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In this study, effects of the slip ratio and contact pressure on the evolution of wear and damage of CL60 wheel material were explored using an MJP-30A wheel-rail rolling-wear and contact fatigue testing machine. Wear maps and damage mechanism maps of wheel material under both dry and wet conditions were constructed. Based on the wear rates of the wheel rollers, the wear map of CL60 wheel material under dry conditions was divided into three areas: mild wear area, severe wear area and catastrophic wear area. While, the wear map under wet condition was divided into two areas: ultra mild wear area and mild wear area. Through the damage mechanism maps, it could be observed that the surface damage transforms from pitting to delamination under dry condition and the peeling damage was gradually aggravated with the increase in slip ratio and contact pressure. Under the wet condition, plowing damage was predominant and delamination damage gradually occurred with the increase in slip ratio and contact pressure.

The effect of rolling direction on the microstructure evolution of CL60 wheel steel was systematically studied using a rolling-sliding wear testing apparatus. The evolution of microstructures in depth and on the sub-surface was investigated using Electron Backscatter Diffraction (EBSD) and scanning electron microscopy (SEM). The results indicated that the microstructure in depth underwent a transition from the sub-boundaries introduced at low strain into grains with large-angle grain boundaries (LAGBs), leading to a full ultra-fine grain (UFG) microstructure at a large strain. Notably, an abnormal growth of the strain-induced UFGs near the surface occurred at the beginning of the rolling direction reversal (RDR). Meanwhile, the microstructure of the surface layer was changed from a fiber structure parallel to the surface under the unidirectional rolling of wheel materials to a wave structure. With the increase in the number of cycles after the RDR, the grain orientation on the sub-surface was changed from {111} to {101} and finally to a random orientation, resulting in a completely reversed plastic deformation layer. Additionally, the number of cycles per reversal and the total number of cycles also played an important role in microstructure evolution.

The wear and rolling contact fatigue (RCF) performance of eutectoid and hypereutectoid rail steels were studied. Subsequently, the microstructure evolutions of subsurface materials of these two rail steels after testing were comparatively investigated. The results indicated that, compared with the eutectoid rail, the hypereutectoid rail had lower wear loss, but longer RCF crack lengths. After the rolling-sliding testing, the original equiaxed and undeformed coarse grains of rails in the matrix were transformed into nano-grains rich in high angle grain boundaries (HAGBs). The microstructure evolution of rail steels under rolling-sliding contact could be explained by two mechanisms. Firstly, the initial deformation and the breaking of the lamellar structure of pearlite grains occurred through the movement of dislocations. Secondly, the formation of the nanostructure grains happened through continuous dynamic recrystallization (cDRX). Compared with the eutectoid rail, the hypereutectoid rail had finer interlamellar spacing and higher contents of low angle grain boundaries (LAGBs) in the matrix. After the rolling-sliding testing, the hypereutectoid rail had more severe LAGBs-to-HAGBs transitions and a more severe cDRX process than the eutectoid rail, which might be the reason for the longer RCF crack lengths it exhibited.

Laser cladding could be applied on railway wheels to improve their service lives. Fe-based alloy powder is widely used as the laser cladding material due to its good self-fluxing ability and low price. However, the friction coefficients and wear rates of Fe-based alloy laser claddings are high. WS2 is used as the additive for common laser cladding treatment, while it has not been used for claddings on railway wheels. Understanding the influence of WS2 concentration on the mechanical and tribological properties of Fe-based alloy laser claddings on railway wheels has significance for extending the application of laser treatment on railway transit. Therefore, laser claddings of Fe-based alloy powders with different contents of WS2 powder (0, 2%, 4%, 6%, 8%) were produced on the railway CL60 wheel material. Rolling-sliding tests were conducted on a twin-disc tribometer using the uncladded and cladded wheel samples against an uncladded U71Mn rail sample. The results indicated that the microstructure of laser claddings was composed of dendritic and eutectic phases. With the increase in the WS2 content from 0 to 6%, the size of dendritic phases was decreased from around 20 μm to less than 10 μm. With 8% WS2, the size of dendritic phases was increased to around 10–20 μm. Laser claddings of Fe-based alloy powders with WS2 included (Fe, Ni) and (Fe, Si) solid solutions, hard carbide (Cr7C3), Ni–Cr–Fe, and CrS phases. The hardness was increased to 730–820 HV0.5 and residual stresses were changed to be compressive state. Rolling contact fatigue (RCF) cracks preferentially initiated and developed along the boundary between dendritic and eutectic phases. The smallest wear rate and shortest RCF cracks occurred on the cladding from powders with 6% WS2. Thus, the optimum content of WS2 in the Fe-based alloy powder was 6% for laser cladding on the railway wheel material.

The surface crack of wheel/rail is a significant problem affecting the safety and maintenance of railway. This study presents the experimental results to explore the formation and damage mechanism of rolling contact fatigue (RCF) surface cracks of wheel/rail materials under dry condition. The results indicate that the surface cracks mouths on the rail roller are perpendicular to the resultant direction of shear force. Fatigue cracks grow along a larger angle to depth on the rail rollers than on the wheel rollers due to the difference of materials. Meanwhile, there are visible subsurface and secondary cracks as well as lamellar structure cracks. The vertical force changed in the later 1.5×105 cycles leads to a significant difference in the cracks propagation.

Wear and damage transitions of two kinds of wheel materials under different slip ratios conditions were explored using a rolling-sliding wear apparatus. Wear debris was analyzed using X-ray diffraction, Raman spectrometer and X-ray photoelectron spectroscopy. The results indicate that the evolution of wear rate of wheel materials can be divided into three regions: linear wear region, non-linear wear region and undefined wear region. The wear debris is mainly composed of Fe, Fe2O3 and Fe3O4. The relative content of Fe3O4 achieves a maximum value under the slip ratio of 12% condition. The transition from linear wear region to non-linear wear region is due to the wheel oxidation, while the transition from non-linear wear region to undefined wear region may be attributed to the formation of white-etching layer (WEL). A wear and damage mechanism mapping is constructed based on the wear and damage behaviors of wheel materials. Specifically, the dominant wear mechanism transforms from oxidative wear to fatigue wear and then changes back to oxidative wear with the slip ratio increasing.

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.

The objective of this study is to investigate the wear and rolling contact fatigue (RCF) damage of wheel and rail materials under alternating temperature conditions. Two series of rolling-sliding tests were performed: (1) at 20 °C for 75,000 cycles, and then continued at −40 °C for 10,000, 30,000, and 75,000 cycles, respectively; (2) at −40 °C for 75,000 cycles, and then continued at 20 °C for 10,000, 30,000, and 75,000 cycles, respectively. The results indicated that the decrease in the temperature would alleviate the wheel wear due to the formation of wear debris layer. Both the rising and dropping of the environmental temperature during the tests could lead to the increase in the rail wear. Besides, the decrease in the temperature could increase the plastic deformation and work hardening of wheel and rail discs. In addition, the crack initiation was correlated with the behaviour of plastic flow on the wheel. At 20 °C, long single cracks initiated and propagated along the highly deformed ferrite boundaries. At −40 °C, white-etching layer (WEL) was observed only on the wheel surface, which was mainly attributed to the severe plastic deformation. Then, the refined ferrites and WELs were the main crack initiation sources on the wheel.

This paper aimed to investigate the wear properties of different wheel-rail material pairs with various hardness values. Twin-disc wear experiments were carried out via cross-matching five types of wheel material (ER7, ER8, CL60, C-class and D-class) and four types of rail material (U71Mn, U75V, PG4 and PG5). The effects of bulk hardness, post-test hardness, hardening ratio, and rail/wheel hardness ratio (HR/HW) on the wear rate of wheel and rail materials were analyzed. The results indicated that the wheel wear rates decreased with wheel bulk hardness and slightly increased with the rail bulk hardness. However, the rail wear rates decreased with the increasing wheel bulk hardness under 1% creepage and 1500 MPa contact pressure. In addition, both the wheel and rail wear rates showed increasing trends with the increase in wheel hardening ratio and the pre-test HR/HW. The surface damage of the harder C-class and D-class wheels, and the high-hardness PG4 and PG5 rail materials were relatively slight. The premium PG4 and PG5 rails possessed significantly shorter cracks than the base material pair (ER8-U71Mn), whereas, the fatigue cracks in U75V rail steel were relatively longer. The results will not only help optimize wheel and rail hardness matching, but also improve the prediction of wear and crack growth reliant on wheel and rail material properties.

Mineral particles are used to improve adhesion between wheel and rail, but they might lead to severe damages of wheel and rail surfaces. To investigate the adhesion enhancement phenomena and damages of both wheel and rail induced by adhesion enhancers, the crushing strengths of four types of mineral particles (zinc oxide, sand, spinel and alumina) were firstly explored on a uniaxial compression tester. Then the adhesion, wear and damage of wheel/rail were studied on a twin-disc machine under the wet condition. The results show that the characteristic crushing strength was 24 MPa for zinc oxide, 40 MPa for sand, 51 MPa for spinel and 73 MPa for alumina, respectively. For particle with the lowest crushing strength (zinc oxide), the adhesion coefficient was the lowest (around 0.20). With the increase in the crushing strength to 40 MPa, the adhesion coefficient was improved to around 0.28. The particles with higher crushing strengths induced larger wheel/rail wear rates and severer rolling contact fatigue (RCF) damages on wheel and rail. The RCF cracks were large in lengths but small in angles, which finally developed into large pieces of material peeling off from the surface. Sand was the most suitable adhesion enhancer considering its good adhesion enhancement and the relatively mild damage on wheel/rail materials.

Defects such as dents on the rail surface might induce severe rolling contact fatigue (RCF) and then threaten the running safety of railway vehicles. This study aims to explore the initiation and propagation of RCF cracks around dents with different sizes through observing both surfaces and cross-sections of the defective rail. The experiments are conducted on a wheel/rail twin-disc machine. Results indicate that the microstructure evolution process around the dent can be divided into three main stages, namely crack initiation, crack propagation and dent removal. Dents in different sizes act very similarly in each stage, including the position, the crack growth path and the final appearance after the dent has been fully worn off. However, dents in different sizes cause different lifetimes of crack initiation and different lasting times of dents at each stage. For the lager dent, cracks initiate later but propagate for a longer time period, so the dent size plays an important role in the RCF evolution process.

The advanced nano-additives can improve the lubrication performance of nanolubricants efficiently, which could greatly reduce energy consumption. Here, we prepared the BN coated with carbon layer (BN@C) by a novel hydrothermal coating method with pristine BN nanosheets as matrix material and glucose as carbon source. And the BN@C exhibited excellent lubrication performance as a lubricant additive. In order to investigate the tribological properties, BN@C was modified with oleic acid as a surfactant, and the friction tests were carried out on an MRS-10A four-ball friction and wear tester. Benefitting from the stable dispersity, ultrasmall particle size and the surface carbon layer of BN@C-OA, the lubrication performance was significantly improved. More impressively, BN@C-OA could enter the interface of friction pairs. The interlayer sliding occurred to improve the anti-wear and anti-friction properties. This study could provide a new avenue to synthesize the coating-containing nanocomposite additive to promote the lubrication properties of nanoparticles in oil.

Rolling contact fatigue (RCF) of rail is a significant factor affecting the maintenance and service safety of railway track. While the driving parameters are known, clearer relationships are needed with fatigue life. The objective of this study was to explore the role of slip ratio in the development of RCF cracks and fatigue life of rail materials under a water lubricated condition. The results indicate that slip ratio has a vital and interesting influence in the wear and RCF life of rail materials. With an increase of slip ratio from 0 to 0.3%, fatigue life of rail materials has an obvious decrease. As slip ratio increases to 1%, the life increases. Then, RCF life has a drop as slip ratio changes from 1% to 5% and 10%. This may be a comprehensive effect resulting from various contact characteristics of stick area and slip area in the contact area and a competitive relationship between wear and RCF. The increase of slip ratio significantly increases the growth angle of cracks and transforms the damage mechanism of rail materials from slight surface fatigue to serious fatigue and pitting damage.

The impact wear behaviour and damage mechanism and transitions of rail weld joint and rail materials were explored using a cyclic impact tester under dry conditions. The results indicate that the impact wear volume of rail weld joint and rail material increases with the number of impact cycles or impact force increasing and the resistance to impact wear of rail weld joint is better than that of rail material. The impact wear mapping including three regions is developed and there is a transition zone with an increase in impact number and impact force. Meanwhile, two kinds of pit formed and the different mechanisms are noted. There is a different crack growth path for rail material and rail weld joint due to the different microstructure of materials.

The cracks of the wheel and rail materials have a vital role in determining the safety of railway transportation. This study is to explore the cracks propagation characteristics of wheel materials under the bending moment condition using a wheel/rail simulation facility and finite element method. The results indicate that the stress concentration is found at the tips of pre-cracks and the maximum equivalent stress and strain are located at the tips and both sides of the pre-cracks, meanwhile the cracks initiate on the tips and both sides of the pre-cracks. With the width of pre-crack increasing or the depth of pre-crack decreasing, the equivalent stress and strain and the crack length all significantly increase. Meanwhile, with an increase in carbon content of wheel materials, the crack length has an obvious drop. The cracks propagation direction is not entirely along the original directions of pre-cracks. When the cracks propagate to a certain stage, the cracks propagating directions easily change, bend and branch cracks initiate from the principle cracks. It is worth noting that the transgranular fracture is dominating cracks propagating mechanism of wheel materials.

The objective of this study is to evaluate the effect of slip ratio on the wear and rolling contact fatigue (RCF) of wheel/rail materials using a rolling–sliding wear testing apparatus. The results indicate that two wear types are presented in terms of wear rate: type I (mild wear) and type II (severe wear). In type I wear, cracks propagate parallel to the surface. While in type II, the peeling is aggravated and spalling can be observed. With the slip ratio increasing, the wear mechanism of rollers transforms from slight oxidation wear and peeling to severe fatigue wear and spalling. Due to the mild wear and light plastic deformation in type I, the angle and depth of cracks show no obvious differences between the wheel and rail rollers. The crack depth and angle increase in type II wear owing to severe plastic deformation, while the depth is smaller on the wheel rollers. The size of flake wear debris presents an increasing trend and the main composition is Fe 2 O 3 and metallic iron, and the content of iron diminishes with increasing oxidation.

Rolling-sliding wear experiments were performed to investigate the wear and rolling contact fatigue (RCF) behaviours of a premium pearlitic rail (PH), a carbon-free bainitic rail (BH) and two standard pearlitic rails (U71Mn and U75V). The wear regime and RCF damage evolution of the PH and BH materials in terms of Tγ/A (i.e. creepages and contact pressures) were compared and analyzed. The high-hardness BH steel presented a wear resistance similar to U71Mn and U75V rail materials, whereas lower wear rate was shown by the PH steel. Concerning the RCF performance, the damage of BH steel (comparable to U75V) was more severe than that of PH steel (comparable to U71Mn). Finally, with the increase in creepages and pressures, the wear and RCF damage of both PH and BH steels increased. These information could provide a guide in choosing rail materials and in development of bainitic rails.

The objective of this study is to explore the wear and rolling contact fatigue (RCF) characteristics of wheel materials under different operating speeds conditions using a small scale wheel/rail facility. The results indicate that the operating speed plays a vital role in the wear and RCF of wheel materials. As the operating speed increases, both the surface hardness and the hardness of the plastic flow layer on the wheel roller decrease while the worn surfaces become rougher. Shear strain hardening of wheel roller decreases with increasing operating speed. Furthermore, the primary damage mechanism of the wheel roller transforms from spalling and slight surface fatigue to severe fatigue cracks as the operating speed increases. Fatigue cracks initiate from the wear surface and grow along with the soft ferrite lines within the plastically deformation layer. RCF damage become more severe and the wear rate of the wheel roller decreases as operating speed increases. Low wear rate can not adequately remove cracks and leads to a visible increase in the angle of fatigue crack propagation and the crack depth. Furthermore, the wear debris is composed of metallic flakes whose primary compositions are iron, Fe 2 O 3 , and Fe 3 O 4 and the size of wear debris decreases, but the thickness increases as operating speed increases.

Decarburization can remain on the surfaces of rail head steels and affect their wear and damage processes. The current research explored the influence of a decarburized layer on wear resistance and damage behavior of rail materials using a rolling–sliding wear testing machine. A decarburized layer decreases the hardness and wear resistance of rail steels, and the wear rate of a decarburized rail is over twice that of the same steel without decarburization. Multi-layer peeling appears on rail rollers without decarburization, but a decarburized layer changes the damage mechanism of the rail steel. With an increase in the depth of decarburization, the damage of rail roller turns from major spalling to pitting and peeling. In addition, surface fatigue cracks become more serious as depth increases. By contrast, shallow decarburization has little effect on rolling contact fatigue (RCF) of the rail material. Only when the depth of the decarburization exceeds a certain thickness (i.e., about 0.5 mm based on the present results), RCF damage sharply worsens as decarburization depth increases. Furthermore, adhesive wear features are obvious on the rail roller only when a decarburized zone remains at the wear surface.

This study discusses a Tγ/A method of plotting wear data from a twin-disc machine for identifying the wear and damage transitions of wheel and rail materials. As found in previous work, three wear regimes (mild wear, severe wear and catastrophic wear) of U71Mn rail material were identified in dry rolling–sliding contact tests. It was determined that the damage mechanism transforms in the different wear regimes. Here earlier studies were extended to establish wear behavior for the presence of a number of third body materials (oil, water, friction enhancers) and a rail cladding process designed to make wheels and rails more durable. This has provided much needed data for Multi-Body Dynamics (MBD) simulations, and will allow better predictions of profile evolution of wheel and rail over a wider range of conditions.

The objective of this study is to construct wear mapping and transitions of wheel/rail materials under different contact pressure and sliding velocity conditions by means of comprehensive consideration of both wear rates and surface damage morphology of wheel/rail rollers. The results indicate that, both the wear rates of wheel rollers and the wear rates of rail rollers increase with contact pressure increasing. With sliding velocity increasing, the wheel wear rates show an increase trend and the rail wear rates decrease. Wear regime maps of wheel/rail materials are divided into two regions: mild wear regime and severe wear regime, and both the wear rates of wheel roller and the wear rates of rail roller are about 2.0×10 −6 g/m on the transition boundaries. The wear mechanisms of the wheel and rail materials are significantly different and transform in different wear regimes. Based on the damage characteristics in different wear regimes, the wear mechanism maps of wheel and rail materials are constructed. Fatigue cracks of wheel material develop along with soft ferrite lines in the plastic deformation area. Furthermore, cracks on the rail rollers develop into the material a depth, then become parallel with the surface and turn towards it.

The objective of this study was to explore the effect of alumina particle on improving adhesion and wear damage of wheel/rail under wet conditions using a rolling–sliding wear apparatus. The results indicate that alumina particles significantly improve adhesion coefficient under wet conditions. The adhesion coefficient declines with the alumina particle size increasing from S (about 75 μm) to L (about 250 μm) and then keeps stable. Meanwhile, the adhesion coefficient increases firstly with the feed rate increasing from 1 to 3 g/min, and then decreases from 3 to 7 g/min, subsequently, keeps stable to 10 g/min. With an increase in particle size and feed rate, the wear rates of wheel/rail rollers increase, the thickness of plastic deformation layers and surface hardness decrease, and the damage mechanism turns from slight spalling to severe spalling and big pit. The embedded alumina particles on the roller surface produce high stress and change the plastic deformation line. Fatigue cracks develop from the surface and the wall of the pit on the rollers, and tend to connect with each other resulting in the removal of material. Furthermore, the interlayer material in the severe cracks tends to break.

The objective of this study is to investigate the influence of water on tribological braking behavior of brake shoe material using a sub-scale frictional braking machine. The results indicate that the friction coefficient of braking interface has a close relationship with the braking velocity and the pressure under the wet condition. The friction coefficient shows a reduction by 30% compared with the dry condition at low braking speed. With an increase in braking velocity, more water is thrown off from the braking interface. This makes the water film becomes thinner and the surfaces becomes closer, which results in more contact and more wear. Therefore, more friction heat is produced and more water is evaporated, which makes the water film thinner and the interface more similar to the dry. The water sealed up in the cracks leads to partial high pressure point on the surface resulting in serious pitting damage of brake shoe. Both the stability of friction coefficient and the wear loss under wet condition are worse than those under dry condition.

The grinding process for maintaining the railroad rails can affect their performance. A rail grinding friction testing apparatus was developed to investigate the effects of rotational speed of grinding stone on removal behavior of rail material. The rail-grinding stone contact consists of a round, flat grinding stone and two test specimens made from Mn–steel rails that are pressed against the face of the stone. The effects of grinding wheel rotational speed on the abrasive removal mechanism of rail material are explored in detail. The results indicate that as the grinding wheel rotational speed increases, the friction coefficient, the surface roughness of rail specimens and the width of the wear grooves decrease. The grinding wear volume, the microindentation hardness of the rail specimens and the surface temperature-rise all increase as the number of grinding cycles increase. Wear debris collected during the test is composed of round particles and curled cutting chips. The debris is mainly composed of Fe 3 O 4 , FeO and Fe. As grinding rotational speed increases, the content of Fe 3 O 4 and FeO increases but the width of the cutting chips decreases.

In this study, the wear and damage behaviors of three heavy haul rail steels (including one hypereutectoid rail steel and two eutectoid rail steels) were investigated at room (around 20 °C) and low (−40 °C) temperatures using a rolling-sliding wear test machine. The results indicated that, compared with eutectoid steels, the hypereutectoid rail steel had a better wear resistance and a better rolling contact fatigue (RCF) resistance at the room temperature, and better wear resistance but worse RCF resistance at the low temperature. Compared with the room temperature, at the low temperature both the hypereutectoid and eutectoid rails had better wear resistance, the RCF resistance of eutectoid steels was improved but the RCF resistance of hypereutectoid rail was reduced. At the room temperature, the worn surfaces of both wheel and rail materials were dominated by surface cracks. On the contrary, at the low temperature, the worn surfaces of wheel and rail materials were dominated by third body layers (TBLs) and oxidized spots, respectively.

Abrasive material and hardness of grinding wheel are two important factors affecting the grinding efficiency and quality. In this study, two kinds of abrasive grains (i.e., zirconium corundum (ZA) and brown fused alumina (BA)) were used to produce eight grinding wheels, among which five with different contents of abrasive grains and four with different hardness levels. Rail grinding experiments were conducted to investigate their grinding efficiency (grinding amount of rail), grinding quality (including surface roughness, surface burn, white etching layer (WEL), and residual stress), and wear types of grinding wheels. The results show that ZA grinding wheel produced larger grinding amount, higher surface roughness, but lower level of surface burn, thinner WEL, and smaller parallel residual stress than BA grinding wheel. With the increase in grinding wheel hardness, the surface roughness and residual stress of ground rail showed decrease trends, but the thickness of WEL increased. The wear type of ZA grains was macro-fracture and the wear type of BA grains was attrition wear. With the increase in grinding wheel hardness, the wear type was changed from grain pullout wear to macro-fracture. Based on the analysis of results, the appropriate grinding wheel was recommended that can improve the grinding process and reduce the grinding cost.

Surface dents on railroad rails may be caused, for example, by the drop of freight goods or the impact of ballast rocks and may have a deep effect on the rail service life. To better understand this problem, this investigation aims at exploring the rolling contact fatigue behavior of the rail materials (as, for example, PD3 steel) after being impacted by two kinds of hard bodies: a simple spherical steel ball and a more realistic ballast rock. The results show that the residual tensile stress, which is distributed on the shoulders of the dent, decreases the rolling contact fatigue (RCF) resistance of the material around the dent. Moreover, the unbalanced wear behavior between the two shoulders of the dent makes the situation even worse on the side of the dent where the tangential force acts firstly. Finally, due to the higher martensite hardness with respect to the matrix material, the crack propagates faster around the dent in presence of white etching layer on the bottom of the dent itself.

The objective of this study is to investigate the braking tribological characteristics of two kinds of metro brake shoe materials using a sub-scale frictional braking machine. The results indicate that the friction coefficient of braking interface has a close relationship with the velocity and pressure. The increase of velocity and pressure raises the temperature-rise of braking interface. The increasing velocity and pressure aggravate the wear of brake shoe rings. However, the wear loss of wheel rings decreases with increasing pressure. The braking surface of brake shoe rings exhibits adhesive wear and spalling, while obvious plowing and abrasive wear are dominant on the braking surface of wheel rings. According to the experimental results, it is concluded that brake shoe B material can be used to prevent and alleviate the occurrence and evolution of groove wear on wheel tread. This might be attributed to the higher percentage of FeC3 versus FeS2 in its composition compared with brake material A. Field testing, completed to 100,000 km thus far, has to be completed on these materials and further work should be performed for evaluating the effect of different brake shoe materials on the groove wear of wheel tread in the field.

The objective of this study is to investigate the effects of rotational speed on rolling wear and damage behaviors of wheel/rail materials using a rolling–sliding wear testing apparatus. The results indicate that, with the rotational speed increasing, the surface hardness of rail roller remains unchanged while the increase of surface hardness of wheel roller declines resulting in a decrease of wheel/rail hardness ratio. The wear loss of wheel roller increases while the wear loss of rail roller declines with increasing rotational speed. The worn surface of rail roller exhibits peeling and spalling damage. Fatigue cracks and adhesive wear are dominating for the worn surface of wheel roller. Furthermore, with the speed increasing the fatigue damage lightens and adhesive wear worsens for the wheel roller. Fatigue cracks of wheel rollers grow along with soft ferrite lines in plastic deformation area. Cracks of rail rollers tend to turn towards the worn surface. There are visible branch cracks and multilayer cracks on the surface of wheel/rail rollers. Branch cracks of wheel rollers are longer than that of rail roller, and the interlayer material of multilayer cracks is easy to break. Wear debris of wheel/rail rollers is composed of Fe2O3 and martensite. The size of debris with flakes structure decreases and the martensite content increases with the rotational speed increasing.

The aim of this study is to investigate the influence of laser cladding Fe-based alloy on microstructure and wear characteristic of wheel/rail materials using a rolling–sliding wear testing apparatus. Especially, the effect of lanthanum oxide on the properties of laser cladding coating was explored in detail. The results show that the laser cladding Fe-based alloy coating consists of dendrites and eutectic and is composed of (Fe, Ni) solid solution and Cr 7 C 3 carbide. The hardness and wear-resistance of wheel/rail materials are enhanced using laser cladding. The wear and surface damage of wheel/rail rollers dramatically alleviate owing to the refinement of the microstructure when adding lanthanum oxide into laser cladding coating. The wear mechanism of wheel/rail rollers turns from severe spalling and delamination wear (untreated specimens) to slight peeling (with 1.2% La 2 O 3 ). Furthermore, the plastic deformation of wheel/rail rollers undergoing laser cladding is significantly thinner than that of untreated rollers. In summary, laser cladding Fe-based alloy coating can be used to prolong the wear life of wheel and rail materials.

The objective of this study is to investigate the effect of laser cladding coating on wear and damage behaviors of heavy-haul wheel/rail materials by means of a laboratory-scale rolling–sliding wear apparatus. The results indicate that the wheel/rail rollers with laser cladding form a uniform and compacted coating without any cracks or stomata. The laser cladding coating markedly improves wear-resistance of wheel/rail rollers. The wear mechanism of wheel/rail rollers undergoing laser cladding is plowing and abrasive wear. However, the wheel/rail rollers without laser cladding exhibit visible adhesion wear and serious spalling damage. Furthermore, there are obvious fatigue cracks in both the surface and subsurface. Excellent wear-resistance of laser cladding coating can effectively alleviate surface damage and prolong wear life of heavy-haul wheel/rail. However, further work should be carried out for clarifying the fatigue characteristic of wheel/rail with laser cladding coating.

The adhesion characteristics of railroad wheels against rails were simulated using a sub-scale wheel/rail configuration. The apparatus consists of a small roller to simulate the locomotive or rolling stock wheel and a large roller to simulate the rail. The scale of the wheel/rail profiles, relative to full size, is 1:4. Results indicated that this laboratory test can be used to adequately simulate and evaluate the adhesion behavior of the wheel/rail interface under various conditions. Under dry conditions, the adhesion coefficient of wheel/rail has a sharp initial increase of between 0% and 1.5% as creep ratio increases, and then a slight reduction of up to 5%. The presence of water or oil markedly decreases the adhesion coefficient of wheel/rail. With an increase of speed and due to the water volume in the wheel/rail surface, the adhesion coefficient drops. With an increase of lateral force, the adhesion coefficient of wheel/rail increases. Axle load has no obvious effect on the adhesion coefficient in the presence of water. Tree leaves have an important effect on the adhesion coefficient and should be cleared away from the contact surface of wheel/rail if water is present. Further work on improving adhesion and damage of wheels on rails should be studied and explored under a range of low adhesion conditions.

The aim of this paper is to investigate the adhesion behavior of wheel/rail under dry and water conditions using a JD-1 wheel/rail simulation facility. The results indicate that a wheel/rail simulation facility has been developed and used to assess the effect of dry and water lubricant conditions on adhesion behavior of wheel/rail. The adhesion coefficient of wheel/rail rises rapidly with the increase of creep ratio and then has a slower and slight decrease up to 5% under dry condition. The water medium can significantly affect the adhesion behavior of wheel/rail. Water lubricant condition gives the lower values of adhesion coefficient with dry condition giving higher values. The increase of speed and attack angle would markedly decrease adhesion coefficient of wheel/rail under dry and water lubricant conditions. However, axle load has no obvious influence on adhesion coefficient of wheel/rail under water condition.

The objective of this study is to investigate the adhesion behavior of wheel/rail under oil, water and sanding conditions using a JD-1 wheel/rail simulation facility, which consists of a small wheel roller serving as locomotive or rolling stock wheel and a large wheel roller serving as rail. The results indicate that the adhesion coefficient of wheel/rail decreases remarkably under oil condition compared with dry and water conditions. With an increasing speed, the adhesion coefficient of wheel/rail decreases under oil, water and sanding conditions. However, with the increase of axle load, the adhesion coefficient of wheel/rail increases under the conditions with mixed oil, water and sand. Sanding can increase adhesion coefficient but damage the wheel/rail surfaces. In addition, the effect of adhesion improving by sanding is better under water condition. The adhesion coefficient is smallest with mixed oil and water.

Rolling contact fatigue (RCF) failure is a permanent and quite severe problem and hence of major concern to the modern railway industry. The selection of rail material should be based on a well-founded understanding of RCF. An analysis of the chemical composition, mechanical performance and microstructure was performed on U75V and U71Mn rail samples with oblique cracks taken from Guangzhou–Shenzhen railway. The results indicate that the strength character of U75V rail is superior to U71Mn rail. The crack propagation angle to the surface of U71Mn rail is smaller than that of U75V rail. A mixture of intergranular and transgranular fracture was found dominant in the process of fatigue crack propagation of U71Mn rail; in comparison, the dominant fracture mode of U75V rail is transgranular and the crack is easier to propagate at a relatively higher rate. The analysis shows that U71Mn rail is more suitable for the high-speed railway.

The coupling relationship between oblique fatigue crack and rail wear in curve track was investigated by means of field analysis and theoretical calculation. The field investigations indicate that while the side wear of rail is serious, the fatigue crack is relatively slight. The increase of rail wear rate can alleviate its fatigue damage. The relationship between side wear of rail and fatigue crack damage seems as competitive and restrictive coupling mechanisms. Thus, a new asymmetrical rail grinding method was developed to prevent oblique crack damage of curve track in Guangzhou–Shenzhen railway. The field test results indicate that the asymmetrical rail grinding increases the guidance force between wheel flange and rail and aggravates rail wear. This new rail grinding method can dramatically alleviate rail fatigue oblique crack damage in high-speed curve track by increasing artificially wear rate.

A reciprocating rolling–sliding test apparatus was developed based on a tension–compression hydraulic machine with a high precision, and a number of tests have been carried out using the new test apparatus. Through the tests and the test result analysis, interesting conclusions were obtained. The friction coefficient varies when a test element begins to roll from rest. The wear mechanisms were changed with an increase in the number of the tangential friction force or an increase of cycles in rolling contact.

This paper presents experimental study of rail corrugation using a JD-1 wheel/rail simulate facility, which mainly consists of a big wheel serving as the rail, and a small wheel serving as the locomotive or rolling stock wheel. The power delivered to each testing wheel can be accurately controlled. The traction or braking force can be obtained by the power applied to the small wheel during continuous test operation. In order to understand the mechanism of the wear, the wear corrugations on the scars of small wheel were examined by optical and scanning electron microscopy. Preliminary results can be drawn as follows: the corrugation depends on the tangential force and vertical oscillation between the rail and wheel of test machine. The tangential force enhanced the wear of contact surface, and the fluctuating force between two contact surfaces could induce asymmetry wear, which could produce original corrugation on the rolling wheel. When the original corrugation initiated, the uneven surface would lead to a rapid growth of the corrugation.

A new rolling testing apparatus was developed on a tension–compression hydraulic machine with a high precision. The aim of this paper is to study the transition of wear mechanisms of steels with the increase of tangential friction force between contact surfaces in rolling. The wear modes were particularly analyzed during the passage from rolling to mixed rolling–sliding contact.

Fretting behaviour have been investigated in oil lubrication, covering a large range of amplitude from 2 to 400 μm. Two types of oil and contact pair on fretting behaviour were studied. A significant reduction in the coefficient of friction occurred above critical displacement amplitude. Analysis of fretting condition in combination with fretting mark examinations reveal that, at an early stage, fretting behaviour depended upon oil boundary lubrication, and was later closely associated with the degree of oxygen access and penetration of oil into the interface. Compared to dry conditions, a great difference in fretting regime behaviour and contact wear was observed.