Šio tyrimo tikslas yra sukurti, realizuoti ir išbandyti metodą leidžiantį atlikti naujo riedėjimo guolio elementų neardoma diagnostiką ir įvertinti surinkimo kokybę. Norint įvertinti guolio kokybę jo neišardant, pasitelkti virpesių pagreičio signalo stebėsenos ir analizės metodai. Atlikti sekantys uždaviniai siekiant įgyvendinti tyrimo tikslą: • Apžvelgti pramonėje naudojami guolių kokybės įvertinimo metodai. • Sukurtas ir realizuotas metodas naujo guolio kokybei nustatyti. • Praktiškai patikrinta metodo teikiama nauda. • Išnagrinėta suteptų ir nesuteptų guolių įtaką kokybės nustatymui. Atliekant virpesių signalų tyrimą sukurtu ir realizuotu guolių elementų virpesių pagreičio vidutinės kvadratinės vertės metodu, galima nustatyti guolio surinkimo kokybę, jo elementų pažeidimus, neatliekant ardymo kas būna neišvengiama taikant kitus metodus. Metodo efektyvumas patvirtintas atliekant tiriamųjų guolių išsamius mechaninius tyrimus, kurių metu buvo išardyti tyrimuose naudoti riedėjimo guoliai ir nuodugniai ištirta jų riedėjimo elementų kokybė ir gauti rezultatai palyginti su realizuoto metodo teikiamais rezultatais. Realizuoti pagalbiniai metodai kaip virpesių pagreičio skirtumo radimas, vyraujančių dažnių paieška, kurie suteikia papildomos informacijos apie guolį ir/ar jo kokybę. Sukurtas ir realizuotas virpesių pagreičio signalo centravimo metodas, patikrinta jo teikiama praktinė nauda. / The purpose of this thesis is to create, implement and test a method which would allow to evaluate the quality of newly made bearing and its elements, without the need of disassembling the bearing. To evaluate the quality of the bearing without disassembling it, vibration signal monitoring and analysis methods were used. The following tasks were completed in order to accomplish the goal of the thesis: • Reviewed bearing quality evaluation and failure detection methods used in industry. • Created and implemented a method which could evaluate the quality of a bearing. • Experimentally tested the efficiency of the method. • Investigated the used oil influence on the quality detection. The quality of the bearing and its elements can be measured using bearing elements vibration acceleration root mean square method. This method does not require the disassembling of the bearing which might not be avoided when using other methods. The efficiency of the method was proven by performing extensive mechanical analysis on studied bearings, which required to disassemble the bearing and check in detail the quality of the bearing. The collected results were compared with the ones received from the implemented method. Some additional methods were created and implemented which would give more information about the bearing and its quality. The vibration acceleration signal centering method was implemented and its efficiency was checked experimentally.

The use of bearings can be found in virtually all aspects of mechanical systems today. Reliability of these critical components is an important issue. Fatigue performance of bearings is a function of many factors, including service conditions, loading, material properties, environmental factors, and manufacturing processes. Crack nucleation, first spall generation and spall growth in rolling contact fatigue are known to be highly sensitive to the heterogeneity of the microstructure. Yet the current state-of-the-art in the design of high performance bearing materials and microstructures is highly empirical requiring substantial lengthy experimental testing to validate the reliability and performance of these new materials and processes. The approach presented here is designed to determine relative rolling contact fatigue performance as a function of microstructural attributes. A fully three-dimensional finite element modeling allows for end effects to be captured that were not previously possible with two-dimensional plane-strain models, providing for a more realistic assessment of inclusion morphology and arbitrary orientations. The scaling of the finite element models has been optimized to capture the cyclic microplasticity around a modeled inclusion accurately and efficiently. To achieve this, two scales of geometric models were developed to incorporate different sized microstructural phenomena, with both models using traction boundary conditions derived from Hertzian contact stresses. A microstructure-sensitive material model adds additional capability. A hybrid model that includes both martensite and austenite phases with additional internal state variable to track the volume fraction of retained austenite due to stress-assisted transformation were developed. This represents an advance over previous models where transform plasticity and crystal plasticity were not simultaneously accounted for in a homogenized element containing both phases. Important links between microstructural features and fatigue indicator parameters (and relative fatigue performance) were determined. Demonstration cases show the relationship between inclusion orientation and relative fatigue performance, allowing for the identification of critical angles which maximize fatigue and reduce performance. An additional case study showed that increasing initial volume fraction of retained austenite reduces relative fatigue life. The tools developed allow for investigations of the influence of many microstructural aspects on relative fatigue performance with a numerical model that were not previously possible.

Submitted by Daniele Amaral (daniee_ni@hotmail.com) on 2016-10-18T18:18:09Z No. of bitstreams: 1 DissJJMC.pdf: 3783297 bytes, checksum: 5f8c40bb2d622e5b243b6288d529dac4 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-21T14:03:42Z (GMT) No. of bitstreams: 1 DissJJMC.pdf: 3783297 bytes, checksum: 5f8c40bb2d622e5b243b6288d529dac4 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-21T14:03:48Z (GMT) No. of bitstreams: 1 DissJJMC.pdf: 3783297 bytes, checksum: 5f8c40bb2d622e5b243b6288d529dac4 (MD5) / Made available in DSpace on 2016-10-21T14:03:54Z (GMT). No. of bitstreams: 1 DissJJMC.pdf: 3783297 bytes, checksum: 5f8c40bb2d622e5b243b6288d529dac4 (MD5) Previous issue date: 2016-08-04 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Magnesium hydride is a promisor candidate for H2 storage, manly due its high hydrogen gravimetric capacity (7.6% wt), low density, abundance and low cost. However, its H-absorption/desorption occurs only at temperatures around 673 K with slow kinetics. Moreover, Mg and MgH2 surfaces are highly reactive, easily forming MgO and/or Mg(OH)2 layers that lower the level the hydrogen storage properties. It described in the literature that the use the severe plastic deformation technique or the incorporation of additives such as LaNi5 improve the hydriding/dehydriding kinetics and lower the dehydrogenation temperature of Mg-based composites. In the present study, Mg-based hydrogen storage alloys has been developed in the following systems: MgH2 and MgH2 + LaNi5 using the cold rolling (CR) under inert atmosphere. The aspect analyzed in this study were the processing parameters (number of passes and roll rotation frequency) and the additive incorporation (LaNi5) during the processing and Habs / des behavior. The micro and nanoestrutural characterization for the obtained materials were made by means of X-ray diffraction (XRD), scanning a transmission electron microscopy (SEM and TEM), and the correlation of results obtained with the process route, showed that larger number of rolling passes and high frequency produces nanocomposites with great improvements in the hydrogen storage properties. Furthermore, was observed a catalytic effect with the addition of LaNi5 to MgH2, due the formation of new phases in hydriding/dehydriding process. The best result for hydrogen storage were obtained for the system MgH2+1,50 mol.% LaNi5 with low Habsorption / desorption temperatures, aspect interesting for MgH2. / O Mg é um material promissor para a armazenagem de hidrogênio, pela sua baixa densidade, abundância, custo relativamente baixo e capacidade de armazenagem de até 7,6 % p. No entanto, sua cinética de absorção/dessorção de H2 é lenta, e ocorre em temperaturas superiores a 300°C. Além disso, as superfícies do Mg e do MgH2 são susceptíveis à oxidação, gerando assim camadas de MgO ou ainda Mg(OH)2 que atuam como barreiras nos processos de absorção/dessorção do hidrogênio. É descrito na literatura que a rota de processamento utilizando a deformação plástica severa, assim como a incorporação de aditivos como o LaNi5 melhoram o desempenho dos nanocompósitos à base de Mg. Neste trabalho MgH2 e MgH2 + LaNi5 foram preparados utilizando a laminação a frio (CR, do inglês Cold Roll) em atmosfera controlada. Os aspectos analisados foram os parâmetros do processo de CR (número de passes e frequência dos cilindros). Os efeitos da adição do LaNi5 durante o processamento e no comportamento de absorção/dessorção de H2. A caracterização micro e nanoestrutural dos nanocompósitos obtidos, através da difração de raios-X, microscopia eletrônica de varredura e transmissão, e sua correlação com a rota de processamento; demonstrou que um elevado número de passes de CR a elevadas frequências produz nanocompósitos com propriedades atrativas para armazenagem de hidrogênio. Além disso, observou-se um efeito catalítico com a adição do LaNi5 ao MgH2, devido a formação de novas fases durante as etapas de absorção e dessorção de H2. As melhores características de armazenagem de hidrogênio foram obtidas para a mistura MgH2+1,50 mol.% LaNi5 na qual as medidas foram realizadas a baixas temperaturas, fato importante para o MgH2.

Este trabalho visa analisar a influência das taxas de resfriamento e temperatura no último passe de laminação a quente de fio máquina de um aço DIN 41Cr4 sobre a microestrutura obtida após a laminação e a sua correlação com aquela resultante do tratamento térmico de esferoidização. Foi avaliado a influência da microestrutura prévia de laminação nos tempos e taxa de resfriamento do tratamento térmico necessários para garantir adequada microestrutura do aço DIN 41Cr4. Foram aplicados conceitos de laminação termomecânica através da variação dos parâmetros: temperatura no último passe de laminação (acabador) e após o último passe de laminação (formador de espiras); velocidade das esteiras do “cooling conveyor” e consequente tempo de permanência das espiras sobre a região de ventiladores e alguns parâmetros no ciclo de tratamento térmico: tempo em patamar e taxa de resfriamento durante a produção de fio máquina redondo de bitolas entre 15,88mm e 16,15mm. A avaliação da resposta às variações impostas ao processo foi realizada através de análises metalográficas de microestrutura no material laminado e no material esferoidizado (grau de esferoidização), descarbonetação e de ensaios de propriedades mecânicas como dureza e tração. A partir dos resultados buscou-se determinar a influência dos parâmetros de laminação na microestrutura do material laminado e a influência desta na resposta ao tratamento térmico de esferoidização. Foram analisadas oito diferentes condições e os resultados mostraram que maiores taxas de resfriamento resultam em microestruturas mais refinadas proporcionando uma simplificação no tratamento térmico, atendendo as propriedades desejáveis no produto final (fio máquina redondo esferoidizado). / This work aims to analyze the influence of the cooling rate, the temperature of the finishing pass and at the coil-forming during hot rolling of DIN 41Cr4 steel wire rod on the microstructure and its influence on plateau times and cooling rate during the spheroidizing heat treatment. For this study thermomechanical rolling concepts were applied through the variation of some hot rolling parameters such as: temperature at the finishing pass and at the coils-former, the cooling conveyor belts velocity and some parameters in the heat treatment cycle: soak temperature and cooling rate during the production of round wire rod with 15,88 mm and 16,15 mm diameter. The evaluation response to changes imposed on the process was evaluated by metallographic analysis of microstructure in hot rolled and spheroidized material (spheroidizing degree), hardness, decarburization and tensile test. Eight rolling conditions and cooling rates were analyzed and results showed that higher cooling rates result in finer microstructures allowing a reduction in heat treatment time to achieve the desirable properties in the final product (spheroidized round wire rod).

O objetivo deste trabalho é comparar diferentes formas de estimação de modelos de apreçamento de ativos. Além dos métodos tradicionais, que utilizam toda a amostra no processo de estimação dos parâmetros do modelo, será utilizado o método rolling, que estima os parâmetros através da utilização de janelas móveis de tamanho fixo. Com isso, utilizando a técnica de backtesting, procura-se averiguar se o método rolling proporciona um ganho na qualidade de ajuste em modelos de apreçamento de ativos. / The aim of this project is to compare methods of estimating asset pricing models. In addition to using traditional methods, which estimate the models parameters by using the entire sample at once, the rolling method will be used. This method estimates the models parameters by using a rolling window of fixed size through the sample. By using backtesting, we seek to investigate whether the rolling approach provides an improvement in the goodness of fit in asset pricing models.

Les caméras sphériques et 360 deviennent populaires et sont utilisées notamment pour la création de vidéos immersives et la génération de contenu pour la réalité virtuelle. Elles sont souvent composées de plusieurs caméras grand-angles/fisheyes pointant dans différentes directions et rigidement liées les unes aux autres. Cependant, il n'est pas si simple de les calibrer complètement car ces caméras grand public sont rolling shutter et peuvent être mal synchronisées. Cette thèse propose des méthodes permettant de calibrer ces multi-caméras à partir de vidéos sans utiliser de mire de calibration. On initialise d'abord un modèle de multi-caméra grâce à des hypothèses appropriées à un capteur omnidirectionnel sans direction privilégiée : les caméras ont les mêmes réglages (dont la fréquence et l'angle de champs de vue) et sont approximativement équiangulaires. Deuxièmement, sachant que le module de la vitesse angulaire est le même pour deux caméras au même instant, nous proposons de synchroniser les caméras à une image près à partir des vitesses angulaires estimées par structure-from-motion monoculaire. Troisièmement, les poses inter-caméras et les paramètres intrinsèques sont estimés par structure-from-motion et ajustement de faisceaux multi-caméras avec les approximations suivantes : la multi-caméra est centrale, global shutter ; et la synchronisation précédant est imposée.Enfin, nous proposons un ajustement de faisceaux final sans ces approximations, qui raffine notamment la synchronisation (à précision sous-trame), le coefficient de rolling shutter et les autres paramètres (intrinsèques, extrinsèques, 3D). On expérimente dans un contexte que nous pensons utile pour des applications comme les vidéos 360 et la modélisation 3D de scènes : plusieurs caméras grand public ou une caméra sphérique fixée(s) sur un casque et se déplaçant le long d'une trajectoire de quelques centaines de mètres à quelques kilomètres. / 360 degree and spherical multi-cameras built by fixing together several consumer cameras become popular and are convenient for recent applications like immersive videos, 3D modeling and virtual reality. This type of cameras allows to include the whole scene in a single view.When the goal of our applications is to merge monocular videos together into one cylinder video or to obtain 3D informations from environment,there are several basic steps that should be performed beforehand.Among these tasks, we consider the synchronization between cameras; the calibration of multi-camera system including intrinsic and extrinsic parameters (i.e. the relative poses between cameras); and the rolling shutter calibration. The goal of this thesis is to develop and apply user friendly method. Our approach does not require a calibration pattern. First, the multi-camera is initialized thanks to assumptions that are suitable to an omnidirectional camera without a privileged direction:the cameras have the same setting (frequency, image resolution, field-of-view) and are roughly equiangular.Second, a frame-accurate synchronization is estimated from instantaneous angular velocities of each camera provided by monocular Structure-from-Motion.Third, both inter-camera poses and intrinsic parameters are refined using multi-camera Structure-from-Motion and bundle adjustment.Last, we introduce a bundle adjustment that estimates not only the usual parameters but also a subframe-accurate synchronization and the rolling shutter. We experiment in a context that we believe useful for applications (3D modeling and 360 videos):several consumer cameras or a spherical camera mounted on a helmet and moving along trajectories of several hundreds of meters or kilometers.

No description available.

Este trabalho visa analisar a influência das taxas de resfriamento e temperatura no último passe de laminação a quente de fio máquina de um aço DIN 41Cr4 sobre a microestrutura obtida após a laminação e a sua correlação com aquela resultante do tratamento térmico de esferoidização. Foi avaliado a influência da microestrutura prévia de laminação nos tempos e taxa de resfriamento do tratamento térmico necessários para garantir adequada microestrutura do aço DIN 41Cr4. Foram aplicados conceitos de laminação termomecânica através da variação dos parâmetros: temperatura no último passe de laminação (acabador) e após o último passe de laminação (formador de espiras); velocidade das esteiras do “cooling conveyor” e consequente tempo de permanência das espiras sobre a região de ventiladores e alguns parâmetros no ciclo de tratamento térmico: tempo em patamar e taxa de resfriamento durante a produção de fio máquina redondo de bitolas entre 15,88mm e 16,15mm. A avaliação da resposta às variações impostas ao processo foi realizada através de análises metalográficas de microestrutura no material laminado e no material esferoidizado (grau de esferoidização), descarbonetação e de ensaios de propriedades mecânicas como dureza e tração. A partir dos resultados buscou-se determinar a influência dos parâmetros de laminação na microestrutura do material laminado e a influência desta na resposta ao tratamento térmico de esferoidização. Foram analisadas oito diferentes condições e os resultados mostraram que maiores taxas de resfriamento resultam em microestruturas mais refinadas proporcionando uma simplificação no tratamento térmico, atendendo as propriedades desejáveis no produto final (fio máquina redondo esferoidizado). / This work aims to analyze the influence of the cooling rate, the temperature of the finishing pass and at the coil-forming during hot rolling of DIN 41Cr4 steel wire rod on the microstructure and its influence on plateau times and cooling rate during the spheroidizing heat treatment. For this study thermomechanical rolling concepts were applied through the variation of some hot rolling parameters such as: temperature at the finishing pass and at the coils-former, the cooling conveyor belts velocity and some parameters in the heat treatment cycle: soak temperature and cooling rate during the production of round wire rod with 15,88 mm and 16,15 mm diameter. The evaluation response to changes imposed on the process was evaluated by metallographic analysis of microstructure in hot rolled and spheroidized material (spheroidizing degree), hardness, decarburization and tensile test. Eight rolling conditions and cooling rates were analyzed and results showed that higher cooling rates result in finer microstructures allowing a reduction in heat treatment time to achieve the desirable properties in the final product (spheroidized round wire rod).

In the first part of this thesis, the FE program MSC.Marc is applied for coupled thermomechanical simulations of wire-rod rolling. In order to predict material behaviour of an AISI 302 stainless steel at high strain rates generated during wire-rod rolling, a material model based on dislocation density is applied. Then, the evolution of temperature, strain rate and flow stress is predicted in the first four rolling passes of a wire block. In the second part of the thesis, an alternative approach to simulation of shape rolling is evaluated. The approach is applied in order to save the computational time in cases where many shape-rolling passes are to be simulated. The approach is a combination of the slab method and a 2D FEM with a generalized plane-strain formulation. A number of various isothermal shape-rolling passes are simulated applying the simplified approach. The simulations are carried out using an in-house 2D FE code implemented in Matlab. The results are compared to fully 3D FE analyses. The comparison shows that the simplified approach can predict roll forces and roll torques with a fair accuracy, but the predicted area reductions are a bit underestimated. The reasons for the deviations between the simplified approach and the 3D FEM are discussed. / QC 20101123

När en lastbil färdas på väg utsätts den för ett antal krafter. Däckens rullmotstånd utgör ungefär 36 till 60 % av färdmotståndet. Att kunna validera rullmotståndet vid egen testning är värdefullt för en fordonstillverkare som Scania. Däcktillverkare tillhandahåller en konstant rullmotståndskoefficient men det är oklart om den går att använda i beräkningar för Scanias testsetup.Provningen går ut på att undersöka om testuppställningen möjliggör uppmätning av däckens rullmotstånd på chassidynamometer med momentnav. För den experimentella delen av examensarbetet har en kvantitativ datainsamlingsmetod använts för vidare maskinell analys och manuellt utföra statistisk undersökning. Testdriven utveckling (TDD) har tillämpats för att utifrån testresultaten kunna arbeta iterativt.Vid testningen går rullmotståndskoefficienten upp, ner eller ligger stabilt. Detta beror på att Kistler (Kistler momentnav består av två fälgar som innehåller universalsensorer för att kunna mäta vridmoment) har elektrisk drift som korrelerar till spridning av uppmätt rullmotståndskoefficient. Kistler momentnav är inte repeterbart på grund av drift. Det är möjligt att kompensera för den elektriska driften i Kistler momentnav och beräkna rullmotståndskoefficienten baserat på sista analyspunkten från körningarna.Mätvärden från Kistler momentnav har spridning. Genom att beräkna medelvärde för rullmotståndskoefficienten fås bättre noggrannhet. Medelvärde indikerar att rullmotståndskoefficienten har inget eller litet hastighetsberoende.Det går att använda Kistler momentnav och chassidynamometer 2 som testuppställning för att mäta upp av däckens rullmotståndkoefficient. Det är möjligt för Scania att fortsätta använda denna testuppställning för att bland annat undersöka fler däck. / When a long haul truck travels on a road it’s subjected to a number of forces. The tires rolling resistance is approximately 36 to 60% off the total travel resistance. Being able validate the rolling resistance during own testing is valuable to vehicle manufacturers like Scania. The tire manufacturers provide a constant rolling resistance coefficient but it’s unclear if it can be used in calculations for Scanias test setup.The purpose of the testing is to investigate if the test setup enables measuring the tires rolling resistance on a chassis dynamometer with torque wheels. For the experimental part of the degree project, a quantitative data collection methodology has been used for further machine analyzation and manually performing statistical analysis. Test driven development (TDD) has been applied to work iterative based on the test results.During testing the value of the rolling resistance coefficient went up, down or was stable. This is dependent on the electrical drift Kistler have (Kistler torque wheel consists of two rims that contain universal sensors to measure torque), that correlated with the distribution of the measured rolling resistance coefficient. It’s possible to compensate for the electrical drift in Kistler torque wheel and calculate the rolling resistance coefficient based on the last analyzation point from the tests.The measurements from Kistler torque wheel are distributed. By calculating the average of the rolling resistance coefficients a higher degree of accuracy is obtained. The average indicates that the rolling resistance coefficient have no or a small speed dependency.It’s possible to use Kistler torque wheel and chassis dynamometer 2 as a test setup to measure the rolling resistance of the tires. It’s possible for Scania to continue using this test setup to investigate more tires.