Carbon fibre reinforced ceramic composites (Cf/C-SiC) have been explored as lightweight and durable disc in a friction brake. This composite was manufactured through infiltration of liquid silicon into a Cf/C perform. It has heterogeneous microstructure, composed of three key phases, silicon carbide, Cf/C, and un-reacted residual silicon. The development of the transfer layer on the friction surface of Cf/C-SiC was studied through microstructural image registration of the surface after a range of braking stops on a laboratory-scale dynamometer test rig. When an organic pad was used as the counter face brake pad, it was found that a steady transfer layer was developed in silicon regions right after initial stops; in carbon-fibre/carbon (Cf/C) regions and most of the silicon carbide region, the friction surfaces were unsteady and any possible friction transfer layers were hardly built up. Large voids and cracks/crevices likely became pools to quickly and efficiently collect the transferred materials generated by the friction, but the compacts formed inside the pools were susceptible to be stripped off by further braking operation. Three types of friction surfaces were generalized: type I, the friction transfer layer had a steady relationship with the matrix and respectable longevity; type II, the transfer layer had an unstable relationship with the matrix and poor durability; type III, the friction transfer layer had a steady relationship with the matrix but short lifetime. After testing against organic pads under the laboratory scale dynamometer testing condition, the friction surface of each key phase in Cf/C-SiC composites disc was studied by transmission electron microscopy (TEM). It was found that the transfer layer developed on Si consists of fine particles of metal silicides, silicates and minerals. The substrate damage of Si was not observed, while the precipitates having high oxygen content were found in the substrate. Formation of an interfacial bonding between transfer layer and silicon substrate is believed to be the key factor for the formation of a stable transfer layer on Si. However, the interfacial bonding between transferred materials and SiC was not detected. Kinks are common features developed on the friction surface of SiC. The interface between carbon fibre and carbon matrix was experienced mechanical damage, in form of microcracks, and the transferred material was developed in the interface. Instead of transfer layer, a thin amorphous film, produced by friction induced amorphisation of carbon fibre, was developed on top of carbon fibre.

This dissertation investigates the effect of electromagnetic braking and gas injection on the fluid flow in a continuous casting slab mold numerically and makes verifications on basis of a small Liquid Metal Model for Continuous Casting of steel (mini-LIMMCAST). Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The non-isotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model. The numerical results were validated by flow measurements at the mini-LIMMCAST facility. Numerical simulations disclose the damping effect on the flow closely depending on the wall conductance ratio. In addition, specific modifications of the turbulence model play a crucial role in reconstructing the peculiar phenomenon of an excitation of nonsteady, nonisotropic, large-scale flow perturbations caused by the application of the DC magnetic field.

Conventional hydraulic brake (CHB) systems used in automotive industry have several limitations and disadvantages such as the response delay, wear of braking pad, requirement for auxiliary components (e.g. hydraulic pump, transfer pipes and brake fluid reservoir) and increased overall weight due to the auxiliary components. In this thesis, the development of a novel electromechanical brake (EMB) for automotive applications is presented. Such brake employs mechanical components as well as electrical components, resulting in more reliable and faster braking actuation. The proposed electromagnetic brake is a magnetorheological (MR) brake. The MR brake consists of multiple rotating disks immersed into an MR fluid and an enclosed electromagnet. When current is applied to the electromagnet coil, the MR fluid solidifies as its yield stress varies as a function of the magnetic field applied by the electromagnet. This controllable yield stress produces shear friction on the rotating disks, generating the braking torque. This type of braking system has the following advantages: faster response, easy implementation of a new controller or existing controllers (e.g. ABS, VSC, EPB, etc.), less maintenance requirements since there is no material wear and lighter overall weight since it does not require the auxiliary components used in CHBs. The MRB design process included several critical design steps such as the magnetic circuit design and material selection as well as other practical considerations such as cooling and sealing. A basic MRB configuration was selected among possible candidates and a detailed design was obtained according to a set of design criteria. Then, with the help of a finite element model (FEM) of the MRB design, the magnetic field intensity distribution within the brake was simulated and the results were used to calculate the braking torque generation. In order to obtain an optimal MRB design with higher braking torque generation capacity and lower weight, the key design parameters were optimized. The optimization procedure also consisted of the FEM, which was required to calculate the braking torque generation in each iteration. Two different optimization search methods were used in obtaining the minimum weight and maximum braking torque: (i) a random search algorithm, simulated annealing, was first used to find an approximate optimum design and (ii) a gradient based algorithm, sequential quadratic programming, was subsequently used to obtain the optimum dimensional design parameters. Next, the optimum MRB was prototyped. The braking performance of the prototype was tested and verified, and the experimental results were shown. Also, experimental results were compared with the simulation results. Due to the lack of accurate material property data used in the simulations, there were discrepancies between the experimental and the simulation results. Other possible sources of errors are also discussed. Since the prototype MRB generates much lower braking torque compared to that of a similar size CHB, possible design improvements are suggested ton further increase the braking torque capacity. These include the relaxation of the optimization constraints, introduction of additional disks, and the change in the basic magnetic circuit configuration.

Os discos de freio, durante a frenagem, são submetidos a tensões térmicas e mecânicas que podem ser relativamente altas quando muito bruscas (frações de segundo), situação em que a temperatura pode chegar a valores próximos de 600ºC. Esta variação de temperatura provoca choques térmicos que podem gerar trincas e/ou uma grande quantidade de deformação plástica no disco. A proposta deste trabalho foi a de investigar, através de experimentos, o comportamento mecânico e físico em quatro ligas de ferro fundido cinzento (A, B, C e E), utilizadas para produzir discos de freio de veículos automotivos. Para tanto, foram realizados ensaios termomecânicos de baixo ciclo em corpos de prova, entre 300ºC e 600ºC, nas condições em fase e fora de fase, adotando o critério de falha em 50% da tensão máxima (ASTM E-606) e em componentes (discos), além daqueles de difusividade térmica desde a temperatura ambiente até 600ºC. As curvas deformação em função da vida ( N) foram obtidas e analisadas segundo norma ASTM E 466/468. A análise microestrutural nos corpos de prova e peças, após os ensaios de fadiga, serviu para revelar a influência da morfologia e quantidade de grafita e da matriz sobre as propriedades mecânicas. A medição das difusividades térmicas teve como objetivo a verificação da influência do carbono equivalente e dos elementos de liga sobre esta propriedade física. Observou-se que, durante os ensaios de fadiga termomecânica em fase, em função da decomposição de parcela da cementita da perlita, houve, nos materiais, a chamada expansão grafítica, que teve influência na parte trativa do ciclo, diminuindo as tensões necessárias para se alcançar determinadas amplitudes de tensão mecânica. Pelos gráficos de amplitude de deformação mecânica em função do número de reversos para falhar, sob fadiga termomecânica em fase e fora de fase, observou-se que a melhor liga de ferro fundido cinzento foi a liga E. Esta constatação implicará em uma significativa redução dos custos de produção dos discos de freio, pois se poderá prescindir do elemento de liga Molibdênio, extremamente caro. Comparando-se os resultados de fadiga termomecânica com os de fadiga isotérmica a 25ºC, 300ºC e 600ºC, pôde-se verificar que os ensaios mais críticos foram os fora de fase, pois conduziram, comparativamente, a vidas menores. / Brake discs are submitted to thermal and mechanical stress that can be relatively high during abrupt braking action happens (fractions of seconds), causing the temperature to reach values as high as 600ºC. This temperature variation results in thermal shocks that can generate cracks and/or a large amount of plastic deformation in the disk. The main aim of this work was to investigate, through experiments, the mechanical and physical behavior of four alloys of gray cast iron (A, B, C and E), used to produce brake discs of automotives vehicles. Low cycle thermomechanical fatigue tests were carried out in components (discs) and in test specimens, between 300ºC and 600ºC, in the conditions in-phase and out-of-phase, adopting the failure criterion of 50% drop of the maximum tensile stress (ASTM E - 606). Thermal diffusivity values were measured from room temperature up to 600oC in order to analyze the effects of carbon content and alloying elements in physical properties. Curves -N were obtained and analyzed according to ASTM E 466/468 standard. Microstructural analysis was employed to reveal the influence of the matrix and morphology/amount of graphite on the mechanical properties. It was observed that, during in-phase thermomechanical fatigue tests, the volume expansion due to cementite decomposition into graphite and ferrite caused a decrease in the tensile stress necessary to achieve the mechanical strain imposed during tests. From M/2 x 2Nf graphs it was inferred that alloy E presented the best performance both in in-phase and out-of phase tests. The lack of Mo in this alloy implies in a significant reduction of cost production of the brake discs, due to the high cost of such alloying element. Out-of-phase thermomechanical fatigue tests resulted in shorter lives compared to isothermal fatigue tests carried out at 25ºC, 300ºC and 600ºC.

Le présent document a pour objet la modélisation transitoire non linéaire du comportement vibratoire des systèmes de frein aéronautiques. Le but est de reproduire numériquement l’apparition et le niveau des vibrations au cours du temps, afin de les maîtriser et d’adapter la conception du frein. Les essais de freinage mettent en évidence deux modes de vibration que sont le whirl et le squeal. Si les niveaux de ces vibrations deviennent trop importants, la structure de la roue et du train d’atterrissage peut être endommagée. Afin d’éviter de tels dommages, la conception du frein doit être adaptée. Pour réaliser cela, Messier-Bugatti-Dowty doit disposer d’un modèle capable de prédire les niveaux de vibration du frein au cours du temps pendant la phase de freinage. Le modèle doit avoir une précision suffisante, être en lien avec la maquette numérique et ne doit pas exiger de recalage. Un premier travail vise à améliorer le modèle éléments finis existant qui se révèle être trop imprécis. Une étude portant sur les effets gyroscopiques permet d’évaluer leur impact sur la fréquence et la stabilité des modes de whirl. Une modélisation plus complète du bâti d’essai améliore la précision de la fréquence du mode de squeal. Enfin, le mode de whirl est mieux simulé grâce au développement d’un modèle de pneumatique à partir de son analyse modale. Ce modèle est ensuite réduit afin de réaliser une intégration temporelle. Une sous-structuration permet de séparer l’ensemble des disques du frein, où le frottement et la non-linéarité se situent, du reste de la structure considérée comme linéaire. Trois techniques de réduction de l’ensemble des disques sont exposées. On évalue leur représentativité par rapport au modèle non-réduit en comparant les fréquences et la stabilité des modes propres. La première méthode est une représentation nodale de l’ensemble des disques. Les équations décrivant la non-linéarité et le frottement sont analytiques. Pour la deuxième méthode, la non-linéarité est déplacée à l’extrémité de l’ensemble des disques pour la découpler du frottement. La troisième méthode, plus ambitieuse et complexe, conserve à la fois l’emplacement de la nonlinéarité aux interfaces frottantes et la géométrie des disques. Une technique de réduction modale permet d’abaisser le nombre de degrés de liberté non linéaires. Pour clore ce rapport, des simulations transitoires sont calculées à partir des modèles réduits. Des études d’influences sont réalisées. Les paramètres étudiés sont le type d’algorithme d’intégration temporelle, l’amortissement introduit, la loi non linéaire, la pression hydraulique d’entrée et le coefficient de frottement. Leurs impacts sur les niveaux et la durée d’apparition des vibrations est évalué. / This report deals with the non-linear transient simulation of the dynamic behaviour of aeronautic brake systems. The objective is to reproduce the occurrence and level of vibrations versus time in order to control and adjust design consequently. The braking tests highlight two eigenmodes, which are called whirl and squeal. If the level of these vibrations becomes too high, the structures of the wheel and the landing gear may be damaged. To avoid damage, the design has to be adjusted. To achieve this, Messier-Bugatti-Dowty requires a model that is able to predict the levels of vibrations of the brake when it is braking. This model must have an adequate accuracy, be linked to the digital mockup and not require tuning. First, the existing finite element model has to be improved because its initial accuracy is not acceptable. A study about gyroscopic effects allows to assess their impact on the frequency and the stability of whirl modes. A complete modelling of the test frame improves the squeal modes’ frequency accuracy. At last, the whirl modes are better simulated due to the development of a tyre model based on modal analysis data. Then, the finite element model is reduced in order to perform a temporal integration. A substructuring allows to separate the set of brake discs (heat sink), where friction and non-linearities are located, from the rest of the structure which is considered linear. Three heat sink reduction techniques are proposed. Their representativeness are estimated compared to the non-reduced model. The first technique is a nodal description of the heat sink. The equations of friction and non-linearity are analytical. For the second technique, the non-linearity is displaced to the extremity of the heat sink to uncouple it from friction. The third technique, more ambitious and complex, keeps the location and non-linearity in friction interfaces and discs geometry. A reduction technique enables to decrease the number of non-linear degrees of freedom. As a conclusion, transient simulations are computed from reduced models. Sensitivity studies are performed. Studied parameters are the type of integration solver, introduced damping, non-linearities, hydraulic pressure, and friction coefficient. Their impacts on level and duration of occurrence of vibrations is estimated.

Electric and hybrid vehicles are particularly suited for use in urban areas since city transportation is mainly characterized by relatively short driving distances, low continuous power requirements, long idling times and high availability of regenerative braking energy. These characteristics, when carefully incorporated into the design process, create valuable opportunities for developing clean, efficient and cost effective urban vehicle propulsion systems. In the first part of the thesis, we present data collected in the city of Bangalore, India from a very commonly seen mode of transportation for hire in India and other emerging economies, namely a three-wheeled vehicle known as the “auto-rickshaw”. From a statistical analysis, it is shown that the typical range is 72.5 km with a mean speed of 12.5 km/h. More than 60% of the time the auto-rickshaw is stationary or has a speed of less than 5 km/h. From a model of the auto-rickshaw, it is shown from simulations that 4 kW DC motor and about 10 kWh of electrical energy is enough to meet 80% of typical requirement. Based on this finding, in this thesis, a novel parallel hybrid architecture is proposed where two 2 kW DC hub motors are directly mounted on the wheels and an internal combustion (IC) engine output is connected to the stator of the DC hub motors to provide additional power when required. To match load and speed, a continuously variable transmission (CVT) is placed in-between the IC engine and the DC hub motor. The proposed hybrid configuration adds speed to the wheel output unlike the normal power split configuration which adds torque. One of the main objective of this work is to study and compare the performance of the above novel speed-addition and compare with the typical torque-addition configuration. A MATLAB/Simulink model for both the configurations, with DC hub motor and a small IC engine, has been created and the fuel consumption has been calculated. It is shown that the proposed speed-addition concept gives better fuel efficiency for the standard modified Indian Driving Cycle. The models have also been compared for actual driving data and an optimal control strategy has been developed using dynamic programming. It is again shown that the proposed speed-addition concept results in better fuel economy. In the last part of the thesis, a low cost experimental test-bed consisting of an auto-rickshaw IC engine, a CVT and a 2 kW DC hub motor has been developed to validate the speed-addition concept and compare with the torque-addition configuration. The torque-speed curves of the IC engine, the DC motor and both of them together, in the speed and torque-addition configuration, have been obtained. It is shown that the speed-addition concept does indeed work and the obtained results are significantly different from the torque-addition configuration.

Many devices are available on the market for the evaluation and rehabilitation of patients suffering from muscular disorders. Most of them are small, low-cost, passive devices based on the use of springs and resistive elements and exhibit very limited (or even not any) evaluation capabilities; extended muscular force evaluation is only possible on stationary, expensive, multi-purpose devices, available only in hospitals, which offer many exercise modes (e.g. isokinetic mode) that are not available on other devices.<p><p>The objective of this thesis is to make the functionalities currently only implemented on bulky multi-purpose devices available at a lower cost and in a portable fashion, enabling their use by a large number of independent practitioners and patients, even at home (tele-medecine applications).<p><p>In order to achieve this goal, a portable rehabilitation device, using a magneto-rheological fluid brake as actuator, has been designed. This particular technology was selected for its high level of compactness, simple mechanical design, high controllability, smooth and safe operation. The first part of this thesis is devoted to the design of MR-fluid brakes and their experimental validation. The second part is dedicated to the design of the rehabilitation device and the comparison of its performances with a commercial multi-purpose device (CYBEX). / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

For an energy efficient current transmission, high demands are set on the construction of transformers. One of the more significant parts is the winding that constitutes the core of the transformer. In order to secure a high quality and reduced loss of energy, companies therefore work actively with decreasing possible sources of error in order to gain better control over the processes.The thesis is an investigative feasibility study with the purpose to examine the possibility to implement amore reliable brake system in a wire winding process aswell as creating documents with possible solutions for how the feeding of wire can be controlled.In the study are first and foremost qualitative methods for data collection used. These partly consist of an interview study with employees, observations from the industry and a literature review aswell as a market study. The methods are chosen to give a broad description of how the process function and what other solutions can be applicable to be used in a final conceptual solution proposal.From the interview study, the needs and requirements were summarized into a list of selection criterias. These criterias were weighted and then used to select one of the concepts for further development. The final solution presented two different proposals for brake types depending on whether the company wants to use a pneumatic or electric brake system. Further in the development, suggestions are given on how the brakes could be controlled. The aim of this point is to be able to create a higher reliability in the regulation of the system's brake pressure and allow the operator to do this from the front of the workstation. / För en energieffektiv strömöverföring ställs det höga krav på konstruktionen av transformatorer. En betydelsefull faktor är de lindningar som utgör kärnan på transformatorn. För att kunna säkerställa en hög kvalitet och minskad energiförlust arbetar företagen aktivt med att minimera möjliga felkällor för att få bättre kontroll över processerna.Rapporten har strukturen av en undersökande förstudie där syftet är att undersöka möjligheten att implementera ett mer pålitligt bromssystem i en trådlindningsprocess samt skapa underlag för möjliga lösningar över hur trådmatningen kan regleras.Som grund används framför allt kvalitativa datainsamlingsmetoder. Dessa utgörs dels av en intervjustudie med anställda, observationer av verksamheten och processen, dels en litteratur- ochmarknadsundersökning. Metoderna används för att få en bred uppfattning av den process som undersöks samt vilka andra lösningar som kan vara tillämpbara för att slutligen användas som underlag till konceptuella lösningsförslag.Från intervjustudien sammanfattade de behov och krav som finns till en lista med urvalskriterier. Dessa kriterier viktades varpå de användes för att välja ett av koncepten för vidare utveckling och förtydligande. I det slutgiltiga lösningsförslaget presenterades två olika förslag på bromstyper beroende på om företaget vill utnyttja ett pneumatiskt eller elektriskt bromssystem. I nästa steg av utvecklingen ges förslag på hur styrning av bromsarna skulle kunna ske. Målet med denna punkt är kunna skapa en högre pålitlighet i regleringen av systemets bromstryck samt tillåta operatören att göra detta framifrån arbetsstationen.

Design of braking system for the formula student car. Calculation of basic forces acting in the braking system, including the design of hydraulic circuits. Mechanical analysis of the most important parts of the braking system and pedal assembly. Thermal analysis of the brake discs. Manufacturing and total cost calculation.

In this diploma thesis active aerodynamic components are designed, specifically brake cooling duct and active automotive wing. Cooling duct prototype and also active regulation controlling electronics including the software were created. Road test was performed to measure the duct parameters. Construction design and the active regulation function of the automotive wing were created. The influence of the wing on aerodynamic characteristics of the car was determined.