Creep Force Model Research Articles

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.

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.

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.

Method for estimating motion state of wheelset and wheel/rail friction coefficient by a single-wheel creep-force model in railway vehicle equipped with instrumented wheelset

Method for estimating motion state of wheelset and wheel/rail friction coefficient by a single-wheel creep-force model in railway vehicle equipped with instrumented wheelset

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.

Wheel-rail contact and friction models: A review of recent advances

Rail transportation is regarded as a reliable, quick, and secure mode of transportation. The wheel-rail contact interaction is crucial to the railway operation since it is responsible for supporting, traction, braking, and steering of railway vehicles. Improper wheel-rail interactions may produce or exacerbate wheel-rail interface issues such as rolling contact fatigue (RCF) and wear, which can threaten the vehicle’s running safety and stability. A review of the evolution and recent literature on wheel-rail contact mechanics and tribology is presented here. Topics covered include the basics of wheel-rail contact problem and methodologies for modeling both the normal contact (Hertzian and non-Hertzian) and tangential contact (Kalker’s theories including CONTACT and FASTSIM algorithms, Polach’s theory, USETAB program, etc.). The paper also reviewed various effects of contaminants and environmental conditions (water, leaves, sand, temperature, humidity, etc.) in wheel-rail contact. Various wheel-rail empirical adhesion models like the Water-induced low adhesion creep force model (WILAC) model and adhesion models based on elastohydrodynamic lubrication (EHL) theory (Greenwood-Tripp [GT] and Greenwood-Williamson [GW] models) are also reviewed. Lastly, the paper discusses the need and challenges for developing and integrating the wheel-rail non-Hertz contact model and adhesion model, as well as open areas for further research.

Estimation Method for Friction Coefficient between Wheel and Rail by a Single-Wheel Creep-Force Model Using Measurement Data of Instrumented Wheelset

The purpose of this study is to improve estimation accuracy for motion variables of a wheelset in a railway vehicle calculated by an observer based on a Kalman filter using a single-wheel creep-force model to evaluate a running safety more realistically. To achieve the purpose, this paper proposes a new estimation method for motion variables of wheelset by estimating the friction coefficient between wheel and rail simultaneously. Validity of the proposed method is verified with simulations to test under various running conditions the values of friction coefficient and track curve radius vary. The verification results show that the proposed method is effective to estimate the friction coefficient when track curve radius is smaller than 700m. Moreover, the proposed method manages to solve a problem that estimation results with low accuracy for the motion variables of the wheelset are calculated when the error between a true and an assumed friction coefficient is large.

Performance evaluation of estimation method for wheelset motion state using a single-wheel creep-force model with instrumented wheelset

The purpose of this study is to build an evaluation method of a railway running safety more realistically using information about contact condition between wheel and rail in a railway vehicle. To achieve this purpose, the authors have proposed an estimation method for motion variables of a wheelset and friction coefficient between wheel and rail by observer based on a Kalman filter using a single-wheel creep-force model with an instrumented wheelset. In the previous studies, the authors mainly have examined effectiveness of the proposed method using numerical simulations but scarcely have been carried out investigation using measurement data. This paper reports the results of the validity test of the proposed method using the measurement data and simulation data mimicking them. The verification results show that the proposed method managed to estimate reasonable values of the friction coefficient, the lateral displacement of the wheel/rail contact point in outer side and the angle of attack in the curve section to some extent.

The development of a high pressure torsion test methodology for simulating wheel/rail contacts

Simulating the wheel/rail contact of a train is traditionally conducted using small-scale twin-disc testing. Here an emerging alternative method, the “high pressure torsion” (HPT) test is introduced. This has advantages over twin-disc testing as only one cycle is used and it is easier to control third body layers during testing. Shear stress data generated is useful on its own, but can also be used to parameterise analytical prediction tools such as the extended creep force model (ECF), which produces creep-force curves from HPT data. This can then be validated against field data to develop a full-scale predictive capability. A detailed account of the HPT methodology development and the procedures for running a typical test are presented along with case studies that illustrate the typical output of HPT testing.

Improved modelling of trains braking under low adhesion conditions

ABSTRACT Predicting the behaviour of trains when braking under low adhesion conditions presents considerable challenges. This paper describes an approach to the problem using a model of the full train braking system known as LABRADOR (Low Adhesion Braking Dynamic Optimization for Rolling Stock) and an improved method for representing the creep force–creepage behaviour when low adhesion is presently known as WILAC (Water Induced Low Adhesion Creep Force Model). The development of these models and their integration are summarized and a number of test cases are presented to demonstrate the improvements which can be gained from this approach. A number of suggestions are made for future enhancements with the aim of providing brake engineers and systems integrators with reliable simulation tools for optimizing train braking performance when low adhesion is present.

Particle swarm optimization based parametrization of adhesion and creep force models for simulation and modelling of railway vehicle systems with traction

Adhesion and creep force models play an important role in the realistic simulation of railway vehicle systems. These models are mainly based on experiments and they are determined heuristically. In previous studies, no metric is defined to demonstrate the level of agreement between these models and measurements. This study aims to provide such metric, and particle swarm optimization based parametrization of adhesion and creep force models is proposed for simulation of railway vehicle systems based on the measurements. Root mean squared error is considered as a metric for the level of agreement between models and measurements. In order to compare two approaches and reveal the superiority of optimal parametrization in simulations with respect to the heuristic approach, measurements taken from a tram wheel test stand, which simulates the traction system of some trams produced in Czechia, are considered. A mathematical model of the traction system of the test stand is obtained for simulation, and two approaches are compared based on the root mean squared error between these simulations and measurements. Several contact conditions are considered during experiments. This study demonstrates the necessity of optimal parametrization of adhesion and creep force models for realistic simulation of railway vehicle systems. Furthermore, particle swarm optimization method is introduced as an automation tool for modelling adhesion between wheel and rail when investigation of a large number of measurements are required for design, analysis and simulation.

Vehicle tests showing how the weather in autumn influences the wheel–rail traction characteristics

Train operators report low adhesion in autumn, which they suspect is caused by fallen leaves on a track surrounded by forest and farmland. To investigate and quantify this effect, vehicle tests have been performed in autumn on a track partially surrounded by forest. To also investigate the influence of different weather conditions, the tests were performed on a day with sunny weather and one with high humidity in the morning and drizzle at noon. The results were then compared to other tests and different creep force models from the literature. The results showed a significant influence of the surrounding forest on the traction especially in sunny weather.

Wheel-rail creep force model for predicting water induced low adhesion phenomena

A computationally efficient engineering model to predict adhesion in rolling contact in the presence of water is presented which may be implemented in multibody dynamics software or in braking models to study train performance and braking strategies. This model has been developed in a project funded by the Rail Safety and Standards Board (RSSB) and Network Rail. It is referred to as the water-induced low adhesion creep force (WILAC) model. The model covers a wide range of conditions from dry over damp to wet. Special emphasis is put on little amounts of water which can cause low adhesion without any oil or grease. Such conditions may be encountered in humid weather or at the onset of rain. The model is parameterised based on experimental results from a tram wheel test rig. Adhesion values as low as 0.06 are observed at high creep with only wear debris and little water present in the contact. The model results also agree with experimental data from locomotive tests in dry and wet conditions.

Third body layer—experimental results and a model describing its influence on the traction coefficient

When adding substances to the wheel–rail contact, they mix with wear particles and form a Third Body Layer (3BL). This layer influences the initial gradient of the traction characteristic.During twin-disc tests presented in this paper, a granular layer consisting of iron and iron oxides with a thickness of up to 50μm was found. In addition, a creepforce model is presented that uses non-linear properties of the 3BL to describe its influence on the traction characteristic. The results of the model were compared to the results of the experiment. A qualitative and quantitative agreement was achieved. This will improve, e.g., the quality of vehicle dynamics simulations, optimizations of control devices for traction and braking, and predictions of wear and damage on wheel and rail.

Reducing Lateral Contact Forces of Low-Floor LRV Using Friction Control (Development of Creep Force Model and Effectiveness for Independently Rotating Wheels)

In this investigation, curving performance for low-floor light rail vehicles (LRV) with friction controls on wheel/rail interface is discussed. To this end, a creep force model subjected to friction modifiers is developed by introducing an equivalent shear modulus of rigidity. Good agreements in the creep force characteristics are obtained between the proposed model and experiment. It is shown with the proposed creep force model that use of friction modifiers on an inner rail is effective for reducing lateral contact forces of LRV with independently rotating wheels.

2309 摩擦制御による低床式LRVの横圧低減に関する研究 : クリープ力モデルの提案と曲線通過解析(OS4 接触問題とトライボロジ,オーガナイズド・セッション(OS))

In this investigation, curving performance for low-floor light rail vehicles (LRV) with friction controls on wheel/rail interface is discussed. To this end, creep force model subjected to friction modifiers is developed and then the validity of the proposed model is presented by comparison with the measurement data. It is shown with the proposed creep force model that use of friction modifiers on inner track is effective for reducing lateral contact forces of LRV with independently rotating wheels.

Effect of curved track support failure on vehicle derailment

In order to investigate the effect of curved track support failure on railway vehicle derailment, a coupled vehicle–track dynamic model is put forward. In the model, the vehicle and the structure under rails are, respectively, modelled as a multi-body system, and the rail is modelled with a Timoshenko beam rested on the discrete sleepers. The lateral, vertical, and torsional deformations of the beam are taken into account. The model also considers the effect of the discrete support by sleepers on the coupling dynamics of the vehicle and track. The sleepers are assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. In the calculation of the coupled vehicle and track dynamics, the normal forces of the wheels/rails are calculated using the Hertzian contact theory and their creep forces are determined with the nonlinear creep theory by Shen et al [Z.Y. Shen, J.K. Hedrick, and J.A. Elkins, A comparison of alternative creep-force models for rail vehicle dynamic analysis, Proceedings of the 8th IAVSD Symposium, Cambridge, MA, 1984, pp. 591–605]. The motion equations of the vehicle/track are solved by means of an explicit integration method. The failure of the components of the curved track is simulated by changing the track stiffness and damping along the track. The cases where zero to six supports of the curved rails fail are considered. The transient derailment coefficients are calculated. They are, respectively, the ratio of the wheel/rail lateral force to the vertical force and the wheel load reduction. The contact points of the wheels/rails are in detail analysed and used to evaluate the risk of the vehicle derailment. Also, the present work investigates the effect of friction coefficient, axle load and vehicle speed on the derailments under the condition of track failure. The numerical results obtained indicate that the failure of track supports has a great influence on the whole vehicle running safety.

A study on the new wheel and rail tangential force model for the high-speed railway vehicles

A new creep force model for a dynamic analysis of the wheel/rail tangential force of high-speed railway vehicles has been devised. The test data of actual in-service Shinkansen vehicles at high speed were analysed with the model, and the calculated results verified the validity of the model. The results confirm that the lateral oscillation of the vehicle can be reduced by improving the suspension. By raising the natural frequency of the bogie steer mode to greater than that of the body yawing mode at commercial speed, bogie motions are controlled by the damping equipments and by the mass of the body. The methodology that arranges the natural frequency of vehicle suspension in this manner has been described, and it could be analysed more precisely by the new wheel/rail tangential force model.

Application of a wheel–rail contact model to railway dynamics in small radius curved tracks

A multibody formulation with Cartesian coordinates is used to describe the kinematic structure of rigid bodies and joints that constitute the vehicle. A track parameterization methodology is implemented for the accurate description of the track spatial geometry emphasizing small radius curves, including its irregularities. A generic formulation is reviewed to determine, during the dynamic analysis, the contact forces that are generated in the wheel–rail interface. This contact model includes an algorithm that identifies the coordinates of the wheel–rail contact points, even for the most general three dimensional motion of the wheelset on the track. The proposed formulation can be applied to study the two points of contact scenario and, since the contact point in the wheel flange does not have to be located in the same plane as the contact point in the tread, it allows analyzing lead and lag flange contact configurations. An elastic force model that allows computing of the normal contact force in the wheel–rail interface, accounting for the energy loss during contact, is implemented and the tangential wheel–rail contact forces are calculated using one of three distinct creep force models: Kalker linear theory; Heuristic nonlinear method; Polach formulation. The methodologies proposed here are demonstrated by their application to the dynamic analysis of the boggie of a metro rail vehicle when negotiating a small radius curved track.

Improved Creep Force Model for Wheel/Rail Contact Considering Roughness and Temperature

SUMMARYSome characteristics of measured creep force curves cannot be explained with common theories of rolling contact. This work proposes extensions for creep force calculation in the case of dry friction. It is based on the creep force law of Shen, Hedrick and Elkins. The approximate consideration of the surface roughness yields a reduced initial slope whereas the introduction of a temperature dependent coefficient of friction can explain the decrease of creep forces at high creepages. The creep force curves calculated with the new model show the same characteristics as in measurements.