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• 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]

• Generation arc is subjected to triple acceleration of P - v - I. • Surface damage is a combination of mechanical and electrical damages after arcing. • Conductive AFM visually confirm the harmful effects of oxidation on conductivity. This study employs copper (Cu)-Cu rolling pairs to investigate the failure characteristics and surface damage mechanism of current-carrying tribological contacts under various conditions (contact load P = 40–180 N, rotation speed v = 4–600 rpm, and current I = 0–2.5 A). Based on synchronous current curves and video observations, the severe current fluctuations caused by the electric arc can be considered a criterion for the failure of rolling electrical contacts. Surface damage assessment through scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM), reveal ablation pits, oxidation, and roughening as primary manifestations of electrical damage. Post-rolling, the Cu on the surface was oxidized to copper (II) oxide. As the degree of oxidation increased, the conductive area in the AFM current map decreased significantly at a sample bias voltage of 1.5 V. Notably, arc generation was subjected to the triple acceleration of the contact load, rotation speed, and current. A back propagation (BP) neural network model was established to predict the running cycles before arc generation. Based on independent validation experiments under P = 120 N, I = 1.0 A, v = 400, and 600 rpm, the average prediction error of the proposed BP neural network model was 8.13 %. The results of this study facilitate the understanding of failure mechanism and predicting life cycles of rolling electrical contacts. [ABSTRACT FROM AUTHOR]

• The hardness of the soft zone is much lower relative to the hardened surface of the raceway. • A hierarchical finite element modeling method of the main bearing is proposed. • The principle of selecting the optimum hardened depth is given. • The effect of the soft zone on the contact characteristics and fatigue life of the raceway is investigated. • This analyzing method can quickly and efficiently clarify the contact state in the soft zone during the rolling process. A hierarchical finite element modeling method is proposed to study the problem of fatigue spalling easily due to low hardness in the soft zone for the main bearing of a tunnel boring machine. Quasi-static analyses of the main bearing are performed based on the global symmetric model and verified by relative displacement tests of the rings. The invariant contact pressure is replaced by the rolling contact of the rollers in the local sub-model. The contact load is used as an input to solve the stress field, and then the effects of soft zone and hardened depth on the contact characteristics and fatigue lifetime of the sub-model are investigated. The results show there are stress peaks at the junction of the hardened and soft zones. The effect of hardened depth on the stress distribution and fatigue lifetime is relatively small. However, the optimum hardened depth is influenced by the contact load and the permissible stress of the material. The minimum lifetime of the raceway during rolling occurs in the soft zone. This paper achieves a fast and effective rolling contact fatigue analysis of the main bearing, which provides a theoretical basis for optimizing the main bearing design. [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]

• Based on the Hertzian contact distribution and creep-slip characteristics, the fatigue life of spinning bearings is predicted using the damage parameter theory of the critical plane method and the L-P theory. • The deviation rate between the finite element simulation and the theoretical calculation results is 6.61% • The rotation speed, friction coefficient and external load affect the fatigue life of spinning bearings, and better lubrication and excellent contact surface to extend the life. • A rotary bearing life experimental device verified the reliability of the theoretically calculated deviation rate is 3.86%. In order to ensure the longer working life of rolling guide bushing, this work proposed a fatigue life prediction model of spinning bearings based on the Hertzian contact distribution and creep-slip characteristic. The influence of different parameters on the fatigue life of spinning bearings was analyzed according to the damage parameter theory of the critical plane method and the L-P theory. Finally, the fatigue life prediction model of spinning bearings was verified through the finite element simulation combined with the experiments. The reliability results show that creep-slip characteristic and deformation lead to the contact zone stress of the spinning bearing firstly increases, decreases subsequently to zero and then increases to the peak value. The increase of rotational speed will make the fatigue life of the spinning bearing firstly increases and then decreases. With the increase of friction coefficient, its fatigue life will become smaller and smaller, and the increase of the external load will decrease its fatigue life. Meanwhile, the prediction error rate of the fatigue life prediction model proposed in this study is 4.60%, which is within the error tolerance. This study provides certain methods and ideas for fatigue life prediction of spinning bearings, and lays a theoretical foundation for the design of highly reliable spinning bearings. [ABSTRACT FROM AUTHOR]

• The model can account for the non-linear lifting of the flange groove and the effects of wheelset traverse and side roll. • The wheel tread and flange are alternately loaded with two wheel load transition areas in the frog area. • Wear in the flange bearing area is significantly higher than in the tread bearing area, with an increase of 59.7%. • RCF damage dominates in the wing rail and the two wheelload transition areas. • Reducing the speed to 15 km/h significantly improves the service performance of the fixed frog. The tram No. 3 turnout fixed frog uses a variation in the depth of the flange groove so that the wheel rolls over the frog area in a continuous flange bearing. This method of travelling over the turnout requires the wheel load to transition back and forth between the tread and the flange, resulting in wheel-rail impact, which in turn affects service life. In order to investigate its service characteristics, this paper has established a transient wheel-rail rolling contact finite element model for the No. 3 turnout fixed frog. The macroscopic dynamic response and microscopic wheel-rail contact solution as the tram passes through the turnout at different axle weights and speeds are analysed in detail, and the changing patterns of wear and fatigue damage are investigated. The research shows that rail wear is particularly severe in the wheel flange bearing area, approximately 1.6 times greater than in the tread bearing area. In addition, when tram speeds are reduced to 15 km/h, there is a significant reduction in wheel-rail impact and wear, thereby improving ride smoothness and safety. The results of this study are of great significance to the operation and maintenance of the No.3 fixed frog turnout. [ABSTRACT FROM AUTHOR]

• A 3D wheel-rail rolling contact FE model was established based on measured corrugation and hardness distribution of rails. • The effect of uneven hardness distribution on the stress-strain distribution within the wheel-rail contact area was analysed. • The wheel-rail rolling contact behaviour in the corrugation zone changes significantly after work hardening. • Work hardening has a major effect on the difference in wear between the crest and the trough. The process of work hardening in the corrugation zone of the steel rail results in an uneven distribution of hardness, with higher hardness in the corrugation troughs and lower hardness in the corrugation crests. To study the influence of hardness on the rolling contact behavior of the wheel-rail at corrugation zone, a three-dimensional wheel-rail transient rolling contact finite element model is established based on the measured corrugation and hardness distribution of the rail to reveal the influence of the non-uniform distribution of hardness at corrugation zone on the wheel-rail contact state and the wear and fatigue of the rail surface. The results indicate that: (1) work hardening in the corrugation zone leads to an increase in equivalent stress and strain within the contact patch between the wheel and rail. However, due to the increase in yield strength, plastic deformation and residual strain are somewhat reduced; (2) The uneven distribution of hardness in the corrugation zone results in an elevation of longitudinal shear strain between the wheel and rail, which may initiate tangential fatigue cracks and spalling of the steel rail surface; (3) the wear on the rail surface is large near the wave crest and small near the wave trough, work hardening will change the wear difference between the wave crest and wave trough while reducing the wear, resulting in the "peak shaving and valley filling" phenomenon developing faster in the early wave wear period and slower in the later period. [ABSTRACT FROM AUTHOR]

This paper presents a case study in sliding/rolling contacts between steel components operating in packaging devices for powder pressing, where the non-conformal contact involving a rotating roller (AISI M2 tool steel) and pins (AISI 440B martensitic stainless steel) led to the formation of macro- and micro-pitting on both mating surfaces. On the basis of metallurgical failure analysis, surface-origin contact fatigue was identified as the main damage mechanism. Microstructural stress raisers such as relatively large carbides, clustered along plastic flow lines, were observed in both steels. A white etching layer (WEL), due to severe sliding/rolling conditions, further enhanced the formation of surface-origin cracks on the roller. Unlabelled Image • Failure analysis of steel roller and pins after field operation. • Morphological and microstructural evaluation of the damaged surfaces. • Surface-origin cracks due to contact fatigue as main cause of damage. • Identification of microstructural stress raisers influencing the contact fatigue behavior. [ABSTRACT FROM AUTHOR]

Abstract RCF tests were conducted on bearings lubricated with three different lubricants: a gearbox oil, a MAC fluid and PFPE oil. The decomposition of the MAC fluid and PFPE was investigated by FTIR and NMR. Gearbox oil tests showed flaking and networks of subsurface cracks with partial intercrystalline crack growth. Cross-sectional analysis revealed the formation of WEAs. FEM correlated the damage with stress fields. The results of the MAC lubricated tests showed surface flaking and intercrystalline crack growth in the subsurface. The PFPE lubricated bearings showed no signs of hydrogen induced damage. Post-experimental hydrogen analysis of the bearings indicated an increased hydrogen concentration in the samples lubricated with the gearbox oil and MAC compared to those lubricated with PFPE. Highlights • Post RCF hydrogen analysis showed concentration variation with various lubricants. • Hydrogen evolution in RCF tests was associated with lubricant decomposition. • The levels of hydrogen in bearings was correlated with damage telltale signs. • Failure patterns were correlated to stress fields obtained from FEM. [ABSTRACT FROM AUTHOR]

Abstract Due to the improvement of the wear property, rolling contact fatigue including shattered rim and shelling are the main failure causes of the high-speed railway wheels. In this paper, shattered rim and shelling occurred on the service wheels of the China Railway High-speed (CRH) trains were systematically investigated. The recorded data of the last ten years CRH operation indicated that all shattered rims and shelling were detected with serving >106 km (corresponding to the fatigue life 107–109 cycles) which is very-high-cycle fatigue (VHCF). The crack initiation region of shattered rim located at the depth of 10–25 mm from the tread, while that of shelling located at the depth <10 mm from the tread. The VHCF features under rolling contact loading were observed on the opening crack surfaces, i.e., similar VHCF features in uniaxial loading including the defect, fish-eye, and crack propagation region and unique VHCF features of the three dimensional crack surface feature, beach bands uniformly distributed in the crack propagation region, absence of fine granular area (FGA). The VHCF model considering the stress distribution, defect size and hardness were applied to discuss the failure mechanism of the shattered rim and shelling. Highlights • The shattered rim and shelling are caused by very-high-cycle fatigue (VHCF) under rolling contact loading. • Unique features were presented in the crack initiation region of VHCF under rolling contact loading. • The multi-axial stress distribution, the large defect, the hardness distribution are responsible for the VHCF behavior. [ABSTRACT FROM AUTHOR]

The aim of present study is to monitor the delamination failure of plasma sprayed Al 2 O 3 –40 wt% TiO 2 composite ceramic coating (AT40 coating) in rolling contact condition by acoustic emission (AE) technology. The AE signals of the delamination failure process were divided into three types (type I: normal contact; type II: fatigue crack initiation; type III: delamination failure) based on the feature of AE count. The waveforms and frequency spectrums of different types of AE signals during delamination failure process of the coatings were obtained by Empirical mode decomposition (EMD) method. The relationship between the waveform/frequency of the AE signals and the delamination failure mechanism of the AT40 coatings were discussed in detail. [ABSTRACT FROM AUTHOR]

• A ratcheting mechanism-based numerical model was applied to predict damage initiation in twin-disc tests of premium rail steels. • Wear- and RCF-dominated damages are distinguished by the depth of the ratcheting mechanism-based damage initiation locations. • A higher creepage results in a shallower damage initiation location and a shorter damage initiation life. • The initial wear rate increases with a higher creepage for wear-dominated damage. • HE2 rail steel presents the longest damage initiation life and the lowest initial wear rate compared to HE1 and LAHT. This work presents a ratcheting mechanism-based numerical model to study the initiation location and initiation life of rolling contact fatigue (RCF) or wear damage and the initial wear rate of premium rail steels under the laboratory twin-disc test conditions. Twin-disc tests are widely used in the studies of rail steels due to their ability to reproduce critical aspects of full-scale wheel-on-rail contact under controlled conditions and a relatively short test period compared to field tests. This study introduces a computational model to simulate the cyclic rolling contact for three premium rail steels (HE1, HE2, and LAHT) against wheel steel AAR Class-C under twin-disc test conditions. The cyclic rolling contact is achieved by repeatedly moving a non-Hertzian distribution of contact pressure and the calculated longitudinal surface traction upon a segment of the circumferential surface of the lower disc until a stabilized maximum ratcheting strain rate is reached. The RCF or wear damage initiation location is determined by the location showing the stabilized maximum ratcheting strain rate, and the damage initiation life is estimated by applying the ratcheting failure mechanism. Wear and RCF damages are distinguished by the depth of the damage initiation location. Wear damage is dominant when the location is near the surface. Otherwise, the damage will be RCF-dominated. The initial wear rate due to wear-dominated damage is estimated by identifying a critical profile and affected volume of worn material within the ratcheting strain rate field. The predicted initial wear rate is compared with the experimental result of the examined contact pair. This research can assist in a more profound understanding of the experiment results of a twin-disc test and provide a numerical basis for an experimental twin-disc test design. Furthermore, it may provide significant references for choosing rail steels. [ABSTRACT FROM AUTHOR]

For heavy vehicle systems, within the power transmission chain from the driving machine to the working components (wheels), gears have a large share of application in the form of gearboxes, differentials and speed reducers. Their purpose is to achieve the highest possible output torque at the working components. In one heavy-duty truck, the gearbox lost its working capacity due to the failure of its vital parts: a tapered roller bearing and a helical gear. The analysis presented in this paper, conducted on the basis of experimental and analytical methods, showed that, due to inadequate installation of the bearings' outer ring in the gearbox housing in one intermediate shaft support, the roller bearing performed its elementary function in very unfavorable working conditions of mechanical and thermal nature. Due to the damage accumulation, the roller bearing gradually lost its working capacity. As a result, the intensity of the working conditions of the entire gearbox increased. At the moment when they reached the critical value from the aspect of the gear teeth bending strength, volumetric destruction occurred, i.e fracture of the helical gear tooth, and thus the cessation of gearbox power transmission. • The importance of proper roller bearing installation on the operation of a complex machine system. • Analytical analysis of the rolling bearing overload model. • Mechanical and geometrical changes in rolling bearing characteristics due to elevated operating temperatures. • The relationship between the gear tooth root fracture and the indirect cause of the fracture (rolling bearing damage). [ABSTRACT FROM AUTHOR]

• A two-stage simulation strategy was proposed to investigate the mechanisms of RCF cracks on the rail, consisting of a dynamic FEM for wheel and rail interaction and a coupled static FEM/BEM for crack growth. • The critical wheel positions for crack propagation during wheel approaching to and departing from the crack were determined and correlated with the different cracking mechanisms. • The orientation of the crack in rail played an essential role in crack growth behaviors. Rolling contact fatigue (RCF) crack is one of dominating damages on the rail surface due to repeated wheel and rail contact. RCF defects, including squats and head checks, can potentially cause rail fracture failure if not treated in time. It is critical to accurately predict the pertinent damage for different operational conditions. A two-stage simulation strategy was proposed to investigate the mechanisms of RCF-induced cracks on the rail, consisting of a dynamic FEM for wheel and rail interaction and a coupled static FEM/BEM for crack growth. It was found that there are two critical wheel positions for crack propagation during wheel approaching to and departing from the pre-existed crack. The different cracking mechanisms at these two critical wheel positions are correlated with the local physical phenomena, i.e. , the traction at the wheel/rail interface, the relative distance between the contact patch and crack, and the sliding at crack faces. The twisting of the cracks from the transverse plane to the longitudinal plane at the railhead significantly reduces crack growth in mode I, enhances crack propagation in modes II and III, and shifts the dominant crack growth from the crack front center to the crack corners. The increased incline of the crack in the rolling direction promotes the crack to grow downward in opening mode I. [ABSTRACT FROM AUTHOR]

• The FaStrip algorithm is modified to estimate elastic-plastic traction distribution. • Softened zones of rail welds experience the highest ratcheting strain rate. • Ratcheting strain rates in the sampled 2000 m radius curved track are higher than those in the sampled tangent track. • The RCF initiation location is highly dependent on the magnitude and pattern of traction distribution. Ratcheting at the rail heads due to cyclic rolling contact stresses is often observed in heavy haul railways, especially when there are large steering forces developed in low-radius curves. Additionally, ratcheting behaviour can be exacerbated when associated with material strength loss in the heat affected zones of rail welds. However, the numerical evaluation of this failure mode requires a sophisticated representation of elastic–plastic contact pressures and traction distributions, which, to the best of the authors' knowledge, cannot be directly measured by any existing tools. In this paper, in order to accurately evaluate the ratcheting performance at rail welds in curved tracks, attempts were conducted to modify the FaStrip algorithm to analytically estimate the traction distributions based on contact pressures and creepages obtained from static finite element analysis and multi-body dynamic simulations, respectively. Cyclic rolling contact was then simulated by repeatedly applying contact pressure and traction on the rail surface consisting of both the rail weld and the parent rail regions. The weld region was divided into 23 sub-zones in the rolling direction to represent the material inhomogeneity within the heat affected zones. Cases on a 2000 m radius curved track and a tangent track were studied for comparison. It was found that the ratcheting strain rate in curved tracks can be significantly elevated due to the higher magnitude of traction, and the location of the elements with the highest ratcheting strain rate was dependent on the traction distribution patterns. The proposed method provides a general tool for predicting rolling contact fatigue initiation life and location, which will benefit the maintenance efficiency of heavy haul rail welds in curved track. [ABSTRACT FROM AUTHOR]

• A pre-strain method to produce large-scale tubular crack growth specimens is presented. • Mode-II fatigue crack growth of severely deformed pearlitic steels was investigated. • Alignment of the microstructure changes the crack path and propagation mechanism. The crack path under cyclic Mode-II loading in undeformed and pre-deformed pearlitic rail steel R260 is investigated. To produce large-scale specimens with pre-deformed microstructures two methods are applied. Firstly, cylinder bars are processed using an axial-torsion machine resulting in a moderate deformation. Secondly, a new high pressure torsion (HPT) setup is developed to achieve a more strongly deformed microstructure. In the fatigue tests, a distinctive change in the crack path is observed. In the undeformed and moderate deformed specimens, the cracks bifurcate and turn into a Mode-I dominated mixed-mode. In the HPT material, the cracks grow in Mode-II without mixed-mode propagation. For rolling contact fatigue cracks in rails these experimental results indicate a strong connection between the propagation mode and the anisotropy of the highly deformed pearlitic microstructure. This microstructure is characteristic near the wheel-rail contact surface. In future, these findings are important to improve numerical-based crack growth prediction models. [ABSTRACT FROM AUTHOR]

• A Voronoi finite element model for crack initiation life of RCF is built. • The coupling damage model considers the microstructure of material. • The impact mechanism of grain characteristics and material defects is revealed. The material microstructure of plays an important role in crack initiation of rolling contact fatigue. To address crack initiation of tapered roller bearings, the inhomogeneous characteristic of material is considered. The random distribution of material grains is simulated with Voronoi graph, and a Voronoi finite element model of rolling contact fatigue is given. Numerical analysis of damage-life constitutive relation is carried out with finite element analysis. The effect of material microstructure inhomogeneity on initiation life of fatigue crack is studied. Researches show that the smaller the grain size, the more difficult the fatigue crack appearing. The larger the difference of elasticity modulus between non-metallic inclusions and matrix material, the greater the impact on fatigue life of crack initiation. The angular and sharp non-metallic inclusions reduce fatigue life more than rounded shape inclusions. Initiation life of fatigue crack has a minimum value on a critical depth of nonmetallic inclusion. The longer distance between two laterally arranged inclusions, the greater it affect the initiation life of fatigue crack. The effect of distance between two vertically arranged inclusions on fatigue crack initiate depends on the depth of inclusions. [ABSTRACT FROM AUTHOR]

• Wheel-rail creepage-adhesion curves at high speed were obtained. • A simplified method was proposed to extract parameters to modify FASTSIM. • Dynamic wheel-rail interactions were obtained by numerical methodology under low adhesion. • Wheel-rail wear performances were primarily investigated under wet condition. The evolution of wheel-rail dynamic interaction of a high-speed railway vehicle is essential for the simulation of wheel-rail rolling contact damage under low adhesion conditions. The main objective of this study is to reproduce the dynamic wheel-rail interaction behaviour under various interfacial contaminations by experimental and numerical modelling methodology. Firstly, the wheel-rail adhesion characteristics under different interfacial contaminations were obtained. Subsequently, a simplified numerical methodology was proposed to extract the parameters from the high-speed adhesion tests to modify the simplified theory of Kalker (FASTSIM). The initial slop reduction factor and the slip-velocity-dependent coefficient of friction (COF) were introduced based on the high-speed experimental curves. Furthermore, the modified wheel-rail rolling contact model was incorporated into a longitudinal vehicle-track coupled dynamic model. The wheel-rail dynamic interaction behaviours under different operational conditions were attained. Finally, the wheel-rail wear performances were primarily investigated for typical traction coefficients under wet conditions. Results show that the wheel-rail creep force drops dramatically when the wheel enters the low adhesion zone (LAZ). There is a sudden increase in the creep force when the adhesion recovers. In addition, the wheelsets begin to slide and have severe wear at LAZ when the traction coefficient is larger than 0.1 at high speed. [ABSTRACT FROM AUTHOR]

• The 2-degree-freedom rolling bearing was established. • The number of balance points depends on the clearance of the rolling bearing. • It generates chaotic vibrations. • It provides satisfactory results and verifies the feasibility of the method. During the installation and operation of transmission equipment, bearing clearance problems occur, which are also one of the main reasons for bearing failure. Therefore, research on bearing clearance has theoretical significance and engineering value. To determine the influence of bearing clearance on bearing vibration, the theoretical model of a 2-degree-freedom rolling bearing was established based on the dynamic characteristics of the bearing vibration. Based on Hertz elastic contact theory analysis of the dynamic characteristics of the rolling bearing, it was observed that for the tested bearings, the number of balance points of the inner ring of the bearing depends on the clearance of the bearing. When bearing inner clearance (e) e < 4.5 μ m is present in the bearing, a stable equilibrium point exists, and periodic vibration occurs in the inner ring of the bearing near the centre of the balance point. When a gap of (e ⩾ 4.5 μ m) is present, and the gap and rotational speed of the bearing increase continuously, the system generates chaotic vibrations, and the area in which the chaotic vibration occurs also increases. The experimental results of the ϕ 127 m m rolling bearing indicated that under the same damping parameters, bearing size and rotational speed, the results of the singular attractors obtained from the experimental data are similar to those obtained by solving the equation of motion. This qualitative result not only confirms the existence of chaotic bearing behaviour, but also verifies the reliability of the theoretical model. [ABSTRACT FROM AUTHOR]

• A simulation method for predicting rolling contact fatigue in railway systems. • A locomotive digital twin with mechatronic traction system co-simulation. • Calibrated shakedown maps using actual rail material mechanical properties. • Wheel-rail contact modelling with variable friction from field measurements. • Rolling contact fatigue hotspots discerning top of rail, gauge face and gauge corner. Rail damage prediction is a complex task because it depends on numerous tribological parameters and the dynamic conditions produced by the vehicles operating at different speeds and configurations. Shakedown maps and Whole-Life-Rail-Model/T-Gamma have been used to predict rail damage, but they involve assumptions that may reduce their accuracy. This paper proposes a simulation modelling method to predict rail surface damage based on a locomotive digital twin, calibrated shakedown maps and friction measurements. The method improves the accuracy of rail damage predictions by including slip-dependent friction characteristics, co-simulation of locomotive traction mechatronic system and the mechanical properties of the wheel and rail materials measured through tensile tests. A set of operating conditions are simulated on a high-performance computing cluster, with stress results being post processed into calibrated shakedown heatmaps. The method clearly indicated the influences of the different operating conditions on rail damage for specific combinations of wheel-rail materials and vehicle-track configurations. [ABSTRACT FROM AUTHOR]

• Flow lips were formed in rails extracted from mild curvature tracks. • WEL and BEL were observed as the outermost layers in the flow lip regions. • Multiple cracks with different propagation angles were found. • Reverse transverse fracture might originate in cracks developed in the flow lips. • The propensity for rail fracture increases with a decrease in track curvature. The microstructure of the flow lips formed at the lower corner of gauge face in the longitudinal section of worn high rails serving in curved tracks has been investigated. The radii of the curved tracks are 1500 m (S1, sharper curve) and 4000 m (S2, milder curve). Sharper curves result in a higher angle of attack (AOA) between rail-wheel thus leading to higher lateral contact forces as well as tangential frictional forces thus facilitating plastic flow. Such conditions favour formation of flow lips where rail material flows from the rail upper gauge face to the lower corner of the gauge face. A combination of optical microscopy (OM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and nano-indentation hardness measurements have been used for the characterization of the flow lip. It is observed that the outermost region of the flow lip consists of a uniformly present white etching layer (WEL) followed by an intermittently present brown etching layer (BEL) where the WEL and BEL thickness is less for milder curves. The WEL has the highest hardness and consists of fine grains of ferrite and particles/fine fragments of cementite. The BEL is relatively softer than WEL and has a similar appearance to WEL, but patches of lamellar structure appear with increasing depth from the outer edge. Beyond the BEL region, layers of deformed pearlitic structure are observed, and a more intact pearlitic structure is observed at a much lower depth for the milder curve than the sharper curve. For both the curvatures at a given depth, the hardness of pearlite bears a Hall-Petch type of relationship to the pearlitic interlamellar spacing. However, the alignment of the deformed microstructure is heavily dependent on the curvature. It has been found to align almost parallel (4°–10°) to the rail longitudinal axis for the milder curvature and at around 21°–35° for the sharper curvature. Cracks originate from the brittle WEL region due to contact fatigue whereas crack propagation is driven by bending stresses. Cracks have been found to move parallel to the alignment of the deformed pearlite along longitudinal direction for the milder curvature. Alignment of pearlite also motivates the crack propagation trajectory for the sharper curvature and hence the crack moves at an angle between 21° and 35° with the longitudinal direction but becomes almost perpendicular after a distance. Shallow cracks travelling parallel to the rail outer edge in S2 can result in spalling of the rail material leading to wear, whereas for sharper curves, cracks run deeper into the railhead. Thus, the tendency for rail failure through 'Reverse Transverse Fracture' – which involves crack initiation at the lower gauge corner and propagation into the railhead – increases with the sharpness of the rail curvature. [ABSTRACT FROM AUTHOR]

• Build a 3D wheel-rail transient explicit rolling contact FE model considering rail spalling failure. • Investigate transient dynamic response characteristics when the train passes rail spalling area under different conditions. • Use the wavelet transform technique to process the dynamic signal and to detect the rail defects dynamically. • The length of spalling has great influence on wheel-rail dynamic interaction and its limit is found. Rail spalling is a typical form of wheel-rail rolling contact fatigue (RCF), and is a difficult problem that has always existed in railways. Once the wheel rolls across the spalling failure area, there will be a violent dynamic wheel-rail interaction. This paper presents an explicit high-speed 3D wheel-rail rolling contact transient explicit finite element model that considers local rail spalling failure. The dynamic wheel-rail interaction under the condition of different spalling lengths and contact stress states, as well as plastic strain of the rail when the wheel rolls across the rail spalling, are calculated using the theory of transient wheel-rail dynamics. In addition, the time–frequency analysis is carried out to obtain the distribution characteristics of dynamic response signals such as axle box acceleration, rail vibration acceleration and dynamic vertical wheel-rail force in time domain and frequency domain. Furthermore, when the vehicle travels at a high speed, the speed and radius of the wheel have little influence on the dynamic vertical wheel-rail force, or on the wavelet energy peak and frequency. The effect of the mutual dynamic correlation is small. But the dynamic vertical wheel-rail force, along with wavelet energy peak and frequency, increase in an approximately linear fashion with the impact acceleration of wheelset and the length of spalling failure. These results can be used to guide the dynamic detection of local defects on rails. [ABSTRACT FROM AUTHOR]

Rolling contact wear is a complex phenomenon that might involve different wear mechanisms (adhesive, abrasive, fatigue and corrosive) and different stress concentration mechanisms (asperity, dent, debris, inclusions, etc.). The interactions among these mechanisms might accelerate or decelerate the overall wear progress. Therefore, it is complicated to model and monitor the fluctuations of wear progress. The current descriptive models are either describing individual physical phenomena within rolling contact wear or describing a specific stage of wear progress. Thus, the interactions among different wear mechanisms and the transition events among different stages of wear progress are not sufficiently addressed. Therefore, the purpose of this paper is to propose a descriptive model of the wear evolution process in rolling bearings over the whole lifetime. The descriptive model utilises a wide range of empirical findings in the literature to describe the wear interactions and evolution in the five-stage scenario: running-in, steady-state, defect initiation, defect propagation, and damage growth. The new descriptive model provides the most probable scenario of wear evolution in rolling bearings, which is useful for modelling and monitoring the wear progress. It illustrates the wear evolution stages, the involved wear mechanisms in each stage, the interaction among wear mechanisms in each stage, the surface topology changes and the influencing factors within each stage. For design, condition monitoring and prognosis purposes, these aspects are significantly important to understand, model, test and monitor the wear evolution process. [ABSTRACT FROM AUTHOR]

• Dynamic experiments of U75VG rail flash-butt welded joint at different regions were carried out. • A new dynamic constitutive model of the U75VG rail flash-butt welded joint was proposed. • The influences of driving speed on the transient contact pressure, equivalent stress, and equivalent plastic strain of U75VG rail flash-butt welded joint were investigated. Rail welded joint is one of weak links in high-speed railway, and its dynamic performance has important effects on the safety, stability, and comfort of the high-speed train. In this work, the dynamic mechanical responses at different regions of U75VG rail flash-butt welded joint were investigated. The results show that the base metal (BM), welding zone (WZ), and heat-affected zone (HAZ) of U75VG rail flash-butt welded joint has an obvious strain rate effect, i.e., the material strength increases with increasing the loading strain rate. The strength of WZ is similar to that of BM, but its toughness is much lower than that of BM. The toughness of HAZ is the same as that of WZ, but its strength is much lower than that of BM and WZ. Based on the experimental results, an improved dynamic constitutive model was established to reasonably simulate the stress–strain curves of different regions from quasi-static loading to dynamic loading. Finite element (FE) analysis of transient rolling contact between rail welded joint and wheel under different conditions was performed. Compared with the results from quasi-static wheel-rail contact simulation, the equivalent plastic strain at each region of rail welded joint increases significantly and presents non-uniform distribution after considering the dynamic effect. When the wheel contacts the junction between different regions, the impact will cause a significant stress concentration at the rail welded joints. The maximum wheel-rail load by the implicit dynamic analysis is about 4 ∼ 12 times that obtained by the quasi-static analysis. Moreover, the maximum contact pressure, equivalent stress and equivalent plastic strain of each area of rail welded joints gradually increase with the increase in axle load and driving speed. [ABSTRACT FROM AUTHOR]

• The wear performance of the defected rail materials under various slip ratios and contact stresses was investigated. • The surface damage of the defected rail materials under various slip ratios and contact stresses was studied. • The effect of slip ratio and contact stress on crack propagation mechanisms near the dent was discussed. The defects on rail surface may have negative effects on the rolling contact fatigue (RCF) performance of the rail materials. This investigation researched on the RCF behaviors of the defected rail materials under various slip ratios and contact stresses. The results show that both the wear loss and the average crack length increase if the slip ratio or the contact stress increases. Moreover, the surface damage characteristics change from simple adhesion spots to significant fatigue crack grouping when slip ratio and contact stress rise. Finally, the experimental results also highlight that the slip ratio provides the deformation area for crack initiation whereas the contact stress accelerates the crack propagation by emphasizing the geometric effects. [ABSTRACT FROM AUTHOR]

• The constitutive relation of materials at different positions were obtained. • A set of dimensionless functions were proposed for Material parameters. • The Young's modulus and hardness decrease from the rail bulk to the surface. • The reduction of hardness is mainly attributed to Young's modulus. Rail decarburized layer has significant impact on the wear and rolling contact fatigue in the wheel-rail interaction. Due to the lack of constitutive relation of rail decarburized layer, it is impossible to analyse accurately the influence of rail decarburized layer on wheel-rail contact. To obtain the constitutive relation of this layer of decarburized non-uniform material, nano-indentation experiments were carried out at different vertical positions in the decarburization layer on a rail specimen with decarburization thickness of 0.55 mm. Young's modulus and hardness were determined using Oliver and Pharr method. Axisymmetric two-dimensional finite element models were established in ABAQUS to simulate the nano-indentation loading process and the power law elastic–plastic stress–strain relationships were obtained for material at different vertical positions in the rail decarburized layer. A set of dimensionless functions were proposed for Young's modulus, hardness, yield stress and strain hardening exponent at arbitrary depth in a rail decarburized layer or in a decarburized layer treated by rail pre-grinding. The results show that the Young's modulus and hardness decrease from the rail bulk to the surface of the decarburized layer. The Young's modulus and hardness near the surface are 11% and 35% lower than those in the rail bulk, respectively. However, the yield stress exhibits an increasing trend from rail bulk to the decarburized surface, where yield stress is 20% higher than the rail bulk. Analysis shows that the main reason that causes the reduction of hardness at the decarburized layer surface is the reduction of Young's modulus but not the yield stress. [ABSTRACT FROM AUTHOR]

• Cause for welded slide plate failure was investigated and analyzed. • Optimization scheme for welded slide plate failure was proposed. • Fatigue performance of old and new product was compared by fatigue simulation. • Strength performance of old and new product was compared by laboratory test. The wheel-rail contact relationship in turnout is more complicated than that in regular track, which will increase the dynamic wheel-rail interaction. The slide plate, being important component of turnout, is prone to produce fatigue damage under the cyclic action of wheel-rail contact force. In this paper, an investigation and analysis has been done on the fatigue damage of welded slide plate, tongue depressor fracture and weld separation. The structural optimization schemes are proposed for various failure modes. The fatigue performance of slide plate for two schemes is evaluated and compared by simulation. The strength performance of slide plate for two schemes is compared by laboratory test. In simulation, two models were established to analyse the wheel-rail dynamic interaction of vehicle-track system and stress characteristics of slide plate, respectively. The fatigue life of the slide plate for two schemes were evaluated and compared, based on the fatigue damage theories. During the test, the ultimate strength of tongue depressor and bond strength between the slide platform and the base plate for two schemes, were tested and compared. The simulation and test results showed that the fatigue and strength performance of slide plate have increased reasonably after optimization. It can provide reference for design of slide plate. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism of the coating spalling under rolling contact was investigated. Fe–Cr coatings were deposited by plasma spray process. The rolling contact fatigue (RCF) experiments of the coatings were conducted. The tests were stopped before mass material losses. RCF traces were examined by a FIB–SEM device. Results show that some round or arc cracks on the coating surface were the origins of spalling. The cross-section SEM image of these cracks revealed that their inceptions are the microdefects within the coating, such as unmelted particles, oxides. The stress resulted from rolling contact was driver for the propagation of crack. [Copyright &y& Elsevier]

• Sleeper hanging defects are studied with a wheel-rail transient rolling contact model. • Rail irregularities are an input for the analysis of wheel-rail contact behavior and rail degradation. • Both rail irregularity geometry and its position affect severity of sleeper hanging. • Sleeper hanging defects exacerbate the plastic deformation of the rail material. • Sleeper hanging defects rarely affect the distribution of adhesion-slip states and rolling contact fatigue. In this study, a wheel-rail transient rolling contact model capable of accounting for the nonlinear displacement-force properties of hanging sleepers is proposed. The sleeper hanging status affected by rail irregularities is an input for an analysis of the wheel-rail contact behavior and related rail degradation in terms of plastic deformation and rolling contact fatigue. The results indicate that the severity of sleeper hanging is significantly affected by the geometric characteristics and the relative position with respect to the sleepers of the rail surface irregularity. The sleeper hanging defects aggravate the wheel-rail impact and increase the wheel-rail contact force amplitude, contact patch size, pressure, and von Mises stress, thus exacerbating the plastic deformation of the rail material. It was also found that the sleeper hanging defects rarely affect the distribution of the adhesion-slip states and rolling contact fatigue. The knowledge gained can serve as guidance for evaluating the condition and conducting the maintenance of ballasted railway tracks. [ABSTRACT FROM AUTHOR]

• We compared the failure of railway thermite welds through real field-testing. • We simulated the dynamic impact force induced by the weld geometry. • We reported the progression of the surface hardness of welds in track condition. • We discussed the noticed failures; wear and cracks. This paper details the field-testing approach and results of thermite welds used in railway applications. Rail steels made from R260 grades are welded by two different processes: the standard process according to the European standards, and a recent technology. Welds are introduced in the same testing location to ensure comparable loading conditions in the aim of studying their degradation behaviours. The total testing-period is 6 months. During the in-service period, the surface hardness of the running band, in the welded area, is recurrently measured. For an accurate assessment of field results, a vehicle/track interaction (VTI) model evaluated the expected dynamic loads induced by the initial vertical irregularities. The simulations show that the highest dynamic load at the wheel/rail contact happens at the location of the maximum absolute gradient, in accordance with previous research. Particularly, dipped welds show relatively high dynamic forces inducing a high loss of the transversal profile. In respect of the field results, the comparison of initial and final surface hardness indicates a significant increase for 'ALFONS' welds over the welded areas. Additionally, all welds depicted a cyclic increase and decrease of the running band hardness. This result is discussed according to the ratcheting susceptibility of welds and eventual wear progression. For a testing-period of 10 weeks, the gauge corner of one 'ALFONS' weld developed a crack. The assessment of the longitudinal profiles revealed changes of the vertical irregularities that may modify the dynamic loads, and further the rolling contact fatigue mechanisms and degradation rates. [ABSTRACT FROM AUTHOR]

Abstract: The deep groove ball bearings of an electric motor, driving an oil-injected compressor, were periodically monitored for vibrations. The ball bearings were replaced when before the expected lifetime of the bearing the measured vibration exceeded the tolerated level. The bearing on the axle side of the motor was the locating bearing while the ball bearing of the fan side (where the fan of the electric motor was placed) was mounted as a (spring-loaded) floating bearing. The outer rings of the fan side bearing showed signs of fretting wear. The outer ring of both bearings was ground through to disassemble the bearings. Visual inspection, optical microscopy and scanning electron microscopy of the raceways indicated that the bearings were subjected to an axial load in the range of the permissible axial load, but for each bearing in a different direction. The placement of the wear marks on the raceways of both bearings indicated an axial loading from the inside towards the outside of the electric motor. Also the wear marks on the raceways of both ball bearings showed the typical washboard pattern of the passage of electric current >0.5A, although the rotor was already equipped with a grounding brush on the non-drive side. While replacing the deep groove ball bearing by a cylindrical roller bearing can easily prevent the fretting wear on the fan side bearing, the origin of the bearing currents merits further investigation. [Copyright &y& Elsevier]

The premature failure of two forged and induction hardened low alloy steel work rolls used for cold rolling of high and medium carbon steel was investigated. Microhardness profiles indicated that the values of the effective induction hardening depth for both rolls are below the user''s requirement. Tensile testing results of the core of the rolls indicated that the tensile and yield strengths are also below the manufacturer''s requirements, the latter being 50% below the minimum requirements. The microstructure of the spalling surface presented tempered martensite, dispersed chromium carbides and spheroidised pearlite. The presence of spheroidised pearlite may have promoted the sub-superficial nucleation of rolling contact fatigue cracks. The heat-treatment schedule should be optimised in order to increase the depth of the hardening layer and the mechanical properties of the core, so that the contact fatigue life of the rolls can be improved. [Copyright &y& Elsevier]

• Alumina inclusions inside the rims responsible for the shattered rim of railway wheel. • Fatigue life of the shattered rim is over 107 in the range of very-high-cycle fatigue. • Proposing a method attempting to evaluate fatigue damage tolerance and the remaining service life of the wheel. The shattered rim on railway wheels is increasingly concerned in recent years. Based on the failure analysis, the mechanism of shattered rim was revealed. The contact stress distribution of wheel/rail with inclusions in the wheel was analyzed by ABAQUS. Then the stress field was imported into FRANC3D to simulate the crack propagation. It is found that the simulation results were in good agreement with those obtained experimentally from the actual shattered rim, which proves the availability of the simulation. Meanwhile, the influence of the size and location of the inclusions on the fatigue life of the wheel was evaluated. Based on the crack propagation curves obtained by simulation, the rolling contact fatigue damage tolerance analysis and remaining fatigue life assessment method of wheels were proposed. [ABSTRACT FROM AUTHOR]

• Residual stress affects crack tip displacements of rail cracks. • CTSD amplitude increases with increasing wheel-rail friction coefficient. • Oblique crack propagates as the combined type of II/III dominated by type II. Fatigue crack is one of the main damages that reduce rail service life and raise rail maintenance costs. In this paper, a three-dimensional elastic–plastic finite element model of wheel-rail contact is established, in which a three-dimensional oblique crack is inserted in the rail. Taking crack tip displacements as fracture parameters, the effect of residual stress on fatigue crack propagation of rails is quantitatively analyzed, and the fatigue crack propagation mechanism of rails under the combined action of wheel load and residual stress are studied. Results show that crack tip displacements under the action of wheel load are quite different from that under the combined action of wheel load and residual stress. For the oblique crack with crack tip entering the residual tensile stress zone, crack tip sliding displacement amplitude increases with the increase of wheel-rail friction coefficient. Under the combined action of wheel load and residual stress, the oblique crack propagates as the combined type of II/III dominated by type II. [ABSTRACT FROM AUTHOR]

• A rolling contact connector prototype with a novel contact structure is presented, which significantly improves the power transmission capacity compared with previous RCC using flexures. • The degradation process of rolling electrical contact characteristics is analyzed by both experimental and numerical methods. • Electrical contact model based on fractal theory is a powerful method for contact failure analysis. The fractal dimension can be used to characterized the wear pattern. Rotary electrical connector is one of the key components for power source and electrical equipment connecting with rotating electrical interfaces, such as artificial space station, earth satellite, radar, wind generator, etc. Rolling contact connector (RCC) is a competitive technology compared to traditional sliding connectors for rotary electrical connecting, especially for long-life applications. In this paper, a novel coupled rolling contact structure of RCC prototype is presented. The degradation of rolling electrical contact is studied experimentally. Scanning electron microscope and confocal laser scanning microscope are utilized to obtain the gradual changes of the microscopic morphology and elemental composition on the rolling contact surfaces. A mathematical model of electrical contact based on fractal geometry is introduced to describe the contact behavior of RCC. Numerical analysis results illustrate the fractal dimension can be used as a key parameter to characterized the wear pattern. The mechanism of rolling electrical contact degradation is discussed in detail. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue has a significant impact on the service life of the infrastructure, in particular on the rail, which undergoes various defects, the severity of which threatens transport safety. Our study focused on the investigation of a curved track on the Algerian railway network laid in the 1980s by checking the design, the rail material, and the operating conditions of the track, and then the degradation of the rail for a classification and defect analysis based on standards. The methodology used consists of a visual field study using conventional measurement methods, supported by on-site and laboratory ultrasonic inspection to highlight the severity of defects for railway safety and to measure the effectiveness of the operator's maintenance policies, which must be improved in terms of defect's detection and removal to extend the infrastructure's life. [ABSTRACT FROM AUTHOR]