Rail Contact Surface Research Articles

Embedding Kalker's variational theory into railway vehicle system dynamics and its efficiency improvement

The wheel–rail contact plays a vital role in railway transportation, hence an accurate wheel–rail contact model is the key to the simulation of railway vehicle dynamics. Though Kalker's variational theory is the canon, fewer works try to embed it into railway vehicle dynamics, mainly due to the computational efficiency problem and the complex wheel–rail geometry processing. This paper proposes a wheel–rail geometry processing method to embed KVT into railway vehicle multi-body dynamics based on the trajectory coordinate formulation, which conveniently introduces the wheel–rail contact surface pair for tracking the potential contact areas. After this prior detection, coarse detection is performed to narrow the range of penetrated elements. Multiple contact patches can also be identified based on the connection topology of discrete elements of wheel–rail surfaces. Thus, Kalker's variational theory can be used on each separate patch for local contact evaluation. An initial prediction method for the contact status is embedded in the multi-body dynamics simulation to accelerate the solution of Kalker's variational problem, in which the tractions with contact divisions obtained from the neighbouring system states are selected as the iterative initial value. The importance of predicting the contact tractions and demarcation for the convergence of the iteration is revealed. The proposed method is fully demonstrated by the Manchester contact benchmark and simulations of a railway vehicle passing through a curved track. As an advantage of embedding Kalker's variational theory, the precise traction pattern is obtained simultaneously along with the vehicle dynamics simulation, and the influencing mechanism of the track geometry on the vehicle system is analysed. The improvement of solution efficiency is also verified in simulations.

Мокрій Т. Ф., Малишева І. Ю. , Лапіна Л. Г., Пасічник С. С. Взаємодія з рейками коліс пасажирського вагона з новим профілем ободу ІТМ-73EP в криволі-нійних ділянках колії

Speeding up the integration of Ukraine into the European railway transportation is an important task in the current development of the Ukrainian railway transport. Currently, the most effective way to travel across borders between countries with different track gauges is the use of gauge-changeable wheelsets. Continuous traffic on the Ukrainian (1520 mm gauge) and European (1435 mm gauge) railways calls not only for gauge changing facilities, but also for the compatibility of the wheel-rail contact pair on both railways: R65 rails and a cant of 1/20 in Ukraine and UIC60 rails and a cant of 1/40 in Europe. At the Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine, a new wear-resistant wheel profile, ITM-73ER, was proposed. As predicted, its use in passenger cars will offer dynamic stability and a high dynamic performance throughout the range of operating speeds on the Ukrainian and European railways and acceptable indices of wheel – unworn rail interaction on both railways. In service, the shapes of the wheel and rail contact surfaces change due to wear, especially in curves. Because the Ukrainian and European railways mostly use wheel and rail profiles of their own, the use of the new wheel profile may impair the wheel–rail interaction process, enhance wheel flange wear, and shorten the wheel life. The goal of this work is to study the effect of the in-service rail head shape change in curves of the Ukrainian and European railways on the wheel–rail interaction indices of a passenger car with ITM-73ER profile wheels. The head shapes of outer rails of the Ukrainian and European railways’ circular curves were predicted for a side flange wear changing from 0 to 8 mm in 2 mm increments. The calculations were made for two circular curves of radius 300 m with UIC60 rails and a cant of 1/40 (Europe) and R65 rails and a cant of 1/20 (Ukraine). To speed up the prediction, it was assumed that the curves were traveled by four-axle fully loaded freight cars, which maximizes the rail wear. The freight car wheels were assumed to be unworn and machined to the S1002 profile (for the European railways) and to the standard profile specified by the Ukrainian State Standard GOST 10791:2016 (for the Ukrainian railways). Using the computed head shapes of R65 and UIC60 rails differing in wear degree, a study was conducted into their effect on the wheel–rail pair strain and stress field and the dynamic indices of car–track interaction for passenger cars with ITM73-ER profile wheels negotiating a circular curve of radius 300 m. It was shown that the use of the ITM-73ER wheel profile in passenger cars will offer improved indices of car–track interaction, for worn rails too, both on the Ukrainian railways and in the combined operation on the Ukrainian and European railways.

Influence of Rotational Speed on Subsurface Microstructure and Wear Property of D2/U71Mn Wheel-Rail Steel

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

Analysis of Electromagnetic Characteristics of Copper-Steel Composite Quadrupole Rail.

The ablation and wear of the four-rail electromagnetic launcher during the working process will aggravate the damage of the armature and rail, and greatly affect the service life of the launcher. To effectively alleviate rail damage, this paper applies the copper-steel composite rail to the four-rail electromagnetic launcher and proposes a new four-rail electromagnetic launcher. Based on the quadrupole magnetic field theory, the physical model of the new four-rail electromagnetic launcher is established, and the electromagnetic characteristics of the ordinary and new launchers are compared and analyzed using the finite element method. On this basis, the influence of composite layer parameters on the electromagnetic characteristics of copper-steel composite quadrupole rail is explored. The study found that the new four-rail electromagnetic launcher can provide a better launch magnetic field environment for smart loads, and the current distribution of the armature and the rail contact surface is more uniform, which can effectively improve the contact condition between the armature and the rail. The composite layer parameters of copper-based composite rail will have a certain impact on electromagnetic characteristics, and copper-steel composite rail of appropriate proportions can be selected according to different needs. The model proposed in this paper has a certain degree of scientificity and rationality.

Electromagnetic Characteristics Analysis of Quadrupole Compound Orbital Electromagnetic Launcher with Different Configurations

During the operation of the Quadrupole Compound Orbital electromagnetic launcher, the current is easy to gather in the armature and the rail contact surface. Serious turn and arc ablation can occur, causing damage to the rail and the armature and affecting the life of the launcher. To better solve the thermal ablation problem of the armature and the rail, three different configurations of the rail and the armature are established, and the current density, magnetic field distribution and electromagnetic force of the rail and the armature are compared and analyzed using the finite element method, and the effect of concave and convex values of the armature rail on current distribution and electromagnetic force is discussed. The results show that the planar armature can effectively reduce the maximum current density and mitigate thermal damage. The concave elliptical rail produces the largest electromagnetic thrust and the smallest radial electromagnetic force, and the armature is more stable during firing. The maximum current density and magnetic field strength are negatively correlated with the concave and convex values; the electromagnetic thrust applied to the concave elliptical armature is negatively correlated with the concave value, while the electromagnetic force applied to the convex elliptical armature is positively correlated with the convex value.

Wheel Rail Wear Prediction and Dynamic Performance Analysis of Linear Metro

In order to improve the safety of linear motor metro operation, the wheel rail wear prediction and dynamic performance analysis of linear motor metro are carried out. Firstly, the working principle and evolution process of the linear motor are analyzed, and the traveling wave magnetic field and slip ratio of the linear motor are calculated. Secondly, the friction principle between wheel and rail is analyzed, and the running data of wheel and rail area are collected by MiniProf series profiler. By calculating the wear energy flow density and wear mass flow density of wheel rail contact surface, the relationship between wear coefficient and energy flow density is obtained, and the wheel rail wear area is obtained, so as to complete the prediction of wheel rail wear. Finally, the running resistance of Metro is analyzed, including mechanical resistance and aerodynamic resistance. Combined with the calculation results of Metro kinetic energy and electromagnetic, the position of linear motor is obtained by modal superposition method in the elastic coordinate system, and the dynamic equation of linear motor Metro is constructed to complete the dynamic performance analysis of Metro. The experimental results show that this research method can accurately predict the wear of linear motor metro, and can study the running stability of Metro from the two aspects of horizontal stability and derailment coefficient.

Analysis of electromagnetic characteristics of the proposed composite four-rail electromagnetic launcher

Abstract In the existing composite four-rail electromagnetic launcher (CFREL), the armature and rail contact surface produces significant heat and bears considerable wear, thereby reducing the potential amount of electromagnetic thrust to be generated. To eliminate the damage caused by the thermal effect of the rail contact surface and to meet the electromagnetic thrust demand of the load, a CFREL is proposed. The proposed CFREL model is constructed, and the launcher’s electromagnetic characteristics are simulated and compared using the finite element method. The current density, distribution of magnetic flux density, and electromagnetic thrust characteristics are analysed. The results showed that the proposed CFREL reduced the maximum current density of the contact surface and effectively eliminated the current concentration of the armature and rail contact surfaces. Effective magnetic field shielding is realised with a larger range, which can better meet the requirements of the intelligent load’s magnetic field environment and provide stronger electromagnetic thrust for the load, hence solving the problem of insufficient thrust.

System Noise Suppression of Muzzle Voltage in Augmented Electromagnetic Railgun Based on VMD and the Application in Armature–Rail Contact Characteristics

The muzzle voltage is an important characteristic parameter of electromagnetic railgun. The contact resistance between the sliding armature and the copper rail surface during the launching process can be calculated by utilizing it to analyze the armature–rail contact characteristics. However, in the engineering experiments of augmented electromagnetic railgun, the detected muzzle voltage waveform will be disturbed by the system noise because of the existence of augmented rail, firing sequence of pulse forming network (PFN), and friction of armature–rail contact surface. Therefore, it is difficult to calculate the contact resistance accurately. This article presents a new noise suppression method variational mode decomposition (VMD) for suppressing the jagged noise in the muzzle voltage. A method for calculating the contact resistance is presented to analyze the armature–rail contact characteristics. A frame for analyzing the contact characteristics of the electromagnetic railgun is presented. The method can suppress the system noise by utilizing the signal mode decomposition in the time domain based on the frequency characteristics of VMD. Then, in order to analyze the armature–rail contact characteristics, the contact resistance can be calculated according to the formula derived from the theory. The results show that the method can suppress the muzzle voltage system noise effectively. And the calculated contact resistance wave is smooth, which is helpful to analyze the armature–rail contact characteristics. The noise component extracted from muzzle voltage contains pulse signals, and the time and amplitude of these pulse signals are related to PFN’s firing sequence and the changing trend of the armature–rail contact resistance. The method proposed in this article provides a new and reliable reference for monitoring the launching state of electromagnetic railgun in engineering experiments.

Study of Wear and Redistribution Dynamic Forces of Wheel Pairs Restored by a Wear-Resistant Coating 15Cr17Ni12V3F

The relevance of this study lies in the need to research the wear process of the elements of dynamic systems and to establish the dependence of the geometric and structural characteristics of wheels restored by plasma surfacing with a coating of 15Cr17Ni12V3F on dynamic, cyclically varying loads. The study was aimed to establish the dependencies between the deviation of the wear area, the formation of contact and fatigue stresses, and the change in the phase structure of the wheel defect. It is important to justify the permissible limits of wear of the transverse profile in the contact zone of a wheel and ridge. The object of the study was the dynamic interaction of the “wheel–ridge–rail contact surface” system. To achieve the goal, the following methodology was adopted: kinematic analysis, strength calculation, the use of mathematical analysis in dynamic system modelling, virtual modelling in the SOLIDWORKS software environment of the GearTrax application, experiment planning, and model correction through the results of metallographic studies. The results of the study are presented as reasonable prediction criteria that consider contact cycles during the formation of fatigue stresses at the stage of defect origin. The process of the dynamic interaction of the contact worn profile of a wheel with a railway rail is explored. Polynomial equations are proposed to substantiate the optimal design and technological parameters of designing a railway carriage wheel. The permissible limits of wear of the transverse profile in the contact zone of the wheel and the ridge are justified while taking the coefficient of the reduction of contact stresses in the metal into account. The dependences of the change in static load on the utilization factor of the railway carriage load capacity are established. The dependences of changes in fatigue stresses on the design deviation of the contact area of wheel wear are established. It is confirmed that the stress concentration under cyclic loads is formed in the ferritic layers of the material structure before the appearance of wear.

A preliminary study on enhancing safety of contact features in the terrain park

ObjectivesTerrain park riders use contact features such as fun boxes and rails. Typical fun box and rail features have a design characteristic that can be changed to improve safety. Fun box edge coping and edges of rails are typically constructed of soft steel. Ski/snowboard edges (HRC50) can easily become engaged in the softer metal, causing a chip to develop, suddenly stopping the rider, probably causing a fall and possible injury. The aim of the study is to examine the effect of terrain park running surface hardness on chip development. DesignTesting on steel specimens was performed to research chip development generated by a ski/snowboard edge on steel used in the construction of contact features and on steel that is proposed for such use. An apparatus was constructed to simulate a ski/snowboard edge moving perpendicular to the long axis of coping or rail edge. MethodsThe author performed observation, photographic documentation, metallurgical testing and environmental testing of various contact features at different ski area terrain parks. Several steel specimens of varying hardness were tested at various load levels to study the propensity of chip development by ski/snowboard edges. ResultsTesting of steel samples showed that increasing the hardness of the rail steel or coping steel reduced the propensity for a ski/snowboard edge to engage in the coping or rail. ConclusionsIncreasing steel coping and rail contact surface hardness to HRC 50 and above will likely reduce engagement by steel snowboard/ski edges, which in turn is expected to reduce the chance of a fall and injury.

The wear resistance research of the rail contact surface depending on the grinding process

The wear resistance research of the rail contact surface depending on the grinding process

Finite element analysis of the wheel–rail impact behavior induced by a wheel flat for high-speed trains: The influence of strain rate

The wheel–rail impact response induced by a wheel flat for high-speed trains is simulated numerically, based on the strain rate-dependent constitutive parameters of wheel–rail materials, using the finite element software LS-DYNA explicit algorithm. Influences of the speed of the train, the length of the wheel flat, and axle load on the wheel–rail impact behavior are discussed over a wide range, in terms of the vertical impact force, von Mises equivalent stress, shear stress, and equivalent plastic strain. The maximum wheel–rail impact forces are 2.6–4.4 times greater than the corresponding static axle loads due to the presence of a wheel flat. The maximum von Mises equivalent stress and equivalent plastic strain have occurred on the wheel–rail contact surface, while the maximum xy shear stress has often occurred on the subsurface of 4–6 mm below the contact surface. The wheel–rail impact responses induced by a wheel flat are sensitive to the speed of trains, flat length, and axle load. Besides, the strain rate effect of wheel–rail materials has a significant influence on the maximum von Mises equivalent stress, shear stress, and equivalent plastic strain, while it has no influence on the maximum vertical impact force. These findings are very helpful to guide the maintenance and repair of wheel–rail components in rail transport.

Numerical analysis of rolling-sliding contact with the frictional heat in rail

Thermal damage caused by frictional heat of rolling-sliding contact is one of the most important failure forms of wheel and rail. Many studies of wheel-rail frictional heating have been devoted to the temperature field, but few literatures focus on wheel-rail thermal stress caused by frictional heating. However, the wheel-rail creepage is one of important influencing factors of the thermal stress. In this paper, a thermo-mechanical coupling model of wheel-rail rolling-sliding contact is developed using thermo-elasto-plastic finite element method. The effect of the wheel-rail elastic creepage on the distribution of heat flux is investigated using the numerical model in which the temperature-dependent material properties are taken into consideration. The moving wheel-rail contact force and the frictional heating are used to simulate the wheel rolling on the rail. The effect of the creepage on the temperature rise, thermal strain, residual stress and residual strain under wheel-rail sliding-rolling contact are investigated. The investigation results show that the thermally affected zone exists mainly in a very thin layer of material near the rail contact surface during the rolling-sliding contact. Both the temperature and thermal strain of rail increase with increasing creepage. The residual stresses induced by the frictional heat in the surface layer of rail appear to be tensile. When the creepage is large, the frictional heat has a significant influence on the residual stresses and residual strains of rail. This paper develops a thermo-mechanical coupling model of wheel-rail rolling-sliding contact, and the obtained results can help to understand the mechanism of wheel/rail frictional thermal fatigue.

An innovative wheel–rail contact model for railway vehicles under degraded adhesion conditions

The accurate modelling of the wheel–rail contact plays a fundamental role in the railway field since the contact forces heavily affect the vehicle dynamics, the wear of the contact surfaces and the vehicle safety. Concerning the wheel–rail contact, an important open problem is represented by the degraded adhesion. A realistic adhesion model is quite difficult to obtain because of the complex and highly non-linear behaviour of the adhesion coefficient and the presence of external unknown contaminants (the third body); this is especially true when degraded adhesion and large sliding between the wheel and rail contact surfaces occur.

Disrupting Armature Ejecta and Its Effects on Rail Damage in Solid-Armature Railguns

Material ejected from aluminum armatures at the rail-armature interface has been identified as a mechanism that degrades both rails and insulators in a railgun, significantly reducing the bore lifetime. With the goal of controlling the onset of armature ejecta, a series of single-shot tests was conducted in a small railgun with a bore cross section of 22 × 44 mm. The tests utilized channels of various sizes and geometries machined into the rail contact surface of the armatures to see if ejecta could be controlled. These tests identified several channel patterns as having the potential to delay the onset of armature ejecta. A series of multiple-shot tests was subsequently conducted in a larger railgun having a bore cross section of 38 × 76 mm. The goal of these experiments was to see if the channel patterns that delayed armature ejecta had a significant impact on rail erosion at start-up. Three test series were conducted. In the first series, three armatures with a nested circular channel pattern were tested. In the second series, three armatures with a large centrally located channel were tested. Both armature designs used equivalent contact areas. These results were then compared to a standard armature contact face with no modifications in a third test series.

Very early stage rolling contact fatigue crack growth in pearlitic rail steels

Abstract This paper reports on metallurgical characterisation of small cracks in pearlitic steels, using observations from both twin disc tests and rails removed from service, plus methods to determine three-dimensional (3D) aspects of such cracks. Tests to varying fractions of rolling contact fatigue (RCF) life have been assessed, based on twin disc tests where “average 100% RCF life” has been defined by eddy current detection of cracks between 200 and 800 μm in depth. Contact surface features and microstructural alterations have been mapped against near-surface strain and compared with worn rail examinations. Initial crack growth along favourably aligned and strained, prior-austenite (PA) grain boundaries, particularly if the boundary contains pro-eutectoid (PE) ferrite, was found to be restricted or halted at the PA grain limit or where the boundary altered to be less-favourably aligned. For samples with up to 55% RCF life, initial crack propagation length was still less than the average PA grain size. 3D aspects of this early growth and the deformed PA grain shapes were found to be linked to ratcheting flakes and flake cracks on test disc and rail contact surfaces. The results have shown how initial RCF crack propagation is very microstructurally influenced.

Railgun Tribology: Characterization and Control of Multishot Wear Debris

Railgun tribology describes the friction and wear sciences of interacting surfaces in relative motion. The novel tribological feature of railguns is the use of high-speed, high-current sliding electrical contacts for the conversion of the electrical energy in a current pulse into projectile kinetic energy. Several wear processes affect the life of components used to construct the bore of a railgun depending upon the severity of the duty cycle. Following multishot testing without refurbishment in solid-armature railguns, wear products have been observed to accumulate on the contact surfaces of rail conductors. Aluminum-alloy armatures produce wear debris that is chemically complex and structurally inhomogeneous. Because electromagnetic propulsion requires that electrical conduction take place across these debris layers, it is important to understand the factors that influence their structure. A critical question for repeatable and predictable railgun performance and for extended rail life is whether easy conduction occurs through these accumulated wear products. It is possible to control the dimensions and properties of these wear debris accumulations on rail contact surfaces using chemical and mechanical aids. Films of rapidly solidified aluminum with layered structures and high levels of gas porosity are the most common debris on copper rails. It is possible to control the structures of these films and to plow them away when they grow thick. Here, results of characterization and control of wear debris are presented and discussed

Railgun Tribology—Chemical Reactions Between Contacts

Many electromagnetic launcher experiments have been conducted with armature-rail pairs made of dissimilar alloys. When the armature is made of an aluminum alloy, the eventual formation of aluminide intermetallics is likely at the sliding contact interfaces with nonaluminum rails. Because most launcher bores are freely accessed by laboratory air, other reactions-oxidation, nitridation, and water vapor-may also occur during the reactive phase of the transfer of aluminum from the armature to the rail surface. The structure and composition of the thin layer that adheres to the rail contact surfaces is important, because it separates the new armature contact in a subsequent launch from the original rail contact surfaces and, thus, affects current transfer and the contact lubrication process. The chemistry and the morphology of the reaction layer on the rails will vary along the length of the launcher. In the armature start-up and low-velocity regions of the rails, the adhering rail deposit shows evidence of liquid-metal-enhanced, high-temperature reactions. Experimental data confirming the presence of these reaction products are presented for the case of the very low-speed and highly energetic propulsion of a copper armature between aluminum alloy rails. A copper aluminide intermetallic-CuAl2-is formed, as predicted from the binary phase diagram. Intermetallics have properties that will degrade the multishot load-carrying capability of rail conductors

Wheel/Rail Non-linear Interactions With Coupling Between Vertical and Lateral Directions

Summary A theoretical model is developed to explore the high frequency wheel/rail interaction with coupling between the vertical and lateral directions. This coupling is introduced through the track dynamics due to the offset of the wheel/rail contact point from the rail centre line. Equivalent models of the railway track in the time domain are developed according to the rail vibration receptances in the frequency domain. The wheel is represented by a mass in each direction with no vertical-lateral coupling. The vertical wheel/rail interaction is generated through a non-linear Hertzian contact stiffness, allowing for the possibility of loss of contact between the wheel and rail. The lateral interaction is represented by a contact spring and a creep force damper in series and their values depend on the vertical contact force. The vibration source is the roughness on the wheel and rail contact surfaces which forms a relative displacement excitation in the vertical direction. Using the combined interaction model with this relative displacement excitation, the wheel/rail interactions with coupling between the vertical and lateral vibrations are simulated. It is found that the lateral interaction force caused by the offset is usually less than thirty percent of the vertical dynamic force. The lateral vibration of the rail is significantly reduced due to the presence of the lateral coupling, whereas the vertical interaction is almost unaffected by the lateral force.

VIBRATION ANALYSIS OF RAILWAY TRACK WITH MULTIPLE WHEELS ON THE RAIL

The major source of railway rolling noise is the structural vibration of the wheel and rail which is generated by the combination of small-scale undulations (roughnesses) on the wheel and rail contact surfaces. Usually, the rail vibration behaviour is studied using a model in which only a single wheel is present. This is not the case in practice, where multiple wheels roll on the rail. It is shown first that the high-frequency excitation from each wheel can be treated independently by using the superposition principle, provided that the rail vibration is considered as a frequency band average. The appropriate application of the superposition principle is then to model the rail vibration as a sum of cases in which all wheels are retained in contact with the rail but the roughness at all but one of them is set to zero. The presence of multiple wheels on the rail leads to reflections of waves in the rail. The paper explores such effects on the rail vibration caused by multiple wheels acting as supplementary dynamic systems. The receptance of a rail with a single additional wheel on it is studied first to acquire a physical insight into the effects of wheels on the rail vibration. Then more complicated models are developed and used to investigate the effects of multiple wheels on a rail. Practical consequences due to the multiple wheel–rail interactions are also presented.