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The layup quality of prepreg fibers onto complex surfaces is the most concerned issue in automated fiber placement (AFP), which is intimately related to the contact stress in tractive rolling contact. An analytical model of tractive rolling contact is proposed in this paper to clarify the defects mechanism during the AFP process, which considers the mold curvatures, mechanical properties of contacted objects, and pose information to make it suitable for irregular surfaces and arbitrary conditions. Classical Hertz theory in this model is expanded to 3D contact area, and multi‐scale deformations are united in the accurate calculation of contact stress under geometric constraints. Based on the model, the phenomena of adhesion, microslip, and the transition between them in AFP are systematically analyzed. For engineering applications, a discrete processing strategy is proposed to quickly obtain the local curvatures of the mold. Additionally, an algorithm is designed to calculate the contact stress of any path. Experimental results on an aircraft component demonstrate the accuracy of the proposed model in restoring the contact stress distribution during AFP. In conjunction with specific layup information, this model exhibits utility in forecasting laying defects and parameter optimization. Highlights: An analytical modeling approach based on Hertz theory is proposed to calculate the contact stress in automated fiber placement.A model‐based algorithm is designed and combined with the proposed discrete scheme to quickly restore the contact stress distribution.Contact states related to stress are systematically investigated and defects analysis based on computational mechanics results is illustrated. [ABSTRACT FROM AUTHOR]

High‐speed trains (HSTs) often face challenges associated with car‐body hunting, resulting from factors such as complex operating environments and wheel‐rail contact degradation. These issues have a significant impact on the ride quality and operational safety. Passive suspension systems are inadequate to provide satisfactory dynamic performance for HSTs in such circumstances. However, active suspension systems can provide an effective solution. To address the car‐body hunting stability of HSTs, this study proposes a novel control approach called displacement inequality constraint following control (ICFC‐BIS) for the active suspension of HSTs. The ICFC‐BIS leverages the beneficial nonlinearity of bio‐inspired structures (BIS) to indirectly achieve excellent dynamic characteristics of the BIS through actuators installed in the suspension of HSTs, eliminating the need for actual BIS installation. Numerical simulation results demonstrate that the proposed ICFC‐BIS can effectively suppress car‐body hunting motion, thereby enhancing the ride comfort of HSTs. Consequently, the operational safety and ride comfort indices of HSTs equipped with active suspension systems are significantly improved. [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]

Rotary sliding mode triboelectric nanogenerator (TENG) provides high efficiency, a continuous and high output strategy for harvesting low-frequency mechanical energy. However, poor durability owing to material abrasion during sliding restricts its practical application. Here, a novel ferromagnetic metal particle-based triboelectric nanogenerator (FMP-TENG) is proposed, which couples the unlimited point contact rolling motion of particles instead of planar contact of film to improve durability of TENG. Besides, due to the extensively enhanced contact area by ferromagnetic metal particles, FMP-TENG improves its electric output, achieving a charge density of 103 μC m-2 and a peak power density of400 mW m-2 Hz-1. After 10 000 cycle running-in, FMP-TENG exhibits excellent durability, which retains 97% of the output charge for 110 000 cycles. In addition, a metal powder mass sensor based on FMP-TENG is also designed, which can effectively detect mass change in ferromagnetic metal powder in a dynamic mechanical platform. A novel strategy is proposed here to solve the problem of durability of sliding TENG in practical applications. [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]

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]

Rail wear occurs continuously owing to the rolling contact load of trains and is fundamental for railway operational safety. A point‐based manual rail wear inspection cannot satisfy the increasing demand for rapid, low‐cost, and continuous monitoring. This paper proposes a depth‐plus‐region fusion network for detecting rail wear on a running band, which is a collection of wheel–rail interaction traces. The following steps are involved in the proposed method. (i) A depth map estimated by a modified MiDaS model is utilized as guidance for exploiting the depth information of the running band for rail wear detection. (ii) The running band of a rail is segmented and extracted from images using an improved mask region‐based convolutional neural network that uses the scale and ratio information to perform instance segmentation of the running band images. (iii) A two‐channel attention–fusion network that classifies rail wear is constructed. In this study, we collected real‐world running band images and rail wear‐related data to validate our approach using a high‐accuracy rail‐profile measurement tool. The case‐study results demonstrated that the proposed method can rapidly and accurately detect rail wear under different ambient light conditions. Moreover, the recall rate of severe wear detection was 84.21%. [ABSTRACT FROM AUTHOR]

Wear characteristics of an (Mo–Nb–Ta–V–W)C high‐entropy carbide were investigated using ball‐on‐flat technique. The experimental material with a high relative density of 99.0%, single phase, average grain diameter of 10.7 μm, and nanohardness of grains 28.6 GPa was prepared by ball‐milling and two‐step field‐assisted sintering. The tribological test was realized during dry sliding in air with the SiC ball as tribological partner at applied loads 5, 25, and 50 N. The microstructure, deformation, and damage characteristics were studied using scanning electron microscopy and confocal electron microscopy. The friction coefficient values during the test with 5 and 25 N were very similar and stable, with a value of approximately.4, whereas during the test with 50 N, it decreased from the value of.48–.42. The specific wear rate increased with increasing load from 3.71 × 10–7 mm3/N m at 5 N to 2.59 × 10–6 mm3/N m at 50 N. The dominant wear mechanism was mechanical wear with intensive grains pullout, fracture, and powder formation, without visible tribochemical reactions and tribo‐layer formation. The wear rate decreased due to the created rolling contacts among the tribopartners thanks to the hard and spherical nanopowders present. [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]

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]

The quest for high‐performance energy efficient aircraft turbine engines has led to the development of a number of high‐performance rolling element bearing materials and engine lubricants with the aim of providing superior mechanical component durability. The heat treatments/surface treatments used to achieve the desired physical and mechanical properties for these newer alloys can result in altered surface chemistry from currently used materials. Surface chemistry plays an important role during lubricant‐bearing material interactions and the formation of beneficial tribological films during component operation. The objective of this study was to analyse the tribo‐films formed on bearing surfaces and investigate the interaction of lubricant additives, specifically the phosphorus‐based anti‐wear additive tricresyl phosphate (TCP), with different bearing materials under relevant bearing operating conditions. Bearing tests were conducted on 208‐size (40 mm bore) angular contact bearings at 127°C and 154°C using gas turbine engine lubricants conforming to MIL‐PRF‐23699G at maximum Hertzian contact stresses of 3.1 GPa and 3.55 GPa. Bearing materials evaluated included AISI M50, M50NiL, nitrided M50NiL (N) and three variants of Pyrowear 675 with silicon nitride rolling elements. Tribo‐films were analysed using Energy dispersive X‐ray spectroscopy and Auger Electron spectroscopy. Results indicate that phosphorus‐rich anti‐wear tribo‐films form on all of the bearing materials studied. The applied thrust load and heat treatment had a significant effect on tribo‐film thickness. The study also suggests that current gas turbine engine lubricants formulated with TCP should form beneficial tribo‐films that enhance bearing fatigue life and performance. [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]

A Failure Assessment Diagram (FAD), developed for rolling contact, was specifically formulated for railway wheel steels. The FAD allows combining a multiaxial fatigue criterion with the linear elastic fracture mechanics concept; in particular, it was used to assess the fatigue failure in wet contact, related to the pressurization of the fluid entrapped in surface cracks. The approach was applied to the results of previous bi‐disc tests carried out on three railway wheel steels, subjected first to a dry rolling‐sliding contact step, then to a wet contact step. The crack size distribution after the dry contact step was evaluated by a statistical approach; subsequently, the stress intensity factor during the wet contact step was estimated by finite elements. The results of the FAD agreed with the damage observed on the cross section of the specimens at the end of the tests. Furthermore, the FAD was used to determine the maximum allowable crack to prevent rolling contact fatigue, this way showing its potential as a damage tolerant approach. [ABSTRACT FROM AUTHOR]

Railway interaction is characterised by the coupling between the train and the track introduced through the wheel/rail contact. The introduction of the flexibility in the wheelset and the track through the finite element (FE) method in the last four decades has permitted to study high‐frequency phenomena such as rolling noise and squeal, whose origin lies in the strongly non‐steady state and non‐linear behaviour of the contact forces that arise from the small contact area. In order to address models with a large number of degrees of freedom, innovative Eulerian‐modal models for wheelsets with rotation and cyclic tracks have been developed in recent years. The aim of this paper is to extend the resulting formulation to an uncoupled linear matrix equation of motion that allows solving each equation independently for each time step, considerably reducing the associated computational cost. The decoupling integration method proposed is compared in terms of computational performance with Newmark and Runge‐Kutta schemes, commonly used in vehicle dynamics, for simulations with the leading wheelset negotiating a tangent track and accounting the rail roughness. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue damage of railway rails in the form of squats, characterised by local depressions and cracks located at the rail surface, has been linked to the occurrence of local rail surface irregularities. This study concerns rolling contact fatigue cracks in the vicinity of fairly smooth surface irregularities, here denoted dimples. The influence of factors such as dimple geometry, cluster effects, and crack size is evaluated. To this end, dynamic vehicle–track simulations featuring realistic wheel and rail profiles are employed to characterise the dynamic impact during a wheel passage. The contact load in the vicinity of the dimples is then mapped onto a 3D finite element model of a rail section containing a crack in the rail head. The crack loading is finally quantified by multimodal stress intensity factors. The analyses establish that also shallow dimples might have a significant impact on the crack loading. This effect is increased for larger or multiple irregularities but decreases as the crack grows. [ABSTRACT FROM AUTHOR]

Probabilistic models employed for life prediction in the bearing industry (Lundberg‐Palmgren [LP], Ioannides‐Harris [IH], and Zatersky models) utilize stresses calculated based on Hertzian assumptions that ignore plastic deformation occurring under high radial loads. However, it is known that subsurface plasticity produces significant deviations from elastic calculations in contact dimensions, pressure, and stresses. In this work, we show that accounting for plastic deformation leads to significantly more accurate life predictions than the general practice of utilizing elastic stress fields. Conventional probabilistic models are also restricted to utilizing stress measures at the macroscopic scale, while the onset of damage under rolling contact fatigue (RCF) manifests on a much smaller scale. By utilizing Dang Van criterion (DVC)—a multiscale high cycle fatigue criterion—in a probabilistic framework to account for stresses at multiple length scales, we propose a formulation that is second in accuracy only to the Zaretsky model, thus outperforming LP and IH models. Thus, we improve the accuracy of conventional probabilistic models by accounting for plastic deformation, while also presenting a new microstructure‐sensitive probabilistic formulation that betters their predictions. [ABSTRACT FROM AUTHOR]

Nowadays, micropitting is perceived as one of the prevalent wear mechanisms, which is responsible for the breakdown of high power density (power throughput/weight) machines. The current work demonstrates the evolution of surface damage and surface topography parameters during micropitting tests. The test surfaces are examined at different load stages utilizing 3D optical profiler, optical microscope, and scanning electron microscope. The effect of slide‐to‐roll ratio (SRR) on surface damage and topography parameters is also presented. It is observed that the severity of micropitting increases with an increase in the number of cycles. It is concluded that surface bearing index (Sbi), kurtosis (Sku), maximum valley height (Sv), and autocorrelation length (Sal) are positively correlated with surface damage, whereas mean summit curvature (Ssc) and skewness (Ssk) are negatively correlated with surface damage. Surface texture ratio (Str) and power spectral density (PSD) of test surfaces are used for analysing surface texture, and it is found that deterioration in surface texture occurs after 6 million cycles. It is also concluded that geometrical isotropy increases with an increase in SRR. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue cracks and thermally induced defects are common problems in the railway industry especially as demands for increasing loads, speeds, and safety continue to rise. Often, the two types of defects are found together in the field, however, whether one causes the other to occur is not completely agreed upon. The effect of thermal damage, in the form of a martensite spot on pearlitic steel test bars, on the fatigue life in uniaxial low cycle fatigue experiments was investigated by the authors. However, the focus of the current work was to characterize the damage evolution from the low cycle fatigue (LCF) tests and correlate the crack initiation and propagation with the initial thermal damage. Residual stress measurements, digital image correlation, and X‐ray tomography were used to characterize the effects of the thermal damage before, during, and after fatigue testing, respectively. It was found that the thermal damage causes strain accumulation and crack initiation at the interface between the two materials. The strain evolution was visualized using digital image correlation (DIC), clearly showing the strain concentrations at the top and bottom of the white etching layers (WEL), where the residual stresses are also most tensile. X‐ray tomography confirmed the planar crack growth from the martensite spot. [ABSTRACT FROM AUTHOR]

High‐strength steels are widely used in high‐performance bearings utilized in most mechanical systems. However, there has been little statistical analysis regarding the fatigue failure behaviour of the material, where surface peeling resulted from contact fatigue during rolling is a significant life‐limiting mechanism. In this study, we examine the statistical behaviour of surface‐crack nucleation, propagation, and peeling in a high‐speed train axle bearing made of GCr15 steel by using a laboratory rolling‐contact equipment. We reveal that cyclic rolling‐contact leads to the formation of a hardness gradient in the outer ring of the bearing. The gradient layer is of several millimetres. The peeling rate could be as high as 28 μm per million cycles when the contact pressure is close to that applied in real service. Peeling‐induced cracking is dominantly transgranular. The incipient angle is about 23.2°, and its depth could be hundreds of micrometres. The findings reported here could be employed to assess the lifetime of bearings made of GCr15 steel and possible other engineering metals. [ABSTRACT FROM AUTHOR]

In this paper, the fully-coupled rolling contact problem between a rigid cylinder and an orthotropic medium is investigated. The governing equations are developed analytically; then, a numerical method, the Gauss-Chebyshev method, is used to solve the coupled integral equations. The rolling contact problem is solved by assuming a central stick zone accompanied with two slip regions. The main purpose of this study is to obtain the surface stresses in the contact area and investigate the effect of material orthotropic properties such as shear parameter and stiffness ratio and also the coefficient of friction on these contact stresses. In addition, the subsurface stresses in the orthotropic medium are determined and a parametric study, was subsequently executed. The current paper shows that the orthotropic parameters and the coefficient of friction significantly influence the contact surface stresses and the distribution of the interior field stresses. By appropriately choosing the values of these parameters, the stresses will decrease; thus, the failure behavior of the orthotropic medium improves. [ABSTRACT FROM AUTHOR]

Wheel wear is studied using SIMPACK dynamic models of high-speed train carriages and backpropagation neural network classifiers based on measurement data. The EDMA-2017 chairs and special issue editors thank authors, organisers and readers for the passion and contributions to apply machine learning research to engineering applications. EDMA-2017, the first International Workshop on Engineering Data- & Model-driven Applications, was held in conjunction with the 10th IEEE International Conference on Cyber, Physical and Social Computing (IEEE CPSCom-2017). [Extracted from the article]

ABSTRACT This paper proposes a numerical approach based on a steady-state algorithm to predict the rolling contact fatigue crack initiation in railway wheels in practical conditions. This work suggests taking into account the cyclic hardening of the wheel's material and one of its originality is to conduct a complete numerical approach whatever the loading level. The main stages are the characterization and modelling of the material behaviour, the determination of the stress-strain fields using a numerical steady-state method and the application of a high cycle fatigue criterion. Computations were made with the Abaqus FE commercial software. Three cases are studied: rolling with or without sliding and skating. The numerical results give several types of mechanical responses: elastic or plastic shakedown. Otherwise, the results show that the location where the shear stress is maximal is not the same as where the risk of crack is the highest. [ABSTRACT FROM AUTHOR]

The stress-strain history and the crack initiation lives of bainitic and head-hardened pearlitic rail steels were determined under rolling contact loading by implementing the semi-analytical Jiang-Sehitoglu rolling contact model that incorporates both ratchetting and multiaxial fatigue damage. The calculations revealed that the bainitic steel withstands higher loads than the pearlitic steel at low shear tractions, however; both materials behave in an increasingly similar manner as the shear tractions increase. Furthermore, maximum damage occurs in both steels when ratchetring and fatigue damage coincide on the surface. In addition to shedding light on the rolling contact fatigue (RCF) performance of bainitic and pearlitic rail steels, the current work also establishes a methodology for the realistic prediction of crack initiation under RCF. [ABSTRACT FROM AUTHOR]

The rolling contact fatigue (RCF) behaviour of the plasma-sprayed CrC-NiCr cermet coatings under different tribological conditions of contact stress was investigated. Four sets of fatigue life data of coatings were characterized by Weibull distributions. The failure modes of the coatings were classified on the basis of worn surface observations of the failed coatings. Results showed that the failure mode of the coating was related to the magnitude of contact stress. The RCF life data of the coatings tested at high contact stresses exhibited high scattering, because the bimodal distribution of the fatigue life data was seen in the Weibull plot. Generally, when the contact stress was relatively low, the coatings were prone to fail in spalling and cohesive delamination. However, at high contact stress, the coatings often failed due to interfacial delamination. At different contact stress levels, the maximum shear stress amplitude was the main reason for the generation of spall and delamination. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue tests were carried out using plates with microholes (diameter was about 100 μm and depth was about 140 μm) under three different loads (maximum values of Hertzian stress were about 3250, 3550 and 3840 MPa, respectively) and the surface cracks initiating from those holes were observed. It was found that there is a threshold value of maximum Hertzian stress whether surface cracks originate from microholes or not, and its value is between 3250 and 3550 MPa. However, flaking failures occurred even when the stress values were lower than the threshold value. In order to investigate the relation between the flaking failures and the cracks, sectional observations of the subsurface cracks were made before and after the surface layer separations. From these observations, it was found that the subsurface cracks caused the flaking failures even when the maximum value of Hertzian stress was lower than the threshold value of surface crack initiation. [ABSTRACT FROM AUTHOR]

Investigations into the causes of damage to rail heads and on rolling contact fatigue, date back a considerable time and are described in a large number of expertise literature on the many different aspects of this complex problem. The present paper is prompted by the naïve observation that fatigue crack propagation is more likely to occur in a tensile stress environment than in a highly compressive one and it therefore seeks to locate a region of radial or longitudinal tensile stresses on a rail head during the rectilinear motion of the train, providing favourable conditions for mode I or mixed-mode crack propagation. [ABSTRACT FROM AUTHOR]

Investigations concerning surface crack growth are necessary for understanding the mechanism of rolling contact fatigue (RCF) of bearings because the surface defects cause flaking failures. In the present work, micro holes were artificially made prior to the RCF tests and the initiation of the surface cracks from the micro holes was observed in order to find the key factors for understanding their features. Crack initiation directions were compared to the stress intensity factors calculated by a simple method based on the √area theory. The extent to which 'contact pressure (wedge effect)' and 'contact stresses' are applicable for understanding the correlations between the crack initiation directions and stress intensity factors is discussed. The crack initiation directions are strongly correlated to the stress intensity factors caused by the contact stresses alone. We concluded that the crack growth and initiation are dominated by stress intensity factors caused by contact stresses rather than the wedge effect. [ABSTRACT FROM AUTHOR]

Plastic flow of near-surface rail material under contact loading is a feature of rail–wheel contact, and severe flow typically leads to both wear, and the initiation and development of small surface-breaking cracks. This paper presents results from a ratcheting based computer simulation, which has been developed to allow the simultaneous investigation of wear, crack initiation and early crack propagation. To identify repeatably small crack-like flaws, image analysis is applied to the visual representation of the wearing surface generated by the model. This representation shows a good similarity to traditional micrographs taken from sections of worn surfaces. The model clearly reveals the interaction of wear with crack development, processes which are linked because wear truncates surface-breaking cracks, and can completely remove small surface-breaking cracks. [ABSTRACT FROM AUTHOR]

Various kinds of defects are induced by rolling contact on the rail track: kidney-shaped cracking, shelling and nowadays squat and head checking, which are studied under the sponsorship of the French national railways company SNCF. Modelling of such defects requires the development of specific computational tools in order to evaluate, in the vicinity of the wheel–rail contact zone, the mechanical state (stress, plastic strain cycle and residual stress pattern), which is at the origin of the damages. Moreover, since the loadings induce multiaxial stress and strain states, it is necessary to use a multiaxial criterion to predict the occurrence of fatigue cracks. This review paper is devoted to the presentation of the main results of this research. [ABSTRACT FROM AUTHOR]

This paper summarizes the forces that develop in the contact patch between the wheel and rail in a railway vehicle. The ways that these forces govern the behaviour of a vehicle running on straight and curved track are explained and the methods commonly used to calculate and utilize the forces summarized. As an illustration, the results from a computer simulation of a typical UK passenger train are presented and certain aspects examined. [ABSTRACT FROM AUTHOR]

The flash temperature in an asperity of the rail due the wheel–rail rolling contact is investigated. First the contact configuration and the total heat produced are explained. Then approaches to heat partitioning between the two contacting bodies are discussed. A new heat partitioning factor is derived for the case of frictional heating and heating due to plastic deformation, thereby taking into account the roughness of the contacting surfaces by a contact intensity factor distribution as well as the local pressure intensification by individual asperities. Several roughness distributions are studied. Finally, an explicit calculation is outlined of the asperity flash temperature at the end of the contact, expressed by two temperatures and two factors contributing to the partitioning of heat between the contacting bodies. [ABSTRACT FROM AUTHOR]

A computer model, which simulates the ratcheting wear of a ductile material subject to repeated loading, is presented and discussed in detail. Variation of material properties is a feature of the model, failure by ductility exhaustion occurring at isolated points or extending regions of failure. Such regions form crack-like features. Mechanisms for removal of weakened material from the surface as wear debris are described. The wear process causes a degree of surface roughness. The simplicity of the model enables simulation of millions of load cycles in only a few hours' computer time. The computer model is used to study the effect of partial slip on wear rate. When creepage is relatively low, the wear rate increases sharply with creepage. When creepage is relatively high, the wear rate is largely insensitive to the creepage. [ABSTRACT FROM AUTHOR]

Two-dimensional elastic-plastic finite element (FE) simulations of a rolling contact problem are presented. The objective was to evaluate three elastic-plastic material models, all of them able to simulate decay in ratchetting rate, by studying the cyclic ratchetting material response and failure of a pearlitic rail steel. The FE simulation, which were performed for different magnitudes of contact pressure and traction forces showed a large accumulation of shear deformation of the surface at the rolling contact. The critical plane (crack plane) for crack initiation on the crack planes was calculated using this model, as well as an empirical model for failure by ratchetting, for comparison. The results from the evaluation of the three material models show that the material model which could best mimic the stress-strain cycles and ratchetting rate, from cyclic uniaxial experiments, was also able to resolve the stress and strain field correctly in the FE simulations and to give reliable results. Low-cycle fatigue governed fatigue crack initiations, and the angles calculated for the crack plane showed good agreement with observations from experiments. [ABSTRACT FROM AUTHOR]

Twin-disc contact simulation tests were carried out to investigate the influence of contact pressure variation on rail steel fatigue life. Both a colloidal suspension of molybdenum disulphide in an oil carrier fluid (similar to a commercial flange lubrication product) and water were used as lubricants. It was found that the reduction from 1500 to 900 MPa of the maximum Hertzian contact pressure (at which a molybdenum–disulphide-lubricated and previously worn rail sample was tested) extended the fatigue life of the rail steel by over five times. For water lubrication a similar reduction in contact pressure produced only a marginal increase in fatigue life. The results were found to be in qualitative agreement with the predictions of the newly developed Three Mechanism (TM) model of rolling contact fatigue, which is introduced here. This model combines the mechanisms of ratcheting and the fracture mechanics-based mechanisms of both shear stress- and tensile stress-driven, fluid-assisted, crack growth. [ABSTRACT FROM AUTHOR]

The analysis is based on the 3D FE model of the rail Rolling-Contact-Fatigue (RCF) ‘squat’-type crack, which tends to be common in tracks with high-speed passengers and mixed traffic. The model incorporates the section of rail and a wheel of real geometry, in which the wheel is rolling over the running band of rail containing the ‘squat’-type crack. The state of stress in the vicinity of the crack front is determined, and consequently the values and ranges of the stress intensity factors (SIFs) KI , KII and KIII at the crack front are calculated for the cycle of rolling. To simulate loading conditions occurring in practice, residual, bending and thermal stresses acting in the presence of the tractive force were taken into account. The results indicate a significant role of face friction and tractive force in the loading mechanism at the ‘squat’. The longitudinal and lateral residual stresses may also influence the loading cycles, especially for the cases with reduced friction between the crack faces. Reduction of the face friction coefficient to values close to zero creates conditions for crack propagation driven by the shear mode mechanism. These results were obtained under a project sponsored by the ERRI D173 Committee, Utrecht, The Netherlands. [ABSTRACT FROM AUTHOR]

Rolling is simulated by a three-dimensional finite-element model with elastoplastic constitutive equations. The use of an explicit finite-element formulation, instead of the more commonly used implicit formulation, has reduced the required computing time. The larger of the models used is one step towards a general and complete computational model of rolling. Results from experiments and from two- and three-dimensional calculations are compared. [ABSTRACT FROM AUTHOR]

This paper considers H ∞ control design of a magnetic bearing from the viewpoint of loop shaping- Feedback control is indispensable for a magnetic bearing, since it is essentially an unstable system. For feedback control, a mathematical model is required- However, it does not always express the exact behavior of the system, hence the mode] has various uncertainties such as the errors of parameters, neglected nonlinearities, or unmodeled dynamics. The controller is needed to guarantee robustness for both stability and performance against these uncertainties on the model First, based on some assumptions, a linear state space model of a magnetic bearing is shown. Second, the experimental machine and the surroundings of its controller are introduced- The experimental machine is a 4-axis controlled horizontal shaft magnetic bearing. The controller consists of a digital signal processor with fast A/D converters and D/A converters. Third, the control system is designed using normalized coprime factor plant descriptions. Selecting shaping functions in this procedure called "The Loop-Shaping Design Procedure (LSDP)," shape the open-loop transfer function and the transfer functions of the closed-loop system can be shaped. Finally, several experiments are carried out according to the aforementioned designed controller. [ABSTRACT FROM AUTHOR]

Abstract: Contact mechanics is a branch of solid mechanics where two or more bodies are involved. The contacting points are characterized by a common tangential plane and a common normal vector given by the surface curvature of the bodies. Additional parameters of contact problems are the material of the bodies, the forces and torques acting on the bodies as well as their time history, location of the centers of mass and the roughness of the surface around the contact point. The classical contact problem is based on spherical bodies surfaces, linear‐elastic material, constant static loading in normal direction and smooth surfaces. The rigorous solution [1] is often used for benchmarking. More details can be found in the monographs [2, 3]. The bodies of mechanical systems in engineering applications get in contact to each other mainly by impacts, rolling or sliding, or by joints. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We introduce a dynamic friction model for the pre-sliding behavior of a single asperity subjected to a constant normal and a varying tangential load based on Cattaneo-Mindlin's theory. The geometry of an arbitrary, axisymmetric asperity is included in the formulation of the governing differential equation. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A universal friction law for turbulent boundary layers on a flat plate with suction is established. Experimental skin-friction distributions obtained for various suction factors and Reynolds numbers are described in similarity variables by a single universal curve. The law is valid for the entire range of suction velocities from zero one till the limiting values corresponding to asymptotic-suction boundary layers. The analysis is not based on any particular turbulence model. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Ancorsteel1000C is commonly used for important components including bearing rollers, gears, connecting rods, wheels and rails; most failures of these components are caused by rolling contact fatigue (RCF). In this study the fatigue damage indicator based on Fatemi-Socie critical plane were determined in a local hot spot area in finite element (FE) model in case of Hertzian stress with zero slip condition. The simulation results compared with respect to experimental data, which is in good agreement. Therefore, this approach can be implemented as a useful tool for lifetime calculations in RCF in the process of structure fatigue design. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Coulomb friction problems can be stated as quasi-variational inequalities. These are variational expressions of certain non-smooth pseudo-potentials which have to be minimized in the sense of a two-person non-cooperative constrained game, consisting of the normal and the tangential player. In this paper we show that spatial Coulomb friction applied to the rolling contact problem in rigid body dynamics may be formulated as a nonlinear complementarity problem in standard form, i.e. as 0 ≤ x f(x) ≥ 0 with continuous and differentiable x → f(x). [ABSTRACT FROM AUTHOR]

Flaking failure caused by surface cracks of silicon nitride ceramic bearings has been investigated from the viewpoint of the ring crack model. However, the relation between surface and subsurface cracks under rolling contact fatigue is not fully understood. In this investigation subsurface cracks branching from an initial surface crack were observed in detail, and the process of flaking failure was investigated. The specimens were observed prior to the separation of the surface layers and it was found that the initial surface cracks grew vertically to the surfaces and did not curve as predicted by the ring crack model. Subsurface cracks branched from the single surface cracks and grew in a direction parallel to the surface. They grew in both the same and opposite directions to the ball movement, with small upward and downward branches. These subsurface cracks grew prior to the semi-circular surface cracks. From these observations it was concluded that the flaking failures are not caused directly by surface cracks, but by subsurface cracks that branch from them. [ABSTRACT FROM AUTHOR]