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

Railway systems play a pivotal role in modern transportation networks, contributing to both efficiency and environmental sustainability. This study investigated the multifaceted aspects of wear phenomena in railway engineering, focusing on their significant implications for environmental costs and operational efficiency. Experimental trials were conducted using a high-performance bi-disc apparatus, evaluating a range of materials, contact pressures, and lubrication conditions. Shakedown maps were employed to assess ratcheting behaviour, while the wear rate was analysed as a function of the fatigue index (FI). The results reveal the intricate interplay of contact pressure, slip ratio, material properties, and lubrication in determining wear and ratcheting behaviour. Oxidative and mild wear mechanisms were identified, and wear debris composition and morphology were characterised. The outcomes from this research clarify the pivotal role that wear processes play within railway systems and the far-reaching environmental repercussions they entail. This exploration contributes to the ongoing optimisation of railway operations, offering valuable insights aimed at mitigating unavoidable pollution sources and strengthening sustainability efforts. By delving into the intricate dynamics of wear phenomena within wheel–rail material, this research paves the way for innovative solutions that not only enhance operational efficiency but also minimise the ecological footprint of railway transportation. [ABSTRACT FROM AUTHOR]

When high-speed trains operate under braking conditions, the wheel-rail interaction increases significantly, which can lead to more serious wear problems. To analyze the evolution of wheel wear and the dynamic characteristics of wheel-rail under braking conditions, this paper first carries out long-term monitoring of the service state of wheel-rail during the operation period. The study analyzed the matching characteristics of the measured wheel-rail profile and calibrated the wear model by using the collected data. The resulting wear prediction model was then used to examine the wheel wear characteristics under braking conditions. The research results indicate that during the operation period, the wheel experiences tread concave wear within a range of ±20 mm of the rolling circle, at a rate of approximately 0.05 mm per 10,000 km. Meanwhile, the rail experiences top surface wear at a natural rate of about 0.09 mm per year. Concave wear causes the contact point of the wheel-rail to appear in two zones, resulting in a sudden change of contact geometric parameters. The concave worn wheel and rail with a 60 N profile have better matching compared to the 60 rail profile. Increasing the braking torque and wheel-rail friction coefficient will significantly increase the wheel wear depth on straight sections. On small-radius curve sections, rail side lubrication can significantly reduce high rail side wheel flange wear. A worn concave wheel can lead to unfavorable wheel-rail contact geometry characteristics and increase low-frequency components in the vehicle's lateral dynamic response. [ABSTRACT FROM AUTHOR]

This paper is concerned with the modeling of power dissipation due to friction and its relation with wear estimation in wheel–rail contact. Wear is a complex multi-scale and multi-physical phenomenon appearing in rolling contact. Wear is generated by high contact stress and the work of friction forces. This phenomenon leads to the appearing of the worn material in the form of wear debris between contacting surfaces. In contact models, wear is usually described in terms of the wear depth function. This function modifies the gap between the contacting bodies as well as the shape of the surfaces of the wheel and rail in contact. In this paper, besides the wear depth function, the dissipated energy, rather than the contact stress, is taken into account to evaluate the wear impact on rail or wheel surfaces. The dissipated energy allows us to more precisely evaluate the wear debris amount as well as the depth of wear and its distribution along the contact interface. A two-dimensional rolling contact problem with frictional heat flow is considered. The elasto-plastic deformation of the rail is considered. This contact problem is governed by a coupled system of mechanical and thermal equations in terms of generalized stresses, displacement and temperature. The finite element method is used to discretize this problem. A discretized system of equations with nonpenetration and friction conditions is transformed and formulated as a nonlinear complementarity problem. The generalized Newton method is applied to numerically solve this mechanical subproblem. The Cholesky method is used to find the solution of the heat-conductive problem. The dissipated power is evaluated based on the resultant force and slip at a reference point. Numerical results including the distribution of slip velocity, power factor and wear rate are provided and discussed. [ABSTRACT FROM AUTHOR]

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Urban rail transit usually contains many small radius curved tracks, and wheel flange wear is prominent, which greatly reduces the service life and increases the maintenance and replacement costs of wheelsets. Two metro lines in Shanghai of China had suffered from severe flange wear since 2017, and the flange wear rate increased gradually over the next three years. This paper presents the understanding and treatment of severe flange wear through field measurement and numerical simulation. The investigation results indicated that the key factors causing severe flange wear were poor rail gauge face lubrication, the use of a low conicity wheel profile for trains running on the two metro lines containing many small radius curved tracks, and the lack of timely maintenance of low rail profiles. Three countermeasures were proposed to mitigate wheel flange wear, which were evaluated through wheel–rail matching analysis and wheel wear prediction. Then, two countermeasures, i.e. improving rail gauge face lubrication and employing the LM-30 wheel profile, were verified through field tests. [ABSTRACT FROM AUTHOR]

Purpose: The CL60 steel wheels of subway vehicles operating on specific lines require frequent refurbishment due to rapid wear and tear. Considering this issue, MoS2-based and graphite-based solid lubricants are used to reduce the wear rate of subway wheels and extend their service life. Design/methodology/approach: Under laboratory conditions, the effect of MoS2-based and graphite-based solid lubricants on the friction and wear performance of subway wheels and rails was evaluated using a modified GPM-60 wear testing machine. Findings: Under laboratory conditions, MoS2-based solid lubricants have the best effect in reducing wheel/rail wear, compared to the control group without lubrication, at 2 × 105 revolutions, the total wheel-rail wear decreased by 95.07%. However, when three types of solid lubricants are used separately, the hardness evolution of the wheel-rail contact surface exhibits different characteristics. Practical implications: The research results provide important support for improving the lifespan of wheel and rail, extending the service cycle of wheel and rail, reducing the operating costs of subway systems, improving the safety of subway systems and providing wear reduction maintenance for other high wear mechanical components. Originality/value: The experiment was conducted through the design and modification of a GPM-60 testing machine for wear testing. The experiment simulated the wheel-rail contact situation under actual subway operation and evaluated the effects of three different solid lubricants, MoS2-based and graphite-based, on the wear performance and surface hardening evolution of subway wheel-rail. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to examine the practicability of the self-designed ambient humidity controllable pin-disc/rolling multifunctional friction and wear test device and to evaluate the friction and wear characteristics of materials under diverse ambient humidity conditions in different contact forms. Design/methodology/approach: The practicability of the self-designed multifunctional friction tester was examined by the friction and wear tests of materials under different ambient humidity conditions [65%RH, 98%RH (relative humidity)] in diverse contact forms (pin/disc and rolling). Meanwhile, the friction and wear properties of pin/disc samples also rolling samples were assessed from three aspects: average friction coefficient, wear mass and wear morphology. Findings: The results prove that the self-designed multifunctional friction tester has practicability. Therefore, it can be used to simulate the friction and wear tests of materials under diverse ambient humidity conditions in different contact forms. Besides, it is evident that the wear damage of pin/disc and rolling samples are greatly improved under high ambient humidity conditions. And when other conditions are identical, the higher the ambient humidity, the smaller the average friction coefficient, wear mass and wear damage degree of pin/disc also rolling samples. Originality/value: This paper offers a self-designed multifunctional friction and wear test device. And the tester not only can realize the control of test ambient humidity, but also achieve the wear test of pin/disc or rolling contact forms. The design and production of the tester can offer convenience for the research of tribology, and provide fundamental guidance for the study of materials under high humidity condition in diverse contact forms. [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]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Most of the published documents on the friction and wear properties of textured contact surfaces with partially distributed units (e.g., dots, grooves) are focused on sliding tribo-pairs or journal bearings. To study the friction and wear performance of rolling bearings with different distributions of pits, several patterns were introduced: OS-1/4 (Outside, 1/4 of raceway), OS-1/2 (Outside, 1/2 of raceway), OS-3/4 (Outside, 3/4 of raceway), IS-1/4 (Inside, 1/4 of raceway), IS-1/2 (Inside, 1/2 of raceway), IS-3/4 (Inside, 3/4 of raceway), TS (Two sides, 2/3 of raceway), FT (fully textured) and SR (Smooth reference), with two circumferential interval angles (CFIAs, 1.5° and 2.0°). The dimensions of the pits are the same in all patterns (diameter of 300 μm and depth of 15 μm), which were only prepared on the raceways of the shaft washers of 81107 bearings (nylon cages) using the laser marking method. All bearings were tested under 4000 N, 250 RPM and starved lubrication using a vertical universal wear test rig. Their mass losses and worn raceways were measured and observed. Their surface equivalent stresses were also analyzed and compared. The obtained results show that the influence of different distributions of pits on the tribological properties of rolling bearings is significant. The friction-reducing and anti-wear performance of TS is acceptable, whether the CFIA is 1.5° or 2.0°. A fully textured pattern cannot provide the best tribological properties and its behavior even becomes worse when the CFIA is 2.0°. In this work, when the CFIA is 1.5°, the friction-reducing and anti-wear performance of OS-1/4 is the best among all patterns. Using a smooth reference as a benchmark for comparison, its friction-reducing and anti-wear performance can be enhanced by 60.46% and 16.05%, respectively. The results of this work will be an important reference for the optimal design of the "washers-cage-rollers" contact system for rolling bearings. [ABSTRACT FROM AUTHOR]

The friction and wear performance of high-performance bearings directly affects the accuracy and maneuverability of weapons and equipment. In this study, high-speed, high-temperature, and heavy-load durability experiments of weapon bearings were carried out, and their wear properties (i.e., surface wear, metamorphic layer, scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), residual stress, and retained austenite) were analyzed in multiple dimensions. The results showed the following: (1) The experimental temperature of the serviced front-end bearing is always lower than that of the rear bearing. (2) The metamorphic layer of the serviced rear bearing (i.e., inner ring, outer ring, rolling body, and cage) > the metamorphic layer of the serviced front-end bearing > the metamorphic layer of the unserviced bearing. (3) The rolling body of the rear bearing at high experimental temperatures contains not only elemental O, but also elemental P and Sr. (4) In the EDS analysis of the rolling elements, with the migration from the "ball edge" to the "ball center", the elemental C in the rolling elements of serviced or unserviced bearings decreases slowly, while the elemental Fe content increases slowly. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Differing from the published documents on the effect of texture distributions of sliding tribo-pairs on their friction and wear properties, this study introduced eight patterns to reveal the influence of different distributions of pits on the tribological behavior of textured rolling element bearings with nylon cages under dry condition, namely: Outside-1/4 (OS1/4), Outside-1/2 (OS1/2), Outside-3/4 (OS3/4), Inside-1/4 (IS1/4), Inside-1/2 (IS1/2), Inside-3/4 (IS3/4), Bothside-1/3 (BS) and full (FP). A fiber laser marking system was used to prepare them on the raceways of the shaft washers of cylindrical roller thrust bearings (81107TN). A vertical universal wear test rig was used to obtain their coefficients of friction under an axial load of 2600 N and a rotating speed of 250 RPM, without any lubricant provided. Their wear losses and worn surfaces were characterized. The influence mechanism of different distributions on the tribological properties was also discussed. The results show that the self-lubricating performance of nylon cages can ensure the continuous operation (≥5 h) of cylindrical roller thrust bearings under dry condition. The influence of outside-distributed patterns on the friction and wear properties of bearings is significant. The friction-reducing effect and wear resistance of full textured group is improved but not the best. The friction-reducing and anti-wear behavior of OS1/2 is similar to that of FP. In this work, OS3/4 can provide the best tribological performance under self-lubricating conditions. Compared with the data of smooth bearings, its average coefficient of friction and wear loss can be reduced by 37.68% and 38.85%, respectively. This work would provide a valuable reference for the raceway design and reliability optimization of rolling element bearings. [ABSTRACT FROM AUTHOR]

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

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]

Rail corrugation is very serious in Cologne egg fastener track; effective control measures are still lacking. The cause of the corrugation wear on a curved metro track is analyzed based on the friction-induced vibration theory. A finite element model is established to study the frequency domain and time domain features of the friction-induced oscillation of this system. The influences of the fastener spacing and the fastener support length on the corrugation wear are investigated to develop countermeasures. The simulation results show that the friction-induced vibration of the wheel-track system is the wavelength-fixed mechanism of the corrugation wear of rail of the curved Cologne egg fastener track. There are two reasons why the low rail corrugation wear is more serious. The contact resultant force between the low rail and the wheel is obviously bigger than that between the wheel and the high rail, resulting in a higher wear rate of the low rail. The contact force fluctuation of the low rail caused by the friction-induced vibration is more severe, resulting in a higher corrugation wear evolution speed on the low rail. The friction-induced oscillation cannot be eliminated only by adjusting the fastener support length and spacing. However, the long-wavelength corrugation wear instead of the more harmful short-wavelength corrugation wear can be produced by adjusting the fastener support length and the fastener spacing to alleviate the influence of corrugation wear on the vehicle-track system. [ABSTRACT FROM AUTHOR]

In order to study the rail corrugation phenomenon with the wavelength of 160-250mm in the steel spring floating slab track of a certain subway straight section, a rigid-flexible coupling dynamics model of the vehicle-steel spring floating slab track is established based on the finite element theory and the vehicle-track coupling dynamics theory. From the point of view of the vibration characteristics of track system and the contact characteristics of wheel and rail, the causes and mitigation measures of rail wave wear are studied by taking the rail wear power as the evaluation index. The generation of rail corrugation may be related to the transverse co-direction/reverse bending vibration modes of the rails on the left and right sides of the 8-15 order, the vertical bending mode of the track plate of the 8-9 order, and the torsional vibration mode of the track plate of the 6-8 order. Under the premise of not affecting driving safety, wear power at the rail wave wear frequency can be reduced by taking the vertical stiffness of the fastener 10~30 MN/ m, the vertical damping of the fastener more than 20 kN·s/m or the lateral damping of the fastener 30 kN·s/m, so as to slow down the development of rail wave wear. [ABSTRACT FROM AUTHOR]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this article, the effect of rotational speed on the subsurface microstructure and wear property of D2/U71Mn wheel–rail steel is studied under pure rolling conditions. Rolling wear experiments were conducted using a GPM-40 rolling wear tester. The subsurface microstructure and surface morphology of the wheel and rail samples under different rotational speed conditions were analyzed using an optical microscope and field emission scanning electron microscopy. The results showed that the rotational speed significantly influences the wear property of the wheel materials. A low rotational speed could increase the friction stress at the wheel–rail contact surface, and the weight loss of the wheel sample was large under low rotational speeds. As the rotational speed increased, the weight loss of the wheel sample decreased gradually, but the change in the weight loss of the rail sample was not obvious. The thickness of the plastic deformation layer of the wheel sample increased as the rotational speed increased. However, the variation of the plastic deformation layer of the rail sample was not obvious. During the rolling wear process, a gradient plastic deformation layer (the surface was a severe plastic deformation layer, and the subsurface was a plastic flow layer) was formed at the wheel–rail sample surface. In the severe plastic deformation layer, ferrite grains were refined obviously, and lamellar cementite was fragmented into cementite particles. In the plastic flow layer, the ferrite grains produced obvious plastic deformation, but the change in the lamellar cementite was not obvious. During the rolling wear process, the relationship between wear and fatigue was competitive. Under low rotational speed conditions, the high weight loss of the wheel sample could inhibit the formation of fatigue cracks. As the rotational speed increased, the weight loss of the wheel sample decreased gradually, and the length of the fatigue cracks increased. The wear mechanism of the wheel sample transformed into fatigue wear. However, the surface worn morphology of the rail sample had no significant change under 600-r/min and 1000-r/min conditions. The length of fatigue cracks of the rail sample is slightly reduced under the 1440-r/min condition due to the increase of a small amount of weight loss. [ABSTRACT FROM AUTHOR]

Wheel wear is a natural phenomenon of wheel–rail rolling contact during vehicle operation. The non-uniform wear in lateral and circumferential directions is normally occurred on wheels. The lateral non-uniform wear will lead to the unexpected hollow wear which can cause flange to flange vibration at low-frequency band, and the circumferential non-uniform wear will result in the vertical vibration which is the originate from the polygon phenomenon. These two forms of wear are coupled to each other on wheels and affect the dynamic behaviours of wheel–rail system. In this paper, a wheel–rail contact dynamics model which includes the 3D geometric shape of wheel profile is established and employed to vehicle system dynamics. The results show that the contact mechanical properties of wheel–rail are greatly affected by the 3D wheel profile. The low-frequency vibration of wheelset caused by hollow wear and the high-frequency vibration by polygonised wear are coupled, which increase the vibrational acceleration of wheel–rail system and even made for the main problem of the periodic separation of wheel and rail and aggravate the wear of wheel polygon. [ABSTRACT FROM AUTHOR]

A train experiences different slip ratios at the wheel/rail contact point as it moves along the rail track, which influences the rolling contact fatigue (RCF) and wear properties of wheel and rail materials. This variation in slip ratios is caused by a change in contact area between the wheel and rail head at curves, as the slip ratio increases compared with when a train is moving on a straight track. When the train is moving on a straight track, the wheel is found to be in contact with the rail head; but that changes when moving around curves, as the wheel flange will now be in contact with the gauge corner of the rail, affecting the severity of wear. Therefore, more research needs to be done to understand the role that slip ratio plays in the wear performance of wheel and rail materials in order to be able to develop models or systems that could be used to predict preventive maintenance. The aim of this work was to investigate the effect of the slip ratio on the wear performance of class B wheels against softer R260 rail steels under rolling and sliding conditions, using a twin-disc setup developed at the University of Pretoria. The results showed that the severity of wear was heavily dependent on the slip ratio - i.e., it increased with the slip ratio, with class B wheels performing better than the softer R260 rail. [ABSTRACT FROM AUTHOR]

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

Rolling contact fatigue (RCF) and wear are important problems for the wheel and rail. RCF and wear is caused by contact stress and the slip ratio between the wheel and the rail. The material properties of the wheel and rail are an important factor to prevent the degradation caused by RCF and wear. In this study, the mechanical properties and fatigue characteristics of the two types of wheel and rail were evaluated, and the effects on wear and contact fatigue were examined. We found that the crack growth rate and the hardness were important factors in the contact fatigue and the wear. The rail steel with a higher crack growth rate and hardness had a low resistance to contact fatigue with large size damage. The hardness ratio and the total hardness are important factors in evaluating the wear resistance. In addition, we found that the residual stress increased proportionally to the maximum shear stress. [ABSTRACT FROM AUTHOR]

To serve in a corrosive environment, a corrosion-resistant rail steel U68CuCr has been developed in China. In the present study, the wear behavior of U68CuCr was investigated and compared with the commonly used rail steel U71MnG by rolling contact friction tests. The results indicate that the mass loss and wear rate of U68CuCr are smaller than those of U71MnG. The wear rates under the dry condition are smaller than those under the water–oil condition. In addition, the formation of oxide and spalling finally achieves the dynamic equilibrium on the surface of two types of rail steels. However, the duration of the lubricative and protective wear debris layer is longer for U68CuCr. Moreover, the worn surface of U68CuCr is relatively flat, while the wear regime of U71MnG is more severe. The amount and volume of the spalling pits of U68CuCr are smaller. Furthermore, the plastic deformation layers are shallower, and the rolling contact fatigue cracks are shorter for U68CuCr because of the finer pearlitic microstructure. The results prove that the U68CuCr rail steel shows good wear-resistant ability, suggesting its superior suitability for application in high-speed railways in a marine environment. [ABSTRACT FROM AUTHOR]

This paper provides experimental data on the effective use of a new lubricating composition, which includes industrial oil of any brand with the addition of a nanometal of the component of a friction pair, which has a lower hardness. It is shown that this composition significantly reduces the wear resistance of the rails and wheels of rolling stock during operation, prevents electrochemical corrosion of the friction pair wheel–rail and, most importantly, stabilizes the coefficient of friction at the optimum level after a relatively short operating time. The experiments were performed on the friction pair, "sample of the bandage material of the railway wheel—a sample of the rail material", with a ratio of hardness of the bandage material (Rockwell hardness, HRC scale—35.3) to the hardness of the rail material of 1.1. Test results show that in the case of industrial lubricant, the BioRail brand, with the addition of a nanomaterial friction pair with lower wear hardness of the rail metal sample, after three hours in operation the wear was practically not observed. Moreover, the average value of the friction coefficient for three hours of operation was maintained at the level 0.25, which is optimal for the friction pair wheel–rail. Similar experiments using only the same lubricant brand showed much worse results. [ABSTRACT FROM AUTHOR]

Majority of the rolling contacts applied in complex interacting machine elements for example bearings and gears perform under Mixed Lubricating (ML) conditions, where the lubricant film can’t fully separate the asperities of the two contacting surfaces. Highly loaded, interacting asperity surrounded with lubricant film, leads to the development of surface originated defects such as scuffing, micropitting, and wear in the ML region. This region exists amid Elastohydrodynamic Lubrication and Boundary Lubrication which needs consolidated knowledge of fluid film and direct contact of asperities, this makes the problem more difficult to solve numerically. Numerous authors have used the Reynolds equation or its modified versions to solve the lubrication problem numerically. However, still, some uncertainty is there to model mixed lubrication operating conditions, with traditional Reynold’s equation, because the assumptions commonly made in Elastohydrodynamic lubrication are not valid within the context of mixed lubrication regime. In this paper previously, used models for mixed lubrication have been examined, and various development in related fields are discussed. Therefore, this review will provide an integrated, synthesized overview of the topic and in turn will lead to benefits for wide-ranging academic, industrial and research communities. [ABSTRACT FROM AUTHOR]

Metro trains often encounter the problem of wheel flange wear when they pass through sharp curves, especially for the poor wheel–rail profile matching or lack of lubrication, evidently increasing the maintenance and replacement costs for wheelsets and rails. Based on the field investigation and numerical simulation, the cause of severe flange wear of the original S1002 wheel profile on a Chinese metro line is analysed. An optimised wheel profile is proposed according to the rolling radius difference (RRD) for improving vehicle curving performance and mitigating wheel flange wear. A wheel wear prediction model is developed by combining the metro vehicle dynamics model considering multipoint contact with the long-term wear simulation model, and then validated with the field measurement results. The performance of the optimised wheel profile is evaluated numerically. The results indicate that the root cause of the wheel flange wear is the improper matching of wheel and rail profiles. The optimised wheel profile generally proves to perform better in terms of wheel–rail contact geometry, mechanical properties, vehicle running stability, curving negotiation and wear performance. The wheel flange thickness loss of the optimised wheel profile is decreased by 55.7% compared with that of S1002 profile. [ABSTRACT FROM AUTHOR]

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

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

• 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]

A suitably designed rail cant can improve the wheel-rail alignment, effectively reduce the wheel-rail contact pressure and reduce the wheel-rail wear. However, the rail base cant has rarely been specifically designed for suppressing rail corrugation. Furthermore, no studies have yet been conducted on using different inner and outer rail cants in small-radius curve sections from the perspective of suppressing rail corrugations and wear. In this study, the growth rate index of rail corrugation is obtained by combining an impact hammer origin admittance test and a coupled vehicle-track multi-body dynamic model simulations. The wear depth of rail surface is obtained by combining a three-dimensional transient wheel-rail rolling contact model and Archard wear theory. From the overall perspective of preventing rail corrugation and slowing down rail wear, based on the multi-objective optimization using a particle swarm optimization algorithm, the optimal configuration of inner and outer rail cants in a small-radius curve section were determined as 1/22 and 1/40, respectively, which provided effective suppression of rail corrugation initiation and further development of rail wear. • Research on the setting of asymmetric rail cant for small radius curves • Exploring the relationship between asymmetric rail cant and rail corrugation • Obtaining the optimal configuration of inner and outer rail cants for comprehensive rail corrugation and wear [ABSTRACT FROM AUTHOR]

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

• 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]

During the damage and defects related to rolling contact fatigue (RCF), together with wear occurring at the rail surface, the microscopic characteristics of the rail material change with the accumulation of wheel cycles. To find the relationship between rail material characteristics and RCF damage under wheel-rail contact situations, a series of twin-disc rolling-sliding tests, based on real wheel-rail contact situations at a radius of 80 mm rail profile, was established for a heavy-haul railway in China. The microscale characteristics of the rail disc contact surface was researched, including crack, wear, roughness, and hardness of the U75V rail with different load cycles. The results show that the damage mechanism of RCF and wear alternately dominates the rail disc surface at the microscale, taking a certain cycle as a boundary which makes the RCF crack number and wear rate have opposite evolutionary trends. The above factors also affect the wear at the surface rail discs, alternating between fatigue and adhesion. Meanwhile, increasing the surface micro-hardness leads to a decrease in the relative wear rate and an increase in the roughness, length and number of RCF cracks. The plastic deformation layers, including the severely deformed layer (SDL) and the transition layer (TL), almost maintain the same thickness and the dynamic equilibrium increases during the cycles. Two kinds of cracks are initiated and propagated at the rail disc surface, one at the SDL and the other at the junction of SDL and TL. The number of each kind of crack depends on the SDL thickness. • The RCF and wear mechanisms dominated the rail surface alternately by a certain cycle. • Increasing the microhardness makes wear decreasing followed by an increase in roughness and RCF cracks. • The adhesive and fatigue wear happened alternately during the cycles. • The fracture mode of along or through the crystal depends on plastic deformation layer. • The thickness of the severely deformed and transition layers changes on opposite while keeps the entire thickness constant. [ABSTRACT FROM AUTHOR]

During the operation of freight cars, uneven wear occurs in the central bowl of the rail truck bolster. This article aims to determine the concentration of the filler of the composite material to reduce the wear of the central bowl of the rail truck bolster. In this work, for the first time, a mathematical model of the distribution of the filler concentration in the projected composite tape was obtained. To reduce the wear of the working surface of the central bowl of the rail truck bolster, as well as to ensure uniform wear distribution, it is proposed to weld a composite tape with variable tribomechanical properties using contact welding. The wear value of the working surface of the central bowl of the bolster of the rail truck bolster when using composite tapes of compositions Fe-Cr-Ni-Cr 3 C 2 and Fe-Cr-Ni-TiC with contact welding was 0.15–0.18 mm per 10,000 km - for a loaded freight car and 0.08–0.10 mm per 10,000 km for an empty freight car. According to the amount of wear, the value of the service life of the center plate assembly is predicted, which is 320,000–420,000 km. [ABSTRACT FROM AUTHOR]

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Purpose: The purpose of this paper is to reveal the friction and wear performance of grooves textured cylindrical roller thrust bearings with different groove dimensions under starved lubrication. Design/methodology/approach: The groove dimensions include: width of grooves (WOG, 50 µm, 100 µm and 150 µm), depth of grooves (DPOG, 7 µm, 11 µm and 15 µm) as well as groove deflection angle (GDA, 45°). A fiber laser marking system was used to prepare groove patterns on the raceways of shaft washers. The friction and wear properties of grooves textured bearings were researched through a vertical universal wear test rig using a customized roller bearing tribo-pair under starved lubrication. Static finite element analyses were conducted to reveal their surface stresses. Through the comprehensive comparison and analyses, the influence mechanism of grooves on the tribological behavior of cylindrical roller thrust bearings was proposed and discussed. Findings: When grooves textured bearings run under starved lubrication, their average coefficients of friction (COFs) and wear losses are all significantly reduced and much lower than those of smooth group. The influence of DPOG on the COF curves is significant, while the influence of WOG on the COF curves is a little weak. The influence of groove dimensions on the surface stresses of grooves textured bearings is weak, whether the WOG or DPOG. In this work, when the WOG is 100 µm and the DPOG is 15 µm, its average COF and wear loss are both the lowest, 0.0066 and 0.61 mg, respectively. Compared with the data of smooth group, its friction coefficient is reduced by 75.3% and its mass loss is reduced by 95.8%, showing a significant improvement in this condition. Originality/value: This work can provide a valuable reference for the raceway design and reliability optimization of rolling element bearings. [ABSTRACT FROM AUTHOR]

The worn status of wheel/rail profiles could change the wheel-rail contact and influence the wear rates of the wheel and rail. Worn wheel profiles of a Chinese intercity train and the worn rail profile of curved tracks were taken into account in this work. According to the dynamics model of the vehicle, teh wheel-rail three-dimensional steady-state rolling contact model, and the Archard wear model, a new fast calculation method of wheel wear rate was proposed. Simulation results show that obviously severe wear would distribute in the flange when the wheel and rail were worn. The side wear of rail gauge corner will seriously aggravate the wear of new wheel flange. The wear of the wheel is serious for teh worn wheel in the initial phase of service. Therefore, the re-profiling of wheels and rails should be scheduled cooperatively, and the wear of flange in the initial phase of service should addressed. [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]

Numerical simulations of rail wear during sliding contact pose significant challenges owing to the complex coupling between thermomechanical contact loads, material properties, and profile changes. This study proposes a modeling approach for rail wear during sliding contact, using nonlocal peridynamic (PD) thermomechanics and a bond damage criterion based on ratchet failure. To facilitate test verification, a two-dimensional PD model for twin-disc testing with elastoplastic materials was developed, and numerical simulations and corresponding twin-disc testing were performed during wheel idling under different loads, idling speeds, and idling times. The PD model accurately predicted rail wear under all operating conditions, exhibiting excellent agreement with the test results, and thus validating the proposed method and supporting the ratchet failure mechanism. Subsequently, thermomechanical modeling of sliding contacts with different creepages was performed. The PD model predicted continuous wear along the contact surface, with an increase in wear depth corresponding to higher creepage values. As the contact temperature increased with creepage, thermal stress and thermal softening caused slight and sharp increases in rail plastic strain, respectively. Therefore, thermal softening is the main factor responsible for the significant increase in wear rate with temperature. Finally, wear results of the PD model and classical Archard's wear model were compared. The PD models can capture variations in wear rates that are difficult to address using the Archard model. • A modeling approach for rail wear during sliding contacts using PD thermomechanics was proposed. • A 2D PD model for twin-disc testing with elastoplastic materials was developed. • Twin-disc testing was conducted to validate the PD model. • The performance of the PD model and classical Archard's wear model were compared. [ABSTRACT FROM AUTHOR]

The effect of contact forces on rail uneven longitudinal wear was investigated using three series of rolling tests, including tests with the same tangential force and varying normal force, tests with the same normal force and varying tangential force, and tests with varying tangential and normal forces. Results indicated that the effect of tangential force on rail uneven longitudinal wear was greater than that of normal force. When the tangential force was the same, rail uneven longitudinal wear occurred under the small normal force condition. As the normal force increased, the wear rate decreased. With the same normal force, rail uneven longitudinal wear occurred under the large tangential force condition. The main damage of the unevenly worn rail was oxidative wear and fatigue wear. The oxidative wear and ploughing were more severe at the crest. Plastic deformation, the degree of grain refinement and fatigue cracks were more severe at the trough. More severe fatigue cracks at the trough lead to more severe wear and then the aggravation of rail uneven longitudinal wear. • The influence of normal force and tangential force on rail uneven longitudinal wear was studied. • The effect of contact forces on rail uneven longitudinal wear was quantified. • The wear and rolling contact fatigue behaviors of rail were investigated in detail. • The damage mechanism of rail uneven longitudinal wear was proposed. [ABSTRACT FROM AUTHOR]

Flange tip lift crossings are widely utilized in modern tramlines to replace traditional crossings to enhance commuters' comfort and prevent crossing nose failures. However, due to altered contact conditions between wheel flanges and ramps of crossings, the use of flange tip lift crossing has led to the critical issue of ramp wear. To resolve this issue, this paper investigated the dynamic contact response of a ramp during in-service loading, as well as the resultant wear of the ramp. With a dynamic finite element model, the local contact pressure and local sliding distance were computed and subsequently applied in a local contact-based wear model to evaluate the nominal wear of the ramp. Our findings indicate that under typical in-service loading conditions, the ramp exhibited up to 120 times more wear than the rail head, owing to increased contact pressure and reduced contact area during the ramp contact. To mitigate this issue, a design change of a gentler ramp inclination from the default 1:100 ramp to a 1:150 ramp could provide approximately 10% wear reduction. In addition, increasing the flange radius by 1 mm could reduce the wear by up to 13%. Conversely, increasing the speed to 45 km/h from the recommended 15 km/h speed may cause up to 5 times more wear. Furthermore, an empty tram showed 56% less wear on the ramp when compared to the condition of the maximum allowable axle load. These results offer an insight into the detrimental wear of ramps used in flange tip lift crossings of tramlines and can assist in the development of new designs and operating guidelines to mitigate ramp wear. • Ramp wear of a tram crossing was investigated using dynamic finite element simulation and a local contact-based wear model. • The wear of the ramp was found to be up to 120 times greater than that on the rail head of tram rails. • Gentler ramp inclination, increased flange radius, reduced vehicle speed and lower axle load can reduce the wear of the ramp. [ABSTRACT FROM AUTHOR]

The presence of fatigue crack is a common damage pattern in railway wheel-rail system, which will reduce service life and increase the maintenance costs of railway transportation. In this study, a two-stage simulation strategy was proposed to investigate the elastic-plastic fatigue crack growth behaviour of the wheel and rail, where a three-dimensional wheel-rail rolling contact finite element model was first built to solve the elastic-plastic wheel-rail contact pressure and tangential traction modification, and then a simplified three-dimensional finite element model of the wheel and rail inserted with vertical cracks under the equivalent moving load was built to explore the fatigue crack growth. Taking the J -integral at the crack tip as an elastic-plastic crack growth parameter, the influences of crack face friction, crack depth and traction coefficient on the crack growth were elucidated. Meanwhile, the competing mechanisms of wheel/rail wear and fatigue crack growth under rolling-sliding contact condition was illuminated based on the Archard wear model. The simulation results indicate that two critical locations for crack growth appear during the contact load approaching and departing from the crack. The Mises stress near the deepest crack tip exceeds the yield stress, causing a small plastic zone with the greatest crack growth rate. The reduction in the crack face friction, and/or the increase in crack depth and traction coefficient will accelerate the propagation of fatigue crack. In the case of only normal contact load or rolling-sliding contact (μ ≤ 0.375), the crack growth on the wheel and rail is dominant compared to wear and crack will continue to grow. • Proposed a two-stage simulation strategy to study wheel-rail fatigue crack growth. • Built 3-D finite element model of the wheel and rail inserted with vertical cracks. • Elucidated influences of key parameters on wheel-rail fatigue crack growth. • Illuminated competing mechanisms of wheel/rail wear and fatigue crack growth. [ABSTRACT FROM AUTHOR]

Nonlocal peridynamic (PD) theory is widely used in damage and thermomechanical coupling simulations. This study applied ordinary state-based PD thermomechanics to model the wheel-rail contact bringing temperature-dependent materials. A two-dimensional coupled thermomechanical model was developed to predict the evolution of the thermomechanical response, thermal damage, and wear in railway rail. The model was verified based on the displacement and temperature fields of the rail. The model results correlated well with the finite element model and analytical method results. The influence of the vehicle speed, rail surface cracks, and wheel idling on the thermomechanical response of the rail was also evaluated in detail. The results show that the influence of the vehicle speed on the temperature field is much greater than that of the contact stress. The contact temperature under the critical creepage could lead to the formation of a brittle white etching layer (WEL). Cracks on the rail surface increased the contact stress and temperature peaks. Thermomechanical loading also promoted rail surface damage. Continuous thermomechanical loading due to wheel idling softened and removed rail surface materials, forming wear pits and a WEL, known as wheel burns. • A 2D thermomechanical coupled PD model of the wheel-rail sliding contact is established. • A novel and concise wear prediction method is provided based on the PD damage model. • The interaction of rail surface cracks and contact thermomechanical loads is studied. • Rail wear and WEL formation (wheel burns) during wheel idling are explored. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to assess the wear mechanism of the commonly used contact lines in rail services. A high-speed sliding electrical contact wear test machine was applied to pantograph-catenary systems (PCS). The friction coefficient, arc discharge energy, current-passing efficiency, contact resistance, and contact loss rate were recorded or calculated. The impact of the test parameters on the wear of the contact line was analyzed. Our results showed that the wear rate of the contact line was inversely proportional to the normal force and directly proportional to the sliding speed. The wear of the contact line at constant current mainly included mechanical and electrical wear. With declining system stability, electrical wear gradually became the key to determining total contact line wear. When the normal force and sliding speed were maintained constant, the wear rate of the contact line fluctuated with changes in the current. Under non-current conditions, mostly mechanical wear occurred in the contact line, and the total wear was the highest. When the current (I) was maintained at 250 A, the electrical wear of the contact line was the highest, and the total wear was the highest under current-carrying conditions. However, at I = 350 A, the electrical and mechanical wear of the contact line were both at a low level, and the total wear of the contact line was the lowest. When I was increased to 450 A, the total wear of the contact line contributed to material transfer wear based on electrical and mechanical wear. In all tests, the maximum wear rate of the contact line (6.9712 × 10−3 g/km) was 3.138 times the minimum wear rate of the contact line (2.2215 × 10−3 g/km). [ABSTRACT FROM AUTHOR]

Long-life and high-reliability bearing is a key technology for developing the next generation of reusable liquid rocket turbopumps. We proposed a concept of superconducting compound bearing to combine the advantages of the superconducting magnetic field and the hydrodynamic fluid field. At the start-up, stop, and low-speed stages, the turbopump rotor system will be suspended by superconducting magnetic field to avoid mechanical friction and wear. The participation of hydrodynamic fluid field will ensure the stability during high-speed operational stage. An axial-type superconducting compound bearing with six tilting pads was erected, and an experimental verification of compound feasibility was conducted on an established testing device. The maximum rotational speed for experiments was 10 000 rpm, and the minimum bearing clearance was 100 μm. Due to the temperature rise on the superconducting pads during rotating, the superconducting magnetic force of the bearing decreases obviously versus the rotational speed. When the bearing clearance was decreased to 100 μm, this decay tendency was slowed down after 6000 rpm, even with an increase of 0.8 K in the cooling temperature of the liquid nitrogen container. It was attributed to the generation of hydrodynamic fluid-film force, and the value is 19.2 N at least. The monitored vibration results also reflected the different characteristics of the two physical fields. The verified superconducting compound bearing is a promising alternative for the rolling element bearings in the existing rocket turbopumps. [ABSTRACT FROM AUTHOR]

The addition of nanoparticles to lubricant is effective for the reduction of wear and friction in the mechanical system. In this research, the effects of additions of copper oxide nanoparticle nanoparticles on the lubrication behavior of biodieseldiesel fuel blends were investigated by using a four-ball tester. Three fuel blends with the addition of 0, 25, 50 and 75 ppm nanoparticle were tested in steady-state conditions at four different rotational speed of 600, 1200 and 1500 rev/min. the results showed that the friction coefficient decreases with the increase in nanoparticles up to 50 ppm because of filling the friction surface with the nanoparticles and replacement of sliding friction with the rolling effect in the contact zone. On the other hand, the FC was enhanced significantly with 75 ppm nanoparticle addition in fuel blends B10 and B20. However, the results showed that the lubrication of fuel blend B50 with the 75 ppm nanoparticle is better than that of other fuel blends in the same situation. Moreover, it was found that with an increase in biodiesel concentration the friction coefficient was reduced due to free fatty acids, monoglycerides, and diglycerides as the components of biodiesel. [ABSTRACT FROM AUTHOR]