Creep Forces Research Articles

Creep slope estimation for assessing adhesion in the wheel/rail contact

AbstractThe UK rail network is subject to costly disruption due to the operational effects of adhesion variation between the wheel and rail. Causes of this are often environmental introduction of contaminants that require a wide‐scale approach to risk mitigation such as defensive driving or rail‐head maintenance. It remains an open problem to monitor the real‐time status of the network to optimise resources and approaches in response to adhesion problems. This article presents an on‐vehicle monitoring method designed to estimate the coefficient of friction by processing data from on‐board sensors of typical rail passenger vehicles. This approach uses a multi‐body physics analysis of a target vehicle to create estimators for both creep force and creep, allowing a curve fitting approach to estimate the coefficient for friction from the creep curves.

Mechanisms Underlying Rail Corrugation on Tracks Equipped with Cologne-Egg Fasteners

Rail corrugation is the most common type of abnormal damage in subway track systems, and there is currently no unified theory that fully explains this specific wear phenomenon. In this research, a coupled rigid–flexible dynamics model and a multi-rigid body dynamics model was established, accounting for the effects of fastener systems, to study severe rail corrugation on tracks equipped with Cologne-egg fastener (CE fastener). The low vertical support stiffness of CE fasteners, combined with heavy train loads, leads to the “soft mud effect.” This effect causes the creep force between the wheel and rail to become saturated more easily, which is the root cause of frequent rail corrugation on both tangent tracks and curved tracks with large radii. Additionally, drawing on the theory of friction-driven self-excitation vibration, a finite element model of a wheelset–rails system with CE fasteners was established to study the unstable vibration caused by wheel–rail sliding. An increased friction coefficient increases the tendency toward unstable vibration in a wheelset–CE fastener–rail system. Three types of composite under-rail vibration absorbers were designed to suppress rail corrugation, with the continuous-type absorber demonstrating the best suppressive effect.

Carbody sway behaviour of railway vehicles due to track irregularity from rail alternate side wear

AbstractTrack irregularity from rail alternate side wear is manifested as uneven rail wear waveforms alternating in the left and right rails with equal intervals, which will cause carbody sway behaviour of railway vehicles and greatly influences the passenger comfort. In this work, the carbody sway behaviour and mechanism due to track irregularity from rail alternate side wear and possible solutions to this issue were studied by the field testing and numerical calculation approaches. First, the carbody sway of an urban rail transit train is introduced with full-scale field tests, through which the rail alternate side wear is characterized and the formatted track irregularity are presented. Then, multibody vehicle dynamic models are developed to reproduce the carbody sway behaviour induced by the track irregularity from the rail alternate side wear. The creep forces acting on the wheel and rail are preliminarily discussed to study the influence of the carbody sway on the wear of the wheel flange and the rail corner. Finally, some potential solutions, e.g. improving the damping ratio of carbody rigid mode and rail grinding, are proposed to relieve this issue. It is concluded that an increased damping ratio of the carbody mode can alleviate the carbody sway and wheel–rail interactions, while properly maintaining track conditions can improve the vehicle performance.

Effect of compressive and tensile forces on glucose concentration and cell viability within the intervertebral disc: A finite element study

Understanding the role of mechanical force on tissue nutrient transport is essential, as sustained force may affect nutrient levels within the disc and initiate disc degeneration. This study aims to evaluate the time-dependent effects of different compressive force amplitudes as well as tensile force on glucose concentration and cell viability within the disc. Based on the mechano-electrochemical mixture theory, a multiphasic finite element model of the lumbar intervertebral disc was developed. The minimum glucose concentration and minimum cell density in both normal and degenerated discs were predicted for different compressive force amplitudes, tensile force, and corresponding creep time. Under high compressive force, the minimum glucose concentration exhibited an increasing and then decreasing trend with creep time in the normal disc, whereas that of the degenerated disc increased, then decreased, and finally increased again. At steady state, a higher compressive force was accompanied by a lower glucose concentration distribution. In the degenerated disc, the minimum cell density was negatively correlated with creep time, with a greater range of affected tissue under a higher compressive force. For tensile force, the minimum glucose concentration of the degenerated disc raised over time. This study highlighted the importance of creep time, force magnitude, and force type in affecting nutrient concentration and cell viability. Sustained weight-bearing activities could deteriorate the nutrient environment of the degenerated disc, while tensile force might have a nonnegligible role in effectively improving nutrient levels within the degenerated disc.

Formation Mechanism of Rail Corrugation for Modern Tram Lines

In order to explain the phenomenon of corrugation on measured line sections of the modern tram, a numerical model of modern tram-track coupling has been established by utilizing the multi-body dynamics method, and the formation mechanism of corrugation has been studied from the perspective of wheel-rail contact creep. The results show that the smaller the curve radius is, the greater the probability of corrugation occurs. The corrugation wavelength range is 40 mm~50 mm, the wave depth range is 0.05 mm~0.1 mm, and the wave depth is relatively small compared with the corrugation wave depth of metro lines, which is in line with the characteristics of the light-load operation of the tram. The formation mechanism of corrugation on modern tram sharp curves can be described as wheel-rail contact creep saturation leads to the generation of corrugation, and the source of creep is related to the guiding mechanism of the longitudinally coupled independent wheelset bogie. The formation of corrugation on the straight line of the modern tram is related to the difference in wheel diameters between the front and rear wheelsets on the same side, which can lead to different longitudinal velocities, thus generating longitudinal creep forces and inducing rail corrugation.

Analytical study and evaluation of self-steering ability of elastically constrained wheelsets under traction/braking conditions

Railway vehicles are often subjected to stationary creep forces, such as those resulting from traction/braking, which can significantly affect their dynamic performance. This paper presents an analytical method to analyse the steering performance of elastically constrained wheelsets under stationary traction/braking torque. Two indices, which are independent of vehicle velocity, the ‘self-steering index’ and the ‘lateral flexibility index’, are proposed to evaluate the steering ability. The impact of traction/braking condition on the steering ability is analysed, in which the saturation characteristics of wheel-rail creep are considered. The findings confirm that stationary longitudinal creep forces, arising from traction/braking, negatively impact the steering ability of elastically constrained wheelsets. The lateral displacements are found to be larger with the same lateral external force and consequently flange contact may occur. To control the system to avoid it reaching this extreme, an optimised torque distribution strategy is proposed to minimise the impact of traction/braking on the self-steering ability. The analytical method presented in this study offers insights into the dynamics of railway vehicles under complex working conditions, facilitating further research in this field.

Wheel-rail contact wear analysis on curved lubricated track for heavy haul locomotive studies

The effect of lubrications on a curved track to heavy-haul wheel-rail contact wear is studied. To analyse wheel-rail contact wear damage due to existing high-adhesive AC locomotive, a methodology for investigation is proposed, and the locomotive models are required to run at 20 km/h under maximum traction efforts, and the simulations include a DC locomotive for comparison. An extended creep force model, which was developed by Polach and has been widely used for the wheel-rail contacts under dry and wet conditions with variable friction coefficients, is further extended to apply for the typical low-coefficient-friction modifier, oil, and grease lubricant conditions. The wear models from two pairs of wheel-rail materials are used to predict the wear rates, and the wear numbers Tγ are presented for discussions. The simulations show that the lubricants significantly reduce the wheel-rail contact wear.

Freight container wagon modelling and simulation analysis due to braking

To improve the wagon brake performance and to investigate the wheel skidding on the rail during braking, the comprehensive rail freight wagon models with consideration of braking are generated by using the Gensys software package, which includes the masses of a wagon carbody, two bolsters, four sideframes, eight axle boxes and eight wheelsets. The nonlinear characteristics of secondary and the primary suspensions are considered among the mass connections. The tangential wheel-rail contact creepages and creep forces are calculated by a modified FASIM method with consideration of decreasing changes after saturation points. The brake type of air-pressed friction shoe on wheel tread surface is taken into account and the reference brake force profiles are considered with the characteristics of increasing friction coefficient with wagon speed decreasing. The wagon rolling resistance is also considered by using the equations used in Australian rail industries. The wagon braking stopping distance at an operation speed and the wheel slipping and skidding during braking situations can be simulated, and the effect of wheel-rail surface conditions (dry, wet, low coefficient friction (LCF) modifier and grease), wagon loading distribution, etc., to the braking performance can be examined, and the discussions on the wagon braking operation are given.

Acceleration-based friction coefficient estimation of a rail vehicle using feedforward NN: validation with track measurements

Low friction can lead to poor adhesion conditions between the rail and wheel, which is detrimental to rail vehicle operation and safety. Up to date knowledge of the rail-wheel friction level is currently not available across rail networks, meaning planning mitigation strategies is difficult. This paper presents a real-time friction coefficient estimation algorithm based on a feed-forward neural network (FNN). Unlike conventional methods, the FNN does not depend on slip/adhesion curves or creep force models, and only requires wheelset longitudinal acceleration and speed. The wheelset acceleration and friction measurements are obtained by running a two-car rail vehicle on a friction-modified track with five different levels of friction conditions at four different vehicle speeds. Four different FNNs are trained for four speed conditions, and their estimation performance were validated by training multiple FNNs and testing them in each speed case using new sets of data. Validation results show that the average mean absolute errors from the four FNNs remains below 0.0083.

Nonlinear dynamics simulation of the helical gear transmission system for high-speed train

Considering the bending-torsional-axial-coupled vibration of the helical gear transmission system, a 10 degrees of freedom high-speed train gear transmission system model, including motor and load, is established based on the lumped parameter method. In addition, the potential energy method based on the slicing principle is used to accurately calculate the time-varying meshing stiffness of helical gears. Furthermore, the influence of geometric parameters of helical gears on the time-varying meshing stiffness is studied, and the impact of time-varying meshing stiffness on the system is further investigated. Meanwhile, by analyzing the dynamic phenomena of the system under different parameter excitations under different parameter excitations, the influence of internal and external excitation parameters such as gear speed, wheel rail creep force, support stiffness, and support damping on the stability of high-speed train gear transmission system is deeply studied.

Можливості підвищення безпеки руху рейкових екіпажів з колесами, що незалежно обертаються

One of the promising ways to achieve high speed and smooth running of rail vehicles during stable movement in straight sections of the track and to improve the characteristics of fitting the vehicles in a curve is the use of independently rotating wheels in their running parts. Such undercarriages are already becoming quite widespread, for example, in urban rail transport vehicles. But independently rotating wheels can rotate in a wheel pair around a common axis with different angular velocities. It follows that during their movement, longitudinal creep forces do not arise, which form the controlling moment and center the wheel pair in the rail track. This can lead to increased angles of attack of the wheels on the rails, increased lateral forces and accelerated wear of the wheels and rails. In turn, this increases the tendency of vehicles with independently rotating wheels to derail by rolling the flange onto the head of the rail. 
 The accumulated global experience of operating similar vehicles confirms this. To overcome the mentioned disadvantages of independently rotating wheels, a number of various technical solutions have been proposed. Some of them relate to ensuring the given elastic-dissipative characteristic of the torsional articulation of the wheels in a wheel pair. A promising direction is the improvement of the characteristics of the connections of wheel pairs with the bogye and bogyes with the vehicle body, the use of mechatronic systems for controlling the position of the wheel pairs in the horizontal plane for their radial installation in curved sections of the track. In this work, attention is paid to the issue of the use in the design of independently rotating wheels of a perspective design scheme that allows independent rotation of the wheel's support surface and its guide surface (flange). The question of the effect of changing the design scheme of the wheel on the safety of movement due to the roll-in of the ridge on the rail head was considered. 
 The influence of a promising design scheme of a wheel in comparison with a traditional design scheme of a wheel on the safety of driving down a rails was investigated. The peculiarities of the distribution of frictional forces in the ridge contact during movement along the rails of the wheels of both design schemes are analyzed. For a wheel of a traditional design scheme, the module and the direction of the friction force vector in the ridge contact are uniquely determined by the geometric characteristics of the contact between the wheel and the rail and the angular speed of the wheel rotation. At the same time, when the wheel of the prospective design scheme moves, the direction and module of the friction force vector of the ridge on the rail also depend on the ratio of the angular velocities of rotation of the supporting surface of the wheel and its guiding surface (flange) around the common axis. The obtained results allow us to draw a conclusion about the expediency of using a promising design scheme in independently rotating wheels to increase the safety of movement of rail vehicles.

Generation of sanded creep curves using the extended creep force model with high pressure torsion data

In this paper an approach for generating predicted full-scale creep force – creep curves from small-scale tribological tests has been outlined and examples produced using rail sands and low adhesion contaminants. A high pressure torsion rig was used to measure the change in shear stress over increasing displacement for British and Austrian rail sands in dry, wet, and leaf contaminated conditions under different normal pressures. In addition, tests with just sycamore leaf powder and graphite were also conducted. This data was then used to parameterise extended creep force models for each contact condition, from which predictions of full-scale behaviour were then made and validated using full-scale data from literature.

Research on wheel-rail dynamic interaction of high-speed railway under low adhesion condition

Due to the inherent openness of the wheel-rail system, the wheel-rail interface is subject to the influence of a third medium, resulting in a low adhesion state. This study investigates the dynamic interaction between the wheel and rail under low adhesion conditions through the development of a numerical model employing anti-skid control strategies and infinite long track simulation technology. The model's validity is established by comparing its calculations with data from both the multi-body dynamics software UM and field tests. The numerical simulations uncover that the implementation of rail side lubrication significantly reduces longitudinal creep forces, thereby diminishing the wheelset's steering capabilities. Furthermore, it induces a notable increase in lateral wheel-rail interaction, consequently lowering safety indicators in vehicle operations. Rail side lubrication is found to substantially reduce rail side wear, resulting in an approximate 60% decrease in the maximum wear depth. Comprehensive friction control on the rail surface concurrently mitigates rail side and top surface wear. In instances of local low adhesion on both sides, the wheelset experiences pronounced stick-slip vibrations, leading to a deterioration in the longitudinal dynamic performance between the wheel and rail. Unilateral low adhesion situations prompt noticeable yawing and shaking motions within the low adhesion zone, resulting in evident lateral impact phenomena. Upon re-entering the normal adhesion zone from the low adhesion zone, the rail wear index experiences a significant peak, which means that the rails in this area are prone to severe local wear or fatigue.

Influences of tram characteristics on wheel polygonal wear evolution

Out-of-round railway wheels continuously excite the vehicle-track system resulting in fluctuating contact forces, creepages and contact patch dimensions. Accompanied wear may influence the evolution of railway wheel polygonization significantly. Especially in curves with a small radius of curvature, which are typical for tramway networks, considerable wear originates due to high lateral creepages. Long-time wear development studies with dominant polygonal orders reveal that some wavelengths of the wheel enlarge rapidly, whereas others are nearly unaffected or even suppressed. Therefore, fundamental research on significant influences on wheel polygonal wear evolution is required. A representative generic system model of a two-axle tram bogie is set up, and a suitable wear model is implemented to study the polygonal wear evolution at trams. It has been found that structural modes can dominate wheel polygonal wear evolution. In particular, the compliance and interaction of the wheelset axle and the resilient wheel may be essential. Evolution tendency curves are presented, and influences on the wheel polygonization are discussed. Wheel–rail contact conditions and related creepage–creep force characteristics appear to be decisive for the evolution directions and evolution speeds.

Mechanism of rail corrugation combined with friction self-excited vibration and wheel-track resonance

In the present study on rail corrugation, a field investigation is carried out on a typical section of a Steel-spring Floating Slab Track (SFST) in the Beijing subway for studying the two distinct types of corrugations generated by the left and right rails in the curved sections of the metro line. Further, study is also done on the vibration response of track components when trains pass over the rail corrugations at a typical SFST curve having small radius of curvature (R = 300 m). The study establishes an SFST rail corrugation analysis model by effectively combining SIMPACK and ABAQUS. The proposed model considers the effects of both, friction self-excited vibration and resonance of the wheel-track system, for analyzing the reasons leading to inconsistent corrugation generated by the left and right rails in the small radius curve section of SFST. The results show that when the train load acts on the middle position of the adjacent steel-spring, it causes the rail to produce vertical bending resonance with the floating slab relative to the baseplate. This, in turn will result in increased corrugation which could reach 200 mm wavelength. At similar frequency, the anti-phase resonance of the unsprung mass and the track vibration mass, directly results in the formation of 200 mm corrugation. The wheelset-SFST system occurs near 68.4 Hz due to vertical torsional resonance of the floating slab. This leads to the rapid development of 200 mm corrugation in the curve's inner rail. When the train passes through the small radius curve section of SFST, the creep force between the guiding wheelset's outer wheel and the outer rail of the curve tends to saturate. This results in generation of 31.5 mm corrugation by the outer rail due to friction self-excited vibration. It is recommended to maintain the vertical stiffness of the fastener system above 50 MN/m to either stop or reduce the generation and development of corrugation at 200 mm and 31.5 mm wavelengths.

Study on the influence of wheel inertia and longitudinal/lateral creep force on the corrugated wear on the metro curved track

Corrugated wear on the metro curved track was studied. Dynamic analysis was implemented to analyze the effects of the vehicle speed and the curve radius on the wheel-rail creep forces. A mixed Lagrangian/Eulerian description-based finite element model of a wheel/rail system was set up. The wheel inertia can be considered in this model. Moreover, the steady rolling of the wheel under different creepage for braking or traction can be simulated. The complex eigenvalue analysis is used to investigate the frequency-domain characteristics of the friction-induced vibration of the wheel/rail system under the steady-state curving of the wheel. The initiation of the corrugation under the friction-induced vibration of the wheel/rail system was studied. The effects of the creep forces in the longitudinal and lateral directions on the friction-induced vibration of the wheel/rail system were revealed. The results show the dominant cause of the corrugation on the low rail surface is the friction-induced vibration of the wheel/rail system at about 320 Hz. The friction-induced vibration on the side of the high rail is not easy to occur. Therefore, the corrugated wear hardly happens to the high rail. The corrugated wear caused by the friction-induced vibration is frequency-fixed. It is necessary to consider the wheel inertia in the study of the friction-induced vibration of the wheel/rail system. Without considering wheel inertia, missing prediction of the friction-induced vibration and overestimation of the occurrence probability and development speed of the corrugation may occur. The lateral creep force plays a leading role in the friction-induced vibration of the wheel/rail system, while the longitudinal creep force has little effect on the friction-induced vibration. The corrugated wear will become more serious as the curve radius becomes smaller.

Rutting Resistance Evaluation of Highly Polymer-Modified Asphalt Binder and Mixes Using Different Performance Parameters

This study focused on evaluating the rutting performance of three different highly polymer-modified asphalt (HiMA) binders (i.e., O, T and B) using binder-based [i.e., multiple stress creep recovery (MSCR) and force ductility (FD)] and mix-based [flow number (FN) and Hamburg wheel tracking test (HWTT)] rutting performance tests. The binder-based rutting indicators were compared with mix rutting performance to determine a parameter that can help in the correct prediction of HiMA rutting resistance. In addition, the study looked into application of a simple performance test, the indirect rutting tolerance index (IDEAL-RT), for HiMA mix rutting prediction. The MSCR test revealed different rankings of recovery at 0.1- and 3.2-kPa stress levels. Moreover, the T and B binders did not satisfy the stress sensitivity criteria (Jnr_difference) of Max 75%. The force ductility tests revealed that the peak force observed for polymer network phase in HiMA was significantly higher than base binder stiffness, which is in contrast with force distribution in polymer-modified binders (PMBs). The mix rutting resistance ranking (O>T>B) was similar in all the tests (i.e., FN, HWTT, and IDEAL-RT). Although IDEAL-RT can be used to compare the rutting resistances of HiMA mixes, detailed future work is required to establish its acceptability in comparing various types of mixes and the minimum requirements of RTIndex. The comparison between binder and mix rutting indicators demonstrated that MSCR testing on binder at stress levels of 6.4 kPa and higher can be used to predict the rutting resistance of HiMA binders. Parameters like slope and cohesion energy and a newly introduced parameter—work done for polymer activation (WPA)—from FD tests can be used to determine the polymeric phase dominance in HiMA binders. Overall, this study provides pavement stakeholders with a framework for rightly predicting the rutting resistance and polymeric phase dominance of HiMA binders and mixes using MSCR, FD, and IDEAL-RT tests.

Top-of-rail friction modifier performance assessment: High pressure torsion testing; creep force modelling and field validation

Top-of-Rail products that give intermediate friction offer many benefits when applied to the wheel/rail interface. Water-based top-of-rail friction modifiers (TOR FMs), have been shown to reduce energy consumption, wear, noise, corrugation and rolling contact fatigue. This work was aimed at developing a test approach, based on the High Pressure Torsion (HPT) method, that allowed an improved assessment of their performance over those that recycle constantly over the same test surface. The outputs would then be used to parameterise the Extended Creep Force (ECF) model to enable full-scale predictions to be made that could be compared with field measurements of wheel/rail interface friction.The HPT method developed used representative amounts of product based on assessment of wayside and on-board application rates. Friction levels achieved matched those expected for intermediate levels. The friction level was sensitive to the amount applied though. The parameterised ECF model was able to predict friction levels that matched those from the field very closely. A framework for using friction measured in small-scale tests has been developed that could now be applied to other third body materials for making valid predictions of full-scale performance.

Kinematic running resistance of an urban rail vehicle undercarriage: a study of the impact of wheel design

Urban railway vehicles are important means of transport in towns and cities due to their high capacity, power source, and low running resistance, which make them efficient for operation. Although these properties are considered advantages, there is still room for improvement in their operational efficiency. The main objective of this article is to investigate the impact of railway wheel design on the level of kinematic running resistance, which is expressed as the amount of mechanical energy losses during the interaction of wheels with rails. This research focuses on simulation computations of two variants of wheel design schemes: the traditional design scheme (TKS) and a perspective design scheme (PKS) characterized by a rotating flange independently of the wheel tread surface. Two undercarriage multibody models have been created, one with TKS and one with PKS, and simulation computations have been performed for running speeds of 10 km/h, 20 km/h, 30 km/h, and 40 km/h on track models in curves with radii of 20, 50, 100, 150, 200, and 250 m. The evaluated indicators affecting the level of mechanical energy losses were creep forces, slip velocities, and average power. The most important findings of this study are that the PKS design scheme resulted in lower values of all assessed parameters.

Analysis of the generation mechanism and evolution of the wheel high-order polygonal wear of subway trains

The present paper aims to study the generation cause of initial high-order polygonization of subway wheels as well as its progression pattern. In analyzing the wear characteristics of out-of-round (OOR) wheels of metro trains obtained via field measurements, the distribution of wheel high-order OOR wear was found to be closely related to the small-radius (i.e., a radius no greater than 400 m) curve track. The friction-induced self-excited oscillation caused by the saturated wheel-rail creep force was used as the frequency-fixing mechanism of the wheel OOR wear, and the wheel polygonization induced via this oscillation was evaluated by finite element simulation. Furthermore, the influence of rail corrugation on the development of wheel OOR wear was analyzed, and it is found that, when the vehicle negotiates a small-radius curve track, an unstable oscillation of 87 Hz induced by the saturated creep force can lead to wheel 12th ∼ 13th-order OOR wear—mainly distributed along the inner wheel tread far from the wheel back. During vehicle operation, the vibrations caused by the wheel 12th ∼ 13th-order polygonization can excite the eigenmodes of the wheelset, leading to an increased wear intensity. In addition, wheel 12th-order polygonal wear interacts with the rail corrugation of the same wear wavelength but different phases, which can cause wheel 10th ∼ 11th- and 13th ∼ 17th-order polygonization.