Isostatic frameworks are statically determinate trusses that are self contained (Le. they exist independent of support or foundation). Isostatic frameworks have been widely used as supporting structures, and recently they have been used as the structure for parallel manipulators. These truss-based manipulators could potentially solve the problems facing conventional manipulators and could make the design of high-degree-of-freedom manipulators feasible. The rigorous scientific study of isostatic frameworks and manipulators based on their structure has been limited. Recent developments in the design of large space structures and truss-based manipulators, however, demand rigorous design and mathematical tools. This dissertation provides a general theory for the design of structures based on frameworks and methods to analyze the kinematics of truss-based manipulators. The objective of the first part of this dissertation is to solve the problems of identification, generation and classification of isostatic frameworks in greater depth than in any past work in this area. Original methods are discussed for the enumeration and generation of isostatic frameworks. The first part also presents an original method to determine the geometry of general frameworks and an improved method to find the forces in their members. The determination of geometry and forces are critical areas in structural design. The second part of this dissertation presents a case study on one of the candidates for manipulator applications, the double-octahedral manipulator. The kinematic analyses of the double-octahedral manipulator includes methods to perform forward and inverse kinematic analysis, velocity and acceleration analysis, singularity analysis and workspace analysis. The closed-form solution to the inverse analysis presented herein is a major breakthrough in the development of the double-octahedral manipulator. Other analysis, such as velocity and acceleration, singularity, and workspace, depend on the inverse solution. It is believed that these solutions will help narrow the gap between theory and application of truss-based manipulators. The determination of singularities and works paces are application of recent ideas of other researchers. However, original implementations of these ideas have yielded astonishing results. The Jacobian and Hessian matrix presented in this dissertation should help in developing the control scheme for this device. C-Ianguage program codes for several of the methods are also provided. The methods have been tested based on the results obtained from these programs. The position analysis algorithms have also been tested on real hardware. Some of the methods developed here have been successfully employed for simulated and experimental vibration control studies. / Ph. D.

Cette étude s’intéresse à l’amélioration et l’allégement des protections balistiques transparentes. L’utilisation conventionnelle de verre assure une haute efficacité face à un projectile, cependant associée à une masse élevée et à une forte épaisseur du blindage. Le remplacement de la face avant par une céramique polycristalline, telle que le spinelle MgAl2O4, assure un gain de performance et une réduction du volume de l’assemblage. L’élaboration de ce matériau requiert la combinaison d’une haute qualité optique dans le domaine du visible et de propriétés mécaniques élevées. Dans ce travail, l’application d’un frittage naturel sous vide d’une poudre commerciale de haute pureté a permis de limiter l’introduction d’impuretés néfastes à la transparence et la croissance granulaire. Une étape supplémentaire de pressage isostatique à chaud s’est montrée nécessaire à l’élimination des pores résiduels et à l’obtention de spinelles transparents de haute qualité optique (80% à 400-800 nm, e = 2 mm, Ø21 mm). Une étude de la microstructure avant et après post-traitement a permis de mettre en relation la taille des grains et des pores avant post-frittage avec la croissance granulaire observée pendant ce traitement. Une optimisation du procédé a ainsi pu être mise en place afin de limiter l’augmentation de la taille des grains et obtenir une microstructure homogène (~ 12 μm). Après un changement des dimensions des échantillons réussi (e = 4 mm, Ø60 mm), différents spinelles à propriétés microstructurales et mécaniques distinctes ont été sélectionnés pour une évaluation en conditions balistiques. / This work focuses on the improvement and the lightening of transparent ballistic armours. The conventional use of glass provides high efficiency against a projectile, however associated with a heavy and thick armour. The replacement of the strike face by a polycrystalline ceramic, such as MgAl2O4 spinel, leads to a performance gain and a decrease of the protection volume. The development of this material requires the combination of a high optical quality in the visible domain and high mechanical properties. In this work, pressureless sintering under vacuum of a high purity commercial powder allowed to minimize the addition of impurities, detrimental to the transparency, and the grain growth phenomenon. An additional step of hot isostatic pressing was necessary to eliminate residual porosity and to obtain transparent spinel with high optical quality (80% at 400-800 nm, t = 2 mm, Ø21 mm). An analysis of the microstructure before and after the post-treatment made it possible to determine the link between the grain and pore sizes before post-sintering and the observed grain growth during this treatment. An optimisation of the process was established in order to restrain the grain size increase, and thus to obtain a homogeneous microstructure (~ 12 μm). After a successful up-scaling of the samples (t = 4 mm, Ø60 mm), several spinel samples with distinctive microstructural and mechanical properties were selected in order to evaluate their performances through ballistic tests.

Esta tese descreve o projeto e manufatura de membranas cerâmicas para separação de emulsões óleo/água. A escolha correta do material para a fabricação de membranas é importante para processos cujo desempenho depende da afinidade entre o meio poroso e o fluido. As condições de manufatura são também importantes, pois determinam a morfologia da membrana, que influencia fortemente as propriedades de transporte e conseqüentemente, a eficiência da membrana. Tendo isso em vista, este trabalho teve como objetivo desenvolver membranas cerâmicas tubulares (porosas e densas) por prensagem isostática, aplicáveis em processos de microfiltração para a separação de emulsões óleo-água. Para tanto, foi realizado um controle rigoroso do tamanho e distribuição dos poros através do uso da sacarose como agente porogênico. Suspensões de alumina e zircônia com sacarose de diferentes dimensões foram preparadas. Após esse processo a barbotina foi seca e granulada para obtenção do pó usado na conformação das membranas porosas ou como suporte das membranas densas. Para a manufatura das membranas densas, uma fina camada da suspensão foi depositada no núcleo do molde que foi preenchido com o pó (de alumina ou zircônia) e então submetido à co-prensagem (isostática) para obter simultaneamente o suporte e o filme de zircônia. Posteriormente, as membranas (porosas e densas) sofreram um tratamento térmico (para queima parcial da sacarose) e foram sinterizadas (a 1500°C). As membranas foram caracterizadas por MEV, porosimetria por intrusão de mercúrio, medidas de peso por imersão (para obtenção da porosidade e densidade aparente), ensaios de permeabilidade ao ar e à água. A caracterização morfológica das membranas constatou a formação de membranas porosas de alumina e de zircônia e de membranas densas: uma integral (\'ZR\'\'O IND.2\'/\'ZR\'\'O IND.2\') e outra composta (\'ZR\'\'O IND.2\'/\'AL IND.2\'\'O IND.3\'). A análise de porosimetria por intrusão de mercúrio apresentou tamanho médio de poros de 1,8 \'mü\'m para as membranas porosas e de 0,01-0,03 \'mü\'m e 1,8 \'mü\'m para as membranas densas, respectivamente para camada seletiva e suporte. Todas as membranas obtiveram porosidade total de aproximadamente 50%, que é considerada uma porosidade satisfatória. Os ensaios de permeabilidade ao ar demonstraram que as membranas de zircônia obtiveram maior permeabilidade do que as membranas de alumina. Já os ensaios de permeação de água, na condição de fluxo tangencial, mostraram que as membranas porosas apresentaram maior fluxo transmembrana do que as membranas densas, na mesma velocidade de escoamento. As membranas densas e porosas foram testadas na separação óleo-água e a maioria apresentou bom desempenho no processo de microfiltração e alta rejeição da fase óleo (entre 98 e 99%). Dentre essas membranas, a membrana densa composta (sinterizada a 1400°C) foi a que obteve melhor desempenho, pois apresentou fluxo permeado de aproximadamente 230 L/h.\'M POT.2\' e coeficiente de rejeição médio de 99,77%, os quais são valores desejáveis para a aplicação de membranas em processos industriais. / This thesis describes the project and manufacture of ceramic membranes for separation of oil/water emulsions. The selection of raw material for the manufacture of membranes is fundamental in processes whose performance depends on the affinity between the porous medium and the fluid. The manufacturing conditions are also important as they determine the membrane\'s morphology. Such morphology strongly influences the transport properties hence the membrane\'s performance. In this context, this work aims to develop tubular ceramic membranes (porous and asymmetric) by isostatic pressing which will be applicable to microfiltration processes for the oil-water emulsions separation. For such a purpose, a rigorous control was realized on the distribution and size of pores by use of the sucrose as porogenic agent. Suspensions of zirconia and alumina with sucrose of different dimensions were prepared. After that process, the slurry was dried and granulated to obtain the dust used in the manufacture of the membranes. For the manufacture of the supported zirconia membranes, a thin layer of suspension was deposited onto the nucleus of the mould, which was filled with the dust (of alumina or zirconia) and then, it was subjected to co-pressing (isostatic) to obtain the support and the zirconia top-layer, simultaneously. Next, the porous and supported membranes underwent a thermal treatment (for a partial burning of sucrose) and were sintered (until 1500°C). They were characterized by SEM, porosimetry by mercury intrusion, measurements of weight by immersion (for the determination of the apparent porosity and density) and water and air permeability tests. The morphologic characterization of membranes identified the formation of zirconia and alumina porous membranes, an asymmetric \'ZR\'\'O IND.2\' membrane (zirconia top-layer on the porous zirconia support) and a supported \'ZR\'\'O IND.2\'/\'AL IND.2\'\'O IND.3\' composite membrane. The results of porosimetry analysis by mercury intrusion presented a mean pore size of 1,8 \'mü\'m for the porous membranes and for the other membranes, 0,01-0,03 \'mü\'m and 1,8 \'mü\'m, respectively, for the top-layer and support. All membranes achieved a total porosity of about 50%, which is considered a satisfactory porosity. The air permeability tests showed that the zirconia membranes achieved higher permeability than the alumina membranes. Otherwise, the water permeation tests in cross-flow condition showed that the porous membranes (of alumina and zirconia) presented higher transmembrane flow than the asymmetric \'ZR\'\'O IND.2\' and supported \'ZR\'\'O IND.2\'/\'AL IND.2\'\'O IND.3\' composite membranes in the same flow average velocity. Such membranes were applied to oil-water emulsions separation and the most they presented good performance in the microfiltration process and high rejection of oil phase (between 98 and 99%). Among those membranes, the zirconia supported membrane (sintered until 1400°C) obtained the most performance because it showed transmembrana flow of about 230 L/h.\'M POT.2\' e rejection coefficient of 99,77%, which are appreciable values for the application of membranes in industrial processes.

Boron carbide nano-powders, singly-doped over a range of compositions, were pressurelessly-sintered at identical temperature and atmospheric conditions in a dif- ferential dilatometer to investigate sintering behavior. Samples that achieved relative densities greater than 93% of theoretical density were post-HIPed. Post-HIPing re- sulted in an increase in relative density as well as an increase in Vicker's hardness. To optimize the sintering behavior, nano-powders with multiple dopants were prepared based on the results of single dopant experiments. These powders were studied using the same heating schedule as the single dopant samples. The powder with optimized composition was selected, and 44.45 mm diameter disks were pressed to determine the effects of sample size. Powder composition #166 with Al, Ti, W and Mg additions was processed using di¢çerent methods in order to create defect-free green bodies after uniaxial press- ing. The 44.45 mm diameter compacts were heat-treated to remove organics and B₂O₃coatings on particles and then encapsulated in an evacuated fused silica am- pule. Encapsulated samples were HIPed at temperatures below the coarsening region observed in the dilatometric traces of multiply-doped nano-powders. The E-HIPed sample showed a relative density of 96% with a limited extent of nano-sized grain microstructure.

Esta tese descreve o projeto e manufatura de membranas cerâmicas para separação de emulsões óleo/água. A escolha correta do material para a fabricação de membranas é importante para processos cujo desempenho depende da afinidade entre o meio poroso e o fluido. As condições de manufatura são também importantes, pois determinam a morfologia da membrana, que influencia fortemente as propriedades de transporte e conseqüentemente, a eficiência da membrana. Tendo isso em vista, este trabalho teve como objetivo desenvolver membranas cerâmicas tubulares (porosas e densas) por prensagem isostática, aplicáveis em processos de microfiltração para a separação de emulsões óleo-água. Para tanto, foi realizado um controle rigoroso do tamanho e distribuição dos poros através do uso da sacarose como agente porogênico. Suspensões de alumina e zircônia com sacarose de diferentes dimensões foram preparadas. Após esse processo a barbotina foi seca e granulada para obtenção do pó usado na conformação das membranas porosas ou como suporte das membranas densas. Para a manufatura das membranas densas, uma fina camada da suspensão foi depositada no núcleo do molde que foi preenchido com o pó (de alumina ou zircônia) e então submetido à co-prensagem (isostática) para obter simultaneamente o suporte e o filme de zircônia. Posteriormente, as membranas (porosas e densas) sofreram um tratamento térmico (para queima parcial da sacarose) e foram sinterizadas (a 1500°C). As membranas foram caracterizadas por MEV, porosimetria por intrusão de mercúrio, medidas de peso por imersão (para obtenção da porosidade e densidade aparente), ensaios de permeabilidade ao ar e à água. A caracterização morfológica das membranas constatou a formação de membranas porosas de alumina e de zircônia e de membranas densas: uma integral (\'ZR\'\'O IND.2\'/\'ZR\'\'O IND.2\') e outra composta (\'ZR\'\'O IND.2\'/\'AL IND.2\'\'O IND.3\'). A análise de porosimetria por intrusão de mercúrio apresentou tamanho médio de poros de 1,8 \'mü\'m para as membranas porosas e de 0,01-0,03 \'mü\'m e 1,8 \'mü\'m para as membranas densas, respectivamente para camada seletiva e suporte. Todas as membranas obtiveram porosidade total de aproximadamente 50%, que é considerada uma porosidade satisfatória. Os ensaios de permeabilidade ao ar demonstraram que as membranas de zircônia obtiveram maior permeabilidade do que as membranas de alumina. Já os ensaios de permeação de água, na condição de fluxo tangencial, mostraram que as membranas porosas apresentaram maior fluxo transmembrana do que as membranas densas, na mesma velocidade de escoamento. As membranas densas e porosas foram testadas na separação óleo-água e a maioria apresentou bom desempenho no processo de microfiltração e alta rejeição da fase óleo (entre 98 e 99%). Dentre essas membranas, a membrana densa composta (sinterizada a 1400°C) foi a que obteve melhor desempenho, pois apresentou fluxo permeado de aproximadamente 230 L/h.\'M POT.2\' e coeficiente de rejeição médio de 99,77%, os quais são valores desejáveis para a aplicação de membranas em processos industriais. / This thesis describes the project and manufacture of ceramic membranes for separation of oil/water emulsions. The selection of raw material for the manufacture of membranes is fundamental in processes whose performance depends on the affinity between the porous medium and the fluid. The manufacturing conditions are also important as they determine the membrane\'s morphology. Such morphology strongly influences the transport properties hence the membrane\'s performance. In this context, this work aims to develop tubular ceramic membranes (porous and asymmetric) by isostatic pressing which will be applicable to microfiltration processes for the oil-water emulsions separation. For such a purpose, a rigorous control was realized on the distribution and size of pores by use of the sucrose as porogenic agent. Suspensions of zirconia and alumina with sucrose of different dimensions were prepared. After that process, the slurry was dried and granulated to obtain the dust used in the manufacture of the membranes. For the manufacture of the supported zirconia membranes, a thin layer of suspension was deposited onto the nucleus of the mould, which was filled with the dust (of alumina or zirconia) and then, it was subjected to co-pressing (isostatic) to obtain the support and the zirconia top-layer, simultaneously. Next, the porous and supported membranes underwent a thermal treatment (for a partial burning of sucrose) and were sintered (until 1500°C). They were characterized by SEM, porosimetry by mercury intrusion, measurements of weight by immersion (for the determination of the apparent porosity and density) and water and air permeability tests. The morphologic characterization of membranes identified the formation of zirconia and alumina porous membranes, an asymmetric \'ZR\'\'O IND.2\' membrane (zirconia top-layer on the porous zirconia support) and a supported \'ZR\'\'O IND.2\'/\'AL IND.2\'\'O IND.3\' composite membrane. The results of porosimetry analysis by mercury intrusion presented a mean pore size of 1,8 \'mü\'m for the porous membranes and for the other membranes, 0,01-0,03 \'mü\'m and 1,8 \'mü\'m, respectively, for the top-layer and support. All membranes achieved a total porosity of about 50%, which is considered a satisfactory porosity. The air permeability tests showed that the zirconia membranes achieved higher permeability than the alumina membranes. Otherwise, the water permeation tests in cross-flow condition showed that the porous membranes (of alumina and zirconia) presented higher transmembrane flow than the asymmetric \'ZR\'\'O IND.2\' and supported \'ZR\'\'O IND.2\'/\'AL IND.2\'\'O IND.3\' composite membranes in the same flow average velocity. Such membranes were applied to oil-water emulsions separation and the most they presented good performance in the microfiltration process and high rejection of oil phase (between 98 and 99%). Among those membranes, the zirconia supported membrane (sintered until 1400°C) obtained the most performance because it showed transmembrana flow of about 230 L/h.\'M POT.2\' e rejection coefficient of 99,77%, which are appreciable values for the application of membranes in industrial processes.

V předložené diplomové práci bylo studováno slinování hexagonálního Al2O3 a kubického MgAl2O4 pomocí slinovacích cyklů složených z beztlakého předslinutí metodou dvojstupňového slinování s následným doslinutím s využitím tlaku (HIPováním). Cílem bylo pokusit se snížit (při zachování vysoké dosažené hustoty) střední velikost zrn a tím zvýšit tvrdost keramiky popř. optickou transparenci. Hlavní úsilí bylo věnováno optimalizaci předslinutí pomocí různých slinovacích cyklů. Přestože bylo vyzkoušeno velké množství různých kombinací teplot a prodlev dvojstupňového slinování, nepodařilo se výrazným způsobem zvýšit výslednou tvrdost vzorků. V případě kubického MgAl2O4 bylo dosaženo hustot blížících se teoretické hustotě, což se projevilo v optické transparentnosti vzorků.

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Apresenta uma metodologia para o projeto e fabricação de moldes para prensagem isostática de pó cerâmico (alumina) utilizando ferramentas computacionais CAD/CAE associadas à tecnologia de Prototipagem Rápida. O processo de prensagem isostática é simulado utilizando o método dos elementos finitos. Para a representação da compactação do pó cerâmico é utilizado o modelo de Drucker-Prager/cap e para a representação do comportamento do material elastomérico é utilizado o modelo hiperelástico de Mooney-Rivlin, ambos disponíveis no programa ABAQUS. Tal simulação visa obter o projeto do molde de forma mais rápida e precisa, ajustando-o até que se alcance um molde adequado para produzir um compacto com uma quantidade de sobrematerial ideal para o processo de usinagem a verde. Para isso utilizou-se como estudo de caso uma esfera cerâmica para implante de quadril. Um protótipo virtual do molde adequado obtido das simulações é então modelado e reproduzido em plástico ABS (Acrylonitrile Butadiene Styrene) pela tecnologia de Prototipagem Rápida FDM (Fused Deposition Modeling). Esse protótipo físico é a base para o desenvolvimento de matrizes rígidas e em silicone, que são utilizadas para a confecção da parte flexível do molde (matriz elastomérica) e de partes rígidas como a gaiola suporte obtidas por vazamento dos polímeros. Constatou-se a viabilidade da utilização da metodologia de projeto e fabricação do molde para prensagem isostática, considerando que as simulações mostraram-se bastante coerentes com os resultados experimentais obtidos de componentes prensados. / This work presents a methodology for the design and fabrication of ceramic powder isostatic pressing moulds using CAD and CAE tools and Rapid Prototyping. The isostatic pressing process was simulated using the finite element method. The compaction behavior of ceramic powder is described by the Drucker-Prager/cap constitutive model and the behavior of elastomeric material is described by the Mooney-Rivlin constitutive model within the commercial finite element software ABAQUS®. These simulations are required to adjust the mould design in order to suit the geometry of the compact and green machining allowance. For this study, it is used a case study consisting of pressing a ceramic sphere for hip implant stem. A virtual prototype was designed from the geometry obtained from the simulations and reproduced in Acrylonitrile Butadiene Styrene (ABS) polymer, using the Rapid Prototyping technology - Fused Deposition Modeling (FDM). Silicone moulds were obtained from the polymer prototype and used to aid in the making of the elastomeric bag and mould support cage. The methodology used in this investigation was validate considering that the simulations yield to a good agreement with measured manufactured components.