new P8 (For radii 700 m < R < 1300 m); however, the results suggest that worn RFW profiles cause very similar rail RCF to that caused by worn P8 wheels.

A fast method to estimate the multiaxial non-proportional elastic–plastic stress–strain in rail rolling contact fatigue problems

This paper aims to propose a new and fast method to estimate the multiaxial non-proportional elastic–plastic stress and strain time histories developed in rails due to rolling contact and evaluate its accuracy for fatigue analysis. The method has the pseudo-elastic stress time history as input, which is obtained by a coupled analytical and numerical method. Therefore, a method originally proposed for notch-root elastic–plastic stress–strain analysis was extended to the Rolling Contact Problem (RCF). The problem is solved incrementally and is established considering a set of equations composed by constitutive and multiaxial notch correction equations. Additionally, a kinematic cyclic plasticity model was included. An equivalent model based on the Finite Element Method was used for comparison purposes. The comparison was made in terms of multiaxial fatigue damage parameters in critical planes, according to fatigue analysis models developed by Matake and Brown & Miller. The more relevant advantage of the method over the non-linear FEM analysis is the possibility to readily obtain long elastic–plastic stress and strain histories and to perform material parameter and load case studies. The method proposed agrees with the equivalent FEM and proved to be a powerful tool for fast wheel-rail failure analysis, especially in RCF problems.

Rail rolling contact fatigue formation and evolution with surface defects

Surface defects can induce serious rolling contact fatigue (RCF) damage at wheel/rail interfaces and even cause fracture failure of rail material. This study aims to explore the formation mechanism of surface defects on rails, and to trace the evolution process of RCF behavior of material around the surface defect. Experimental studies were conducted on a wheel/rail twin-disc machine considering two forms of defects: indentation defects caused by ballast impacts (IDBs) and indentation defects caused by cone penetration head impacts (IDCs). Results indicate that IDB can cause RCF cracks that propagate downward deep into the subsurface of rail due to the formation of a material hardening layer (MHL), causing severe damage. IDCs with different sizes and angles were grouped into an affected group and a non-affected group by considering a critical size dividing line and whether the MHLs existed on the defect surface or not. The evolution process of a crack in the affected group includes four main periods: fracture of the MHL, crack initiation, the rail steel matrix filling up the MHL gap and crack propagation downward. Further, the increase in both the angle and the depth of the IDC would lead to severe RCF damage.

On the modelling of normal wheel-rail contact for high-frequency vehicle–track dynamics analyses

ABSTRACT A transient wheel–rail rolling contact (RC) model and a vehicle–track coupled dynamics (CD) model are separately developed for a Hertzian contact in elasticity to calculate normal wheel–rail interactions at high frequencies. Short-wave irregularities with a wavelength of 20 ~ 400 mm are considered for a speed of 50 ~ 500 km/h. Results of 180 cases show that contact forces predicted by the CD model are significantly different from those by the RC model, suggesting that ignored or greatly simplified structural and wheel-rail flexibilities, transient effects, finite contact patch, etc. in the CD approach, play important roles in high-frequency interactions. Using the RC predictions as reference, a modified non-linear Hertzian spring is developed to improve the accuracy of the CD model. Such a modification provides references for determination of contact spring and contact filter effect at high frequencies, even though not applicable in a direct way.

Gearless Track-Friendly Metro with Guided Independently Rotating Wheels

Track–vehicle severe interaction on track with small curve radius results in rail wear and corrugation, and wheel polygonization, which drain considerable resources for rail grinding and wheels re-profiling in metro lines. To reduce the damage caused by track-vehicle severe interaction, the paper analyzes the reasons leading to rail wear and then proposes an architecture of a metro vehicle with independently rotating wheels driven directly by permanent magnet synchronous motors. The architecture is axle guidance, offered by passive linkages, which ensures that all axles are oriented radially, while control strategy was kept as simple as possible, identifying only two basic traction conditions. The concept is first discussed and then validated through a comprehensive set of running dynamics simulation performed with a multibody software to evaluate rail wear and rolling contact fatigue in traction/braking, coasting with different cant deficiency/excess conditions. The multibody dynamics simulation shows that the proposed architecture is virtually capable of avoiding both wear and rolling contact fatigue damages, and achieves the highest possible track friendliness. The concept of the proposed architecture is a track-fiendly metro architecture and could be a good reference for reducing rail-track interaction damages and maintainace cost.