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Rolling contact fatigue (RCF) cracks online detection using eddy current testing (ECT) is in urgent demand. However, RCF cracks detection and evaluation in this way under moving conditions remains challenging due to the velocity effect in ECT. This paper aims to study the response of a transmitter-receiver eddy current probe to cracks under moving conditions and evaluate the depth and inclination angle of RCF cracks. In this paper, a high-speed eddy current testing system is developed to experimentally investigate the influence of coil gap, detection speed, and the lift-off on the eddy current probe's response under moving conditions. In addition, the temporal and amplitude features of the eddy current signal are extracted to characterise the depth and inclination angle of the RCF cracks. The experimental results indicate the eddy current probe's response can be improved by increasing the coil gap (coil centre distance) suitably, which can be done to compensate for the attenuation of the eddy current signal caused by detection speed and lift-off. The probe's response hardly changes with an increase in detection speed when the driver and pick-up coils of the eddy current probe completely overlap. The crack depth and inclination angle can be evaluated under moving conditions. [ABSTRACT FROM AUTHOR]

This paper presents a rolling contact fatigue life prediction model for bearing steel. In the initial stage of rolling contact, the gradient structure appears in the subsurface region of bearing steel and the hardness shows a gradient distribution along the contact depth direction due to the roller compaction effect. This indicates that the fatigue resistance of bearing steel varies in the subsurface region. Besides, each subsurface material volume element is subject to different stress cycles. Based on Weibull theory, the survival possibility of subsurface volume elements is formulated. Then the rolling contact fatigue life is evaluated considering the stress state and anti-fatigue performance of each elementary volume of the subsurface material. According to the phenomenon and assumption, the model proposed for gradient material was applied in the rolling contact fatigue life prediction of the bearing steel GCr15 and validated with the fatigue experiment data in the open literature. Furthermore, the accuracy of the proposed model results was compared with the traditional empirical rolling contact fatigue life prediction models. [ABSTRACT FROM AUTHOR]

Here a comprehensive 3-D wheel-rail rolling contact finite element model was developed to investigate the influence of wheel-rail material properties on the dynamic wheel-rail interaction. The wheel-rail contact responses induced by two typical wheel tread defects (i.e. wheel flat and tread spalling) were discussed and compared to the responses of perfect wheel in this work. The dynamic wheel-rail responses of three typical material models involved (i.e. rigid, elastic, and elastic-plastic models) were investigated in terms of contact force, contact pressure/stress, and wheel/rail degradation. Furthermore, the strain rate levels during wheel-rail rolling contact at various train speeds were estimated with emphasis on the elastic-plastic model, which was helpful for determining strain rate range of wheel/rail material property tests. Finally, the influences of strain rate effect and initial fatigue damage of wheel/rail materials on dynamic wheel-rail responses were discussed. These results illustrated that the rigid model grossly overestimated wheel-rail impact force caused by wheel tread defects, while the elastic model overestimated wheel-rail contact pressure/stress, damage index, and frictional work. The strain rate effect could significantly increase Mises stress and inhibit plastic deformation of wheel-rail system, while the initial fatigue damage would reduce Mises stress and aggravate plastic deformation. [ABSTRACT FROM AUTHOR]

The atomic‐level fundamental understanding of the rolling contact fatigue (RCF) mechanism using molecular dynamics (MD) simulation is yet to be understood more clearly. In this paper, the atomistic behavior of the single‐crystal Ni is studied under dynamic rolling contact loading with the help of MD simulations at varying temperatures of the specimen. The deformed material is investigated using atomic strain analyses to evaluate the shear, volumetric strain distribution, and von Mises stress. Furthermore, dislocation and stacking–fault analyses are done to determine the deformation mechanism of the material with the oscillation cycles. Simulation studies infer that dislocation defects tend to increase with the temperature of the specimen logarithmically. The deformation majorly results in partial dislocations, indicating low stacking fault (SF) energy. The present work opens up a new field of study to understand the RCF mechanisms, which can provide the foundational work to understand other face‐centered cubic (FCC) materials. Highlights: The degree of straining and defect generation depends on cycles and ambient temperature.Specimen undergoes relaxation as von Mises stress decrease with increasing cycles.Partial dislocations are more dominant, indicating low stacking fault energy. [ABSTRACT FROM AUTHOR]

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. • A nonlocal thermomechanical coupled modeling method for rolling contacts using peridynamic is proposed. • Fully coupled, ordinary state-based PD thermomechanical equations are derived. • An algorithm for rolling thermal contacts in PD is proposed based on the penalty method. • A typical 2D wheel–rail rolling contact model is established for a case study. [ABSTRACT FROM AUTHOR]

In this study, finite element method (FEM) is applied to investigate the effect of material defect orientation on subsurface crack initiation in rolling bearings. First, the history of stress intensity factors (SIFs) of a subsurface cubic material defect is calculated. SIFs calculation is conducted when it is parallel to the rolling surface of a bearing ring ( φ = 0 ∘ ) under a ball rolling on the ring. Then, the effect of defect orientation, varying from φ = 0 ∘ to φ = 30 , 45 and 60 ∘ , on the history of SIFs is investigated. It is deduced that changing the defect orientation results in a threefold increase in the equivalent SIF range compared to parallel orientation. [ABSTRACT FROM AUTHOR]

An improved moment of load path model for rolling contact fatigue life prediction is proposed in this paper. First, the complex multiaxial stress variation of the subsurface materials under rolling contact conditions was analyzed by the finite element method. Next, the equivalent stress parameter was presented to characterize the complex stress state based on the improved moment of load path method. The key concept of the proposed method is building a new coordinate system for analyzing the load path of the complex multiaxial stress state. The efficiency of the proposed model was validated with different kinds of fatigue test results in the existing literature. The model results show a good agreement with the test data. Finally, the model was used to obtain the relationship of the Hertz stress versus fatigue life under rolling contact conditions according to the fatigue life data. Highlights: The proposed multiaxial life prediction model considers the hydrostatic stress.The correlation of the multiaxial test data is built using a defined stress parameter.Rolling contact fatigue life is predicted by the proposed multiaxial model. [ABSTRACT FROM AUTHOR]

The friction coefficient at the wheel–rail interface is crucial for the traction, braking and guidance of the railway vehicle. Real-time knowledge of the friction coefficient could reduce wheel–rail damages as well as improve the vehicle running performance. The friction coefficient is very difficult to be directly measured; hence an indirect measurement method using an unscented Kalman filter was proposed in this paper. A re-adhesion controller was also developed. The method was assessed in a Simpack-Simulink co-simulation environment. The friction coefficient estimation method was found to be accurate, and the re-adhesion controller improved the vehicle braking performance as well as reduced the wheel–rail damage. [ABSTRACT FROM AUTHOR]

In this study, finite element method (FEM) is applied to investigate the effect of material defect orientation on subsurface crack initiation in rolling bearings. First, the history of stress intensity factors (SIFs) of a subsurface cubic material defect is calculated. SIFs calculation is conducted when it is parallel to the rolling surface of a bearing ring ( φ = 0 ∘ ) under a ball rolling on the ring. Then, the effect of defect orientation, varying from φ = 0 ∘ to φ = 30 , 45 and 60 ∘ , on the history of SIFs is investigated. It is deduced that changing the defect orientation results in a threefold increase in the equivalent SIF range compared to parallel orientation. [ABSTRACT FROM AUTHOR]

Surface initiated rolling contact fatigue (RCF) of gears and rolling bearings can lead to premature failure in mechanical transmission systems. The orientation of surface crack initiation closely depends on surface tractive force, while the mechanism leading to this dependence is still obscure. In this work, a numerical model is proposed to investigate the effect of friction on surface crack initiation in RCF. An inhomogeneous contact solver based on semi‐analytical method (SAM) is developed by combining the damaged‐coupled constitutive relation and the Eshelby's equivalent inclusion method. The damage accumulation and concurrent degradation of material properties are modeled with continuum damage mechanics (CDM). The effect of surface tractive force on the orientation of surface crack initiation is simulated and analyzed. Results indicate that the progressive evolution of damage under the cyclic loading is accompanied by the stress variation around the damaged area. The damaged area increases, and the crack initiation life decreases with an increasing coefficient of friction. Highlights: A new damage evolution model incorporating an inhomogeneous contact solver is developed.The possible causes of the orientation of surface crack affected by friction traction are analyzed.The simulated results of damage evolution and stress variation agree well with open literatures. [ABSTRACT FROM AUTHOR]

This experimental research work is conducted to determine statistical models of wear evolution and surface roughness components in a misaligned contaminated EHL rolling contact. To achieve this goal, experiments were realized on an original test rig representing the real operating conditions of gears or roller bearings. In fact, the rolling contact tests are carried out using the contact between two steel disks with the presence of misalignment defect and solid contaminants within lubricant oil. In order to investigate the influence of four operating input variables like misalignment angle (α), rotational velocity (V), load (Q), and contaminant concentration (C) on the studied responses (i.e., wear (W) and surface roughness components (Ra, Rt, and Rz)), the Box-Behnken design (BBD) was adopted. Thereafter, the results obtained were analyzed using both response surface methodology (RSM) and analysis of variance (ANOVA). It is found that the rotational velocity (V) is the most significant factor affecting the wear (W) and the surface roughness components (Ra, Rt, and Rz) of a misaligned contaminated EHL rolling contact with 75.51%, 79.2%, 89.07%, and 59.65% of contributions, respectively, whereas load (Q), misalignment angle (α), contaminant concentration (C), and two-level interaction effect (α × C and C × Q) are significant factors but have a lesser effect on the wear variability with 8.23%, 5.57%, 2.42%, 2.68%, and 2.62% contributions, respectively. It is also deduced that the misalignment angle (α) is statistically significant when studying the mean depth roughness (Rz) with 15.67% of contributions. Finally, it is revealed that the obtained higher values of determination coefficient (more than 90%) show clearly the reliable of the implemented quadratic models. [ABSTRACT FROM AUTHOR]

Wheel burn can affect the wheel–rail contact state and ride quality. With long-term operation, it can cause rail head spalling or transverse cracking, which will lead to rail breakage. By analyzing the relevant literature on wheel burn, this paper reviews the characteristics, mechanism of formation, crack extension, and NDT methods of wheel burn. The results are as follows: Thermal-induced, plastic-deformation-induced, and thermomechanical-induced mechanisms have been proposed by researchers; among them, the thermomechanical-induced wheel burn mechanism is more probable and convincing. Initially, the wheel burns appear as an elliptical or strip-shaped white etching layer with or without deformation on the running surface of the rails. In the latter stages of development, this may cause cracks, spalling, etc. Magnetic Flux Leakage Testing, Magnetic Barkhausen Noise Testing, Eddy Current Testing, Acoustic Emission Testing, and Infrared Thermography Testing can identify the white etching layer, and surface and near-surface cracks. Automatic Visual Testing can detect the white etching layer, surface cracks, spalling, and indentation, but cannot detect the depth of rail defects. Axle Box Acceleration Measurement can be used to detect severe wheel burn with deformation. [ABSTRACT FROM AUTHOR]

Vehicle-track interaction in a switch panel diverging route is studied with a focus on the way its components may interact in the lateral direction. Taking one of the cases of S&C benchmark as the base model, several variants of the co-running track model are considered. In the first series of simulation, the effect of the lateral separation of the switch rail and stock rail is investigated, showing that only small differences are found in terms of wheel/rail forces between a track model where both rails are coupled, and one where they are free to move with respect to one another. Only transient effects are visible at the beginning and at the end of the two-point contact on both rails. While small, these differences can have some influence in terms of rolling contact fatigue and wear prediction. In the second series of simulation, co-running track models are developed including the baseplate and taking into account such effects as switch rail/stock rail contact at the undercut plane and dry friction. Significant changes are observed in the load distribution within the switch panel. Conclusions should be consolidated through experimental field measurement and using more realistic track models, e.g. discretely supported rail beam models. [ABSTRACT FROM AUTHOR]

This research paper reviews the recent works on the rolling contact fatigue of rail wheels. The topic covered includes the mathematics equations of rail-wheel contact stress and fatigue, RCF defects in the rail, the development of cracks, and the strategies used to reduce the rate of RCF defects. Therefore, the main understandings of RCF as they currently stand are crucial for the improvement and mitigation on rail fatigue failures in the future. This research paper has not been published yet and has not been discussed yet by the Malaysia Railway Network. [ABSTRACT FROM AUTHOR]

The research is aimed to understand the effect of WC/C coating on the bearing rolling elements to improve fatigue life in surface distress conditions. The 1–1.5 microns optimized coating thickness was deposited on the steel substrate using the PVD process. The coating's physical and chemical properties were analysed by X-ray diffraction, scanning electron microscope, contact profilometer, nanoindentation hardness, and micro scratch indenter. The wear properties were compared on a ball-on-disc tribometer with and without a coated specimen. The bearing tests were performed in contaminated and clean lubrication conditions to prove the coating's effect on bearing life in surface distress conditions. Results show that coated roller bearings perform at least two times that of the standard bearing. The overall benefit of less friction and wear resistance was due to the polishing action and coating transfer mechanism of multi-layer coating which increases oil film thickness between contacts and hence improve bearing life. [ABSTRACT FROM AUTHOR]

The influence of the initial surface roughness on the wheel–rail contact has been a concern for railway systems especially since the introduction of rail grinding and wheel reprofiling as maintenance strategies. Currently, there are no universally accepted procedures for surface finishing of rails and wheels, so there is a need to keep studying the role of surface topography in reducing the maintenance costs and improving the wheel–rail system's performance. This work studies the evolution of roughness of wheel samples during twin-disc tests performed to simulate wheel–rail contact up to 2.2 × 105 cycles under two different lubrication conditions. The results showed that under dry conditions the surfaces with larger kurtosis at the beginning of the tests had a better response to rolling contact fatigue. Under lubricated conditions, however, the effect of the initial roughness was less significant. [ABSTRACT FROM AUTHOR]

The formation and propagation of cracks in rolling contact fatigue were observed by synchrotron radiation computed laminography, and the effect of stringer‐type inclusion orientation was examined. For longitudinal inclusions, cracks started forming at their tips. After cracks propagated toward the rolling direction, a longitudinal crack was kinked simultaneously at both its tips, and propagated toward the direction perpendicular to the rolling direction to form lateral cracks. After kinking, horizontal cracks were formed from the deepest point of a lateral crack, leading to flaking. On the other hand, for specimens with lateral inclusions, cracks propagated to the lateral direction without the formation of longitudinal cracks. Since the propagation life of lateral cracks and that of horizontal cracks were unrelated to the inclusion orientation, the rolling contact fatigue life of specimens with longitudinal inclusions was considerably longer than that of specimens with lateral inclusions. [ABSTRACT FROM AUTHOR]

Aiming at early detection of subsurface cracks induced by contact fatigue in rotating machinery, the knowledge-based data analysis algorithm is proposed for health condition monitoring through the analysis of acoustic emission (AE) time series. A robust fault detector is proposed, and its effectiveness was demonstrated for the long-term durability test of a roller made of case-hardened steel. The reliability of subsurface crack detection was proven using independent ultrasonic inspections carried out periodically during the test. Subsurface cracks as small as 0.5 mm were identified, and their steady growth was tracked by the proposed AE technique. Challenges and perspectives of the proposed methodology are unveiled and discussed. [ABSTRACT FROM AUTHOR]

The rolling contact fatigue is commonly seen in industrial applications. Studies mainly focus on fatigue evolution caused by heat treatment. However, the combined machining includes thermal-mechanical coupling and transformation. The generated residual stress can be another factor to decide contact fatigue. A sequent study is conducted to investigate the influence of residual stress on contact fatigue after prestress grinding hardening. To figure out the rolling crack initiation and propagation on residual stress surface, a united calculation combined with finite element method and analytic method is proposed. Based on the above analysis, the rolling contact fatigue can be adjusted by controlling the initial residual stress of machining surface, which is meaningful for surface anti-fatigue manufacturing with longer life span requirements. [ABSTRACT FROM AUTHOR]

In this study we analyzed the rolling contact fatigue behavior of two types of coatings made by thermal coating, by the method of atmospheric plasma spraying (APS) from two commercially available powders: Ni5Al5Mo and Al2O3 - 13 TiO2. The contact fatigue behavior was studied on an installation specially designed. The specimens were tested for 54 hours (at 1380 rpm), at a load of 944 N. For both types of coatings, the appearance of a wear path was observed, much more obvious in the case of the Ni matrix layer, also confirmed by profilometry. The mechanism of the wear phenomenon was predominantly of plastic deformation type (the material was pushed towards the edges of the wear path) in the case of NiAlMo coating. In the case of ceramic coating, the wear path width was very small (300-450 µm), with very few changes at the surface level of the coating, which recommends this type of material for applications that require wear resistance to rolling. [ABSTRACT FROM AUTHOR]

In this paper, a comparative study of the very‐high‐cycle fatigue (VHCF) behavior of railway wheel steel under axial loading and rolling contact loading was conducted. Fatigue tests were performed with an ultrasonic fatigue test machine under axial loading, and the fracture surfaces from the fatigue tests and shattered rims taken from the failed railway wheels were observed. The wheel steel under axial loading presents a VHCF behavior with Mode I crack, and that under rolling contact loading is a VHCF behavior with mix Mode II–III crack. For the VHCF behavior with Mode I crack, surface and interior crack initiation occurred with equal probability at both low and high stress levels and produced a dual linear S–N curve since the value of fatigue limits for the surface and interior crack initiation are close. For the VHCF behavior with mix Mode II–III crack, cracks were initiated from the interior Al2O3 inclusion, and the fatigue life was beyond 107 cycles. Fatigue bands were observed on the fracture surface under rolling contact loading. The ferrite nanograins formed due to the stress state of shear plastic strain with a large compressive stress. The formed nanograins were softer than the matrix caused by the redistribution of the carbon. Highlight: The VHCF under rolling contact loading is a failure mode of mix Mode II–III crack.The NG massively formed in the VHCF with mix Mode II–III crack.The shear plastic strain with a large compressive stress will help NG formation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study aims to describe the wear and rolling contact fatigue (RCF) behavior of microalloyed forged railway wheel steel Class D (7NbMo), with microstructures of upper bainite (UB - 350 HV 0.5), lower bainite (LB - 450 HV 0.5), and pearlite (PE - 350 HV 0.5), against 7C steel with a tempered martensite microstructure (660 HV 0.5) in a twin-disc tribometer. The results showed that bainite (LB and UB) exhibited greater wear resistance compared to pearlite (PE). The primary wear mechanism for all three microstructures was the fatigue wear. An analysis of the PE disc revealed continuous (single-layer) RCF cracks, which were relatively large and deep. In contrast, UB and LB cracks were discontinuous (multiple layers), thin, and smaller but more numerous (higher crack density). These characteristics indicated that bainitic microstructures also had greater resistance to RCF than pearlite did. Therefore, the combination of mechanical properties and the morphological arrangement of the microstructure led bainite to develop a shallower depth of deformed layer with a higher capacity for plastic deformation per unit volume. The greater wear and RCF performance of bainite compared to those of pearlite may be associated with how they release the accumulated deformation energy after reaching saturation in relation to volume deformation absorption: regarding bainite, the material releases energy by opening crack surfaces; conversely, regarding pearlite, it is through the detachment of large and wide cracks. [Display omitted] • Bainites exhibit superior wear resistance/RCF compared to pearlite in rolling and sliding. • Surfaces of bainitic discs UB and LB display mild peeling with reduced spacing. • Bainite possesses a greater capacity to absorb plastic deformation per volume. • Tribological performance may relate to the microstructural morphology's deformation energy release. • Bainites release energy through crack surface opening. [ABSTRACT FROM AUTHOR]

• A 3D FE model of wheelset-turnout-sleeper structure is established. • The ratcheting effect of turnout material is simulated. • A mixed implicit-explicit FE method is used to simulate the wheelset passing through the turnout. • The transient contact behavior of high-speed turnouts under cyclic loading is investigated. • The evolution of ratcheting strain of rail under different numbers of cycles and crossing speeds is discussed. The present work introduces a three-dimensional finite element model for the wheel-turnout-sleeper system, incorporating a cyclic constitutive model that accurately captures the nonlinear hardening behavior of rail steel under cyclic loadings. At the same time, a mixed implicit-explicit finite element method is employed to investigate the transient rolling contact behavior of wheel-turnout. Through dynamic analysis, the transient rolling contact status of the wheel-turnout, stress and strain responses of the turnout, and wheel-rail forces are investigated under varying crossing speeds and number of cycles. It is found that during the wheelset crossing, the contact stress remains relatively stable on the stock rail, and multi-point contact occurs at the wing rail and long point rail, and the contact stress on the surface of the long point rail is more significant. With an increase in crossing speed in the same cycle, there is a gradual rise in contact stress on the long point rail face. At the same crossing speed, with the increase in the number of cycles, the contact position between the wheelset and the long point rail gradually moves back, and the top width of the contact position gradually expands. Meanwhile, the fluctuation range of vertical displacement of the wheel center diminishes, and the wheel flange moves away from the long point rail. Additionally, a progressive accumulation of ratcheting strain is observed on the rail, and the ratcheting strain on the long point rail significantly exceeds that on the stock rail. The research results will help to provide a reference for the optimization and design of the critical cross-section profile of the long point rail and will have guiding significance for the maintenance and repair of turnouts. [ABSTRACT FROM AUTHOR]

• Typical factors affecting the wheel-rail dynamic response are comprehensively considered to reveal the short-term load characteristics of frog under complex conditions. Meanwhile, based on the ellipsoidal Gaussian extrapolation theory, long-term wheel-rail load characteristics are obtained. • Combined with the strain energy fatigue parameter theory, a prediction method for the fatigue life of nose rail under complex conditions based on load spectrum preparation was proposed. • The location between the 30 mm and 35 mm sections of the nose rail has the shortest rolling contact fatigue crack initiation life and should be focused on during damage inspection. The rail profile irregular variation and wheel-rail relationships complexity at the gap in the frog enhance the wheel-rail impact forces, frequently resulting in rolling fatigue damage under complex cyclic loads. Therefore, it is particularly important to study the transient rolling contact load characteristics of fixed frog and to compile load spectrum considering various complex conditions for analyzing the fatigue damage of frog and extending the service life of structure. In this paper, a 3D transient FE model of wheelset and fixed frog is established, revealing rolling contact behavior of wheel-rail in frog area from both macro and mesoscopic perspectives. In order to investigate long-term load characteristics of wheel and rail under complex service conditions, the changes of line conditions, load conditions, rail wear state and other influencing factors in actual operation are taken into account. Based on elliptic Gaussian kernel density theory, a method for compiling the load spectrum of fixed frog nose rail is proposed, and the FP method is used for fatigue crack initiation life prediction of nose rail in fixed frog. The results show that the force state is more severe when passing through the frog in straight reverse direction, and resonance is prone to occur in the third and fifth vertical bending modes of the frog, as well as the fourth and sixth vertical bending modes of the stock rail. The increase in factors such as speed, axle load, wheelset lateral displacement towards frog side and wing rail wear will exacerbate wheel-rail impact and shorten frog service life. Different factors have an impact on the overall amplitude, oscillation center range, and maximum frequency load of the wheel-rail force in the long-term load spectrum of the frog. The fatigue crack initiation area of nose rail is mainly in 30 mm–35 mm sections, which is consistent with the on-site flaw detection results, verifying the accuracy of the calculation method developed in this paper. [ABSTRACT FROM AUTHOR]

Surface-defect-induced pitting gradually becomes the limitation of the rolling contact fatigue life of the M50 bearing steel as the subsurface initiation spalling probability decreases recently. Dent formation lives residual stress (RS). However, it was ignored in past studies on surface-initiated pitting. Therefore, this study established a continuous simulation model from particle compression to cycle rolling contact loading to study the dent-induced RS effects on damage evolution. The constitutive model of damage evolution incorporated continuum damage mechanics and cohesive mechanics. The results show that the depth-width ratio of the dent and RS increases as the load and hardness increase. RS makes both subsurface-initiation-damage and surface-initiation-damage advance, and affects the direction and speed of the surface damage evolution. Moreover, the size of the pitting in the rolling direction increases as hardness increases. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue tests with different stresses and cycles have been conducted to study the formation mechanism and crack source of butterfly white etching area (WEA) in different stages of M50 bearing steel. The results suggest that the structural transformation is prior to cracks. The initial microstructure is the nanocrystalline α-Fe formed by dislocation assisted carbon migration. With the extension of cycles, unlike the previous studies, the butterfly-origin carbide is refined into Mo 2 C and M 7 C 3 nanocrystalline by the accumulated dislocation clusters. Subsequently, the increase of interfacial energy drives the metal elements diffusion and thus the formation of amorphous structures. A new mechanism called diffusion-assisted dislocation has been proposed for butterfly WEA formation. [Display omitted] • The evolution of butterfly WEA in M50 bearing steel has been studied under different stresses and cycles. • A new detailed formation mechanism of butterfly WEA is proposed. • The structural transformation of butterfly WEA is prior to cracks. • M 2 C carbides are more likely to cause butterfly WEA and cracks. [ABSTRACT FROM AUTHOR]

This study investigated the microstructural alteration of GCr15 bearing steel under Rolling Contact condition. It was found that Decay Region, a feature microstructure, formed in the subsurface of materials with the dominant effect of cyclic contact stress. The Decay Region is composed of discretely distributed micro-regions where phase transition occurred, presenting a hollow crescent shape. The microstructure after phase transformation was highly susceptible to corrosion by Nital solution. The formation of Decay Region was related to the orthogonal shear stress and there was an upper threshold. Excessively high stress suppressed the appearance of Decay Region. During Rolling Contact, the hardness of materials evolved simultaneously. The evolution of hardness and microstructure exhibited a parallel development, as the dominant stresses were different. [ABSTRACT FROM AUTHOR]

While large accumulated plastic deformations occur in the rail surface layer where rolling contact fatigue cracks initiate, many available Low Cycle Fatigue (LCF) crack initiation criteria focus on small plastic strains. Accordingly, this paper evaluates available fatigue crack initiation criteria for highly shear-deformed R260 steels, reflecting the conditions in the surface layer of rails. Furthermore, modified crack initiation criteria are suggested. The evaluation is based on three different experiments: Large shear strain increments under varying axial loading (predeformation), strain-controlled LCF tests after some predeformation, and axial High Cycle Fatigue (HCF) experiments. For the predeformation, Finite Element (FE) simulations, with a large-strain plasticity model for cyclic and distortional hardening, provide predictions of the local stress and strain histories. A cross-validation procedure is used to assess the accuracy and reliability of both established and modified fatigue crack initiation criteria. The proposed modifications to one of the criteria show an improved fit to the experimental data. However, there is a tendency to overfitting, which can be improved by including more experimental data. • Three crack initiation criteria in rolling contacts of rail steel are evaluated. • Large strain cyclic axial-torsion experiments are used. • Finite element simulations are done using a large strain plasticity model accounting for anisotropy. • A cross-validation approach is used to assess the criteria. • Improved crack initiation criteria are proposed, leading to enhancements in fitting without worsening the prediction. [ABSTRACT FROM AUTHOR]

• Vanadium addition causes an increase in both yield strength and yield ratio. • Vanadium addition reduces strain hardening ability, and weakens wear resistance. • RCF crack initiation of V-alloyed stee is delayed by increasing yield strength. • RCF crack growth size is restricted by reducing plastic deformation capacity. • Increasing yield ratio improves RCF resistance, but weakens wear resistance. This study aims to evaluate the effect of vanadium microalloying on rolling contact fatigue (RCF) and wear behavior of railway wheel steels. It involves microstructural analysis and mechanical testing, including hardness, tensile, and rolling/sliding tests on the test steels, followed by electron backscatter diffraction, residual stress, and microhardness analyses after rolling/sliding tests. The findings demonstrate that vanadium microalloying leads to the alleviation of dynamic recrystallization, strain hardening, and compressive residual stress within the outermost layer beneath the worn surface, indicating a reduction in the plastic deformation capacity during dry rolling/sliding conditions. RCF resistance of railway steel can be enhanced through vanadium microalloying, as it simultaneously delays crack initiation by increasing yield strength and restricts crack growth by reducing plastic deformation capacity. While vanadium microalloying enhances the matrix hardness of wheel steel, it concurrently diminishes its strain hardening ability, potentially compromising its wear resistance. In addition, this study found that the yield ratio, being indicative of plastic deformation capacity and strain hardening ability, can serve as a suitable parameter for characterizing the RCF and wear resistances of tested steels. It exhibits a positive correlation with RCF resistance and a negative correlation with wear resistance. [ABSTRACT FROM AUTHOR]

The rail is subjected to cyclic stress and plastic deformation, excessive accumulation of which can promote rail degradation. A finite element (FE) model of three-dimensional (3D) cyclic rolling contact (CRC) with the implementation of an improved cyclic plasticity constitutive material model is developed to analyze the 3D elastic–plastic stress. Comparisons of the FE simulation results of 2D repeated moving pressure (RMP), 3D RMP, and 3D CRC models are conducted to elucidate the differences. The evolution and distribution patterns of the elastic–plastic mechanical behavior of wheel–rail contact with the number of cycles are also investigated. The FE results show that the 2D RMP model is conservative in predictions, and the results derived from the 3D RMP and 3D CRC models are comparable, while opposite results are available for some essential components. The 3D CRC model is a necessary choice especially for fatigue life prediction study. Due to the partial slip and cyclic rolling, the stresses and strains near the rail surface layer are significant and continuously accumulate. The residual equivalent plastic strain and the ratchetting strain increase with the increase of the tangential traction and the axle load, which will accelerate rail damage. • A 3D cyclic rolling contact FE model is proposed to study elastic–plastic stress. • Validation of the improved cyclic plasticity constitutive model by experiments. • FE simulation results and necessity choices are compared for three models. • The evolution of residual stresses and ratchetting strains in rail is revealed. [ABSTRACT FROM AUTHOR]

• Local quenching causes gradient distribution of microstructure and hardness in wheel. • The statistical correlation is: Hardness = −2.77 × Fraction of proeutectoid ferrite + 328.07. • Wear and rolling contact causes microstructure evolution of wheel. • Microstructure and hardness show a significant synergistic evolution law. High-speed train wheels have complex service environments during wheel–rail contact, and a comprehensive understanding of the microstructural inhomogeneity at the rim is critical for service safety assessment. The local quenching process in the vicinity of the rim will cause a difference in microstructure, directly affecting the service performance of the material. In this study, high-throughput characterization method based on material genome engineering was used, the methods for characterising and identifying the microstructure of wheel steel were developed using high-throughput scanning electron microscopy, and the accuracy and reproducibility of the methods were evaluated. A point-to-point research scheme for microstructure image and hardness data was designed based on the concept of statistical mapping characterization. The area fraction of the proeutectoid ferrite and micro-Vickers hardness distribution in a large size range of the key area of the rim and their internal correlation was obtained, these helped avoid statistical and representativeness limitations of traditional local selection analysis of microstructure and hardness. The results indicates that the area fraction of proeutectoid ferrite and micro-Vickers hardness showed a clear gradient distribution, and opposite distribution trend, with a high negative correlation. In addition, by observing the correlation between microstructure and hardness, and studying the evolution of microstructure, it was found that the microstructure and hardness of the rim near the tread demonstrated a significant synergistic evolution law under the influence of service, this was observed both statistically and microscopically. These findings enhanced the application prospects of the microstructure-performance statistical mapping method, and were beneficial in efficiently evaluating the service life and safety of key components. [ABSTRACT FROM AUTHOR]

To withstand increasing mechanical and thermal loads affecting rails and wheels due to intensified rail transportation, comprehensive knowledge of evolving near-surface microstructures in the wheel-rail contact is vital. Stratified surface layers (SSLs) observed in the field gained attention recently. This study extensively investigates a textbook example of SSL detected on a rail wheel. Results show crack initiation in the white etching layer (WEL) with propagation into the underlying brown etching layer (BEL) with changing crack growth direction. Within the BEL, a microstructural gradient is observed with decreasing grain size and increasing hardness with increasing distance from surface. This work provides new insights in the microstructural and micro-mechanical characteristics of SSLs and improves the knowledge of evolving stratification in wheel-rail contacts. [ABSTRACT FROM AUTHOR]

The Rolling Contact Fatigue (RCF) behaviour of through-hardened AISI 4140 samples under formulated lubricant with nano-graphene additives were investigated. Results showed that the reference oil added with 1% (wt.) of nano-graphene particles has significantly improved life by 6 folds. The increased RCF performance is attributed to the efficient action of graphene nano particle which improves the antiwear and pitting resistance of contact pairs. Moreover, spectroscopy and microscopy analyses indicated that graphene particles are adsorbed on the contact surface and delay the surface pit formation. Adding nano-graphene particles in the reference lubricant is an effective way to improve the RCF life under thin oil having low lubricant viscosity and also for the samples having lesser surface hardness such as through- hardened compared to induction-hardened samples. • RCF studies on through hardened (TH) and induction hardened (IH) AISI 4140 steel. • Improved RCF life of IH steel attributed to high compressive residual stress and hardness. • Graphene nano-lubricant (GNL) improves RCF performance of TH steel. • Adsorbed graphene – decreases the wear rate, surface pitting and its propagation. [ABSTRACT FROM AUTHOR]

Based on the measured spectra of rail roughness and track structures longitudinal roughness, the rail grinding limit is studied with the help of an established coupled dynamic metro vehicle–track model and a rolling contact fatigue model. The results indicate that metro rail grinding control should be regulated according to corrugation wavelength range and operating speed. Based on the rolling contact fatigue model, longer wavelength of rail corrugation has less influence on the wheel rolling contact fatigue. For the metro lines with a maximum operating speed of 80 km/h, the average levels of rail corrugation in the wavelength ranges of 30–65 mm, 65–125 mm, and 125–250 mm should be less than 5.4, 24.8, and 33.8 dB re 1 μm, respectively; for the ones with the operating speed of 80–120 km/h, the corresponding average corrugation levels in the three wavelength ranges should be less than 4.4, 9.8, and 29.8 dB re 1 μm, respectively. [ABSTRACT FROM AUTHOR]

This paper describes the elastic tire–pavement tractive rolling contact, by means of a semi-analytical method, in order to analyse top-down cracking. The model includes the actual tire profile and assumes the tyre to be elastic, linear and homogeneous, as modelled by an equivalent Young's modulus. The pavement is modelled as a half-space layer composed of asphalt concrete acting as a homogeneous elastic material. Results display the vertical contact stress and shear contact stress in both braking and turning cases; they also highlight the stick/slip zones within the contact area. When applied, these stresses allow computing the tensile strain responses at the pavement surface. Analysis shows that the maximum tensile strains are able to cause top-down cracking. Such strains are higher than the level considered in current pavement design models. A top-down cracking analysis is ultimately conducted according to the French method of bottom-up pavement design. [ABSTRACT FROM AUTHOR]

In railway heavy haul transportation, the wheel-rail contact interaction has a strong influence on the performance of the entire system. According to the vehicle longitudinal movement conditions - straight/curved tracks and travel speed, contact interaction takes place on different portions along the wheel/rail geometric profiles. Determining wheel/rail contact patches is fundamental both for vehicle dynamics and to predict the locci prone to rolling contact fatigue (RCF), due to high contact pressures. This work presents a quasi-static model to determine the wheel-rail contact locations and pressures for a given steady-state scenario of straight or curved track. The model is able to consider generic wheel and rail profile geometries with several contact pointwise interactions. Each contact pair is solved by the called 'master-master methodology', developed generally for a 3D environment. A proposed simplification leads to a two-dimensional model, able to produce results in fast processing time and very low computational cost. The result gives predictions related to RCF-prone location. The model is motivated for application together with a methodology to quantify the accumulated contact pressure, considering a family of distinct wheelsets and their combined interactions with the rails. We present a case study considering real measured wheel and rail profiles. [ABSTRACT FROM AUTHOR]

A semianalytical model is introduced to assess rolling contact fatigue problems in railway applications. The constitutive law is based on the nonlinear kinematic and isotropic hardening model of Chaboche–Lemaitre, which allows the cyclic elastoplastic strain under the contact surface to be evaluated. The much higher computational effectiveness in comparison with finite element (FE) analyses is quantified. The Dang Van multiaxial fatigue criterion is implemented to evaluate the rolling contact fatigue in the subsurface elastic region where cracking is relatively rare but more dangerous than surface cracks. The influence of the presence of sulfides in the wheel matrix in decreasing fatigue strength is also assessed by means of Murakami's approach. The model is used to compare conditions under small‐scale twin‐disk experiments to full‐scale wheel/rail contact conditions. It is found that, for the same Hertzian pressure, the small‐scale contact is more conservative in that it causes a deeper plasticized layer as compared with the elliptical full‐scale contact. In the investigated cases, crack initiation is also not expected according to Dang Van criterion in neither of the studied contact conditions. Highlights: A semianalytical model is developed to study the rail–wheel contact problem.Full‐scale rail–wheel contact and small‐scale twin‐disk contact problems are compared.The line contact problem experiences a deeper plasticized layer.The subsurface crack initiation is assessed using the Dang Van fatigue criterion. [ABSTRACT FROM AUTHOR]

This study presents a boundary element model to analyze contact pressure distribution and the subsurface stress field in rough rolling elements. The methodology is demonstrated by the stress field of the backup roll and work roll in the cold/temper rolling process and characterized by a parallel orientation of roughness lay with rolling direction, resulting in a cluster of highly elongated elliptical micro-contacts. The numerical outcomes revealed that the amplitude of in-plane and out-of-plane shear stress components are strongly dependent on the ellipticity of the micro-contacts. Comparison with experimental results shows that the crack plane is oriented transversal to the rolling direction and the crack initiation location corresponds to the location where the shear stress components are maximum. [Display omitted] • Longitudinal roughness lay creates highly elongated micro-contacts. • Micro-contacts ellipticity is influenced by surface features and applied load. • Micro-contacts ellipticity influences in-plane and out-of-plane shear stresses. • RCF crack features are explained by numerical modeling using surface topography. [ABSTRACT FROM AUTHOR]

Belgrospi-like damage is a special type of rolling contact fatigue (RCF) characterized by periodically grouped crack nests with short-pitch corrugation, which has been observed on sharp curved track in China. A 3D finite element model of the elastic–plastic wheel–rail transient rolling contact on a sharp curved track is developed to investigate the dynamic rolling interaction on corrugated rail. The competitive relationship between wear and RCF under cyclic loading is evaluated. Important findings include that the slope of corrugation geometry (CG) causes the center of the upslope the greatest dynamic contact solutions, which have a phase lead with respect to the CG. Under long-term cyclic loading, the rail material failure due to the continuous accumulation of plastic shear strain is RCF. [Display omitted] [ABSTRACT FROM AUTHOR]

A better understanding about the rolling contact fatigue and micropitting performance of machine component surfaces lubricated with environmentally friendly lubricants is critical to designing and further formulating new lubricants intended to be used in rolling–sliding contacts such as those found in gear and bearing applications. In this work, the frictional behaviour and rolling contact fatigue (RCF) performance of DLC, Cr/a-WC:H/a-C:H and a-C:Cr coatings under glycerol-based lubrication in rolling sliding contact conditions have been investigated. Traction maps, Stribeck curves, and fatigue plots have been generated by using a micropitting test rig (MPR). The initiation and progression of micropitting was monitored by means of white light optical interferometry and scanning electron microscopy (SEM). Results indicated that glycerol-based lubricants exhibited a significant friction reduction as the hydrodynamic effect is enhanced at higher rolling-speeds. Under boundary lubrication the friction coefficient was significantly higher compared to the values obtained with a commercial mineral-based transmission oil. Compared to uncoated steel surfaces, DLC coatings effectively reduced the volume loss and micropitting progression. Irrespective of the coating thickness, DLC showed an excellent tribological behaviour when the base lubricant favours the onset of mild-wear, over micropitting. When the lubricant formulation favoured the onset of micropitting, the coatings tended to prematurely fail due to debonding from the substrate, and local micro-spallation. The experiments demonstrated that friction reduction does not necessarily correspond with a reduction of micropitting. • The tribological properties of DLC coatings under glycerol–based lubrication were investigated. • Glycerol–water lubrication triggered superlubricity in a DLC–coated contact. • Micropitting and mild–wear equilibrium was influenced by the lubricant formulation. • DLC coatings inhibited micropitting progression under glycerol–based lubrication. [ABSTRACT FROM AUTHOR]

Polygonal wear is a type of damage commonly observed on the railway wheel tread. It induces wheel-rail impacts and consequent train/track components failure. This study presents a finite element (FE) thermomechanical wheel-rail contact model, which is able to cope with the three possible generation and development mechanisms of polygonal wear: initial defects, thermal effect, and structural dynamics. The polygonal wear-induced impact contact and further development of wear are simulated. The simulated elastic contact solutions are verified against the program CONTACT. Different material properties (elastic, elasto-plastic and elasto-plastic-thermo, i.e. with thermal softening) and initial polygonal profiles are then applied to the FE model to investigate the influence of wheel/rail material and wear amplitude on wheel-rail contact stress and wear development. The simulations indicate that the wheel-rail impact-induced temperature may reach up to 362 ℃ at the contact interface, and the high temperature at the contact area influences wheel-rail contact stress and wear depth. • An innovative thermomechanical FE model is presented to study polygonal wear growth. • The simulated contact solutions are verified against the program CONTACT. • Using elastic material models causes overestimation of contact stress and wear depth. • Incorporating thermal effects is crucial for wear predication with high slip ratio. • The simulated contact temperature reaches up to 362 ℃ at the wheel-rail interface. [ABSTRACT FROM AUTHOR]

Railway wheel polygonization is a type of uneven wear of material which worsens the running stability of trains. As a significant factor influencing the wear, wheel-rail hardness matching (i.e., the hardness ratio H W / H R) might affect the formation of a polygonal wheel. Thus, rolling-sliding wear tests were conducted using three wheel steels matching two rail steels to explore the influence of H W / H R (ranging from 0.649 to 1.263) on the initiation and evolution of wheel polygonal wear. The results show that when matching the softer rail, the wheel was less likely to become polygonal with an increase in H W / H R. When matching the harder rail, the wheel presented earlier polygon initiation under a moderate H W / H R of 0.792. The largest H W / H R of 1.263 presented the best anti-polygon condition for wheel material. The wear mechanism of polygonal wheel was dominated by abrasive, fatigue and oxidative wear at the crest and fatigue wear at the trough. • Evolution of wheel polygon wear is analyzed via rolling-sliding test with high-speed camera and vibration sensor. • Effect of wheel-rail hardness ratio on wheel polygon wear is explored. • Wheel polygon wear is easier to form with wheel hardness decreasing and rail hardness increasing. • Wear mechanism at crest is different with that at trough. [ABSTRACT FROM AUTHOR]

For premium grades (and rail surface treatments such as 'laser cladding') there is little plastic damage expected during typical operating conditions, and smooth surface contact models predict a long life. However, damage still develops, including rolling contact fatigue, affecting premium steels from multiple suppliers. A model is described predicting stress intensity factors and indicative crack growth rates for cracks driven by surface roughness stresses. Accompanying field data quantify the asperity separation and tip radii for rails from metro, mixed traffic and a freight line in ground or unground conditions. The results predict that in rough surface contact small surface cracks (50–100 μm, exceeding microstructural dimensions) can grow faster than crack removal by wear, even when smooth surface models predict no growth. The model has application in identifying how rail grinding marks or wheel roughness may be an important factor in determining rail life through raised stresses at the rail surface (leading to wear), and increased stress intensities and growth rates for incipient cracks. • Prediction of rough surface rolling contact fatigue crack stress intensity factors. • Relevant to harder steels where roughness is long lasting with little plastic flow. • Newly collected field data on rail surface roughness. • Cracks of 50–100 μm predicted to have growth faster than their removal by wear. • Crack growth predicted that would not be expected from smooth surface models. [ABSTRACT FROM AUTHOR]

Wear and Rolling Contact Fatigue (RCF) on wheels and rails are influenced by relative motions between the studied rail and wheel pair, and therefore influenced by train dynamics. Wear and RCF assessments using a train dynamics approach provide more accurate and comprehensive results comparing with conventional assessments that often do not consider train dynamics. In addition, considering material property differences, currently available rail wear maps are not able to accurately describe the wear performance of materials that have significantly different properties. This paper presented a method for rail/wheel wear and RCF assessments using 3D train dynamics models. The use of train models allows the consideration of coupler forces, traction, and brakes during the assessment. Wear assessments were conducted by using an in-house rail wear map model developed from the twin disc wear machine at the Centre for Railway Engineering (CRE). The new rail wear map was developed by using the AS 60 rail material (hardness 340 HB). The results indicated that the methods proposed in this paper could be used for rail/wheel wear and RCF assessments. Traction/braking forces and coupler lateral forces had evident influences on wear and RCF assessment. Different wear maps were also shown to have significant influences on the wear rate results. • A more comprehensive method to assess wheel-rail wear and RCF. • A new wear map for the AS 60 rail material. • Evidence of influences of traction/brake, coupler forces, and wear maps for wear and RCF assessment. [ABSTRACT FROM AUTHOR]

• First S-N curve of surface initiated damage under rolling contact fatigue. • Uniquely conservative mechanical fatigue failure definition used for surface damage. • RCF and torsional fatigue S-N curves have similar fatigue strength exponent. • Study unveils that torsion tests can predict RCF surface damage results 10x faster. • Different operating regimes identified based on RCF surface damage severity. This paper presents fundamental findings on equivalence of rolling contact fatigue (RCF) driven surface damage and torsional fatigue modes of failure. Fatigue experiments were conducted for both modes of failure using AISI 4130 case carburized steel specimens. A Thrust Bearing Surface Pitting Rig (TBSPR) was designed and developed to perform RCF tests on flat test specimens using thrust ball bearings. The experiments were conducted in boundary lubrication regime, simulating the contact conditions in tribological machine components. The current investigation presents a novel approach where the effect of contact pressure and number of fatigue cycles on the initiation of surface damage was characterized by surface profilometry of the wear track after each test to generate a stress-life (S-N) map. The S-N map provides unique insights to early detection of RCF driven fatigue damage. The S-N map was utilized to generate the surface damage S-N curve. Torsional fatigue experiments were conducted on the same material, and the S-N curves of both failure modes were compared. The comparison shows key similarities between the two S-N curves, as they differ by a simple scaling factor. This investigation demonstrates that RCF driven surface damage characteristics can be predicted by conducting much simpler, and faster, torsion fatigue tests. This paper also presents a novel methodology to determine contact pressures to avoid incipient micropitting/microdenting damage. [Display omitted] [ABSTRACT FROM AUTHOR]

• S–N curves for RCF surface damage at two roughness levels. • Torsional fatigue and RCF surface damage S–N curves have similar slope. • Contact mechanics model to obtain surface stress concentration in rough contact. • Torsion tests and modeling of measured rough surfaces predicts RCF performance. This paper presents a novel approach to predict the effect of surface roughness on surface damage in rolling contacts. Rolling contact fatigue (RCF) tests were conducted on AISI 4130 case carburized steel specimens at two different roughness levels, R a = 0.3 μ m and 0.1 μ m , under boundary lubrication regime. The RCF experiments were performed using a Thrust Bearing Surface Pitting Rig employing a ball-on-flat configuration. Surface damage was assessed at different combinations of contact pressure and fatigue cycles using optical surface profilometry. Subsequently, the surface damage stress-life (S–N) results were generated at both roughness levels. Torsional fatigue experiments were also performed on the same material. The torsional fatigue S–N results were combined with stress concentrations at the RCF test surfaces due to roughness to predict the surface damage S–N results. A dry circular contact model incorporating the surface roughness was developed and utilized to compute the stress concentration at the contact. The S–N results based on the von-Mises stresses were compared for RCF and torsional fatigue. The predicted results corroborated well with the experimental findings. The approach developed in this investigation illustrates the fundamental relationship between RCF and torsional fatigue. [ABSTRACT FROM AUTHOR]

• A crystal plasticity damage model proposed for RCF of GGS. • FEM implementation to predict crack initiation and spalling lifetime. • Effect of the residual stress on RCF behavior is investigated. A dislocation density-based crystal plasticity damage model is presented for a numerical study on the spalling behavior of gradient grained structures under rolling contact fatigue loading. The topology of the gradient grained structure is constructed using Voronoi tessellations. The fatigue damage is coupled into a dislocation density-based crystal plasticity model where the evolutions of the dislocation density and fatigue damage are considered. The process of spalling is characterized by the evolution of fatigue damage in the polycrystalline structures. The evolutions of contact pressure, stresses, dislocation density, plastic strain, and fatigue damage of gradient grained structures with regard to rolling cycles are investigated. Moreover, the effect of the gradient form and residual stress on the rolling contact fatigue behavior is studied. The simulation results reveal that the gradient grained structures and the residual stress influence the rolling contact fatigue resistance. [ABSTRACT FROM AUTHOR]

• Zig-zag morphology, grain refinement and secondary cracks are typical characteristics of zig-zag crack region. • The plastic deformation zone at the crack tip being limited to a few grain diameters caused the zig-zag morphology. • Grain refinement and secondary cracks formed during the severe pressing of crack. Shattered rim is a century-old problem that restricts the reliability of railway wheels in service. In this paper, the formation mechanisms of the zig-zag crack region on the shattered rim of railway wheel were investigated. First, the zig-zag crack region was observed using both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and was identified as a typical region for crack propagation in giga-cycle rolling contact fatigue behavior. The zig-zag crack bands have a height range of 3–30 μm, with an average of 13.4 μm, and a width range of 0–500 μm, with an average of 184.6 μm. The size values of band height and width are close to the values of the pearlite and protoaustenitic grain size. The formation of the zig-zag morphology in the zig-zag crack region is due to the periodic deflection of the propagation path relative to the initial propagation plane, which is a result of the limited plastic deformation zone at the crack tip that extends only a few grain diameters. The grain refinement and secondary cracks in the zig-zag crack region are attributed to the large compressive and shear stresses induced by the applied rolling contact loading. [ABSTRACT FROM AUTHOR]

[Display omitted] Material microstructure plays a key role in crack initiation under rolling contact fatigue. When studying microstructure with crystal plasticity finite element method (CPFE), mesh sensitivity study is of great importance, as the surface-near region is under high uniaxial stresses. In this paper, a new structured mesh strategy is purposed and compared with the classical unstructured mesh strategy. Modelling tests on a bi-grain and a polycrystal model show the calculation of geometrically necessary dislocation (GND) density, recently proposed as a suitable fatigue damage indicator, is highly dependent on mesh morphology, when GND hotspots tend to appear near distorted elements even in homogeneous materials. With uniform mesh size and shape, structured mesh elements can provide physically more acceptable GND calculations, which is particularly important in loading scenarios with complex stresses, such as rolling contact fatigue. Computational efficiency is also improved compared to unstructured models because a smaller number of elements are required in a structured mesh model and pre-processing of the mesh is not required. [ABSTRACT FROM AUTHOR]