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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]

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]

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]

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]

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]

• 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]

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]

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]

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]

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]

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]

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]

• 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 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]

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]

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]

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]

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]

The out–of–roundness of wheel treads are an inherent degradation characteristic of the wheels of railway vehicles, and the interface behaviour of the wheel and rail caused by out–of–roundness features has essential research value in high–speed train running safety and quality. Sliding–rolling contact wear testing was conducted to evaluate the effect of the out–of–round wheel on the wheel–rail damage behaviour, by using a twin–disc setup. The effects of four wheels, three wheels of different eccentricities and one normal wheel were taken as a control group. The characteristics of the wheel–rail interface adhesion, wheel surface damage and compressive residual stress (CRS) distribution were compared and analysed. The results showed a dramatic increase in the fluctuation amplitude of the wheel–rail vertical force of the eccentric wheels, and the adhesion coefficient of the wheel–rail interface significantly decreased. Furthermore, eccentric wheels dramatically accelerate the wear loss of the rail used as a counterpart during wheel–rail rolling contact. The surface damage behaviour of the eccentric wheels is obviously different along the circumferential direction, and non–uniform wear was observed. The damage mechanism of the worn surface presented varying characteristics, which could be divided into a severely damaged zone (located at the maximum of the rolling radius r max) and a slightly damaged zone (located at the minimum of the rolling radius r min). The surface contact stress of the severely damaged zone was high, this finding can be explained by the extremely rough worn surface caused by the severe fatigue delamination characteristics and the initiation and propagation of fatigue cracks in the severely damaged zone. Furthermore, the values of surface hardness and residual stress were relatively low. By contrary, an adhesion layer was observed on the worn surface of the slightly damaged zone. The adhesion layer protects worn surface in the slightly damaged zone was relatively flat, and the CRS was relatively high. [Display omitted] • The influence of eccentric wheels on the adhesion and damage characteristics of wheel-rail sliding-rolling contact interface were discussed and studied. • Two different types of damage, that is, slightly and severely damaged zones, were identified and compared, and their failure mechanisms were revealed, respectively. • Response of contact stress, residual stress and material removal mechanisms under different eccentricity were summarized and discussed. [ABSTRACT FROM AUTHOR]

As traffic density and axle loads increase, the macroscopic wheel-rail contact can lead to severe rail wear. This paper constructs a multi-scale analysis framework from macroscopic force characteristics to microscopic wear mechanisms based on explicit finite element methods and molecular dynamics models. The study shows that the mutual proximity and annihilation of reverse dislocations in the rail material under the action of wheel-rail forces is an important cause of grain boundary fragmentation, while the proliferation of dislocations on the Subsurface leads to work hardening of the rail. The analytical framework proposed in this paper achieves a multiscale correlation between wheel-rail macroscopic contact and material microscopic response, and the conclusions obtained reveal the microscopic wear mechanism of rail materials. [ABSTRACT FROM AUTHOR]

Abstract A comprehensive knowledge of geomechanical characteristics of the formations above a reservoir (cap rock, in particular) can prevent a large spectrum of problems during drilling operation. Furthermore, access to such information during drilling operation greatly contributes to proper adjustment of controllable parameters and enhanced rate of penetration (ROP). Unfortunately, due to the high costs associated with the acquisition of petrophysical logs, these sets of data are commonly acquired within the reservoir interval only, i.e. at most 20% of total drilled length. As such, the present contribution is an attempt to use the concept of mechanical specific energy (MSE) to estimate geomechanical parameters of rock. For this purpose, data was collected from two vertical wells drilled into an oilfield in southwest of Iran. Firstly, based upon available drilling reports and Tukey method, outlier data points were detected and omitted. Then, MSE was evaluated using different models proposed for this purpose previously. The evaluation results indicated that, the results obtained from Dupriest and Koederitz (2005) model were in good agreement with actual conditions at the considered wells. Therefore, the obtained MSE from this model along with flow rate (FR), bit tooth wear (CT), and Depth logs were used as input for multivariate nonlinear regression (MNLR) method as well as multi-layer perceptron neural network combined with cuckoo optimization algorithm (MLP-COA) and also with particle swarm optimization (MLP-PSO) to estimate confined compressive strength (CCS), uniaxial compressive strength (UCS), internal friction angle (ϕ), and Poisson's ratio (ν). Models were trained on data from one well and then validation-tested on the other well's data. Results of adopting these models indicated that, as far as the estimation of geomechanical parameters was concerned, intelligent models were of higher accuracy and reliability than the regression model. A comparison between the results of MLP-COA and MLP-PSO models showed that, COA outperforms PSO algorithm in achieving a model of higher accuracy and reliability. Results of the three models indicated that, the presented method in this research possesses large potentials for estimating CCS, UCS, and ϕ parameters, and it can be stipulated with certainty that, the proposed method can be used to estimate the parameters at other wells across the field under study provided further data is available from more wells and even the formations overlying the reservoir. However, application of this method for estimating ν shall be practiced with care. Highlights • Mechanical Specific Energy (MSE) concept in drilling was used for determination of geomechanical parameters. • Data was acquired from two wells in southwest of Iran. • Multi-Layer Perceptron (MLP) neural network with Cuckoo Optimization Algorithm (COA) and Particle Swarm Optimization (PSO) as training algorithms was used for prediction of Confined Compressive Strength (CCS) Uniaxial Compressive Strength (UCS), friction angle (ϕ (and Poisson's ratio (ν). • Built models showed that they are more capable in prediction of CCS, UCS and ϕ than prediction of ν. • MLP-COA model is superior to MLP-PSO and multivariate non-linear regression models. [ABSTRACT FROM AUTHOR]

Abstract This study determined the influence of discrete laser spot hardening on the scuffing wear and rolling contact fatigue resistance of Cu-Ni austempered ductile iron (ADI) specimens. The frequency of the single laser pulses were such so as to produce patterns of separated spots, adjacent spots or overlapping spots. Lubricated sliding wear tests were carried out to determine the behaviour of ADI under starved lubrication conditions, usually occurring during the start-up of gears. ADI specimens hardened with adjacent and separated laser spots displayed higher resistance to scuffing than the surfaces treated with overlapping laser spots and the control samples (those tested in the as-austempered condition). Results obtained also show that laser hardening increased the average rolling contact fatigue life over the as-austempered ductile iron specimens. This improved performance was attributed to the higher volume of martensite formed and hence higher surface hardness, and also the residual compressive stresses induced in the laser-treated surfaces. This benefit outweighed the negative effect of the slight roughness induced by the laser treatment. Highlights • Overlapping laser spots caused back-tempering. • Scuffing tests showed that adjacent laser spots exhibited the best performance. • Laser hardening improves the rolling contact fatigue resistance of ADI. [ABSTRACT FROM AUTHOR]

In this article, a wheel life prediction model considering wear and rolling contact fatigue (RCF) is developed and applied to a heavyhaul locomotive. For wear calculations, a methodology based on Archard's wear calculation theory is used. The simulated wear depth is compared with profile measurements within 100,000 km. For RCF, a shakedown-based theory is applied locally, using the FaStrip algorithm to estimate the tangential stresses instead of FASTSIM. The differences between the two algorithms on damage prediction models are studied. The running distance between the two reprofiling due to RCF is estimated based on a Wöhler-like relationship developed from laboratory test results from the literature and the Palmgren-Miner rule. The simulated crack locations and their angles are compared with a five-year field study. Calculations to study the effects of electro-dynamic braking, track gauge, harder wheel material and the increase of axle load on the wheel life are also carried out. [ABSTRACT FROM AUTHOR]

Friction modifier (FM) is a newly developed third medium to control the service performance of wheel/rail. The wheel/rail performance is influenced by the wheel/rail contact conditions and FM application parameters. Therefore, the effects of FM application parameter and the wheel/rail contact parameters on the adhesion and damage behaviors of wheel and rail materials should be explored. In this study, the influences of application amount of FM, the wheel/rail contact stress and the creepage on the adhesion and damage behaviors were studied using a twin-disc machine. Results indicated that the increase in contact stress would reduce the wheel/rail minimum adhesion coefficient and effective holding time of FM. The increase in the creepage would increase the adhesion coefficient and reduce the holding time. Under the wheel/rail contact stresses of 800 and 1100 MPa, the application of FM could reduce wheel/rail wear and damage. But under 1500 MPa, FM could cause serious rail surface damages. Moreover, the surface crack propagation process of rail mainly included three stages: initial stage, transition stage and rapid propagation stage. The "oil wedge effect" was the main mechanism for aggravating the surface damages of rail under 1500 MPa. • Wheel/rail adhesion coefficient is reduced with the increase in FM application amount and contact stress, and the decrease in creep rate. • The minimum adhesion coefficient has a negative relationship with the holding time. • Under 800 and 1100 MPa, the application of FM could alleviate the wheel and rail wear and damages. • Under 1500 MPa, FM will cause serious surface damages to the rail with initial cracks. [ABSTRACT FROM AUTHOR]

This work aimed to evaluate the effects of contact stress and slip ratio on wear and rolling contact fatigue of ER9 wheel steel and R260 rail steel couple under unlubricated conditions using a dual disk test. It was demonstrated that as either contact stress or slip ratio increased, so did the wear rate and surface damage of both ER9 wheels and R260 rail rollers. The wear rate of the ER9 wheel steel containing proeutectoid ferrite and the smaller structure size of pearlite increased significantly when compared to the rail steel containing fully pearlite in each pair. After testing according to the conditions used in this work, the surface hardness of the pearlitic rail steel was higher than that of the ferrite-pearlite wheel steel. The average hardening ratio of ER9 wheel steel and R260 rail steel was 0.7 and 1.28, respectively. This was consistent with the subsurface deformation angle. With full pearlite in the microstructure of rail steel, the main wear mechanism was predominantly caused by fatigue cracking and peeling, with some adhesive wear. Whereas the most prominent mechanism of the ferrite-pearlite wheel steel was adhesive wear, which was followed by spalling and small fatigue cracks. • Wear behavior of the ER9 wheel and R260 rail couple under different conditions. • Hardening ratio of the ER9 wheel steel is lower than that of R260 rail steel. • Voids occur at proeutectoid ferrite/ferrite and broken cementite interfaces. • Relationship of wear rate, surface crack angle, and deformation angle. • Surface damage caused by microstructure in the ER9 wheels and R260 rail steel. [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]

This study presents the wear and damage behaviours of U71Mn rail material with a friction pair of ER8 wheel material under different temperature conditions, which were explored using a rolling-sliding wear testing device. It turns out that, compared to those at 20 °C room temperature, the adhesion coefficient, wear rate and hardness all increase at low temperatures. Meanwhile, three types of damage mechanisms are proposed according to wear and rolling contact fatigue (RCF) behaviours under different temperature conditions: (a) room temperature (RT) damage mechanism, (b) ductile-brittle transition temperature (DBTT) damage mechanism, (c) below ductile-brittle transition temperature (BDBTT) damage mechanism. With the temperature decreasing from room to low temperature, the wear mechanism transforms from abrasive wear to adhesive wear and surface fatigue. Meanwhile, the rail material gradually becomes brittle and the subsurface damage at low temperature is more serious than that at room temperature. Furthermore, the subsurface damage at −15 °C is the worst. At low temperature, there is a wider size range of wear debris than that at room temperature. [ABSTRACT FROM AUTHOR]

Wettability and stress concentration are the main challenges affecting the engineering application of copper/alumina dissimilar joints. In this paper, continuous drive friction welding of copper to alumina was conducted using 2.5 mm thick AA1100 aluminum as interlayer. The effects of friction pressure and friction time on the tensile strength of joints were evaluated, and the interface microstructure evolution and fracture morphologies were also analyzed. Obvious mutual diffusion occurred at the alumina/aluminum and aluminum/copper interfaces, enhancing wettability and proving metallurgical bonding. Microcracks formed in alumina base due to thermo-mechanical coupling effect in welding. As increasing friction pressure and friction time, the tensile strength increased till reaching a peak value of 35 MPa, and then decreased. The optimized parameters were determined as friction pressure of 12 MPa and friction time of 12 s. All samples failed at the aluminum/alumina interface, leaving a pit structure on alumina base. The application of pure aluminum interlayer is essential to obtain sound copper/alumina joints by diminishing stress concentration and wetting alumina, and the optimized residual aluminum layer is about 0.47 mm thick. The friction interface transferred from alumina/aluminum to inner plasticized aluminum layer, and then moved to aluminum/copper till the welding process finished. [ABSTRACT FROM AUTHOR]

Tool and pin geometries play significant roles in material flow, stirring and weld quality in friction stir spot welding (FSSW) process. The present work investigates the influence of tool pin length (0 mm i.e. pinless, 0.2 mm and 0.4 mm) and pin diameter (3.3 mm and 4.95 mm) on lap shear strength during the FSSW of similar and dissimilar aluminum and copper alloy. Pinless tools are differently designed from H13 die steel single material and embedded aluminum and/or copper rods in H13. Results indicate that the maximum lap shear strength is achieved with pinless tools (single material). However, when tools with pins are used lap shear strength decreases with increase in tool plunge depth but increases with pin diameter. For pinless tool obscure hook formation is noted and crack is initiated from the joint interface. Asymmetric strain distributions as observed from the finite element analysis and hook formation observed during microscopic analysis may be responsible for quick failure when higher plunge depth of pin is used. Shear fracture in presence of micro-voids/dimples elongated along the loading direction are observed in similar FSSW whereas in case of Cu-Al dissimilar joints, formation of intermetallic compounds and quasi-cleavage fracture is observed. [ABSTRACT FROM AUTHOR]

Most existing wheel/rail hardness matching studies have been carried out using pearlite steels with different hardnesses; no relevant wheel–rail hardness matching research has been carried out for other microstructure types such as bainite and other tempered materials. In this paper, a CL60 wheel (pearlite) was quenched and tempered to obtain wheel materials with a certain hardness gradient, and matching tests between different wheel materials and a quenched U75V rail were carried out to explore the influence of wheel microstructures on wheel–rail damage. The results showed that with increasing tempering temperature, the wheel microstructure changes from tempered troostite to tempered sorbite, with ferrite changing from a needle shape to a multilateral shape; additionally, the cementite particles grow obviously larger, resulting in a gradual decrease in wheel hardness. With the increase in the wheel/rail hardness ratio, the wear rate of the wheel and wheel–rail system first increases and then decreases; the wear rate of tempered sorbite is the highest. Wear surface analyses indicate that typical peeling appears on the wear surfaces of the CL60 wheel as well as the coupled rail. Tempered sorbite shows slight peeling; however, severe peeling and delimitation occur on the wear surface of its coupled rail. Moreover, severe peeling and serious material delamination are present on the wear surface of tempered troostite, and typical peeling appears on its coupled rail surfaces. The fatigue crack initiation and propagation behaviors of wheel and rail materials are closely related to their microstructures. The cracks in pearlite always initiate on the surface and propagate along the ferrite line. Short and shallow fatigue cracks appear on the tempered sorbite with a high wear rate, and the cracks in the tempered troostite easily expand into the centre of the samples, indicating poor rolling contact fatigue (RCF) resistance. Therefore, the pearlite structure shows better comprehensive mechanical properties for wheel service; moreover, more attention should be given to wheel microstructure when conducting research on wheel–rail matching. • The CL60 wheel were heat treated and wheel materials with a certain hardness gradient were obtained. • Matching tests between quenched U75V rail and different wheels were carried out. • Wear and rolling contact fatigue behaviours were proposed and studied. • Ratcheting behaviours and propagating mechanism of RCF cracks were analyzed and revealed. [ABSTRACT FROM AUTHOR]

In the last few years, top-of-rail friction modifiers have been designed and used in many railway systems all over the world. These adhesion enhancers are applied by either off-board or on-board system in order to achieve the intermediate level of friction and positive adhesion curve. Previous scientific effort was mainly focused on the effects of water-based friction modifier on adhesion, rolling contact fatigue, railway noise and corrugation formation. The objective of this study is to investigate the abilities of oil-based friction modifiers to control adhesion and reduce wear at wheel rail interface. For this purpose, two commercial oil-based friction modifiers were particularly utilised. A ball-on-disc tribometer was employed to investigate their traction and braking performance for various slip ratios under dry conditions. Furthermore, the effect of friction modifier amount has been studied. At the end of the performed tests, wear rate, surface damage and changes of surface topography were determined and compared to dry and oil-contaminated contact. The results indicate that oil-based friction modifiers are able to control adhesion in wheel-rail contact but it is strongly dependent on the applied amount of friction modifiers. Regarding to the friction behaviour and wear, the content of metal particles seems to be the crucial parameter. [ABSTRACT FROM AUTHOR]

Wear problems exist in multi-layer windings of ultra-deep coal mine hoisting ropes that are wound around drums. Wear decreases the life of such hoisting ropes directly, and that in turn threatens mine safety. An investigation of winding hoisting ropes was conducted using a custom test rig to study the effects of different contact loads, crossing angles and displacement amplitudes on rope friction and wear. Results show that the coefficient of friction (COF) in the steady-state period changes very little with an increase in contact load and that it stabilizes at about 0.61. Additionally, the COF slightly decreases with an increase of crossing angle. As the amplitude of sliding motion increases to 30 mm and 50 mm, the COF increases linearly. Using thermal imaging, the temperature rise in the steady-state period increases with the contact load and crossing angle. Moreover, the maximum wear depth increases linearly with an increase of contact load. Nevertheless, the wear depth changed very little when the amplitude is less than 30 mm, but it increases rapidly until an amplitude of 70 mm. The major wear mechanisms of ropes without lubrication include adhesive wear, abrasive wear and fatigue wear. [ABSTRACT FROM AUTHOR]

Over a century of scientific research on the sliding friction of ice has not been enough to develop an exhaustive explanation for the tribological behavior of frozen water. It has been recognized that ice shows different friction regimes, but a detailed description of all the different phenomena and processes occurring at the interface, including the effect of surface roughness of both the ice and the antagonist material is still missing. In this work the effect of surface morphology on the friction of steel/ice interfaces is studied. Different degrees of random roughness on steel surfaces are introduced and the friction coefficient is measured over a wide range of temperature and sliding velocity. Correlation between the surface roughness and the lubrication regime and friction coefficient is discussed. A theoretical model is developed in order to explain this correlation, and to control the tribological behavior of the system by a proper selection of surface roughness parameters. [ABSTRACT FROM AUTHOR]

Sliding electrical contact behavior of the brass fiber brush with 23% packing fraction was investigated as sliding against coin-silver and Au plating under vacuum and air conditions. The friction coefficient, contact resistance and electrical noise of the brushes were analyzed. The microstructure and worn surfaces of the brass fiber brush and counter discs were observed to discover the involved wear mechanisms. The friction coefficients in vacuum are much higher than those in air. The contact resistances and electrical noises of the brush against both discs in vacuum are extremely low. The contact resistance against coin-silver quickly increases as the sliding condition varies from vacuum to air, which is much higher than that against Au plating. Sliding speed has an insignificant effect on the contact resistance and electrical noise of fiber brush. Formation of oxide film and loose oxide particles on the worn surfaces of fibers and the coin-silver disc leads to the increase of contact resistance and electrical noise. The transfer of gold from Au plating to worn surfaces of brass fibers is used to prevent the oxidation of fibers and keep the contact resistance and electrical noise in a relatively low level. The multi-contact mechanism of brass fiber brush has been also discussed. [ABSTRACT FROM AUTHOR]

A methodology is proposed to examine the tribological behavior of materials subjected to successive ascents and descents in temperature. The experimental approach is based on performing two types of high temperature reciprocating sliding tests and subsequently correlating the evolution of the coefficient of friction of the tribosystem with test temperature. In the first series, the sliding tests are conducted at increasing temperatures with the aim to identify the temperature regions where changes in friction might occur. These changes can be either due to a surface modification (e.g. a change in the oxidation and/or wear mechanism) or structural one (e.g. phase transformation). In the second series, tests are performed under isothermal conditions selected based on the outcome of the elevated temperature results, with the aim to evaluate the influence of oxidation on the frictional behavior of the thermally stable system. As a case study, electroplated intermetallic Ni-Sn coatings containing either 16 or 64 wt% Sn of interest on jet engine bearings, were investigated. These coatings were tested between 25 and 400 °C in ambient air relevant for that application. [ABSTRACT FROM AUTHOR]

Parasitic friction losses during piston ring-cylinder liner interactions in an internal combustion (IC) engine consume large portions of the available fuel energy. This work investigates whether the tribological performance of grey cast iron (CI) cylinder liner would be improved using a piston ring coated with non-hydrogenated diamond-like carbon (NH-DLC) in comparison to uncoated CI and steel rings. Coefficient of friction (COF) values and volumetric wear losses of CI were determined using ball-on-disk type tests as a function of sliding distance. CI tested against itself during boundary lubricated sliding with synthetic engine oil showed a COF of 0.14 and a volumetric wear of 11.0×10 −4 mm 3 after 6×10 5 cycles, whereas the use of NH-DLC coated counterface resulted in a COF of 0.11 and lesser wear of 0.5×10 −4 mm 3 . Dilution of the engine oil by ethanol containing E85 biofuel was beneficial as COF was further reduced to 0.08 for CI tested against NH-DLC while maintaining low wear of 0.2×10 −4 mm 3 . According to TEM and XPS analyses, an oil residue layer (ORL) formed on the CI contact surfaces as a result of sliding-induced degradation of zinc-dialkyldithiophospahte (ZDDP) additive in the oil. The ORL, which consisted of nano-crystalline particles of sulphides and phosphates of zinc (anti-wear components) embedded in an amorphous carbon matrix, was responsible for maintaining low wear. Ethanol dilution of the synthetic oil facilitated the formation of ORL. TEM/EELS studies of the NH-DLC counterface provided evidence for OH adsorption and passivation of carbon bonds at the surface that reduced the friction. It is anticipated that piston rings coated with NH-DLC run against CI liners would show low friction and wear during boundary lubricated sliding, an effect that could be enhanced when ethanol diluted oil is used. [ABSTRACT FROM AUTHOR]

A model which can predict the length of the surface crack and crack depth in rails was developed in a previous study by the authors B. Dirks, R. Enblom, A. Ekberg, M. Berg (2015) [1] . In the present study, verification of this crack prediction model in combination with a wear prediction model was done against wheel measurements. For a period of 15 months, the wheels of three units of a Stockholm commuter train were measured with respect to wear and crack development for verification of the wheel life prediction tool. Vehicle–track dynamics simulations were used to calculate the forces and contact positions for the wear and crack prediction models. It can be concluded that the wear prediction model gives reasonable results, especially considering the large scatter in the wheel profile measurements. Although the wheel life prediction tool could not be verified, since the crack prediction model had to be recalibrated for the current wheel application, the results appear promising. [ABSTRACT FROM AUTHOR]

Wheel treads are subject to different types of damage such as wear, rolling contact fatigue (RCF), thermal cracks, plastic deformation and flats caused by wheel sliding. These types of damage cause changes in the tread profile of the wheel, which necessitates frequent wheel reprofiling in order to maintain the ride comfort of the vehicle. In this study, a series of full-scale tread braking experiments, including wheel–rail rolling contact, were conducted to clarify the factors influencing the wheel tread profile evolution. The experiments focused on plastic deformation and the wear caused by the rolling contact and tread braking. The results showed that the maximum tread indentation was 0.20 mm at the rolling contact center when the stop braking action was repeated 40 times. This was caused by the plastic deformation of the wheel tread, which, in turn, was the result of high contact pressure and material softening from high temperatures caused by tread braking. The results were supported by the observed tread protrusions near the rolling contact area and also by the difference in the rolling contact area hardness and that of the other wheel tread areas. [ABSTRACT FROM AUTHOR]

A novel wheel–rail contact model is proposed to be implemented for multi-body dynamics simulation, in order to facilitate accurate online calculation of damage phenomena such as wear and rolling contact fatigue. The normal contact, i.e. contact patch and pressure distribution, is calculated using a fast non-elliptic algorithm called ANALYN. The tangential contact, i.e. tangential stress distribution, stick–slip division and creep force calculation, is treated using an alternative to the FASTSIM algorithm that is based on a strip theory which extends the two-dimensional solution of rolling contact to three-dimensional contacts. The proposed contact model is compared to the Hertz+FASTSIM model and evaluated using the CONTACT code in terms of contact patch and stress distribution as well as creep force curves. The results show that the proposed model can significantly improve the estimation of the contact solution both in terms of creep force estimation and contact details, such as stress distribution, needed for damage predictions. [ABSTRACT FROM AUTHOR]

In order to simulate the rail profiles evolution in the switch panel of a railway turnout, the simulation of vehicle–turnout dynamic interaction, the wheel–rail rolling contact model and rail material wear model are integrated as a numerical simulation tool for rail wear of the switch panel in this paper. A multi-body dynamical model of the CRH2 Chinese high speed vehicle is created using Simpack software, with turnout model is based on the standard CN60-1100-1:18 turnout design for high speed railway. To reproduce the actual operating conditions of railway turnouts, the dynamic simulation also takes account of stochastic variations in input data. The rolling contact between wheel and rail is modelled using a semi-Hertzian method and an improved FASTSIM algorithm. The distribution of contact stresses and relative motions of each unit in the contact patches are obtained through rolling contact calculations; these are then used to predict the wear on rails caused simultaneously by the vehicle׳s multiple wheels, based on Archard׳s wear model. Rail profiles at several positions along the longitudinal dimension of the turnout are simulated for non-uniform wear. The numerical methodology is applied to predict the evolution of rail profiles as the vehicle switches into the turnout track in a diverging movement. The shapes of the worn rail profiles obtained via simulation are then compared with field measurements, and the effectiveness of the wear prediction methodology is thereby validated. [ABSTRACT FROM AUTHOR]