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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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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]

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]

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]

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.)

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]

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]

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]

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]

• A thermomechanically coupled peridynamic model for simulating wheel idling was established. • A dynamic simulation was conducted on rail wear during wheel idling. • The peridynamic model has the potential to provide wear coefficients for classical wear models. • The thermomechanical damage mechanism of rails during wheel idling was discussed. Wheel idling is an extreme sliding contact scenario that accelerates rail failure. Using temperature-dependent elastoplastic materials, a peridynamic (PD) model for wheel-rail contact was developed to investigate the thermomechanical damage behavior of rails during wheel idling. Numerical simulations of loading and unloading during wheel idling under different loads were performed, and the results of contact stress, temperature, plastic deformation, and material damage were obtained and analyzed. During loading, the temperature of the rail surface increases rapidly to over 1200 °C, which is well above the austenitization temperature. The intense thermal softening caused by high temperatures deteriorates the wheel-rail contact relationship and leads to a surge in plastic deformation. The softened surface material was continuously removed by the contact load, leading to severe wear damage, and the wear depth increased significantly with the load and idling time. The wear coefficients for the Archard wear model were derived using the wear results from the PD model. During unloading, the surface material cools rapidly at a rate of 1400 ° C / s through heat transfer into the rail, undergoing martensitic transformation and forming a brittle and hard white etching layer. The thickness of the WEL decreases as the wear depth increases. [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]

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]

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]

• 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]

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]

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]

• 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]

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]

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

Analysis of the results of studies in a low-viscosity model medium of high-speed ball bearings, racers and rolling elements made of corrosion-resistant 95H18Sh steel with a massive bronze separator on a special multipurpose installation was carried out. Water was used as the low-viscosity model medium in accordance with GOST 2874-82. The dynamics of damage formations on bearing working surfaces, depending on the level of load-velocity parameters and on the pumping rate of lubricoolant water medium, was demonstrated. A limit level of contact stresses was established, above which damages of working surfaces have a pitting character; while under contact stresses not exceeding this limit, working surfaces are exposed only to mechanochemical wear. Recommendations for developers of bearing assemblies on the ascertainment of permissible load levels on bearings in the design of rolling contact bearings were given. [ABSTRACT FROM AUTHOR]

Modelling techniques of Double Concave Friction Pendulum (DCFP) system are presented. Seismic responses of the three-dimensional single-story building isolated by DCFP with different coefficient of friction and initial time period of top and bottom sliding surfaces are investigated under triaxial ground excitations and compared with unilateral and bilateral ground excitations. The influence of vertical flexibility on horizontal response is investigated. It is observed that the triaxial ground motion has noticeable effect on response of the building relative to unilateral ground motion. The error in peak resultant absolute deck acceleration and the error in peak resultant isolator deformation, occurring by neglecting vertical ground motion component, could be significant. [ABSTRACT FROM AUTHOR]

The tribological behavior of the PVD-TiAlN coated carbide inserts in dry sliding against two-phase (α-β) titanium alloy,Ti6Al4V grade, was investigated. A modified pin-on-disc device was used to conduct experiments under variable normal load and sliding speed. Scanning electron microscopy (SEM) and X-ray micro-analyses by EDS were applied for observations of wear scars and wear products. It was revealed that the increase of sliding speed contributes to decreasing the friction coefficient under a low normal force, whereas the increase of the normal loading causes the friction coefficient is less sensitive to changes in the sliding speed and its values are equal to μ = 0.26-0.34. The adhesive nature of wear along with severe abrasive action of the Ti alloy were documented. [ABSTRACT FROM AUTHOR]

Angle of attack is an important wheel-rail contact parameter. It serves for estimation of the rolling stock curving performance. Together with wheel-rail contact forces, angle of attack influences the wear index. This paper presents experimental ontrack measurements of the angle of attack using a specially designed laser device installed on track. Experiments are performed on three types of rail vehicles: shunting locomotive series 631-301, motor unit 412-077 and trailing unit 416-077 of electromotor train 412/416. Experimental measurements are compared with multibody system (MBS) simulations using specialized computer package VAMPIRE Pro. We have found good agreement between the results obtained experimentally and by simulations. Using these data, we have also performed relative comparison of wear indices of the outer wheels of the leading wheelsets for each of the tested vehicles. [ABSTRACT FROM AUTHOR]

Vibration of a blade couple damped by a dry friction contact in the shroud is investigated by means of hysteresis loops and response curves analysis. The studied system is excited by one harmonic external force in a frequency range near to the lowest eigenfrequency of real blades. Blades are connected by means of a damping element consisting of dry friction part linked in series with linear spring. This ''stick-slip'' damping element is supposed to be either weightless or of a very small mass which models the mass of elastically deformed parts of contacting bodies near the friction surface. Two approximate mathematical models of ''stick-slip'' dry friction elements are suggested and analysed. The response curves of blade couple connected by stick-slip damping element are presented for different values of slip friction forces and two values of mass of elastically deformed parts. [ABSTRACT FROM AUTHOR]

Abstract: Harfacing welding is a widely used method on severe worn, corroded or oxidized surfaces to regain its functionality. For metal-to-metal sliding or rolling contact applications, in which oxidative wear, subsurface fatigue and adhesive wear are the main wear mechanisms, the materials usually selected are steels with a carbon contents between 0,1 and 0,7% and up to 20% of alloy content, such as martensitic tool steels. Among them, H13 tool steel has a great number of applications. Variables such as sliding speed, load, or contact stress may have decisive influence on wear rates. Laboratory tests like Pin-On-Disk (POD) are frequently used to evaluate the tribologic behaviour of different pairs of material. The objective of this work was to study the influence of the pin geometry (flat and spherical) in a POD test on the wear resistance of a weld-deposited hardfacing of H13 modified steel against low carbon steel AISI 1020 under different load and sliding speed conditions. It was observed an influence of the pin geometry on the wear rates, especially at high sliding speeds. Under light loads, the worn volume of the flat pin was greater, while under heavier loads it is the spherical pin the one with greater worn amount. [Copyright &y& Elsevier]

Abstract: Surface micro dents may act as lubricant reservoirs to reduce friction and wear in sliding and rolling contact applications. Surface patterning has become a valuable technique for fabricating micro dents. Alternative methods such as micromachining present obvious limitations in comparison with laser shock peening (LSP). In this paper, the use of micro LSP along with an automatic XY table proves to be an attractive and reliable method for producing micro dent arrays with enhanced surface integrity. Surface topography, residual stress, and microhardness of the fabricated micro dent arrays on polished Ti–6Al–4V surfaces have been characterized. It has been shown that LSP is capable of efficiently fabricating mass micro dent arrays with controllable size via adjusting laser power. The center area of the peened dents has the highest hardness. In addition, high compressive residual stress can also be produced. [Copyright &y& Elsevier]

Abstract: The present work shows a new numerical treatment for wear simulation on 3D contact and rolling-contact problems. This formulation is based on the boundary element method (BEM) for computing the elastic influence coefficients and on projection functions over the augmented Lagrangian for contact restrictions fulfillment. The constitutive equations of the potential contact zone are Signorini’s contact conditions, Coulomb’s law of friction and Holm–Archard’s law of wear. The proposed methodology is applied to predict wear on different contact and rolling-contact problems. Results are validated with numerical solutions and semi-analytical models presented in the literature. The BEM considers only the degrees of freedom involved on these kind of problems (those on the solids surfaces), reducing the number of unknowns and obtaining a very good approximation on contact tractions using a low number of elements. Together with the formulation, an acceleration strategy is presented allowing to reduce the times of resolution. [Copyright &y& Elsevier]

Abstract: Rolling contact and cavitation testing were integrated in a testing methodology to study their combined effect on silicon nitride rolling elements. This testing methodology is well suited to perform controlled cavitation and rolling contact experiments. Acoustic cavitation method and a rotary tribometer were utilized to achieve this objective. Silicon nitride degradation initiated with the formation of blisters in rolling contact. This blisters underwent cracking in the subsequent testing, thereby allowing the lubricant to squeeze in due to rolling contact. Erosion pits formed and their density increased along with their growth by detaching grains and bridging into adjacent pits. As the erosion severity in the rolling contact increased the material eventually failed in a short period of time with respect to the testing conditions. The effect of cavitation and rolling contact parameters on material damage is detailed in this paper thereby allowing an evaluation of material systems for cavitation-rolling contact fatigue (RCF) conditions. [Copyright &y& Elsevier]

Abstract: If a wheel rolling over a rail transmits a tangential traction, frictional microslip occurs in part of the contact area, resulting in energy dissipation and localized wear. If the applied forces oscillate in time, the resulting wear will be non-uniform, resulting in ‘corrugations’ that can grow with progressive passes, depending on the dynamics of the overall system. In this paper, a linear perturbation method is used to obtain closed-form expressions for the receptance of a two-dimensional rolling contact subjected to small oscillations in normal force and rotational speed superposed on a mean value in the limit of large coefficient of friction. Corresponding expressions are also obtained for the amplitude and phase of the energy dissipation in the contact, which is expected to correlate with the local wear rate. The results are compared with a simpler Winkler model of the contact and with other models that have been used for the analysis of rail corrugation. Surprisingly good agreement is obtained with numerical results due to Gross-Thebing for the receptances due to oscillations in rotational speed. [Copyright &y& Elsevier]

The complex nature of slip-rolling contacts in many applications such as gear tooth flanks, rolling bearings, and heavy machinery often makes determining the friction and wear properties, as well as the fatigue resistance, of tribosystems difficult. The establishment of the tribological profile of a tribocouple under high Hertzian contact pressure and under slip-rolling will allow for the measurement and comparison of friction and wear coefficients as well as slip-rolling resistance by continuously monitoring the wear rate, coefficient of friction, temperature, oil film thickness, and/or electrical contact resistance using high-resolution signal analysis (HRA). A twin disc system can provide insight into the adhesive behavior of material and lubricant products such as alternative base oils and additives, ceramics, alloys, and thin film coatings. The strength and endurance of these products are often characterized through fatigue and resistance tests, which apply high Hertzian contact pressures to the rolling contact until seizure or failure is obtained. The further observation of the formation of tribofilms on the surface of contact yields information about the reactivity and thermochemical properties of additives. This review aims to illustrate how the implementation of different screening methodologies can be used as a meaningful tool for assessing the aforementioned tribological profile properties for the development of slip-rolling tribosystems. [ABSTRACT FROM AUTHOR]

To investigate the relationship between surface microstructure and wear mechanism in D2/U71Mn wheel-rail material under different contact stress conditions, rolling wear tests using a GPM-40 wear machine to simulate the wheel-rail operation was performed. After wear tests, an optical microscope (OM), scanning electron microscope (SEM) and micro-hardness testers were used to characterize the microstructure and fatigue wear cracks. The results show that the thickness of the plastic deformation layer and surface hardness is increased with the increase of contact stress. Under high contact stress condition (1200 MPa), the severe plastic deformation layer led to the formation of fatigue wear of wheel-rail samples. Under a contact stress of 700 MPa, the wear mechanism of samples is adhesive wear and wear rate is low. With the increase of contact stress, the fatigue cracks are gradually severe. Under a contact stress of 1200 MPa, the wear mechanism of samples becomes fatigue wear and the fatigue wear cracks cause the increase of wear rate. The fatigue wear can accelerate the wear failure of wheel-rail samples. The fatigue wear cracks of wheel samples are severer than that of rail samples due to both the rate of plastic strain and the content of proeutectoid ferrite. [ABSTRACT FROM AUTHOR]