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Schematic view of a) pure sliding contact b) rolling/sliding contact under acceleration. Where F N is the resulting normal force; v is the forward speed; r is the wheel radius; ω is the rotational
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![Table 3 . Examples of wheel-rail adhesion coefficients [48].](profile/Saeed-Abbasi-18/publication/236418472/figure/tbl1/AS:668497927487498@1536393734868/Examples-of-wheel-rail-adhesion-coefficients-48_Q320.jpg)
The wheel−rail contact is a safety critical interface. Wear, particle emission and adhesion are all wheel−rail contact phenomena and are discussed here. All three phenomena are material and system parameters and are linked together. Different countermeasures to one phenomenon such as adhesion enhancement with a friction modifier can increase the we...
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Context 1
... Adhesion, traction and friction From a strict tribological point of view adhesion is the force that is required to separate two surfaces which have been brought into contact and is a term usually used to describe how well surface coatings or paint are bonded to the surfaces which they coat [32, 33]. However, the word adhesion has become widely used among the wheel-rail research community to describe the tangential force resulting at the wheel-rail contact as used in [ 34, 35]. Friction force is defined as the resistance encountered by one body moving over another body [36]. The difference between friction and adhesion can be illustrated with the help of Figure 20. Figure 20 (a) shows a block sliding at velocity, v along a stationary plane surface. The block is subject to a normal force, F N (due to the weight of the block) and a horizontal force, F . The horizontal force which opposes the motion of the block is deemed the friction force, F f . The static friction force is equal to the horizontal force required to initiate sliding while the kinetic friction force is equal to the horizontal force required to maintain sliding [36]. Generally the static friction is higher than the kinetic friction. The ratio between the friction force and the normal force is referred to as the friction coefficient (Equation 1). Figure 20 (a) presents a case of pure sliding and the friction force is dependent on: interaction and deformation of microscopic asperities in the contact and adhesion forces between the two sliding surfaces ...
Context 2
... Adhesion, traction and friction From a strict tribological point of view adhesion is the force that is required to separate two surfaces which have been brought into contact and is a term usually used to describe how well surface coatings or paint are bonded to the surfaces which they coat [32, 33]. However, the word adhesion has become widely used among the wheel-rail research community to describe the tangential force resulting at the wheel-rail contact as used in [ 34, 35]. Friction force is defined as the resistance encountered by one body moving over another body [36]. The difference between friction and adhesion can be illustrated with the help of Figure 20. Figure 20 (a) shows a block sliding at velocity, v along a stationary plane surface. The block is subject to a normal force, F N (due to the weight of the block) and a horizontal force, F . The horizontal force which opposes the motion of the block is deemed the friction force, F f . The static friction force is equal to the horizontal force required to initiate sliding while the kinetic friction force is equal to the horizontal force required to maintain sliding [36]. Generally the static friction is higher than the kinetic friction. The ratio between the friction force and the normal force is referred to as the friction coefficient (Equation 1). Figure 20 (a) presents a case of pure sliding and the friction force is dependent on: interaction and deformation of microscopic asperities in the contact and adhesion forces between the two sliding surfaces ...
Context 3
... Adhesion, traction and friction From a strict tribological point of view adhesion is the force that is required to separate two surfaces which have been brought into contact and is a term usually used to describe how well surface coatings or paint are bonded to the surfaces which they coat [32, 33]. However, the word adhesion has become widely used among the wheel-rail research community to describe the tangential force resulting at the wheel-rail contact as used in [ 34, 35]. Friction force is defined as the resistance encountered by one body moving over another body [36]. The difference between friction and adhesion can be illustrated with the help of Figure 20. Figure 20 (a) shows a block sliding at velocity, v along a stationary plane surface. The block is subject to a normal force, F N (due to the weight of the block) and a horizontal force, F . The horizontal force which opposes the motion of the block is deemed the friction force, F f . The static friction force is equal to the horizontal force required to initiate sliding while the kinetic friction force is equal to the horizontal force required to maintain sliding [36]. Generally the static friction is higher than the kinetic friction. The ratio between the friction force and the normal force is referred to as the friction coefficient (Equation 1). Figure 20 (a) presents a case of pure sliding and the friction force is dependent on: interaction and deformation of microscopic asperities in the contact and adhesion forces between the two sliding surfaces ...
Context 4
... since the invention of the wheel it has been known that it is far more efficient to move heavy objects on wheels or rollers rather than sliding them over solid surfaces. Typically for a steel cylinder rolling on a steel surface, the coefficient of rolling resistance (free rolling) is of the order of 0.001 [37]. For most metal pairs in sliding contact the friction coefficient is in the order of 0.3 – 1.0 [38]. The coefficient of rolling resistance for any rolling contact is inversely proportional to the contact modulus. For example the coefficient of rolling resistance for a pneumatic tyre on asphalt is typically 0.01. Driving locomotive wheels however, are not pushed along the track but have a torque applied about their center of rotation. Figure 20 (b) shows a cylinder rolling along a stationary plane surface. This is analogous to the case of a wheel rolling along a rail. The wheel is subject to normal force, F N and travels along the rail at velocity, v . The wheel is subject to torque, T which maintains the angular velocity of the wheel, ω and also causes a reactive tangential force, F T , at the wheel-rail interface. The tangential force of a driving wheel is known as traction which ultimately propels the wheel along the rail. During deceleration, the tangential force opposes the running direction indicated as F T in brackets in Figure 20 (b). The tangential force in accelerating or decelerating cases is named adhesion. The ratio between the adhesion force and the normal force is known as the adhesion coefficient (Equation 2) ...
Context 5
... since the invention of the wheel it has been known that it is far more efficient to move heavy objects on wheels or rollers rather than sliding them over solid surfaces. Typically for a steel cylinder rolling on a steel surface, the coefficient of rolling resistance (free rolling) is of the order of 0.001 [37]. For most metal pairs in sliding contact the friction coefficient is in the order of 0.3 – 1.0 [38]. The coefficient of rolling resistance for any rolling contact is inversely proportional to the contact modulus. For example the coefficient of rolling resistance for a pneumatic tyre on asphalt is typically 0.01. Driving locomotive wheels however, are not pushed along the track but have a torque applied about their center of rotation. Figure 20 (b) shows a cylinder rolling along a stationary plane surface. This is analogous to the case of a wheel rolling along a rail. The wheel is subject to normal force, F N and travels along the rail at velocity, v . The wheel is subject to torque, T which maintains the angular velocity of the wheel, ω and also causes a reactive tangential force, F T , at the wheel-rail interface. The tangential force of a driving wheel is known as traction which ultimately propels the wheel along the rail. During deceleration, the tangential force opposes the running direction indicated as F T in brackets in Figure 20 (b). The tangential force in accelerating or decelerating cases is named adhesion. The ratio between the adhesion force and the normal force is known as the adhesion coefficient (Equation 2) ...
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Citations
... A recent process for manufacturing the bainitic steel is subjected to a discontinuous cooling program, which entails fast-tracked cooling at a rate of 1 to 10 °C/s from the austenite phase region to a stop cooling temperature range of 500 to 300 °C, then cooled further to an ambient atmosphere temperature. The bainitic steel from which produced steel is not carbide-free [5][6][7][8][9][10]. ...
In this investigation, an attempt has been made to identify the metallurgical properties with the change of silicon contents, either theoretically by utilizing Thermo-Calc (the Scheil–Gulliver model implemented in the Thermo-Calc software) or JMatPro software, as a computational prediction technique, in addition to experimental examinations by dilatometer. Microstructures of investigated steels were evaluated optically at low magnification using optical microscopy. Scanning electron microscopy was used to study the observed microstructure at high magnification . ASTM standard specification E-8 was utilized for measuring the tensile property values, while fracture surfaces of the tensile samples were inspected by EDS (point-analyzer) employed in scanning electron microscopy. The investigated steel’s as-polished surface was studied using the experimental results, which revealed that the steel microstructure ranged from full-bainitic to full-pearlitic structures according to the variation of silicon contents. The count of non-metallic inclusions decreased and vice versa by the area occupied by non-metallic inclusions with the rising silicon content. The steel containing silicon of 0.87 wt.% has the best toughness combined with high tensile strength and hardness incomparable with conventional steel. Elongation (16.2%) combined with an ultimate tensile strength (1113 MPa) was achieved for the steel containing 0.87 wt.% Si.
... In the wheel-rail tribological system, wear tests are commonly twin-disc and pin-on-disc, which simulate contact in a straight or curved path, respectively. In the curved path, the contact conditions of the wheel flange with the rail gauge face are severe, promoting higher slip and contact pressures than in the straight path (contact of the wheel tread with the rail running surface) ( Ref 11,12). However, the twin-disc test offers the greatest correlation with overall wheel-rail contact conditions and has been used extensively to test the RCF and wear resistance of wheels and rails ( Ref 13). ...
This work aimed to characterize a new class D microalloyed forged wheel (called 7NbMo). For this purpose, the following analyses were carried out: obtaining CCT curves for the steel (cooling rates of 0.5-50 °C/s), investigating the microstructure below the rolling track (scanning electron microscopy and hardness), performing mechanical tensile and fracture toughness tests, and verifying the wheel's tribological behavior using twin-disc tests (wear, cracks, and, optical microscopy and scanning electron microscopy analyses of the disc’s surface and subsurface). There was an increase in the hardenability of the steel, caused by the addition of microalloying elements, which impacted the microstructure of the wheel up to 15 mm below the rolling track. In this region, tempered bainite and martensite were identified, which provided high values of mechanical resistance. However, the twin-disc tests showed that higher values of hardness and mechanical properties did not suppress the disadvantage of the presence of tempered martensite in the microstructure, since the 7NbMo discs showed the same weight loss of the pearlitic discs and did not achieve better results in the rolling contact fatigue as expected for class D wheel material.
... The author concluded that a reduced curve radius leads to a significant increase of the wear rate two orders of magnitude. (Olofsson et al., 2013) focused on the tribology of the wheel-rail contact and the dependency of adhesion, wear and particle emission. Counter measures to improve one of these phenomena will necessarily cause an impact on the others. ...
The sources of non-exhaust emissions from railways have been identified in the past. However, the quantification of the emission from railways is subject to a large degree of uncertainties, as published emission factors vary by orders of magnitude. The presented study aims a detailed quan-tification of the wheel-rail contact. For this reason, a series of tests at a wheel-rail test bench was conducted. The emission monitoring covered particle mass, particle size distribution and filter sampling in order to enable a chemical analysis of the particle composition. According to the test results the cumulative PM10 emissions of the wheel-rail contact (entire train) range from 0.33 to 5.57 g/km. The average proportions of PM2.5 and PM1 in the PM10 emissions were 87.5% and 68.46% respectively. While in straight-line driving and in wide curves the number of axles is the most dominant parameter, in tight curves, the bogie length becomes more relevant.
... One advantage of the use of polymers when compared to steel dies is their low interfacial adhesion energy, which leads to a low coefficient of friction (COF) [16]. Two main processes that impact the wear of polymers are interfacial wear (adhesion) and cohesive wear (mainly abrasion) [17]. Polymeric tools are characterised by lower Hertzian contact pressures, leading to viscoelastic and sometimes plastic deformations, which occur at relatively low loads [18]. ...
Sheet metal forming processes, the purpose of which is to give the shaped material appropriate mechanical, dimensional and shape properties, are characterised by different values of unit pressures and lubrication conditions. Increasing the efficiency of tool work by increasing their durability, efficiency and reliability is still one of the main indicators of increasing production efficiency. Tool wear in metal forming technologies significantly differs from the character of wear in other methods of metalworking, such as machining. This article presents the characteristics of tool wear mechanisms used in sheet metal forming. Possibilities of increasing the durability of tools by applying coatings produced by laser techniques, chemical vapour deposition and chemical vapour deposition are also discussed. Great emphasis is placed on self-lubricating and functional materials and coatings. Current trends in lubricants and lubrication methods in sheet forming, including tool texturing, are also presented.
... There is a strong relationship between adhesion and friction processes, characterised by the surface conditions and the presence of third body layers at the point of contact between rails and wheels. Understanding wheel-rail contact requires a deeper understanding of the surface interactions and the presence of a third body [5], a solid interfacial layer in the wheel-rail contact interface characterised by contaminants and surface roughness [6]. One factor that affects the rails' friction condition is the selfcleaning process. ...
The proper representation of friction contact conditions between each wheel and the rail is necessary to accurately model the behaviour of a heavy haul locomotive since friction conditions at the wheel-rail interface affect the locomotive’s dynamic performance under traction and braking conditions. In normal operations, a phenomenon commonly known as rail cleaning effect occurs. The rail cleaning effect causes increased friction coefficients between the following wheel treads and the rail head. The wheel-rail interaction causes the third body layer to be partly or wholly eliminated from the surfaces in contact and generates new layer. An experimental analysis of the changes in friction coefficients under simulated locomotive wheel-rail contact conditions, in terms of contact pressure and slip, is presented in this paper. For this study, data processing equations are presented to obtain the experimental traction coefficient and slip. Furthermore, the rail cleaning effect is examined under different slip conditions. The experiment shows the traction coefficient increases for a given number of cycles until reaching a steady value, demonstrating that the rail cleaning effect is measurable in various slip conditions on a twin disc machine.
... measured using a torque sensor (JN338, China, range: 0-100 N m, accuracy: 0.1 N m) and a revolution sensor (JN338, China, range: 0-6000rpm, accuracy: 1rpm), respectively. Moreover, the normal force (range: 0-6kN, accuracy: 0.1 N) could be applied by adjusting a hydraulic cylinder and measured using a load sensor (CYB-12S, China, range: 0-6 MPa, accuracy: 0.1%).Therefore, different traction coefficients μ (i.e., the friction coefficient for partial slip or full slip under traction condition[57]) could be achieved by applying a normal force and adjusting different creepages, as well as setting a constant creepage and applying different normal forces. The (a) appearance drawing and (b) schematic diagram of MJP-30A twin-disc testing apparatus. ...
... An increasing concentration of particles made this effect more pronounced, meaning that the effectiveness of the lubricant was degraded even more quickly. In their paper on the tribology in the wheel-rail contact of locomotives, Olofsson et al. [6] discussed the role that particles play in wear. The role is, independently of where the particles originate, essentially twofold. ...
Particles exist in any tribo-system, whether it is closed to the environment or not. These particles originate from various sources, for example: contaminants such as dust or fibres from the environment; wear debris from abrasive/adhesive wear; and particles that are intentionally included in lubricant formulations. The particles affect the tribo-system in which they occur, but it is not always clear how. In this work, three types of chemically inert particles of similar size but different hardness are mixed with an otherwise pure oil and tested tribologically. Three tribological testing methods, pin-on-disc, four-ball, and bending-under-tension, are used to investigate the effect of the particles on friction and wear under sheet metal forming conditions. The hardness of the particles had a large effect on wear development, but little to no effect on the coefficient of friction found by pin-on-disc testing. Including particles of any hardness helped the oil in which they were included resist variation in load, leading to less wear for higher loads compared to the pure oil.
... In dry contact conditions (without lubricant), surface damage occurs [23]. Furthermore, when oil and water are added simultaneously, they generate a boundary or mixed film that reduces adhesion between the rail and the wheel [24]. Compared to dry circumstances, the presence of leaves effectively lowers the coefficient of friction by a factor of four. ...
This study reports on the tribological behavior of Indian rail track and wheel materials under different contaminants. A pin-on-disc tribometer was selected for the experimental analysis in ambient conditions (temperature of 24.9 °C and relative humidity of 66%). Sand, mist, leaves, and grease were the contaminants used in this investigation. The railway track was used to make the pin, and the wheel was used to make the disc. The acquired results were analyzed using frictional force and wear depth as a function of time as the variables. These pollutant effects were compared to no-contaminant conditions. It was observed that the sand increased the friction force and wear depth, whereas oil decreased friction and wear. Mist and leaves also reduced friction and wear. The effect of leaves was higher than the mist. The effect of load on various contaminants was also investigated. The results showed that as the load increased, the friction force and wear also increased for all contaminants. The results of this study can help in understanding the wear phenomenon of wheels and rail tracks in different parts of India.
... The Tγ/A values were calculated from the test data regarding the contact force, instantaneous slip and measured traction coefficient. The dry wear rate results are compared in Fig. 12a with wear rates for rail materials with similar hardness values as reported in the scientific literature in [31] for rail material RH400HT and in [32] for UIC60 rail material. ...
... The results are compared with wet wear rates obtained for similar rail materials, as reported in [33] for 260 grade rail and in [34] for UIC60 rail. The presence of water reduced the wear rate across all the slip set points during the Fig. 12. a) Dry rail wear rate results -RH400HT data from [31], UIC60 data from [32]; and b) Wet wear rate results. 260 grade rail data from [33], UIC60 wet data from [34]. ...
Locomotive-track interaction is commonly represented by a complex mechanical system which is modelled in numerical studies. Numerical studies alone are not enough to precisely describe the behaviour of this mechanical system due to the various elements that can only be delivered from field and laboratory experimental programs. One such element is wheel-rail wear that has been found to contribute a considerable portion of the total cost of maintaining heavily used railway systems. Simulation studies are typically used for predicting wear of wheels and rails, but the majority of these do not consider in-train forces nor provide detailed modelling of traction and braking events and often rely on historic wear rates for comparable materials, reducing the accuracy of the wheel-rail volume loss estimation. This paper proposes a methodology for wear rate experimental measurements that allow improving the accuracy of wear analyses using dynamic simulations. The proposed method considers in-train forces by performing longitudinal train simulations whose results are then implemented on a detailed locomotive vehicle dynamic model with a traction mechatronic system co-simulation approach. The wheel-rail contact stress and slip results are then post-processed into a Dynamic Load Spectrum that contains contact stress and wheel slip occurrences. The Dynamic Load Spectrum was used to measure the wear rates for Australian AS60 head hardened rail steel material operating in combination with Class B wheel steel material. The experimental program delivered more realistic wear rates that correspond to actual industry operational scenarios. The measured wear rates were used to estimate the rail material volume loss for a specific train trip.
... This underlines the importance of railway emissions in air quality. Growing awareness of this issue has led some researchers to investigate the non-exhaust particle emissions from railways (e.g., Abbasi et al., 2013Abbasi et al., , 2011Abbasi et al., 2012aAbbasi et al., , 2012bOlofsson et al., 2013). Different methods were used for this purpose. ...
Many railway tracks have been electrified, thus eliminating exhaust emissions. However, railways still emit particles due to abrasion and wear. The main such particle sources are brakes, wheel-rail contact, and pantographs and contact wire. However, information on the quantities of such particles is rare. Estimations in published data are quite heterogeneous, with PM10 emission levels varying by a factor of ten. In an attempt to improve the database and to reduce uncertainties, a series of test bench tests was conducted on pantograph-catenary contact. In order to study the impact of specific parameters, i.e. of train speed, contact force and current intensity, on the emitted particle mass and size distribution, parameter levels were varied across the tests. A chemical analysis of emitted particles provided information on the respective contributions of contact strip and contact wire. PM10 emission factors were found to lie in the range of 0.14–0.62 g/km.
