The adhesion in the wheel-rail contact can be effectively controlled by using the friction modifier. Adhesion control can reduce excessive wear of the contact bodies or noise. The essence of this diploma thesis is to determine the optimal amount of friction modifier in wheel-rail contact depending on the climatic and operating conditions. For experimental study of the behavior of the friction modifier, the twin-disc device is used. Twin-disc simulates and controls the most important operating parameters such as speed, slip, attack angle or contact pressure. On the basis of these findings, the off-board top-of-rail lubricator system was designed. This system controls the amount of friction modifier according to current climatic and operating conditions.

This diploma thesis deals with the experimental study of the influence of operating conditions on the tribological aspects of the wheel flange and rail gauge contact. The wheel flange contact occurs when the vehicle moves on a curve track and it leads to severe up to catastrophic wear regime. For effective reduction of wear is important to apply a suitable amount of lubricant at appropriate intervals into the contact. The issue in this work comprehensively studies using of three laboratory apparatus and six methods that are theoretically and experimentally compared. Assessed are friction, wear, distribution and film thickness of lubricants for different contact conditions. The resulted amount of lubricant and interval of its application eliminates development of seizure at low consumption of lubricant. The understanding of mechanisms that occur in the wheel-rail contact not only helps to reduce operating costs and improved to energy efficiency of movement of vehicle on a track, but it is the basis for safe, reliable and ecological operation of rail transport.

A conceptual design of an innovative two-axle lightweight railway vehicle for commuter services is carried out at KTH Railway Group. An active wheelset steering is introduced to improve the curving performance of the vehicle, which is one of the critical performance requirements. This thesis aims to improve the steering performance of the active wheelset steering. Look-up tables for estimating time-varying wheel-rail contact parameters are introduced to supervise a simple PID controller of the active steering system in order to improve steering performance. The look-up table (LUT) estimation is focused on time-varying wheel-rail contact parameters, including creep coefficients and contact patch variables due to their direct influence on curving performance and lateral stability of the wheelset. As a result, the estimated longitudinal unit creep forces (UCF) have the potential to supervise the gains determination of PID controller because it can appropriately distinguish running conditions. The estimation of longitudinal UCF is achieved by the combination of the results from the LUT of creep coefficients and the LUT of contact patch variables. The result from longitudinal unit creep force estimation is shifted to the first quadrant to use as critical gain in the Ziegler-Nichols tuning method for the PID controller. The critical oscillation period for PID tuning can be expressed as a function of vehicle speed. Consequently, the PID controller for the active steering system uses time-varying gains with real-time tuning. The proposed control system for active wheelset steering is validated with nine running conditions using SIMPACK and MATLAB/Simulink co-simulation. The proposed control system provides a stable wheelset lateral displacement control regardless of the running condition. The active steering system significantly reduces wheel-rail wear, which demonstrates the effectiveness of the proposed active steering system. / KTH:s Järnvägsgruppen utvecklar en konceptuell design av ett innovativt, två-axligt, lättvikts järnvägsfordon för tunnelbana eller pendeltåg. En aktiv hjuparsstyrning introduceras för att förbättra kurvtagningsförmågan hos fordonet, vilket är ett av de kritiska prestandakraven hos dessa fordon. Det här examensarbetet har som målsättning att förbättra styrningsprestandan av den aktiva hjulsatsstyrningen. För att uppskatta tidsvarierande hjul-rälskontaktparametrar introduceras pre-definierade tabeller (LUT) som en övervakning av en enkel PID-kontroll för det aktiva styrningssystemet, för att förbättra styrprestandan. Uppskattningen som baseras på tabellen fokuserar på tidsberoende hjul-rälsparametrar, inklusive krypkoefficienter och kontaktytans storlek och form. Dessa variabler är i fokus på grund av deras direkta effekt på kurvtagningsförmågan och den laterala stabiliteten hos hjulparet. Den uppskattade longitudinala enhets krypkraften (UCF) har potential att bestämma förstärkningen hos PID-kontrollen på grund av att den, på ett lämpligt sätt, kan skilja mellan olika körtillstånd. Uppskattningen av longitudinell UCF uppnås genom en kombination av resultat för krypkoefficienter och kontaktytavariabler i LUT. Resultaten från den longitudinella UCF-uppskattningen skiftas till den första kvadranten för att användas som kritisk förstärkning i Ziegler-Nichols justeringsmetod för PID-kontroller. Den kritiska oscillationsperioden för PID-justering kan utryckas som en funktion av fordonets hastighet. Utgående från detta använder PID-kontrollen tidsvarierande förstärkning med realtidsjustering för den aktiva styrningen. Det föreslagna kontrollsystemet valideras mot nio körtillstånd med hjälp av SIMPACK och MATLAB/Simulink-simuleringar. Det föreslagna kontrollsystemet tillhandahåller en stabil lateral förflyttning av hjulparet oberoende av körtillstånd. Det aktiva styrsystemet reducerar hjul-räls slitaget signifikant, vilket demonstrerar effektiviteten hos det framtagna aktiva styrsystemet.

The wheel-rail contact mechanics and dynamics that are of great importance to the railroad industry are evaluated by applying statistical methods to the large volume of data that is collected on the VT-FRA state-of-the-art roller rig. The intent is to use the statistical principles to highlight the relative importance of various factors that exist in practice to longitudinal and lateral tractions and to develop parametric models that can be used for predicting traction in conditions beyond those tested on the rig. The experiment-based models are intended to be an alternative to the classical traction-creepage models that have been available for decades. Various experiments are conducted in different settings on the VT-FRA Roller Rig at the Center for Vehicle Systems and Safety at Virginia Tech to study the relationship between the traction forces and the wheel-rail contact variables. The experimental data is used to entertain parametric and non-parametric statistical models that efficiently capture this relationship. The study starts with single regression models and investigates the main effects of wheel load, creepage, and the angle of attack on the longitudinal and lateral traction forces. The assumptions of the classical linear regression model are carefully assessed and, in the case of non-linearities, different transformations are applied to the explanatory variables to find the closest functional form that captures the relationship between the response and the explanatory variables. The analysis is then extended to multiple models in which interaction among the explanatory variables is evaluated using model selection approaches. The developed models are then compared with their non-parametric counterparts, such as support vector regression, in terms of "goodness of fit," out-of-sample performance, and the distribution of predictions. / Master of Science / The interaction between the wheel and rail plays an important role in the dynamic behavior of railway vehicles. The wheel-rail contact has been extensively studied through analytical models, and measuring the contact forces is among the most important outcomes of such models. However, these models typically fall short when it comes to addressing the practical problems at hand. With the development of a high-precision test rig—called the VT-FRA Roller Rig, at the Center for Vehicle Systems and Safety (CVeSS)—there is an increased opportunity to tackle the same problems from an entirely different perspective, i.e. through statistical modeling of experimental data. Various experiments are conducted in different settings that represent railroad operating conditions on the VT-FRA Roller Rig, in order to study the relationship between wheel-rail traction and the variables affecting such forces. The experimental data is used to develop parametric and non-parametric statistical models that efficiently capture this relationship. The study starts with single regression models and investigates the main effects of wheel load, creepage, and the angle of attack on the longitudinal and lateral traction forces. The analysis is then extended to multiple models, and the existence of interactions among the explanatory variables is examined using model selection approaches. The developed models are then compared with their non-parametric counterparts, such as support vector regression, in terms of "goodness of fit," out-of-sample performance, and the distribution of the predictions. The study develops regression models that are able to accurately explain the relationship between traction forces, wheel load, creepage, and the angle of attack.

The electromechanical design and development of a sophisticated roller rig testing facility at the Railway Technologies Laboratory (RTL) of Virginia Polytechnic and State University (VT) is presented. The VT Roller Rig is intended for studying the complex dynamics and mechanics at the wheel-rail interface of railway vehicles in a controlled laboratory environment. Such measurements require excellent powering and driving architecture, high-performance motion control, accurate measurements, and relatively noise-free data acquisition systems. It is critical to accurately control the relative dynamics and positioning of rotating bodies to emulate field conditions. To measure the contact forces and moments, special care must be taken to ensure any noise, such as mechanical vibration, electrical crosstalk, and electromagnetic interference (EMI) are kept to a minimum. This document describes the steps towards design and development of all electromechanical subsystems of the VT Roller Rig, including the powertrain, power electronics, motion control systems, sensors, data acquisition units, safety and monitoring circuits, and general practices followed for satisfying the local and international codes of practice. The VT Roller Rig is comprised of a wheel and a roller in a vertical configuration that simulate the single-wheel/rail interaction in one-fourth scale. The roller is five times larger than the scaled wheel to keep the contact patch distortion that is inevitable with a roller rig to a minimum. This setup is driven by two independent AC servo motors that control the velocity of the wheel and roller using state-of-the-art motion control technologies. Six linear actuators allow for adjusting the simulated load, wheel angle of attack, rail cant, and lateral position of the wheel on the rail. All motion controls are performed using digital servo drives, manufactured by Kollmorgen, VA, USA. A number of sensors measure the contact patch parameters including force, torque, displacement, rotation, speed, acceleration, and contact patch geometry. A unified communication protocol between the actuators and sensors minimizes data conversion time, which allows for servo update rates of up to 48kHz. This provides an unmatched bandwidth for performing various dynamics, vibrations, and transient tests, as well as static steady-state conditions. The VT Roller Rig has been debugged and commissioned successfully. The hardware and software components are tested both individually and within the system. The VT Roller Rig can control the creepage within 0.3RPM of the commanded value, while actively controlling the relative position of the rotating bodies with an unprecedented level of accuracy, no more than 16nm of the target location. The contact force measurement dynamometers can dynamically capture the contact forces to within 13.6N accuracy, for up to 10kN. The instantaneous torque in each driveline can be measured with better than 6.1Nm resolution. The VT Roller Rig Motion Programming Interface (MPI) is highly flexible for both programmers and non-programmers. All common motion control algorithms in the servo motion industry have been successfully implemented on the Rig. The VT Roller Rig MPI accepts third party motion algorithms in C, C++, and any .Net language. It successfully communicates with other design and analytics software such as Matlab, Simulink, and LabVIEW for performing custom-designed routines. It also provides the infrastructure for linking the Rig's hardware with commercial multibody dynamics software such as Simpack, NUCARS, and Vampire, which is a milestone for hardware-in-the-loop testing of railroad systems. / Ph. D.

This dissertation aims to study the benefit of rail grinding on service life of railroad rails, focusing on failures due to rolling contact fatigue (RCF) at the rail head. Assuming a tangent rail with one-point contact at the running surface, a finite element analysis of a full-scale wheel-rail rolling contact with a nonlinear isotropic kinematic hardening material model is performed to simulate the accumulation of residual stresses and strains in the rail head. Using rolling stress and strain results from the sixth loading cycle, in which residual stresses and strains are at their steady-state, as input, two critical plane fatigue criteria are proposed for fatigue analyses. The first fatigue criterion is the stress-based approach—namely the Findley fatigue criterion. It suggests an important role of tensile residual stresses on subsurface crack nucleation and early growth in the rail head, but applications of the criterion to the near-running-surface region are limited because of plastic deformation from wheel-rail contact. The second fatigue criterion is the strain-based approach—namely the Fatemi-Socie fatigue criterion. Contributed mainly from shear strain amplitudes and factorized by normal stress components, the criterion also predicts fatigue crack nucleation at the subsurface as a possible failure mode as well as fatigue crack nucleation at the near-surface, while maintaining its validity in both regions. A collection of fatigue test data of various types of rail steel from literature is analyzed to determine a relationship between fatigue damages and number of cycles to failure. Considering a set of wheel loads with their corresponding number of rolling passage as a loading unit (LU), optimizations of grinding schedules with genetic algorithm (GA) show that fatigue life of rail increases by varying amount when compared against that from the no-grinding case. Results show that the proposed grinding schedules, optimized with the exploratory and local-search genetic algorithms, can increase fatigue life of rail by 240 percent. The optimization framework is designed to be able to determine a set of optimal grinding schedules for different types of rail steel and different contact configurations, i.e. two-point contact occurred when cornering.

Depuis plus d'un siècle, l’usure ondulatoire représente un des problèmes de maintenance les plus important pour les réseaux ferroviaires. Celle-ci est à l’origine d’émissions sonores incommodantes pour le voisinage et de vibrations structurelles pouvant réduire la durée de vie des infrastructures et matériels ferroviaires. Ce phénomène périodique présent à la surface des rails est intimement lié à la dynamique du contact roue-rail qui résulte des paramètres régissant le frottement, la dynamique du train et de la voie… Afin de mieux appréhender les conditions menant à l’apparition de l’usure ondulation, un modèle numérique a été proposé pour compenser l’impossibilité d’instrumenter localement et de façon fiable un contact roue-rail dynamiquement. Tout d'abord, un outil approprié a été choisi pour modéliser la dynamique du contact roue-rail afin de reproduire numérique de l’usure ondulatoire des voies rectilignes. Le code d'éléments finis dynamique implicite Abaqus a été choisi pour instrumenter numériquement localement le contact roue-rail. Ainsi, tant l'origine que l'évolution de l’usure ondulatoire dans des phases transitoires (accélération / décélération) sont étudiées. Une étude de sensibilité a été menée pour mettre en évidence la sensibilité de l’usure ondulatoire apparaissant dans des conditions transitoires au passage d’une ou plusieurs roues ainsi que d’un défaut géométrique présent à la surface du rail. Des conditions dynamiques locales d’adhérence-glissement (stick-slip), liées à la dynamique de la roue et du rail couplés par le contact, est identifié comme origine de l’usure ondulatoire des voies rectilignes dans des conditions transitoires. Deuxièmement, les résultats obtenues avec le modèles précédent ont mis en évidence une décroissance de l’amplitude de l’usure ondulatoire reproduire numérique en fonction du nombre de roue passant sur le rail. Ce résultat semble être en contradiction avec les observations de rails réels. Ce problème est lié à la difficulté de gérer la dynamique de contact, et tout particulièrement dans le cas où il y a des impacts locaux, dans les modèles éléments finis classiques tels que ceux implémentés dans Abaqus. Pour palier ce problème, une méthode de masser redistribuée a été implémentée dans Abaqus et utilisée sur le cas précédent. Les résultats montrent un accroissement plus réaliste de l’usure ondulatoire en fonction du nombre de roues. / For more than a century, rail corrugation has been exposed as one of the most serious problems experienced in railway networks. It also comes with a series of problems for maintenance, such as rolling noises and structural vibrations that can reduce lifetime of both train and track. This periodical phenomenon on rail surface is closely linked to wheel-rail contact dynamic, which depends on friction, train dynamics… To better understand corrugation birth conditions, a numerical model is suggested to complement the experimental limitations and to instrument a wheel-rail contact both locally and dynamically. At first, an appropriate tool was chosen to create the dynamic wheel-rail contact model to reproduce straight-track corrugation, also called “short-pitch” corrugation. The implicit dynamic finite element code Abaqus was chosen to investigate the dynamic local contact conditions. Both the origin and the evolution of straight-track corrugation under transient conditions (acceleration / deceleration) are studied. The parametrical sensibility of corrugation is thus investigated both with single/multiple wheel passing(s) and with geometric defect. A stick-slip phenomenon, linked to both wheel and rail dynamics coupled through the contact, is identified as the root of straight-track corrugation under transient conditions. Secondly, results obtained with the previous model have highlighted a quick decrease of corrugation amplitude with the increase of wheel passings over the rail. This last result seems to be in contradiction with reality. This problem comes from the difficulty to reliably manage contact dynamics, and particularly with local impacts, with the use of classical finite element models such as the one implemented in Abaqus. To compensate for this lack, a mass redistribution method is implemented in Abaqus and used with the previous case. The results show a more realistic corrugation growth according to the number of wheel passings.

The diploma thesis deals with construction design and practical realisation of experimental apparatus for investigation of wheel flange track vehicle lubrication. Experimental apparatus in full-scale uses optical interferometry for investigation of lubrication behaviour in wheel flange contact. It is an innovative approach which has not been used for such experiments so far. The aim of the following measurement with this apparatus is to determine the minimal amount of ecological lubrication in wheel flange contact under certain conditions when there is no lubrication film interruption. The apparatus enables to measure real rail wear. This work contains the apparatus description for the study of wheel flange lubrication, wheel flange contact specifications, the description of its influence on wear and acoustic emission, and a detailed description of the experimental apparatus.

Ce travail réalisé dans le cadre d'une collaboration industrielle avec la société ALSTOM Transport porte sur l'étude de la dégradation des voies ferrées urbaines. Les composantes de voie retenus pour cette étude sont le rail et la dalle de voie en béton. Concernant le rail, différents problèmes sont abordés : contact roue – rail, usure du rail, usure ondulatoire du rail, et fatigue de contact de roulement (RCF) du rail. Un outil numérique avec des interfaces graphiques, nommé CONUS, est développé pour le problème de contact roue – rail et le problème d'usure du rail. Des théories classiques (Hertz, Kalker, Archard, etc.) sont implantées dans cet outil. La méthode stationnaire est implantée dans un code de calcul par éléments finis pour étudier l'état asymptotique de l'acier du rail sous le chargement répété des trains. Ceci nous permet de prédire les régimes de RCF du rail. La mécanique de l'endommagement est utilisée pour prédire la fatigue du matériau béton. Le formalisme de Marigo couplé avec le modèle d'endommagement de Mazars permet de modéliser la dégradation progressive de la rigidité du matériau sous chargement cyclique. Une campagne d'essais de fatigue du béton en flexion a été réalisée. Elle a pour but de valider le modèle théorique et d'identifier les paramètres du matériau. Le dimensionnement d'une dalle de voie en béton a fait l'objet d'une application de cette méthode. Le modèle de réseau de poutres (lattice model) a été utilisé pour étudier la propagation des fissures dans les structures en béton. Ce modèle a été implanté dans le logiciel de calcul par éléments finis, CESAR-LCPC. Les résultats numériques (propagation de fissures) obtenus pour les structures simples sous chargement statique sont en tout point comparables avec les résultats d'essais expérimentaux. Ce modèle a ensuite été utilisé pour étudier la fissuration sous chargement de fatigue. Pour cela un modèle d'endommagement simple modélisant la dégradation des éléments «poutres» s'est avéré suffisant pour décrire la cinématique de propagation des fissures / This work is part of the collaboration between the laboratory Navier (UMR ENPC /IFSTTAR/ CNRS) and ALSTOM Transport company (TGS/Trackway). It focuses on the study of the degradation of urban railways. The components of track considered in this study are the rail and the concrete slab. Regarding the rail, different problems are discussed : wheel – rail contact, rail wear, rail corrugation and rolling contact fatigue (RCF). A numerical tool with graphical interfaces, called CONUS, is developed to predict the behaviour of the wheel - rail contact, the rail wear, and the rail corrugation problems. Classical theories (Hertz, Kalker, Archard, etc...) are implemented in this tool. The stationary method is implemented in a finite element software to study the asymptotic state of the rail steel under repeated loading of trains.The damage mechanics is used to predict the fatigue life of concrete. Marigo's formalism coupled with Mazars' damage model is used to predict the gradual degradation of material stiffness under cyclic loading. A campaign of fatigue tests for concrete in bending was conducted. It aims at validating the theoretical model and identifying material parameters. We applied this method in order to design the concrete slabs of urban railway. The lattice model was used to study the crack propagation in concrete structures. This model was implemented in the finite element software, CESAR-LCPC. The numerical results obtained for simple structures under static loading are consistent with the results of laboratory experiments. This model was then used to study the crack propagation under fatigue loading. For that purpose, a simple damage model of degradation of the "beams" elements describes the kinematics of crack propagation with a satisfying accuracy

En este trabajo se ha llevado a cabo el desarrollo de una herramienta computacional para la simulación dinámica de vehículos ferroviarios. El modelo está basado en técnicas multicuerpo debidas a Shabana. Con respecto a otras metodologías existentes, la propuesta hace uso de un conjunto de sistemas de referencia que permite el empleo de coordenadas independientes sin la posibilidad de configuraciones singulares debidas a grandes giros. El conjunto de sistemas de referencia sirve de base para formular de manera precisa el problema de contacto rueda-carril. El programa está diseñado para considerar de forma flexible distintas configuraciones de vehículo así como diversas geometrías de trazado. La estructura del programa está abierta a cambios orientados a la mejora del modelo de contacto rueda-carril o a la implementación de la dinámica estructural de la vía. Se ha implementado un modelo eficiente que permite detectar con precisión las coordenadas de los puntos en contacto localizados en la interfase entre la rueda y el carril. La herramienta de simulación desarrollada en esta tesis se ha aplicado para diferentes casos-estudio con el objetivo de validar la idoneidad de la metodología propuesta en el análisis del sistema ferroviario. Se ha realizado una comparación entre los resultados obtenidos por la herramienta de simulación presentada y los resultados ofrecidos por varios programas comerciales de simulación dinámica en el análisis del vehículo de Manchester Benchmark. Además, la herramienta se ha empleado para desarrollar un análisis dinámico del vehículo de la locomotora TGV y los resultados obtenidos se han comparado con los ofrecidos por el programa comercial SIMPACK para el mismos modelo de vehículo, bajo las mismas condiciones de operación. Finalmente, sobre la base de la calidad de los resultados, se puede concluir que la herramienta de simulación es fiable y eficiente para emplearse en el análisis dinámico de los diferentes sistemas ferroviarios. / Elsayed Abdel Hameed Amer Shaltout, R. (2013). MULTIBODY APPROACH FOR RAILWAY DYNAMIC ANALYSIS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/27622 / TESIS