[pt] Construção de barragens de terra é uma atividade milenar, empregada com o objetivo de atender às mais diversas necessidades humanas como o armazenamento de água, irrigação, regularização de cursos d água, geração de enregia elétrica, etc. Ao longo da história, o projeto destas obras de terra passou de conceito simples, baseados em técnicas empíricas e regras intuitivas, para as análises modernas que consideram o comportamento da barragem em suas diversas fases de vidas (construção, enchimento do reservatório, regime de plena operação), sob carregados estáticos e sísmicos, condições de contorno complexas e sofisticadas relações constitutivas dos materiais da estrutura e do maciço de fundação. Nesta trabalho a construção, primeiro enchimento do reservatório e a resposta sísmica da barragem de terra de Pomacocha, Peru, são analisados pelo método dos elementos finitos, utilizando o software ABAQUS (versus 6.3). Os campos de tensão e de deslocamentos para diversos estágios de aplicação dos carregamentos estático e sísmico são apresentados, incluindo-se histórias de deformação e de tensão para determinados pontos do corpo da barragem e do solo de fundação. / [en] Dam construction is a millenary activity, carried out with the objective of fulfilling human necessities as water supply, land irrigation, water flow regularization, electric power generation, etc. Along the history, the design of these earthworks evolved from simple concepts, based on empirical techniques and rules of thumb, to modern analyses that consider all phases of a dam s life (construction, first reservoir filling, full operation) understatic and seismic loads, as well as complex boundary conditions and sophisticated constitutive relationships for the structure itself and the foundation mass. In this work, the construction, first reservoir filling and the seismic response of the Pomacocha Dam, located in Peru, are analyzed by the finite element method using the software ABAQUS (version 6.2). At several loading stages the corresponding stress and displacement are presented as well as, for some specific points in the dam body and in the foundation soil, the characteristic stress and strain histories during the static and seismic loads.

Ces travaux présentent l'étude de transformateurs par voie acoustique, basés sur la technologie CMUT (Capacitive Micromachined Ultrasonic Transducer ), visant à développer des composants monolithiques assurant l'isolation électrique au sein de la commande des interrupteurs à semi-conducteurs. S'agissant de microsystèmes électromécaniques, les CMUTs offrent des perspectives intéressantes en terme d'intégrabilité monolithique avec les interrupteurs à semi-conducteurs. L'architecture proposée est constituée de deux transducteurs CMUTs de part et d'autre d'un substrat en silicium. Un outil de modélisation a été développé dans le but de prédire le comportement du transformateur. Des protocoles de mesure du rendement des dispositifs fabriqués ont été mis en place permettant une évaluation quantitative des performances des prototypes (un rendement de 32 % est atteint avec une marge de progression à 60 %). L'exploitation du modèle développé, et validé par les résultats de caractérisation, a permis de mettre en évidence les limites et perspectives d'amélioration de ces dispositifs. / This work is a study of CMUT (Capacitive Micromachined Ultrasonic Transduer)based acoustical transformers as a step in the development of insulating components in semiconductor switches control chain. CMUT transducers being electromechanical systems (MEMS), their monolithic integration with semiconductor switches is full of interesting perspectives . The proposed architecture consists of two CMUTs layered on each side of a silicon substrate. A computational tool was designed to predict the behaviour of the transformer. Measurement protocols of the power efficiency of the constructed transformers were set up and allowed to quantify the prototypes' performances (A 32 % efficiency is currently reached, with improvements attainable up to 60 %). Exploring the results of the developed model, validated by bench measurements, allowed to determine the current limits of the transformers as well as perspectives of improvement.

[pt] Esse trabalho teve como objetivo principal avaliar a resistência à falha da infraestrutura de uma prótese parcial fixa em zircônia de três elementos e aparafusada sobre implantes, através de análise de tensões por elementos finitos e determinação da resistência à fadiga da estrutura. Como objetivo secundário, foram avaliadas as distribuições das tensões nos demais componentes da prótese. Na análise de tensões, dois modelos distintos foram gerados, sendo o primeiro com prótese, implantes e parafusos similares àqueles adotados na clínica odontológica. Um segundo modelo, usado como controle, adotou uma geometria simplificada. As cargas mastigatórias foram aquelas usuais da literatura especializada e a análise por elementos finitos foi realizada através do programa Ansys Workbench 14.5. Os resultados das distribuições de tensões mostraram semelhanças entre os dois modelos, com pequenas variações relacionadas às geometrias empregadas. As tensões calculadas ficaram abaixo dos limites de resistência mecânica da zircônia e das ligas de titânio. No cálculo da vida em fadiga da prótese de zircônia um modelo analítico foi adotado prevendo uma vida infinita para o componente. / [en] The main goal of this work was to evaluate the failure resistance of a zirconia fixed partial denture of three elements screwed on implants by means of a finite element stress analysis and the determination of the fatigue strength of the structure. As a secondary objective, the stress distributions in the other components of the prosthesis were evaluated. In order to promote the stress analysis, two different models were generated, the first making use of prosthesis, implants and screws similar to those adopted in the dental clinic. A second model, used as control, adopted a simplified geometry. The masticatory loads were those presented usually in the literature and finite element analysis was performed making use of Ansys Workbench 14.5 program. The stress distribution results showed similarity in both models, with small variations related to the adopted geometries. The calculated stresses were smaller than the ultimate strength of the zirconia and titanium alloys. Concerning the fatigue life of the zirconia prosthesis an analytical model was adopted and estimated an infinite life for the component.

Cette thèse porte sur l'analyse d'un phénomène particulièrement important dérivant des conséquences mécaniques des transformations de phases solide-solide dans les aciers : la plasticité de transformation ou TRIP (Transformation Induced Plasticity) et son interaction avec la plasticité classique. Ce sujet est abordé à la fois par des investigations expérimentales et par une approche de modélisation numérique, pour les transformations martensitiques. / This thesis concerned with the analysis of a particularly important phenomenon which corresponds to one of the mechanical consequences of solid-solid phase transformations in steels: the transformation plasticity or TRIP (TRansformation Induced Plasticity) and its interaction with classical plasticity. This subject is addressed from the point of view of experimental investigations as well as with a nuimerical modelling approach, concerning martensitic transformations.

[pt] Neste trabalho avalia-se uma metodología de cálculo para a previsão da pressão de falha de um duto que contem colônias de corrosão, chamada Método das Linhas Ortogonais de Ruptura (MLOR). As colônias de corrosão são representadas por defeitos retangulares, localizados na superfície externa do duto. O objetivo do MLOR é ser mais exato que os métodos semi-empíricos da ASME e DNV utilizados até o momento. O MLOR também tem como objetivo evitar resultados não conservativos que podem ser obtidos com o método Mixed Type of Interacting (MTI). O MLOR apresenta outra forma de avaliar a perda de espessura efetiva de um grupo de defeitos. Ele propõe que se tracem linhas representativas do caminho pelo qual a ruptura do duto tem maior possibilidade de ocorrer, usando linhas paralelas às direções longitudinal e circunferencial do duto. Estas linhas são chamadas de linhas ortogonais de ruptura (LOR). Também considera-se o emprego de um fator de resistência circunferencial f no cálculo de uma espessura efetiva para a colônia. Este fator multiplica somente os comprimentos das LOR que estiverem na direção circunferencial do duto. O material íntegro existente entre dois defeitos é considerado na resistência à ruptura por meio da seleção de um caminho crítico que une os defeitos retangulares e que usa as direções longitudinal e circunferencial. Para a avaliação do MLOR usou-se pressões de falha para tubos com colônias de defeitos determinados experimentalmente e já publicados, além de simulações numéricas feitas pelo método dos elementos finitos (MEF), utilizando-se para isto o software comercial ANSYS. Por fim, neste trabalho concluiu-se que o MLOR apresentou bons resultados (máximos erro médio igual a -0.14 por cento e desvio padrão do erro igual a 3.53 por cento) quando comparados com os resultados experimentais e numéricos, já publicados, de nove corpos de provas em tamanho real. / [en] This dissertation comprises the evaluation of a new calculation methodology developed to predict the burst pressure of pipeline segments containing corrosion colonies. The new methodology is called Method of Orthogonal Lines Rupture (MLOR). The corrosion colonies are represented by rectangular defects, located on the outer surface of the pipeline segment. The objective of MLOR is to determine more accurate results than those calculated by the semi-empirical methods of ASME and DNV. The MLOR has also the objective of avoiding non-conservative results that can be obtained with the Mixed Type Interacting method (MTI). The MLOR presents a new way to assess the loss of effective thickness of a group of defects. It proposes the drawing of lines parallel to the longitudinal and circumferential directions that intend to represent the path by which the rupture of the pipeline is more likely to occur. These lines are called Orthogonal Lines of Rupture (LOR). It is also considered the employment of a strength circumferential factor f in the calculation of the effective thickness of the colony. This factor multiplies only the lengths of the LOR which are associated with the circumferential direction of the pipeline. Using that, the intact material existing between two defects is considered in the calculation of the rupture resistance. The critical path connects the rectangular defects using lines parallel to the longitudinal and circumferential directions. The evaluation of the MLOR was accomplished by comparing its burst pressure calculations with already published results determined for nine full scale tests carried out with specimens that contained specially designed and constructed colonies of defects. The comparisons encompassed those experimentally published test results and also results determined by numerical simulations that employed the finite element method (ANSYS commercial software). Finally, the dissertation concludes that the MLOR showed good results (maximum average error equal to -0.14 percent and standard deviation of the error equal to 3.53 percent) compared with experimental and numerical results.

Dans le cadre des procédés de chauffage et de trempe réalisés lors d’opération de mise en forme des matériaux, le rayonnement thermique joue un rôle prépondérant. Lors de l’élaboration de modèles numériques permettant la simulation de ces procédés, il est donc nécessaire de disposer d’outils performants pour simuler ce phénomène.La simulation numérique de tels procédés soulèvent de nombreuses problématiques, comme la représentation d’un environnement complexe impliquant plusieurs composants (pièces, bruleurs, buses d’injection, parois), la gestion des divers phénomènes physiques couplés (écoulement, transfert thermiques, ébullition, rayonnement). Dans cette perspective, les méthodes dites « d’immersion », permettant un traitement généraliste de ces divers problèmes, rencontrent depuis quelques années un intérêt grandissant dans la communauté scientifique.C’est dans ce contexte que s’inscrit le projet Thost, au sein duquel est réalisée cette thèse. L’objectif est donc de développer des outils pour la modélisation du rayonnement dans le contexte d’immersion de volume propre au logiciel Thost. Deux approches sont développées : l’une consistant en l’adaptation d’une méthode existante au contexte de l’immersion de volume, l’autre explorant l’élaboration d’une formulation pour un modèle particulier de rayonnement. Les outils développés sont ensuite mis à l’épreuve sur des simulations de cas industriels fournis par nos partenaires. / For heating and quenching operations occurring during material forming processes, thermal radiation is the the predominant physical phenomenon. Hence, when one tries to simulate such processes, it is important to have at disposal powerful tools for the numerical modelling of thermal radiation.The numerical simulation of these processes often rises numerous problems and questions, as the representation of a complex environment, involving several components ( ingots, burners, nozzles, walls), to deal with different coupled physical phenomena ( flow, heat transfer, boiling, thermal radiation). In this regard, some “immersed” numerical methods, allows a generalist treatment of these different problems, have gained popularity and drag interest of the scientific community in the recent years.The Thost project, aiming to produce a software for heat transfer during material forming processes, fits in the framework, and this PhD is part of this project. The goal is therefore to design tools for numerical modelling of thermal radiation within the immersed volume method of the Thost software. Two approaches are presented: one consisting in the adaptation of an existing method to the context of the immersed volume method, another concerning the development of a formulation for a specific model of radiation. These methods are then tested on industrial applications provided by our partners.

La réalisation de revêtements métalliques en surface de matériaux composites à matrice organique est possible par le procédé cold spray. La construction de tels revêtements à partir de particules de cuivre sur un substrat contenant des fibres de carbone n'a pu aboutir que grâce à l'ajout d'une poudre polymère. Malgré son rôle dans la construction des dépôts, le polymère présente le désavantage d'être un très bon isolant électrique ayant, de ce fait, une influence très néfaste sur la conductivité des dépôts cold spray. Ces travaux ont donc été concentrés sur l'étude de l'influence de la microstructure de ces dépôts sur leur conductivité électrique. Plusieurs poudres de cuivre ont été mélangées dans diverses proportions avec du PEEK, un polymère thermoplastique. La projection cold spray de ces mélanges a abouti à la formation de dépôts homogènes sur les substrats composites. L'influence des caractéristiques des poudres et des paramètres de projection sur les caractéristiques des dépôts a été étudiée. De même, la déformation du PEEK lors de la projection a été analysée car elle joue un rôle important dans la construction du dépôt. L'étude des propriétés mécaniques du PEEK et des conditions de projection ont permis de simuler sa déformation. Dans la microstructure du dépôt, la présence du PEEK limite les contacts entre les particules de cuivre, abaissant fortement la conductivité électrique des dépôts. Un modèle morphologique de la microstructure a été développé afin d'étudier l'influence de la morphologie de la phase de cuivre sur la conductivité des dépôts. Ce modèle a permis de simuler des microstructures présentant diverses morphologies en 3 dimensions. Il ouvre ainsi la possibilité d'étudier numériquement l'influence de la morphologie de la microstructure des dépôts sur leur conductivité électrique. La conductivité a été mesurées expérimentalement sur des échantillons de dépôt. Un mélange de poudre et des paramètres optimaux ont alors pu être identifiés pour obtenir un dépôt cold spray sur un substrat composite à matrice organique avec une conductivité satisfaisante mais encore inférieure à celle du cuivre massif. / The Cold Spray process allows to manufacture metallic coatings onto Carbon Fiber-Reinforced Composite (CFRP). This process relies on the spraying of high-velocity powder particles to result in high deformation and build up to form a dense coating. However, forming a coating made of copper particles onto a substrate containing carbon fibers was achieved out only by mixing metallic powder with a polymer powder. Although the polymer allow to build up the coating onto CFRP, it is highly electrically insulating. It would therefore decrease the electrical conductivity of the coating drastically. Investigations were carried out on the influence of the coatings microstructure on electrical conductivity. Various copper powders, with different morphologies, granulometry and oxygen contents were mixed with PEEK powder, i.e. a thermoplastic polymer. Cold spray of these powders leads to homogeneous coatings onto CFRP. The characteristics of these coatings were studied as a function of the influence of powder characteristics and spraying parameters. The deformation of the PEEK was also investigated as it governed the build up of the coating. Mechanical testing of PEEK samples and in-situ spraying measurements were performed to feed impact simulations. Then, simulated and experimental impact morphologies of copper particles onto PEEK were compared. The PEEK behavior under impact also prevented sound contacts between copper particles, which decreased the coatings electrical conductivity significantly. A morphological model of the microstructure of the coating was developed to reproduce microstructures in 3D numerically. It allows to investigate numerically the influence of the copper phase morphology on coating conductivity. This conductivity was measured experimentally for various starting copper powders. A carefully selected blend of copper and PEEK powders and optimized spraying parameters lead to homogeneous coatings onto CFRP with an acceptable electrical conductivity but still below bulk copper conductivity.

Les propriétés mécaniques et fonctionnelles des matériaux métalliques sont conditionnées par leurs microstructures, qui sont elles-mêmes héritées des traitements thermomécaniques subis. Etre capable de prévoir et simuler la microstructure et ses hétérogénéités lors des procédés de mise en forme complexes est récemment devenu crucial dans l'industrie métallurgique. C'est également un véritable challenge d'un point de vue numérique qui met en évidence l'importance des matériaux numériques dans les nouvelles méthodes de modélisation. Dans ce travail, nous nous intéressons à un modèle en champ complet récent basé sur la méthode level set (LS) dans un cadre éléments finis (EF) pour la modélisation des mécanismes de recristallisation.Les points forts de cette approche par rapport à l'état de l'art ont motivé le développement d'un logiciel appelé DIGIMU® par la société TRANSVALOR avec le soutien de grandes entreprises industrielles. Toutefois, le principal inconvénient de cette approche, commun aux autres méthodes en champ complet utilisant des maillages EF non structurés, reste son coût numérique important.Le principal objectif de ce travail a donc été d'améliorer considérablement le coût numérique de la formulation LS utilisée dans le contexte de maillages EF non structurés. De nouveaux développements génériques ont été réalisés pour améliorer l'efficacité globale du modèle. La formulation 2D LS existante, déjà utilisée pour modéliser la croissance de grains, la recristallisation statique et l'effet d'ancrage de Smith-Zener, a été étendue et améliorée afin de modéliser ces mécanismes en 3D pour des polycristaux à grand nombre de grains en des temps de calcul raisonnables. / Mechanical and functional properties of metallic materials are strongly related to their microstructures, which are themselves inherited from thermal and mechanical processing. Being able to accurately predict and simulate the microstructure and its heterogeneities after complex forming paths recently became crucial for the metallurgy industry. This is also a real challenge from a numerical point of view which highlights the importance of digital materials in new modeling techniques. In this work, we focus on a recent front-capturing full field model based on the level set (LS) method within a finite element (FE) framework to model recrystallization mechanisms.The strengths of this approach comparatively to the state of the art have motivated the development of a software package called DIGIMU® by the company TRANSVALOR with the support of major industrial companies. However, the main drawback of this approach, common with other front-capturing full field approaches working on unstructured FE meshes, is its important computational cost, especially in 3D.Main purpose of this work was finally to drastically improve the numerical cost of the considered LS-FE formulation in context of unstructured FE meshes. New generic numerical developments have been proposed to improve the global efficiency of the model. The existing 2D LS formulation, already used to model grain growth, static recrystallization and the Smith-Zener pinning effect, has been extended and improved in order to model these mechanisms in 3D for large-scale polycrystals with reasonable computational costs.

On s'intéresse dans ce mémoire aux équations de la magnétohydrodynamique (MHD) dans des milieux hétérogènes, i.e. dans des milieux pouvant présenter des variations (éventuellement brutales) de propriétés physiques. En particulier, on met ici l'accent sur la résolution des équations de Maxwell dans des milieux avec des propriétés magnétiques inhomogènes. On présentera une méthode non standard pour résoudre ce problème à l'aide d'éléments finis de Lagrange. On évoquera ensuite l'implémentation dans le code SFEMaNS, développé depuis 2002 par J.-L. Guermond, C. Nore, J. Léorat, R. Laguerre et A. Ribeiro, ainsi que les premiers résultats obtenus dans les simulations de dynamo. Nous nous intéresserons par exemple au cas de la dynamo dite de Von Kármán, afin de comprendre l'expérience VKS2. En outre, nous aborderons des cas de dynamo en précession, ou encore le problème de la dynamo au sein d'un écoulement de Taylor-Couette. / We focus on the magnetohydrodynamics (MHD) equations in hetereogeneous media, i.e. media with (possibly brutal) variations on the physical properties. In particular, we are interested in solving the Maxwell equations with discontinuous magnetic properties. We introduce a method that is, to the best of our knowledge, new to solve this problem using only Lagrange Finite Elements. We then discuss its implementation in SFEMaNS, a numerical code developped since 2002 by J.-L. Guermond, C. Nore, J. Léorat, R. Laguerre and A. Ribeiro. We show the results of the first dynamo simulations we have been able to make with this solver. For instance, we present a kinematic dynamo in a VKS setup, as well as some results about dynamo action induced either by a Taylor-Couette flow, or by a precessionnally driven flow.

De nos jours, de nombreuses pièces mécaniques sont fabriquées en polymères. Ces matériaux présentent un comportement complexe très sensible à la vitesse de déformation et à la température. De nombreux modèles de comportement mécanique, tenant compte de cette double sensibilité, ont été développés au cours des dernières années dans le but de décrire le comportement élasto-viscoplastique des polymères en grandes déformations sur de larges plages de vitesses de déformation et de températures. Afin de prévoir la tenue de pièces mécaniques en polymère soumises à un ensemble de sollicitations complexes, l'utilisation de méthodes numériques, telles que la méthode des Éléments Finis (EF), s'avèrent incontournables. Cependant, la qualité de la prévision numérique est fortement dépendante de la loi de comportement utilisée. Ainsi, nous proposons d'étudier deux modèles de comportement qui ont été introduits dans deux codes de calcul par EF : un modèle phénoménologique simple, introduit dans CAST3M, et un modèle micromécanique, introduit dans ABAQUS/Explicit. Le modèle phénoménologique permet de modéliser le comportement mécanique des polymères vitreux en petites déformations sur une plage de vitesses de déformation et de températures réduite. Un essai de compression reproduisant le dispositif des barres d'Hopkinson a été simulé pour plusieurs vitesses de déformation et températures. Une bonne corrélation a été trouvée entre résultats expérimentaux et les prévisions numériques. De plus, de rapides estimations du coefficient de Taylor-Quinney et de la contrainte à l'interface, liée au frottement entre l'échantillon et les barres de compression, ont pu être trouvées. Le modèle micromécanique décrit le comportement des polymères amorphes en grandes déformations sur de larges gammes de vitesses de déformation et de températures. Il a été développé au sein de notre équipe de recherche par Richeton et al. [Int. J. Solids Struct. 44 (2007) 7938] et propose une dépendance à la vitesse de déformation et à la température de différentes propriétés matériau (module élastique, contrainte seuil, durcissement structural). Afin de modéliser le comportement de structures polymères soumises à des chargements dynamiques ou à de la mise en forme, un sous-programme VUMAT est écrit. Après validation de l'intégration numérique du sous-programme sur des essais de compression/traction simple, deux applications ont été simulées. La première application a consisté en la modélisation d'un essai d'impact d'une plaque polymère par un projectile hémisphérique. La seconde application est un essai de forgeage à froid. Dans les deux cas, les prévisions numériques sont en accord avec les résultats expérimentaux issus de la littérature. / Nowadays, numerous structural parts are made in polymeric materials. These materials exhibit a complex behavior strongly sensitive to strain rate and temperature. Numerous constitutive equations have been developed during the last decades in order to describe the elastic-viscoplastic behavior of polymers in finite strain for a wide range of strain rates and temperature. To provide for the holding of mechanical parts polymer subject to a complex set of loads, the use of numerical methods, such as Finite Element (FE) method, is unavoidable. However, the quality of the numerical prediction is strongly dependent to the used constitutive equations. Thus, we proposed to study two models of mechanical behavior implemented in two FE softwares: a simple phenomenological model, introduced in CAST3M, and a micromechanical model, introduced in ABAQUS/Explicit. The phenomenological model allows simulating the mechanical behavior of glassy polymers in small strains over a reduced range of strain rates and temperatures. A compressive test reproducing the Split Hopkinson Pressure Bar device is simulated for several strain rates and temperatures. A good correlation is found between experimental results and numerical predictions. Moreover, an estimation of Taylor-Quinney coefficient and the interfacial stress, due to the friction between the polymer sample and the compressive bars, have been found. The micromechanical model describes the mechanical behavior of amorphous polymers in finite strain over a wide range of strain rates and temperatures. It has been developed in our research team by Richeton et al. [Int. J. Solids Struct. 44 (2007) 7938] and proposes to take into account the strain rate and temperature dependence of various material properties (elastic modulus, yield stress, orientational hardening). In order to simulate the mechanical behaviour of polymeric structures under dynamic loadings or during forming processes, a VUMAT subroutine is written. After validation of the numerical implementation of the VUMAT subroutine for simple compressive/tensile tests, two applications were simulated. The first application is a normal impact test of a polymeric plate by a hemispherical projectile. The second application is a cold forging test. In both cases, numerical predictions are in agreement with the experimental results from the literature.