Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation. / <p>QC 20161013</p> / Centre for Eco2 Vehicle Design

Předložená disertační práce se zabývá experimentálním studiem modifikátorů tření a maziv pro temeno kolejnice, které jsou aplikovány do kontaktu kola a kolejnice za účelem optimalizace adheze a redukce hluku. Hlavním cílem práce bylo objasnit vliv aplikovaného množství a složení těchto látek na adhezi v kontaktu. Hlavní pozornost byla věnována zejména potencionálním hrozbám souvisejících s kriticky nízkou adhezí, která může nastat po aplikaci těchto látek. Experimentální studium probíhalo v laboratorních i reálných podmínkách, konkrétně v tramvajovém provozu. V případě laboratorních experimentů byl využit komerční tribometr a dvoudiskové zařízení umožňující simulovat průjezd vozidla traťovým obloukem. Kromě samotné adheze bylo při experimentech sledováno také opotřebení a míra hluku. Výsledky ukázaly, že maziva pro temeno kolejnice jsou schopna poskytovat požadované třecí vlastnosti, nicméně jejich chování je silně závislé na aplikovaném množství. V případě předávkování kontaktu dochází ke kriticky nízkým hodnotám adheze, které vedou k výraznému prodloužení brzdné dráhy. V případě modifikátorů tření bylo ukázáno, že chování těchto látek je výrazně ovlivněno odpařováním základního média. Výsledky také ukázaly, že nadměrné množství částic pro modifikaci tření může způsobit kriticky nízké hodnoty adheze. U obou výše zmíněných typů produktů byl prokázán pozitivní vliv na míru opotřebení a míru poškození povrchu, zatímco významná redukce hluku byla dosažena pouze v případech, kdy došlo ke značnému poklesu adheze. V závěru této práce jsou uvedena doporučení pro další výzkumné aktivity v této oblasti.

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.

Les phénomènes dynamiques observés lors de la circulation des trains provoquent des nuisances, notamment sonores et vibratoires, qui sont amplifiées par la présence de défauts sur la roue et sur le rail. Pour les analyser, il est nécessaire de prédire avec robustesse le comportement dynamique des composants impliqués dans l’interaction véhicule-voie et donc de simuler les efforts de contact générés pour des interfaces non idéalisées.L’objectif de cette thèse est donc de proposer un modèle semi-analytique global compatible avec l’intégration de multiples défauts géométriques sur les surfaces en contact. Afin de simuler l’interaction véhicule-voie dans le domaine temporel et garantir une applicabilité en phase de dimensionnement, une attention particulière est portée sur le compromis entre la précision des résultats et les temps de calcul associés.Le modèle ainsi proposé est composé d’un demi-bogie, dont le comportement vertical est représenté par un ensemble de masses-ressorts-amortisseurs, circulant sur une voie ballastée. Cette dernière est assimilée à une poutre bi-appuyée, supportée périodiquement à l’emplacement des traverses. Ces deux systèmes sont couplés en contact grâce à une procédure Distributed Point Reacting Spring (DPRS) sous forme discrétisée.Une validation du modèle est, d’une part, proposée en considérant des travaux antérieurs dans le cas de géométries parfaites. D’autre part, de multiples combinaisons de défauts, localisés comme le méplat ou répartis comme l’usure ondulatoire, sont introduites dans la simulation. La variabilité spatiale, particulière au cas de l’écaillage, est modélisée par des champs aléatoires. / The appearance of dynamic phenomena during the running of train on track leads to issues such as noise and vibration pollution, which can be further amplified by the presence of defects on the treads. In order to analyze them, it is necessary to predict with reliability the dynamic behavior of the vehicle-track interaction components, in particular the contact forces produced by non perfect treads.The aim of this PhD thesis is to provide a semi-analytical vehicle-track interaction model able to take into account multiple defects on the surfaces in contact. In order to conduct simulations in the time-domain and ensure applicability in the sizing phase, a special attention is given on the compromise between the accuracy of the results and the simulation times.The proposed model is therefore composed of half a bogie running on a ballasted track. This latter is modeled by a pinned-pinned beam with periodic supports located at the sleepers while the vertical behavior of the bogie is given by masses, springs and dampers. These two models are coupled in contact by a discretized Distributed Point Reacting Spring (DPRS) procedure.A validation of the model, based on previous work, is firstly proposed for perfect treads. Then, multiple combinations of defects, either localised as wheelflat or spread as corrugation, are introduced in the simulation. The spatial variability, specific to shelling, is modeled by random fields.

Due to the increase in demand on freight transportation it becomes necessary to avoid delays to ensure that the goods reach its destination on time. The main factors causing disturbances in the traffic on the mainline is the breakdown of vehicles mainly due to damaged wheels. The damaged wheels are identified through the wheel-rail impact force measurements provided by the wheel impact load detectors (WILD). This calls for the optimal schedule of maintenance of wheelsets and wagons in general. During the maintenance, the officials manually check for defective wheels and the exchange of wheelsets is performed based on the type of damage. The classification of wheel damages plays a vital role in providing ease of damage identification and insights to deduce a strategy for wheelset exchange. In this study, an attempt to classify the damaged wheelsets is done by analysing the wheel-rail impact force data from the wayside detectors. The data from the detectors are acquired from PredgeAB, a Luleå based startup pioneering in providing decision support on optimal maintenance schedules and predictive maintenance of rail wheels. Through their detection and prediction solutions it was observed that of all the wheels marked as damaged by the detectors 10% were undamaged. The source of the deviation in the impact force readings could help Predge make better estimations in damage detection and prediction. In this study, the sources contributing to the deviation is studied using multi-body simulations in GENSYS. A new method for modelling wheel damage is developed to overcome the shortcomings of the software. The findings of this study can then be used appropriately to make classifications of wheel damages. / På grund av den ökade efterfrågan på godstransporter är det nödvändigt attundvika förseningar för att säkerställa att varorna når sin destination i tid. Deviktigaste faktorerna som orsakar störningar i trafiken på huvudlinjen är stopp ispår av fordon, främst på grund av skadade hjul. De skadade hjulen identifierasmed hjälp av mätningar av slagkraft mellan hjul och spår som tillhandahållsav hjulbelastningsdetektorer (WILD). Detta kräver ett optimerat schema förunderhåll av hjulsatser och vagnar i allmänhet. Under underhållet kontrollerartjänstemännen manuellt för defekta hjul och utbytet av hjulsatser utförs baserat på typen av skada. Klassificeringen av hjulskador spelar en viktig roll närdet gäller att underlätta identifiering av skador och ge insikt för att bedöma enstrategi för hjulbyte. I den här studien görs ett försök att klassificera de skadade hjulsatserna genom att analysera data från slagkraften mellan spår ochhjul från detektorer. Uppgifterna från detektorerna hämtas från PredgeAB, enLuleå-baserad uppstartsbolag som är pionjärer för att ge beslutsstöd om optimala underhållsscheman och prediktivt underhåll av järnvägshjul. Genom sinadetekterings- och prediktiva lösningar observerades att 10% av alla hjul märktasom skadade av detektorerna var oskadade. Källan till avvikelsen i slagkraftavläsningarna kan hjälpa Predge att göra bättre uppskattningar när det gällerupptäckning och förutsägelse av skador. I den här studien studeras de källorsom bidrar till avvikelsen med simuleringar av flera kroppar i GENSYS. En nymetod för modellering av hjulskador har utvecklats för att övervinna programvarans brister. Resultaten av denna studie skulle kunna användas på lämpligtsätt för att göra klassificeringar av hjulskador.

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.