The life of railway wheels and rails has been decreasing in recent years. This is mainly caused by more traffic and running at higher vehicle speed. A higher speed usually generates higher forces, unless compensated by improved track and vehicle designs, in the wheel-rail contact, resulting in more wear and rolling contact fatigue (RCF) damage to the wheels and rails. As recently as 15 years ago, RCF was not recognised as a serious problem. Nowadays it is a serious problem in many countries and ''artificial wear'' is being used to control the growth of cracks by preventive re-profiling and grinding of, respectively, the wheels and rails.  This can be used because a competition exists between wear and surface initiated RCF: At a high wear rate, RCF does not have the opportunity to develop further. Initiated cracks are in this case worn off and will not be able to propagate deep beneath the surface of the rail or wheel. When wheel-rail damage in terms of wear and RCF can be predicted, measures can be taken to decrease it. For example, the combination of wheel and rail profiles, or the combination of vehicle and track, can be optimised to control the damage. Not only can this lead to lower maintenance costs, but also to a safer system since high potential risks can be detected in advance. This thesis describes the development of a wheel-rail life prediction tool with regard to both wear and surface-initiated RCF. The main goal of this PhD work was to develop such a tool where vehicle-track dynamics simulations are implemented. This way, many different wheel-rail contact conditions which a wheel or a rail will encounter in reality can be taken into account. The wear prediction part of the tool had already been successfully developed by others to be used in combination with multibody simulations. The crack prediction part, however, was more difficult to be used in combination with multibody simulations since crack propagation models are time-consuming. Therefore, more concessions had to be made in the crack propagation part of the tool, since time-consuming detailed modelling of the crack, for example in Finite Elements models, was not an option. The use of simple and fast, but less accurate, crack propagation models is the first step in the development of a wheel-rail life prediction model. Another goal of this work was to verify the wheel-rail prediction tool against measurements of profile and crack development. For this purpose, the wheel profiles of trains running on the Stockholm commuter network have been measured together with the crack development on these wheels. Three train units were selected and their wheels have been measured over a period of more than a year. The maximum running distance for these wheels was 230,000 km. A chosen fatigue model was calibrated against crack and wear measurements of rails to determine two unknown parameters.  The verification of the prediction tool against the wheel measurements, however, showed that one of the calibrated parameters was not valid to predict RCF on wheels. It could be concluded that wheels experience relatively less RCF damage than rails. Once the two parameters were calibrated against the wheel measurements, the prediction tool showed promising results for predicting both wear and RCF and their trade-off. The predicted position of the damage on the tread of the wheel also agreed well with the position found in the measurements. / <p>QC 20150526</p>

Virtual durability simulations have been explored in the automotive industry to complement physical testing in designing durable vehicles. Simulations are useful to check the validity of the design before even building the prototype of the vehicle. They are also useful in checking the effect of changes in vehicle design to the durability of the vehicle. Buses are designed and tested for durability before they are sold to customers. Bus manufacturers use special test tracks consisting of different kinds of maneuvers/obstacles to test the buses for durability. Proving ground durability test schedules defines the combination of different test track maneuvers/obstacles at which the bus is to be run. The test schedules are created to achieve accelerated fatigue damage in the bus comparable with the fatigue damage occurring in typical customer usage. This thesis is an attempt to check if a proving ground durability test schedule can be simulated in a computer. A Multibody dynamic model of the bus with its constituent subsystems is modeled in a multibody simulation software MSC ADAMS. Sub-systems like bus chassis frame and axle are modeled as flexible as their dynamic properties are assumed to influence the simulation results. The virtual bus is run on the virtual version of the test tracks. Loads at suspension torque rods, anti-roll bars, axles and displacement of dampers are extracted from the simulation. The load signals are post-processed to derive fatigue damage. The simulation model is compared with the test results of a single standard test track maneuver. The simulation model is tuned by adjusting the parameters to match with the test results of the given maneuver. Finally, the tuned model is used to run the bus in a test schedule. Results achieved at the end of the thesis shows that well-tuned simulation model is necessary for simulating test schedules with enough accuracy. Comparison with test results are to be treated with caution as the conditions of the test bus should be exactly same as the simulation model; which is difficult to achieve. Future extension of the work involves improving the accuracy of simulations and using simulations to iterate new kinds of maneuvers/obstacles to improve existing test schedules. / Virtuell hållfasthetsprovning utnyttjats inom fordonsindustrin för att komplettera fysisk provning med avseende att konstruera hållfasta fordon. Simuleringar är användbara för att kontrollera designen innan första prototypen har byggts men även för att kontrollera hur hållfastheten påverkas av olika fordonskoncept. Bussar utvecklas och provas så att de ska klara målen för hållfasthet innan de säljs. Busstillverkarna använder speciella provbanor bestående av olika hinder och manövrar för att testa hållfastheten. Tillsammans med speciella provningsprogram som specificerar vilka provbanehinder och manövrar som bussen ska provas enligt kan hållfastheten säkerställas. Dessa provprogram är framtagna för att den accelererade utmattningen på provbanan ska matcha den utmattning bussen utsätt för hos kund. Denna avhandling undersöker huruvida provprogram kan utvecklas digitalt via simuleringar. Multidynamiska modeller av bussens delsystem modelleras i programvaran MSC ADAMS. Delsystem som buss chassi ram och axlar modelleras som flexibla då deras dynamik egenskaper anses påverka simuleringsresultaten. Den virtuella bussen provas på en digital provbanan. Krafterna i reaktionsstag, kränghämmare, axlar och förskjutningen i stötdämpare beräknas. Dessa kraft- och förskjutningssignalser används senare för att beräkna utmattning. Simulerade resultat av ett hinder jämförs med resultat från fysisk provning för att därefter justera vissa parametrar för att virtuella resultat ska matcha fysiska. Efter att modellen är optimerad kan slutligen delskadan för ett helt provprogram simuleras. Resultat visar på att en väll optimerad simuleringsmodell är nödvändig för att simulera fram provprogram med bra noggrannhet. Att jämföra simulerade resultat med fysiska ska göras med viss aktsamhet då den fysiska bussen bör vara identisk med den virtuella; vilket är mycket svårt att uppnå. Framtida arbete inom ämnet bör innefatta förbättringar av simuleringsnoggrannheten och använda simulering för framtagandet av nya hinder/manövrar för att förbättra befintliga provprogram.

Analisa o comportamento tribológico do pneumático. Discute o coeficiente de atrito do pneu, a influência do pavimento e os avanços na modelagem. Apresenta uma metodologia para estimativa do desgaste de pneus pelo método dos elementos finitos. Usa o conceito de trabalho de abrasão. Considera nas condições de contorno do modelo de pneu o efeito do camber e do ângulo de deriva. Investiga a interação vibracional entre o pneu e a suspensão como causa de desgaste irregular. Utiliza modelagem de ônibus rodoviário por multicorpos com eixo flexível. Emprega técnica tempo-freqüência para análise do acoplamento modal entre pneu e suspensão. Propõe novos modelos para estudo do desgaste em pneus analisando-se um modelo completo de veículo pelo método dos elementos finitos. Sugere análises de sensibilidade considerando os parâmetros de regulagem da suspensão e condições operacionais dos componentes. Propõe análises estocásticas da especificação do pneu para otimização do sistema pneu-suspensão. / The tire tribological behavior is analyzed. The friction coefficient of rubbers is presented, and its inherent modeling difficulties regarding the operational condition dependence during measurements are discussed. The influence of the pavement roughness and the advances in friction modeling are presented. A predictive methodology to evaluate the tread wear using finite element method and the concept of frictional energy was used. Camber, lateral forces and slip angles are taken into account as boundary conditions for the tire simulations in steady state. The vibrational interaction between tire and suspension concerning irregular wear on front axle truck tires was investigated. A multibody bus model with flexible front axle was used for modal analysis purposes. A time-frequency methodology was applied to identify modal vibrations of the tire and suspension assemblage. A new simulation model for the tire wear was proposed intending to analyze the whole vehicle with under the finite element method. Sensitivity analysis of the vehicle suspension setup and operational conditions of components was suggested. Stochastic analysis of tire specification is recommended to optimize the tire-suspension system.

Analisa o comportamento tribológico do pneumático. Discute o coeficiente de atrito do pneu, a influência do pavimento e os avanços na modelagem. Apresenta uma metodologia para estimativa do desgaste de pneus pelo método dos elementos finitos. Usa o conceito de trabalho de abrasão. Considera nas condições de contorno do modelo de pneu o efeito do camber e do ângulo de deriva. Investiga a interação vibracional entre o pneu e a suspensão como causa de desgaste irregular. Utiliza modelagem de ônibus rodoviário por multicorpos com eixo flexível. Emprega técnica tempo-freqüência para análise do acoplamento modal entre pneu e suspensão. Propõe novos modelos para estudo do desgaste em pneus analisando-se um modelo completo de veículo pelo método dos elementos finitos. Sugere análises de sensibilidade considerando os parâmetros de regulagem da suspensão e condições operacionais dos componentes. Propõe análises estocásticas da especificação do pneu para otimização do sistema pneu-suspensão. / The tire tribological behavior is analyzed. The friction coefficient of rubbers is presented, and its inherent modeling difficulties regarding the operational condition dependence during measurements are discussed. The influence of the pavement roughness and the advances in friction modeling are presented. A predictive methodology to evaluate the tread wear using finite element method and the concept of frictional energy was used. Camber, lateral forces and slip angles are taken into account as boundary conditions for the tire simulations in steady state. The vibrational interaction between tire and suspension concerning irregular wear on front axle truck tires was investigated. A multibody bus model with flexible front axle was used for modal analysis purposes. A time-frequency methodology was applied to identify modal vibrations of the tire and suspension assemblage. A new simulation model for the tire wear was proposed intending to analyze the whole vehicle with under the finite element method. Sensitivity analysis of the vehicle suspension setup and operational conditions of components was suggested. Stochastic analysis of tire specification is recommended to optimize the tire-suspension system.

Tracked vehicles are designed to operate in various terrains, ranging from soft mud to hard tarmac. This wide range of terrains presents significant challenges for the suspension system, as its components must be suitable for all types of terrain. The selection of these components is crucial for minimizing acceleration levels within the vehicle, ensuring that personnel can comfortably endure extended durations inside. BAE Systems Hägglunds AB develops and produces an armored tracked vehicle called the CV90. Within the CV90’s suspension system, a key component known as the torsion bar, a rotational spring, plays a primary role in reducing the vehicle’s motion. The CV90 vehicle has seven wheels on each side, with each wheel having its dedicated torsion bar. To measure the whole-body vibration experienced within the vehicle, a measurement called the Vibrational Dose Value (VDV) is utilized. The main objective of this thesis is to develop a data-driven model to optimize the suspension system by identifying the combination of torsion bars that generates the smallest VDV. The data used for optimization is based on simulations of the CV90 vehicle in a virtual environment. In the simulation, the CV90 vehicle, with its full dynamics, is driven over a specific virtual road at a particular velocity. The simulation itself cannot be manipulated; only the input values can be adjusted. Thus, we consider the simulation as a black box, which led us to implement the black-box optimization algorithm known as Particle-Swarm. In this thesis, four different roads, each with velocities ranging from four to seven different levels, were provided to the optimization model. The results show that the model identifies a combination of torsion bars that generates a small VDV for all combinations of velocities and roads, with an average VDV improvement of around 20% - 60% compared to a reference case. Since this thesis serves as a proof of concept, the conclusion is that the devised method is effective and suitable for addressing the problem at hand. Nonetheless, for seamless integration of this method into the tracked vehicle development process, further research is necessary.