Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Para reabilitar a ausência de um elemento dentário posterior, as próteses parciais fixas (PPF) com retentores intracoronários são uma alternativa aos implantes osseointegrados. O objetivo deste estudo foi avaliar a distribuição de tensões nessas próteses com três combinações de materiais: cerâmica de zircônia parcialmente estabilizada por ítria (ZPEI) revestida por cerâmica de fluorapatita (α), cerâmica de dissilicato de lítio (β) ou compósito fibrorreforçado (γ). Na composição α, foram analisadas a presença ou ausência da cerâmica de revestimento na parede cervical das caixas proximais e três variações na área total da seção transversal dos conectores (4 mm de largura x 3,2, 4,2 ou 5,2 mm de altura). Em 8 modelos bidimensionais de elementos finitos, uma carga vertical de 500 N foi aplicada na fossa central do pôntico e as tensões principais máximas (tração) e mínimas (compressão) foram apontadas em MPa. Inicialmente foram avaliados os 6 modelos com PPF de ZPEI e suas variações. Os maiores valores das tensões de tração foram encontrados no terço cervical dos conectores. Quando presente nestas regiões, a cerâmica de revestimento recebeu tensões acima do limite de sua resistência à flexão. Na comparação entre os modelos sem cerâmica de revestimento na parede cervical das caixas proximais, mesmo aquele com conectores de 3,2 x 4 mm, cuja infraestrutura apresentava 2,5 x 3 mm, poderia ser recomendado para uso clínico. Altos valores de tensões de compressão foram registrados entre o terço oclusal e médio dos conectores, correspondente à união entre as cerâmicas, o que poderia ocasionar, devido à flexão, falhas adesivas. Posteriormente, o modelo de ZPEI com a cerâmica de fluorapatita ausente da parede cervical das caixas proximais e área total dos conectores de 4,2 x 4 mm foi comparado aos dois outros materiais com conectores de mesma área. Na PPF de dissilicato de lítio, os valores representaram uma provável violação do limite de sua resistência à flexão. A PPF de compósito fibrorreforçado apresentou tensões bem abaixo do limite de resistência à flexão de sua infraestrutura, mas, como no modelo de ZPEI, tensões compressivas se concentraram com alto valor entre o terço oclusal e médio dos conectores, local de união entre a resina composta e a infraestrutura de fibras. Os resultados mostraram que a cerâmica de dissilicato de lítio e a presença da cerâmica de fluorapatita na parede cervical das caixas proximais deveriam ser contraindicadas para a condição proposta. Parece viável uma área de conectores na infraestrutura de ZPEI com no mínimo 2,5 x 3 mm. A PPF de compósito fibrorreforçado apresenta resistência estrutural para a situação estudada, mas, como também aquelas compostas de ZPEI, aparenta ter como pontos fracos a adesão entre a infraestrutura e o material de cobertura e a própria resistência deste último. / Inlay-retained fixed partial dentures (IRFPD) are an alternative to osseointegrated implants to replace a single missing posterior tooth. The aim of this study was to evaluate the stress distribution within these prostheses with three material combinations: yttria-tetragonal zirconia polycrystal (Y-TZP) ceramic veneered with fluorapatite ceramic (α), lithium-disilicate ceramic (β) or fiber-reinforced composite (γ). In composition α, an analysis was conducted on the presence or absence of the veneering ceramic on the cervical wall of the proximal boxes and three variations in the total area of the connectors cross-section (4 mm in width x 3.2, 4.2 or 5.2 mm in height). In 8 two-dimensional finite element models, a vertical load of 500 N was applied on the central fossa of the pontic. Maximum (tension) and minimum (compression) principal stresses were then shown in MPa. First, the 6 models with Y-TZP fixed partial dentures (FPD) and their variations were evaluated. The highest values of tensile stresses were found at the cervical third of the connectors. When present in these regions, the veneering ceramic received stresses beyond its flexural strength limit. In the comparison among models without veneering ceramic on the cervical wall of the proximal boxes, even the model with connectors of 3.2 x 4 mm, whose framework presented 2.5 x 3 mm, could be recommended for clinical use. High values of compressive stresses were recorded between the middle and occlusal thirds of the connectors, corresponding to the juncture of the ceramics. Owing to flexure, these stresses might lead to adhesive failures. Then, the Y-TZP model without fluorapatite ceramic on the cervical wall of the proximal boxes and total connector area of 4.2 x 4 mm was compared to the other two materials with connectors of the same area. For the lithium-disilicate FPD, the observed values would probably exceed its flexural strength limit. The fiber-reinforced composite FPD presented stresses far below the flexural strength limit of its framework, but, as observed in the Y-TZP model, high values of compressive stresses were concentrated between the middle and occlusal thirds of the connectors, where the juncture of the composite and the fiber framework is located. The results showed that the use of lithium-disilicate ceramics and the presence of fluorapatite ceramics on the cervical wall of the proximal boxes should be contraindicated for the condition proposed. A minimum of 2.5 x 3 mm for the connector area of the Y-TZP framework seems viable. The fiber-reinforced composite FPD presented structural resistance for the situation studied but, as was also the case of the Y-TZP fixed partial dentures, its weak points seem to be the adhesion between the framework and the veneering material, as well as the resistance of the veneering material itself.

La projection hybride combinant la projection plasma et la refusion laser est une solution alternative permettant de diminuer ou même d'éliminer la présence de pores et de fissures au sein d'un dépôt brut de projection. Lors d'un procédé de projection plasma ou de refusion laser, le système substrat/dépôt subissant l'élévation de température,la fusion, la solidification et le refroidissement rapide est ainsi soumis à des gradients de température élevés, un niveau de contraintes élevé, et même un risque de formation de fissures. Il est alors important de pouvoir maîtriserles variations de température et la distribution des contraintes résiduelles au sein même du système. Concernantles travaux effectués dans cette thèse, des modèles thermiques et mécaniques ont été développés à l'aide dulogiciel ANSYS, de sorte à améliorer notre compréhension des comportements thermique et mécanique des revêtements élaborés par projection plasma avec refusion laser.Tout d'abord, la simulation du procédé de projection plasma a été développée afin de prédire les champs transitoires de température, la déformation finale de l'échantillon et les contraintes résiduelles dans des dépôts céramiques (alumine) et métalliques (NiCrBSi). Les contraintes résiduelles résultent de l'équilibre entre contraintes de trempe (toujours en tension) et contraintes thermiques lors du refroidissement final (en compression ou en tension suivant le cas). En raison de la faible limite d'élasticité du dépôt, les contraintes thermiques dominent les contraintes résiduelles dans le cas du dépôt d'alumine. En revanche, les contraintes de trempe dans le dépôt de NiCrBSi sont plus importantes. Par ailleurs, l'augmentation de l'efficacité du système de refroidissement mis en oeuvre permet de diminuer le niveau des contraintes résiduelles dans le dépôt d'alumine. Inversement les contraintes résiduelles au sein du dépôt de NiCrBSi augmentent lorsque le refroidissement en cours de projection est accru. L'analyse thermique permettant de simuler le procédé de refusion laser à posteriori d'un revêtement de NiCrBSi a été effectuée de sorte à évaluer les effets des paramètres du laser sur le champ de température engendré et laforme du bain refondu. Un coefficient d'absorption de 0.5 a été estimé par comparaison de l'épaisseur du bain refondu obtenue par les méthodes numérique et expérimentale. De plus, les morphologies de revêtements refondus ont été caractérisées par méthodes expérimentales. Selon l'analyse mécanique de la refusion laser à posteriori, les contraintes résiduelles sont en tension dans le dépôt refondu, mais en compression vers la zone non-refondue.Concernant le modèle portant sur l'élaboration de couches multiples, permettant de simuler le procédé de refusion laser in-situ, une diminution des contraintes transitoires au sein des couches préalablement élaborées est induite par l'accumulation progressive de chaleur au cours du processus d'élaboration. Après refroidissement final, les contraintes résiduelles suivant la direction de déplacement présentent une amplitude plus importante que suivant les autres directions. De plus, des solutions permettant de diminuer le niveau des contraintes dans le dépôt après refusion ont été recherchées, en faisant notamment varier l'efficacité du système de refroidissement ou le préchauffage du substrat. Il s'avère que l'amplitude des contraintes résiduelles dans le dépôt après refusion est plus sensible à la variation du préchauffage du substrat qu'à la modification de l'efficacité du système de refroidissement. / The hybrid spraying process consisting in plasma spraying and laser remelting is an alternative method to minimize or even eliminate the potential defects within the as-sprayed coatings.During the treatment of plasma spraying or laser remelting, the substrate/coating system undergoing heating, melting, solidification and fast cooling processes is submitted to high temperature gradients, high stress levels and even risks of crack formation. It is therefore important to control the temperature variation and stress level within the substrate/coating system. In this study, thermal and mechanical models established with ANSYS were developed to provide a fundamental understanding of thermal and mechanical behaviors of deposited coatings during plasma spraying and laser remelting processes.3D simulation models were first developed to predict the temperature field, the final deformation of the specimen, and the residual stresses within ceramic (alumina) and metallic (NiCrBSi) coatings. The final residual stresses result from the balance between quenching stresses (tensile) and thermal stresses (compressive or tensile). Due to the low value of the yield stress, the thermal stresses (compressive for that case) dominate the final stress level in the case of the ceramic coating (alumina). On the contrary, the final residual stresses within the NiCrBSi coating are tensile. It is also predicted that an increase of the cooling efficiency induces a lower stress level for the alumina coating, while improving the cooling efficiency slightly increases the residual stresses for the case of the metallic coating (NiCrBSi).Thermal analysis to predict laser post-remelting of a NiCrBSi coating was then carried out to investigate the effects of the laser parameters on the temperature field as well as on the remelted pool shape. An absorption coefficient of 0.5 was estimated by comparison of the remelted pool depths obtained by experimental and numerical methods. In addition, the morphologies of theremelted coating were characterized by experimental methods. According to the mechanical analysis for laser post-remelting of NiCrBSi coatings, the predicted residual stresses were tensile within the remelted coating, whereas those within the non- emelted zone were reversed from tensile before remelting to compressive after laser post-remelting. According to the numerical analysis of in situ laser remelting by a multi-layer model, transient stresses in the former deposited layers were decreased progressively due to the heat accumulation during the following deposition process. For the residual stresses after final cooling, the stress component along the displacement direction presents a higher level in comparison with the transverse andthrough thickness components. Solutions allowing decreasing the stress level within the remelted coating were studied by changing the cooling efficiency and the initial temperature of the substrate. It was noted that the generated residual stress (tensile) was more sensitive to the initial temperature of the substrate, than to the efficiency of the cooling system. In particular, increasing the initial temperature of the substrate could significantly decrease the stress magnitude within the remelted coating, and even reverse the residual stresses within the nonremelted part of the coating to compressive values.

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Para reabilitar a ausência de um elemento dentário posterior, as próteses parciais fixas (PPF) com retentores intracoronários são uma alternativa aos implantes osseointegrados. O objetivo deste estudo foi avaliar a distribuição de tensões nessas próteses com três combinações de materiais: cerâmica de zircônia parcialmente estabilizada por ítria (ZPEI) revestida por cerâmica de fluorapatita (α), cerâmica de dissilicato de lítio (β) ou compósito fibrorreforçado (γ). Na composição α, foram analisadas a presença ou ausência da cerâmica de revestimento na parede cervical das caixas proximais e três variações na área total da seção transversal dos conectores (4 mm de largura x 3,2, 4,2 ou 5,2 mm de altura). Em 8 modelos bidimensionais de elementos finitos, uma carga vertical de 500 N foi aplicada na fossa central do pôntico e as tensões principais máximas (tração) e mínimas (compressão) foram apontadas em MPa. Inicialmente foram avaliados os 6 modelos com PPF de ZPEI e suas variações. Os maiores valores das tensões de tração foram encontrados no terço cervical dos conectores. Quando presente nestas regiões, a cerâmica de revestimento recebeu tensões acima do limite de sua resistência à flexão. Na comparação entre os modelos sem cerâmica de revestimento na parede cervical das caixas proximais, mesmo aquele com conectores de 3,2 x 4 mm, cuja infraestrutura apresentava 2,5 x 3 mm, poderia ser recomendado para uso clínico. Altos valores de tensões de compressão foram registrados entre o terço oclusal e médio dos conectores, correspondente à união entre as cerâmicas, o que poderia ocasionar, devido à flexão, falhas adesivas. Posteriormente, o modelo de ZPEI com a cerâmica de fluorapatita ausente da parede cervical das caixas proximais e área total dos conectores de 4,2 x 4 mm foi comparado aos dois outros materiais com conectores de mesma área. Na PPF de dissilicato de lítio, os valores representaram uma provável violação do limite de sua resistência à flexão. A PPF de compósito fibrorreforçado apresentou tensões bem abaixo do limite de resistência à flexão de sua infraestrutura, mas, como no modelo de ZPEI, tensões compressivas se concentraram com alto valor entre o terço oclusal e médio dos conectores, local de união entre a resina composta e a infraestrutura de fibras. Os resultados mostraram que a cerâmica de dissilicato de lítio e a presença da cerâmica de fluorapatita na parede cervical das caixas proximais deveriam ser contraindicadas para a condição proposta. Parece viável uma área de conectores na infraestrutura de ZPEI com no mínimo 2,5 x 3 mm. A PPF de compósito fibrorreforçado apresenta resistência estrutural para a situação estudada, mas, como também aquelas compostas de ZPEI, aparenta ter como pontos fracos a adesão entre a infraestrutura e o material de cobertura e a própria resistência deste último. / Inlay-retained fixed partial dentures (IRFPD) are an alternative to osseointegrated implants to replace a single missing posterior tooth. The aim of this study was to evaluate the stress distribution within these prostheses with three material combinations: yttria-tetragonal zirconia polycrystal (Y-TZP) ceramic veneered with fluorapatite ceramic (α), lithium-disilicate ceramic (β) or fiber-reinforced composite (γ). In composition α, an analysis was conducted on the presence or absence of the veneering ceramic on the cervical wall of the proximal boxes and three variations in the total area of the connectors cross-section (4 mm in width x 3.2, 4.2 or 5.2 mm in height). In 8 two-dimensional finite element models, a vertical load of 500 N was applied on the central fossa of the pontic. Maximum (tension) and minimum (compression) principal stresses were then shown in MPa. First, the 6 models with Y-TZP fixed partial dentures (FPD) and their variations were evaluated. The highest values of tensile stresses were found at the cervical third of the connectors. When present in these regions, the veneering ceramic received stresses beyond its flexural strength limit. In the comparison among models without veneering ceramic on the cervical wall of the proximal boxes, even the model with connectors of 3.2 x 4 mm, whose framework presented 2.5 x 3 mm, could be recommended for clinical use. High values of compressive stresses were recorded between the middle and occlusal thirds of the connectors, corresponding to the juncture of the ceramics. Owing to flexure, these stresses might lead to adhesive failures. Then, the Y-TZP model without fluorapatite ceramic on the cervical wall of the proximal boxes and total connector area of 4.2 x 4 mm was compared to the other two materials with connectors of the same area. For the lithium-disilicate FPD, the observed values would probably exceed its flexural strength limit. The fiber-reinforced composite FPD presented stresses far below the flexural strength limit of its framework, but, as observed in the Y-TZP model, high values of compressive stresses were concentrated between the middle and occlusal thirds of the connectors, where the juncture of the composite and the fiber framework is located. The results showed that the use of lithium-disilicate ceramics and the presence of fluorapatite ceramics on the cervical wall of the proximal boxes should be contraindicated for the condition proposed. A minimum of 2.5 x 3 mm for the connector area of the Y-TZP framework seems viable. The fiber-reinforced composite FPD presented structural resistance for the situation studied but, as was also the case of the Y-TZP fixed partial dentures, its weak points seem to be the adhesion between the framework and the veneering material, as well as the resistance of the veneering material itself.

This master thesis deals with an impact of particular static and dynamic forces and temperature strain on horizontal synchronous generator. In connection with this, a stress distribution in construction and an assessment of security to terminal state of flexibility and weariness is being solved together with finding the most critical places on horizontal synchronous generator.

This thesis deals with stress, strain and reliability analysis of synchronous generator stator including an inhomogeneous temperature field. Using the finite element method, stress and strain are calculated, and from these values safety against yield strength is determined, which is followed by the life calculation of the most stressed weld joint and the determination of its possible damage during the period required by the customer.

No description available.

The need for modern transportation systems together with the high demand for sustainable pavements under applied loads have led to a great deal of research on concrete pavements worldwide. Development of finite element techniques enabled researchers to analyse the concrete pavement under a combination of axle group loadings and environmental effects. Consequently, mechanistic approaches for designing of concrete pavements were developed based on results of finite element analyses. However, unpredictable failure modes of concrete pavements associated with expensive maintenance and rehabilitation costs have led to the use of empiricalmechanistic approach in concrete pavement design. Despite progressive knowledge of concrete pavement behaviour under applied loads, concrete pavements still suffer from deterioration due to crack initiation and propagation, indicating the need for further research. Cracks can be related to fatigue of the concrete and/or erosion of materials in sub-layers. Although longitudinal, midedge and corner cracks are the most common damage modes in concrete pavements, Austroads method for concrete pavement design was developed based on traditional mid-edge bottom-up transverse cracking introduced by Packard and Tayabji (1985). Research presented in this thesis aims to address the most common fatigue related distresses in concrete pavements. It uses comprehensive finite element models and analyses to determine the structural behaviour of concrete pavements under vehicular loads and environmental effects. Results of this research are supported by laboratory tests and an experimental field test. Results of this research indicate that the induced tensile stresses within the concrete pavement are significantly affected by vehicle speed, differential temperature gradient and loss of moisture content. Subsequently, the interaction between the above mentioned factors and concrete damage modes are discussed. Typical dynamic amplifications of different axle groups are presented. A new fatigue test setup is also developed to take into consideration effects of pavement curvature on fatigue life of the concrete. Ultimately, results of the research presented in this thesis are employed to develop a new guide for designing concrete pavements with zero maintenance of fatigue damage.