Comment obtenir des données anatomiques pendant une neurochirurgie ? a été ce qui a guidé le travail développé dans le cadre de cette thèse. Les IRM sont actuellement utilisées en amont de l'opération pour fournir cette information, que ce soit pour le diagnostique ou pour définir le plan de traitement. De même, ces images pre-opératoires peuvent aussi être utilisées pendant l'opération, pour pallier la difficulté et le coût des images per-opératoires. Pour les rendre utilisables en salle d'opération, un recalage doit être effectué avec la position du patient. Cependant, le cerveau subit des déformations pendant la chirurgie, phénomène appelé Brain Shift, ce qui altère la qualité du recalage. Pour corriger cela, d'autres données pré-opératoires peuvent être acquises, comme la localisation de la surface corticale, ou encore des images US localisées en 3D. Ce nouveau recalage permet de compenser ce problème, mais en partie seulement. Ainsi, des modèles mécaniques ont été développés, entre autres pour apporter des solutions à l'amélioration de ce recalage. Ils permettent ainsi d'estimer les déformations du cerveau. De nombreuses méthodes existent pour implémenter ces modèles, selon différentes lois de comportement et différents paramètres physiologiques. Dans tous les cas, cela requiert un modèle anatomique patient-spécifique. Actuellement, ce modèle est obtenu par contourage manuel, ou quelquefois semi-manuel. Le but de ce travail de thèse est donc de proposer une méthode automatique pour obtenir un modèle du cerveau adapté sur l'anatomie du patient, et utilisable pour une simulation mécanique. La méthode implémentée se base sur les modèles déformables pour segmenter les structures anatomiques les plus pertinentes dans une modélisation bio-mécanique. En effet, les membranes internes du cerveau sont intégrées: falx cerebri and tentorium cerebelli. Et bien qu'il ait été démontré que ces structures jouent un rôle primordial, peu d'études les prennent en compte. Par ailleurs, la segmentation résultante de notre travail est validée par comparaison avec des données disponibles en ligne. De plus, nous construisons un modèle 3D, dont les déformations seront simulées en utilisant une méthode de résolution par Éléments Finis. Ainsi, nous vérifions par des expériences l'importance des membranes, ainsi que celle des paramètres physiologiques. / The general problem that motivates the work developed in this thesis is: how to obtain anatomical information during a neurosurgery?. Magnetic Resonance (MR) images are usually acquired before the surgery to provide anatomical information for diagnosis and planning. Also, the same images are commonly used during the surgery, because to acquire MRI images in the operating room is complex and expensive. To make these images useful inside the operating room, a registration between them and the patient's position has to be processed. The problem is that the brain suffers deformations during the surgery, in a process called brain shift, degrading the quality of registration. To correct this, intra-operative information may be used, for example, the position of the brain surface or US images localized in 3D. The new registration will compensate this problem, but only to a certain extent. Mechanical models of the brain have been developed as a solution to improve this registration. They allow to estimate brain deformation under certain boundary conditions. In the literature, there are a variety of methods for implementing these models, different equation laws used for continuum mechanic, and different reported mechanical properties of the tissues. However, a patient specific anatomical model is always required. Currently, most mechanical models obtain the associated anatomical model by manual or semi-manual segmentation. The aim of this thesis is to propose and implement an automatic method to obtain a model of the brain fitted to the patient's anatomy and suitable for mechanical modeling. The implemented method uses deformable model techniques to segment the most relevant anatomical structures for mechanical modeling. Indeed, the internal membranes of the brain are included: falx cerebri and tentorium cerebelli. Even though the importance of these structures is stated in the literature, only a few of publications include them in the model. The segmentation obtained by our method is assessed using the most used online databases. In addition, a 3D model is constructed to validate the usability of the anatomical model in a Finite Element Method (FEM). And the importance of the internal membranes and the variation of the mechanical parameters is studied.

Pour les applications aéronautiques, les fibres en céramique piézoélectrique à âme métallique permettent d'imaginer des solutions pour avoir des dispositifs actifs et des capteurs complétement intégrés dans des structures, telles que les composites renforcés par des fibres.La démarche de cette étude est d'élaborer et de caractériser de telles fibres qui présentent de nombreux avantages : l'activation en mode radial permet d'utiliser de faibles tensions de commandes, l'utilisation d'un cœur et d'une matrice conducteurs permet de s'affranchir du dépôt d'électrodes et de garantir leur continuité, la présence d'un coeur métallique améliore la résistance mécanique de la fibre, l'utilisation sous forme de fibres fines et longues permet de l'intégrer à des profils de formes complexes sur de grandes longueurs. Dans un premier temps, le procédé d'enduction est utilisé pour la réalisation de ces fibres en déposant des particules céramiques à base de titano-zirconate de plomb (PZT) sur des fils de platine. Le développement et l'optimisation d'un procédé multicouche permet de réaliser des fibres avec des épaisseurs parfaitement contrôlées pour obtenir les capacités de déformations optimales en alternant des cycles dépôt/traitement thermique avant une opération de frittage finale. La caractérisation d'échantillons massifs traités dans les mêmes conditions permet de s'assurer des propriétés piézoélectriques atteintes pendant les différents traitements thermiques. Les caractérisations électromécaniques réalisées sur les fibres permettent de vérifier le comportement en tant qu'actionneur et que capteur, bien qu'il s'avère difficile de remonter aux caractéristiques intrinsèques des fibres.Dans un second temps, une réflexion est menée sur les moyens à mettre en oeuvre pour envisager un développement à grande échelle de ce type de fibre. Dans ce sens, des expérimentations sur la mise en place du procédé continu de coextrusion avec un polymère chargé sont menées, de même que sur la réduction de la température de frittage à l'aide d'additifs pour substituer les fils en platine, mais aussi sur la réduction du temps de frittage à l'aide de techniques non conventionnelles comme le frittage laser et le frittage micro-ondes. Ces investigations ouvrent des pistes sérieuses pour imaginer une production continue de fibres piézoélectriques à âme métallique.Enfin, des travaux de modélisation par éléments finis du comportement de ces fibres, intégrées ou non dans une structure, permettent de mettre en évidence l'influence du dimensionnement des fibres sur les déformations résultantes, en fonction notamment de l'épaisseur du matériau actif déposée et des propriétés élastiques des différents éléments. Différentes configurations sont imaginées pour utiliser ces fibres dans des structures en tant qu'actionneur et capteur. / Metal core piezoelectric fibres are suitable for active devices and sensors fully embedded in structuresas fibres reinforced polymers for aeronautic applications.The aim of this study is to develop and characterize such fibres that have many advantages: radial mode activation allows the use of low voltage control, the use of a core and a conductive matrix eliminates the deposition of electrodes and the necessity to maintain their continuity, the presence of a metal core improves the mechanical strength of the fibre, the use of thin and long fibres permits their integration in profiles with complex shapes over long distances.In a first step, a dip-coating process is used to realize such fibres by depositing ceramic particles based on lead zirconium titanate (PZT) on platinum wire. The development and optimization of a multilayer process, by alternating deposition cycles / heat treatment prior to the final sintering step, lead to the production of fibres with perfectly controlled thickness in order to obtain optimal strain capability. Characterization of bulk samples under the same thermal conditions allows to measure equivalent piezoelectric properties as fibres submitted to the same heat treatments. Electromechanical characterizations performed on the fibres confirm their behaviour as actuator and sensor, although it is still difficult to determine the effective piezoelectric properties of the fibres.In a second step, the possibility to develop a large-scale production of this type of fibre is investigated.In this regard, experiments are carried on coextrusion process with a PZT loaded polymer, as well as the reduction of the sintering temperature by using additives to replace the platinum core. In addition, reducing the sintering time using unconventional techniques such as laser sintering and microwave sintering are investigated. It is then open serious leads to imagine a continuous production of metal core piezoelectric fibres.Finally, a finite element modelling approach of the behaviour of these fibres, integrated or not in a structure, allows to highlight the influence of fibre sizing on the resulting strains, in particular according to the thickness of the active deposited material and elastic properties of the individual elements (metal core, matrix). Different configurations are analysed to use these fibres in structures as actuator and sensor.

Motivado por diversos processos de manufatura, tais como conformação de metais a frio ou mesmo manufatura aditiva, este trabalho consiste no desenvolvimento de um código computacional para a simulação numérica de problemas bidimensionais que abordam três tipos de não-linearidade: a geométrica, presente em situações de grandes deslocamentos; a física, presente no modelo constitutivo do material; e a de contato. Na primeira etapa, desenvolve-se um programa para análise dinâmica bidimensional de sólidos elásticos, utilizando a abordagem posicional do método dos elementos finitos, que engloba naturalmente a não-linearidade geométrica em sua formulação. Em seguida, implementam-se modelos constitutivos não-elásticos para problemas com grandes deformações. No modelo elastoplástico, adota-se o critério de von Mises com encruamento cinemático baseado na lei de Armstrong-Frederick. Essa formulação é então generalizada para o caso visco-plástico, onde é considerado o modelo de Perzyna em conjunto com a lei de Norton. No caso visco-elástico, utiliza-se uma formulação que parte do modelo reológico de Zener. Por fim, apresenta-se um modelo visco-elasto-plástico que consiste no acoplamento dos modelos visco-elástico e visco-plástico descritos anteriormente. Em todos os casos, utiliza-se a decomposição multiplicativa do gradiente da função mudança de configuração. Com respeito à aplicação 2D, consideram-se as hipóteses de estado plano de deformações e estado plano de tensões, onde a última é resolvida numericamente por um procedimento local de Newton-Raphson. Para o problema de contato, aplica-se a estratégia Nó-a-Segmento, sendo as condições de não-penetração impostas com a introdução de multiplicadores de Lagrange. A formulação é testada em cada uma das etapas por meio de exemplos numéricos de verificação. Além disso, para mostrar as potencialidades do código desenvolvido, são propostos diversos exemplos numéricos, sendo alguns inspirados por processos de manufatura existentes. Nesses exemplos, são estudados os efeitos de diferentes parâmetros dos materiais e diferentes taxas de deformação na resposta numérica, permitindo uma análise do comportamento dissipativo decorrente da plastificação e da viscosidade, incluindo a influência desses sobre o amortecimento dinâmico. / Motivated by several manufacturing processes, such as cold metal forming or even additive manufacturing, in this work we develop a computational code for numerical simulation of two-dimensional problems addressing three types of nonlinearities: geometric nonlinearity, present in large displacements situations; physical non-linearity, present in the material constitutive model; and contact non-linearity. In the first step, we develop a computational program for dynamic analysis of two-dimensional elastic solids using the positional finite element method, which naturally takes into account geometric non-linearity in its formulation. Following, we implement inelastic constitutive models for large strain problems. In the elasto-plastic model, we adopt von Mises yeld criteria and kinematic hardening based on the Armstrong-Frederick law. The formulation is then generalized to the visco-plastic case, where we consider Perzyna model associated with Norton\'s law. In the visco-elastic case, Zener\'s rheological model is employed. Finally, we present a visco-elasto-plastic model by coupling the visco-elastic and visco-plastic models described previously. In every case, the multiplicative decomposition of the deformation gradient is employed. Regarding the 2D application, we consider both plane strain and plane stress hypothesis, where the latter is solved numerically by a local Newton-Raphson procedure. For the contact problem, we employ the Node-to-Segment strategy, imposing non-penetration conditions with the introduction of Lagrange multipliers. The resulting computational code is tested in each step by means of numerical verification examples. In addition, to show the potentialities of the developed code, several numerical examples are proposed, some of which inspired by existing manufacturing processes. On these examples, we study the effects of different material parameters and strain rates on the numerical response, allowing an analysis of the dissipative behavior due to plasticity and viscosity, including the influence of these on the dynamic damping.

Les outillages de mise en forme en acier martensitique de type AISI H11 sont des pièces critiques dont le comportement en service est étroitement lié à leurs structures internes et à leur évolution. Les conditions des sollicitations lors de la mise en oeuvre du procédé est souvent à l'origine de modifications microstructurales en surface, à savoir la morphologie des lattes de martensite, les orientations cristallographiques, l'état d'écrouissage interne ou encore le profil de surface. Ces aspects peuvent éventuellement altérer les performances mécaniques de l'acier AISI H11. Afin d'appréhender et d'optimiser le comportement mécanique de celui-ci, une approche multi-échelle est mise en oeuvre dans ce travail. Celle-ci s'articule autour d'une investigation expérimentale et d'un traitement numérique. L'étude expérimentale s'attache à reproduire, à l'échelle du laboratoire, des surfaces équivalentes à celles issues lors des procédés de mise en oeuvre des outillages. Des techniques de caractérisation spécifiques, à savoir le MEB, l'EBSD, la nanoindentation ou encore l'altimétrie permettent de mettre en évidence un gradient de la stéréologie du matériau en surface et sous-surface. Les hétérogénéités locales induites concernent la morphologie des lattes de martensite, les orientations cristallographiques, l'état d'écrouissage interne mais également le profil de surface. Des essais mécaniques in-situ associés à la technique de corrélation d'images numériques sont réalisés pour des chargements monotones quasi-statiques et cycliques de type traction-traction. Une investigation des champs mécaniques locaux en surface est ainsi effectuée, elle permet d'analyser les schémas de localisations des déformations non linéaires liés aux artéfacts stéréologiques. Le traitement numérique s'intéresse à une modélisation multi-échelle, et plus particulièrement à des calculs par la méthode des éléments finis sur des microstructures virtuelles générées par tesselations de Voronoï. Celles-ci sont effectuées de manière à reproduire les structures martensitiques et considèrent des relations d'orientations spécifiques (de type Kurdjumov-Sachs) à l'issue du traitement thermique entre les lattes de martensite et le grain austénitique parent. Les équations constitutives du modèle de plasticité cristalline (élasto-viscoplastique) de Méric-Cailletaud sont implantées dans le code de calcul par éléments finis Abaqus dans le cadre de l'hypothèse des petites perturbations (HPP) et de la théorie des transformations finies. La formulation du modèle dans le contexte de la théorie des transformations finies est effectuée dans le cadre d'une description spatiale où la notion de dérivée objective est considérée. Celle-ci consiste en celle d'Oldroyd ou de Truesdell de manière à ce qu'une telle formulation soit équivalente à une description lagrangienne. Le traitement numérique a permis de reproduire de manière qualitative les schémas de localisation en surface mise en évidence lors de l'investigation expérimentale. L'influence des divers paramètres stéréologiques, évoqués ci-dessus, sur les champs mécaniques locaux a été analysée. De par cette approche, il a été possible de mettre en évidence certains mécanismes élémentaires, notamment les effets d'interaction et de surface. Enfin, il a été constaté que la prise en compte des rotations des réseaux cristallins par la théorie des transformations finies permet de relâcher certaines zones de localisation des champs mécaniques autour d'artéfacts stéréologiques. / AISI H11 martensitic tool steels are critical mechanical components that behaviour during service is drastically linked to their internal structures and their possible evolution. Their manufacture processes are often at the origin of microstructural changes at the surface, namely the morphology of martensitic laths, the crystallographic orientations, the internal hardening state and the surface profile These aspects can potentially alter the mechanical performance of AISI H11 martensitic steel. In order to get better insight into and optimize its mechanical behaviour, a multi-scale approach involving an experimental investigation and a numerical treatment is taken in this work.The experimental investigation focuses to reproduce, at the laboratory scale, equivalent surfaces to those resulting from tool steels manufacture processes. Specific characterization techniques, namely SEM, EBSD, nanoindentation and altimetry enable to highlight a stereology gradient of the material in surface and sub-surface. The induced local heterogeneities consist in morphology of martensitic laths and crystallographic orientations, internal hardening state and surface profile. In-situ mechanical tests with digital image correlation technique (DIC) are carried out for monotonous quasi-static and tension-tension cyclic loads. An investigation of the local mechanical fields at the surface is thus performed and allows to analyze the localizations schemes of nonlinear strains which are related to stereological artifacts.The numerical treatment is focused on a multi-scale modelling, and more particularly on finite element calculations on virtual microstructures which are generated by Voronoi tesselations. The latters are carried out such that to reproduce martensitic structures and consider a specific orientation relationship between martensitic laths and parent austenitic grains (i.e. Kurdjumov-Sachs) after the heat treatment. The constitutive equations of the (elasto-viscoplastic) crystal plasticity of Méric-Cailletaud are implemented in the finite element code Abaqus in the context of the small strain assumption and the finite strain theory. The formulation of the model in the context of finite strain theory is is given a spatial description where the notion of objective derivative, namely the so called one of Oldroyd or Truesdell, is used in such a way that such formulation is equivalent to a Lagrangian description.The numerical treatment has allowed to qualitatively reproduce the localization patterns at the surface which have been highlighted in the experimental investigation. The influence of the different stereological parameters mentioned above on the local mechanical fields was analyzed. By this approach, it was possible to highlight some elementary mechanisms including interaction and surface effects. Finally, it was found that the inclusion of lattice rotations via the theory of finite strain allows to release certain areas of mechanical fields localization that are related to stereological artifacts.

Electromagnetic coupling phenomena between overhead power transmission lines and other nearby structures are inevitable, especially in densely populated areas. The undesired effects resulting from this proximity are manifold and range from the establishment of hazardous potentials to the outbreak of alternate current corrosion phenomena. The study of this class of problems is necessary for ensuring security in the vicinities of the interaction zone and also to preserve the integrity of the equipment and of the devices there present. However, the complete modeling of this type of application requires the three- -dimensional representation of the region of interest and needs specific numerical methods for field computation. In this work, the modeling of problems arising from the flow of electrical currents in the ground (the so-called conductive coupling) will be addressed with the finite element method. Those resulting from the time variation of the electromagnetic fields (the so-called inductive coupling) will be considered as well, and they will be treated with the generalized PEEC (Partial Element Equivalent Circuit) method. More specifically, a special boundary condition on the electric potential is proposed for truncating the computational domain in the finite element analysis of conductive coupling problems, and a complete PEEC formulation for modeling inductive coupling problems is presented. Test configurations of increasing complexities are considered for validating the foregoing approaches. These works aim to provide a contribution to the modeling of this class of problems, which tend to become common with the expansion of power grids. / Les phénomènes de couplage électromagnétique entre les lignes aé- riennes de transmission d\'énergie et des structures voisines sont inévitables, surtout dans les zones densément peuplées. Les effets indésirables découlants de cette proximité sont variés, allant de l\'établissement des tensions dangereuses à l\'apparition de phénomènes de corrosion dus au courant alternatif. L\'étude de cette classe de problèmes est nécessaire pour assurer la sécurité dans les alentours de la zone d\'interaction et aussi pour préserver l\'intégrité des équipements et des dispositifs présents. Cependant, la modélisation compl ète de ce type d\'application implique la représentation tridimensionnelle de la région d\'intérêt et nécessite des méthodes numériques de calcul de champs spécifiques. Dans ces travaux, des problèmes liés à la circulation de courants électriques dans le sol (ou de couplage dit conductif) seront abordés avec la méthode des éléments finis. D\'autres problèmes résultants de la variation temporelle des champs électromagnétiques (ou de couplage dit inductif) seront aussi considérés et traités avec la méthode PEEC (Partial Element Equivalent Circuit) généralisée. Plus précisément, une condition limite particulière sur le potentiel électrique est proposée pour tronquer le domaine de calcul dans l\'analyse par éléments finis des problèmes de couplage conductif et une formulation PEEC complète pour la modélisation de problèmes de couplage inductif est présentée. Des con gurations tests de complexités croissantes sont considérées pour valider les approches précédentes. Ces travaux visent ainsi à apporter une contribution à la modélisation de cette classe de problèmes, qui tendent à devenir communs avec l\'expansion des réseaux électriques.

O estudo do comportamento mecânico do complexo sistema advindo da interação entre solo/subestrutura/superestrutura é o tema do trabalho. Neste contexto, a representação do maciço é feita usando-se o método dos elementos de contorno (MEC) em abordagem 3D, de maneira que se possa simular o maciço com características mecânicas não-homogêneas, além de se considerar uma camada de apoio indeslocável a distâncias prescritas a priori e condição de aderência perfeita. A subestrutura também é representada via MEC tridimensional, a qual está imersa dentro deste meio heterogêneo. A infra e a superestrutura são modeladas empregando o método dos elementos finitos (MEF), com o uso de elementos estruturais reticulares e elementos laminares. São apresentados alguns exemplos em que se valida a formulação e outros que demonstram a potencialidade e a necessidade de se empregar a formulação para a melhor análise do complexo fenômeno em estudo. Por fim, demonstra-se a obrigatoriedade de se otimizar a formulação, empregando-se duas grandes ferramentas numéricas: o paralelismo e o emprego de um adequado método de resolução de sistemas esparsos. / The analysis of the soil-structure system interaction is a vast field of interest in the area of civil engineering. A realistic representation of its behaviour. Thus, in the present research, the soil is considered a non-homogeneous continuum supported by a rigid and adhesive interface and modelled by boundary element method via Kelvin solution in 3D space. The foundation is also modelled by this above-mentioned modelling technique. The raft foundation and the superstructure are represented by finite shell and 3D frame elements. In order to estimate the accuracy and the potentiality of the proposed numerical formulation, some examples are validated when compared to similar approaches, and others simulations are presented to stress the necessity of coupling the non-homogeneous soil-foundation-radier-superstructure system as a whole. Finally, to acquire numerical time efficiency, it is shown that it is imperative to apply parallel processing and sparse techniques for the solution of the final system.

Neste trabalho, propõe-se uma formulação não linear baseada no método dos elementos de contorno, para representação de domínios poro-elasto-plásticos reforçados. Esta formulação é apresentada para os casos saturado e não saturado. Para o problema poroso enrijecido um acoplamento com o método dos elementos finitos é empregado, e a técnica de mínimos quadrados permite a regularização dos deslocamentos e do vetor de forças de superfície ao longo das interfaces de acoplamento. São empregadas expressões analíticas para o tratamento das integrais de contorno e de domínio presentes na formulação do método dos elementos de contorno. A formulação de Biot é empregada para a descrição de meios porosos saturados e uma formulação energética baseada nos trabalhos de Coussy é adaptada para a extensão ao caso não saturado. Neste caso, a pressão capilar e energia das interfaces são levadas em consideração. O nível de saturação é descrito pelo modelo de Van Genuchten e o comportamento do esqueleto é descrito ou pelo modelo de Drucker-Prager ou pelo modelo de Cam-Clay modificado. O problema não linear obtido por uma descrição temporal associada a discretização espacial é resolvido pelo método de Newton-Raphson. No caso saturado, o operador tangente consistente é definido e utilizado para obtenção da solução do sistema. Exemplos numéricos são apresentados para validar a formulação proposta. / In this work a nonlinear formulation of the boundary element method (BEM) is proposed to deal with saturated and unsaturated poro-elasto-plastic 2D reinforced domains. To model reinforced porous domains a BEM/FEM (Finite Element Method) modified coupling technique is employed. The coupling is made by using the least square method to regularize the displacement and traction distributions along the interfaces. Analytical expressions have been derived for all boundary and domain integrals required for the formulation. The Biot formulation is used for the description of the saturated porous environments and an energetic consistent formulation based on work of Coussy is adopted for its extension to the framework of unsaturated porous media. In this case, the capillar pressure and the interface energy are taken into account. The Van Genuchten model is used for the determination of saturation level in non-saturated poro-elasto-plastic problems. The Drucker-Prager modified model if used for the saturated poro-elasto-plastic problems and the modified Cam-Clay model for the representation of non-saturated poro-elasto-plastic problems. For the saturated case, the consistent tangent operator is derived and employed inside a Newton procedure to solve non-linear problems. Numerical solutions are presented to validate the proposed models.

O objetivo do presente trabalho é o desenvolvimento de um código computacional que possibilite a análise dinâmica de estruturas tridimensionais em regime elástico-linear acopladas ao solo, tratado como meio infinito elastoplástico. As superestruturas são tratadas por elementos finitos simples de casca e de barra geral, as estruturas de fundações são tratadas por elementos de casca que simulam o contato com o solo, modelando radiers, túneis e reservatórios enterrados. Blocos são modelados por elementos de contorno tridimensionais. O solo é modelado de duas maneiras distintas: na região plastificada emprega-se a solução fundamental de Kelvin (estática) e na região não plastificada (elástica) adota-se a solução fundamental do problema de Stokes. O acoplamento entre os meios é feito aplicando-se a técnica de subregiões. Deve ficar claro que todo procedimento estático equivalente foi implementado. Vários exemplos numéricos são apresentados, onde se percebe a eficiência do código computacional desenvolvido / The objective of the present work is the development of a computational code that makes possible dynamic analyses of three-dimensional structures in elastic-linear behavior coupled to the soil, modeled as elastoplastic infinite medium. Simple finite elements, shell and general bars, are used to model elastic structures. The structures of foundations are modeled by shell’s elements which simulate the contact with the soil, modeling radiers, tunnels and buried reservoirs. Blocks are modeled by three-dimensional boundary elements. The soil is modeled in two different ways: in the plastic region Kelvin’s fundamental solution (static) is used and in the elastic region the fundamental solution of the Stoke’s problem is adopted. The coupling among the media is done applying the sub-region technique. It is important to note that the equivalent static procedure has been implemented. Several numerical examples are presented, demonstrating the efficiency of the developed computational code

No presente trabalho, uma combinação do método dos elementos de contorno (MEC) com o método dos elementos finitos (MEF) é apresentada para a análise da interação entre estacas e o solo, considerado como um meio infinito tridimensional e homogêneo. O meio contínuo tridimensional de domínio infinito é modelado pelo MEC, enquanto as estacas consideradas como elementos reticulares são tratadas pelo MEF. As equações das estacas oriundas do método dos elementos finitos são combinadas com as do meio contínuo obtidas a partir do método dos elementos de contorno, resultando em um sistema completo de equações, que convenientemente tratadas, proporcionam a formulação de coeficientes de rigidez do conjunto solo-estacas. Finalmente, uma formulação para a análise do comportamento não-linear do solo na interface com a estaca é desenvolvida, tornando o modelo mais abrangente. / In the present work a combination of the Boundary Element Method (BEM) and the Finite Element Method (FEM) is used for pile-soil interaction analyses, considering the soil as a homogeneous, three-dimensional and infinite medium. The three-dimensional infinite continuous medium is modeled by the BEM, and the piles are, considered as beam elements, modeled by the FEM. This combination also is used for studying the interaction of plates sitting on a continuous medium. The pile equations generated from the FEM are combined with the medium equations generated from the BEM, resulting a complete equation system. Manipulating properly this equation system, a set of stiffness coefficients for the system soil-pile is obtained. Finally, to make the model more comprehensive, it presented a formulation to take into account the soil nonlinear behavior at the pile interface.

Analisa o comportamento tribológico do pneumático. Discute o coeficiente de atrito do pneu, a influência do pavimento e os avanços na modelagem. Apresenta uma metodologia para estimativa do desgaste de pneus pelo método dos elementos finitos. Usa o conceito de trabalho de abrasão. Considera nas condições de contorno do modelo de pneu o efeito do camber e do ângulo de deriva. Investiga a interação vibracional entre o pneu e a suspensão como causa de desgaste irregular. Utiliza modelagem de ônibus rodoviário por multicorpos com eixo flexível. Emprega técnica tempo-freqüência para análise do acoplamento modal entre pneu e suspensão. Propõe novos modelos para estudo do desgaste em pneus analisando-se um modelo completo de veículo pelo método dos elementos finitos. Sugere análises de sensibilidade considerando os parâmetros de regulagem da suspensão e condições operacionais dos componentes. Propõe análises estocásticas da especificação do pneu para otimização do sistema pneu-suspensão. / The tire tribological behavior is analyzed. The friction coefficient of rubbers is presented, and its inherent modeling difficulties regarding the operational condition dependence during measurements are discussed. The influence of the pavement roughness and the advances in friction modeling are presented. A predictive methodology to evaluate the tread wear using finite element method and the concept of frictional energy was used. Camber, lateral forces and slip angles are taken into account as boundary conditions for the tire simulations in steady state. The vibrational interaction between tire and suspension concerning irregular wear on front axle truck tires was investigated. A multibody bus model with flexible front axle was used for modal analysis purposes. A time-frequency methodology was applied to identify modal vibrations of the tire and suspension assemblage. A new simulation model for the tire wear was proposed intending to analyze the whole vehicle with under the finite element method. Sensitivity analysis of the vehicle suspension setup and operational conditions of components was suggested. Stochastic analysis of tire specification is recommended to optimize the tire-suspension system.