Neste trabalho, foi desenvolvido um material híbrido inédito carvão ativado/nanotubos de carbono/nanopartículas de prata para as aplicações em bateria de íons de lítio e capacitor eletroquímico de dupla camada. O compósito foi preparado por crescimento dos nanotubos de carbono diretamente sobre o carvão ativado via deposição química de vapor e depois nanopartículas de prata foram incorporadas no carvão ativado/nanotubos de carbono. A morfologia do compósito foi analisada por microscopia eletrônica de varredura. Investigação das propriedades de intercalação de lítio no carvão ativado (CA), carvão ativado/nanotubos de carbono (CA/NTC), carvão ativado/prata (CA/Ag) e carvão ativado/nanotubos de carbono/prata (CA/NTC/Ag) foi conduzida por voltametria cíclica e ciclos de carga/descarga, utilizando dois diferentes eletrólitos. Verificou-se que o ânodo de CA/NTC/Ag apresenta mais elevado valor de capacidade específica reversível que a grafita em eletrólito comercial, provavelmente devido à rede tridimensional com elevada condutividade eletrônica formada por nanotubos de carbono e nanopartículas de prata nos poros e nas rugosidades do substrato. Além disso, os nanotubos de carbono podem exibir elevada capacidade de armazenamento de lítio. Outra vantagem do CA/NTC/Ag é que a rede de nanotubos de carbono acomoda a expansão de volume das partículas de prata durante a ciclagem do eletrodo, mantendo-as bem adsorvidas na superfície do CA/NTC. Os resultados confirmaram a existência do sinergismo entre os componentes do CA/NTC/Ag, que promove características eletroquímicas superiores àquelas dos constituintes isolados. / In this work, an unpublished hybrid material activated carbon/carbon nanotubes/silver nanoparticles was developed for lithium ion battery and electrochemical double layer capacitor applications. The composite was prepared by growing carbon nanotubes directly on the activated carbon via chemical vapor deposition and after silver nanoparticles were incorporated on the activated carbon/carbon nanotubes. The composites morphology was analyzed by scanning electron microscopy. Investigation of lithium intercalation properties in activated carbon (AC), activated carbon/carbon nanotubes (AC/CNT), activated carbon/silver (AC/Ag) and activated carbon/carbon nanotubes/silver (AC/CNT/Ag) was carried out by cyclic voltammetry and charge/discharge cycles by making use of two different electrolytes. It was found that the AC/CNT/Ag anode presents higher reversible specific capacity value in comparison with graphite in commercial electrolyte, probably due to the three dimensional network with high electronic conductivity formed by carbon nanotubes and silver nanoparticles in the substrates pores and roughness. Furthermore, carbon nanotubes can exhibit high lithium storage capacity. Another advantage of the AC/CNT/Ag is that the network of carbon nanotubes accommodates volume expansion of the silver particles during electrode cycling, keeping them well adsorbed on the surface of the AC/CNT. The results confirmed the existence of synergism between the components of the AC/CNT/Ag, which promotes electrochemical characteristics that are higher than those of the individual constituents.

De modo a satisfazer aspectos de resistência, custo ou conforto, o aperfeiçoamento do desempenho das estruturas é uma meta sempre almejada na Engenharia. Melhorias têm sido alcançadas dado ao crescente uso de materiais compósitos, pois estes apresentam propriedades físicas diferenciadas capazes de atender as necessidades de projeto. Associado ao emprego de compósitos, o estudo da plasticidade demonstra uma interessante alternativa para aumentar o desempenho estrutural ao conferir uma capacidade resistente adicional ao conjunto. Entretanto, alguns problemas podem ser encontrados na análise elastoplástica de compósitos, além das próprias dificuldades inerentes à incorporação de fibras na matriz, no caso de compósitos reforçados. A forma na qual um compósito reforçado por fibras e suas fases têm sua representação e simulação é de extrema importância para garantir que os resultados obtidos sejam compatíveis com a realidade. À medida que se desenvolvem modelos mais refinados, surgem problemas referentes ao custo computacional, além da necessidade de compatibilização dos graus de liberdade entre os nós das malhas de elementos finitos da matriz e do reforço, muitas vezes exigindo a coincidência das referidas malhas. O presente trabalho utiliza formulações que permitem a representação de compósitos reforçados com fibras sem que haja a necessidade de coincidência entre malhas. Além disso, este permite a simulação do meio e do reforço em regime elastoplástico com o objetivo de melhor estudar o real comportamento. O modelo constitutivo adotado para a plasticidade é o de von Mises 2D associativo com encruamento linear positivo e a solução deste modelo foi obtida através de um processo iterativo. A formulação de elementos finitos posicional é adotada com descrição Lagrangeana Total e apresenta as posições do corpo no espaço como parâmetros nodais. Com o intuito de averiguar a correta implementação das formulações consideradas, exemplos para validação e apresentação das funcionalidades do código computacional desenvolvido foram analisados. / In order to satisfy strength, cost or comfort aspects, the improvement of the structural performance is a mark always desired in Engineering. Progress has been achieved due to the use of composite materials, because these present different physical properties capable of attending the needs of projects. Associated to the use of composites, the study of plasticity presents an interesting alternative to raise the structural performance by providing an additional resistance capability to the set. However, some problems may be found in the elastoplastic analysis of composites, besides the inherent difficulties of fiber insertion in the matrix, in the case of fiber reinforced composites. The way that the fiber reinforced composite and its phases are represented and simulated are of extreme importance to assure that the obtained results are compatible to the reality. As more refined models are developed, problems arise concerning computational cost and the need of compatibilization of the degrees of freedom between the nodes of the mashes of the matrix and the reinforcement, many times demanding the coincidence of the refered meshes. The present work utilizes formulations that allow the representation of the fiber reinforced composite without the need of mesh coincidence. It also enables the simulation of the medium and the reinforcement at the elastoplastic regime, with the objective study better the real behaviour. The constitutive model for the plasticity adopted is the von Mises 2D associative with a positive linear hardening and the solution of this model was obtained through an iterative procedure. The positional finite element method is adopted with a Total Lagrangean description and uses the positons of the body in space as nodal parameters. With the aim to ensure the correct implementation of the considered formulations, examples for validation and presentation of the functionalities of the developed computacional code were analized.

Recentes melhorias nos processos de fabricação e nas propriedades dos materiais associadas a excelentes características mecânicas e baixo peso tornaram os materiais compósitos muito atrativos para aplicação em estruturas aeronáuticas. No entanto, mesmo novos projetos ainda são muito conservadores, pois os fenômenos de falha dos compósitos são muito complexos. Então, é estratégico entender melhor, bem como prever esses complexos mecanismos de falha, desenvolvendo modelos de materiais mais precisos que venham a diminuir o número de ensaios experimentais, gerando rapidez e economia aos projetos estruturais. Assim, este trabalho apresenta o desenvolvimento de um modelo de material baseado na Mecânica do Dano Contínuo para simular a falha progressiva de estruturas laminadas de carbono/epóxi quando submetidas a carregamentos quase estáticos e de impacto. Várias análises numéricas foram realizadas via elementos finitos, a fim de prever a falha dessas estruturas de material compósito sob essas solicitações. O modelo de dano proposto foi implementado como sub-rotinas em linguagem FORTRAN (UMAT-User Material Subroutine e, VUMAT-User Material Subroutine para simulações explícitas), que foram compiladas junto ao programa comercial de Elementos Finitos ABAQUSTM. Além disso, ensaios experimentais foram realizados, a fim de calibrar parâmetros relacionados ao modelo de material, bem como avaliar as potencialidades e as limitações do modelo de material proposto. / Recent improvements in manufacturing processes and material properties associated to excellent mechanical characteristics and low weight have become composite materials very attractive for application on civil aircraft structures. However, even new designs are still very conservative, because the composite structure failure phenomena are very complex. So, it is strategic to known better and to predict these complex failure mechanisms, developing more accuracy material models, which reduce the number of experimental tests, inducing a fast and economic structural design. Thus, this work show the development of a material model based on Continuum Damage Mechanics to simulate the progressive failure of carbon/epoxy laminate structures under quasi-static and impact loadings. Several numerical analyses were performed via Finite Element Method in order to predict the damage on composite structures under these conditions. The proposed damage model was implemented as a UMAT (User Material Subroutine) and VUMAT (User Material Subroutine for explicit simulations), which were linked to ABAQUSTM. Moreover, experiments were carried out in order to calibrate the material model parameters and to evaluate the potentialities and limitation of the proposed material model, as well.

La modélisation de matériaux composites est un domaine d’étude qui bénéficie d’un intérêt croissant. En effet, la vulgarisation de l’utilisation de tels matériaux nécessite le développement de nouveaux modèles afin de mieux comprendre leur comportement. L’industrie automobile et aéronautique s’efforce d’optimiser le choix des matériaux en fonction des spécificités de chaque application, afin de réduire la masse des équipements et de leur assurer de meilleurs caractéristiques mécaniques et thermiques. Les matériaux composites se sont aussi présentés comme une éventuelle alternative au métal pour le rôle de blindage électromagnétique. Leur généralisation dans cette optique se heurte néanmoins à une relative méconnaissance de leur comportement électromagnétique. A cet effet, il est nécessaire de disposer de méthodologies permettant d'évaluer l'efficacité de blindage de boîtiers en matériaux composites et de cerner les différents mécanismes et paramètres correspondants.Par ailleurs, le déploiement de ces matériaux alternatifs à plus grande échelle est freiné par d'autres contraintes liées essentiellement à la difficulté de l'analyse électromagnétiques 3D complète de systèmes complexes abritant des boîtiers en matériaux composites. En effet, la complexité topologique de certains composants complique considérablement leur insertion dans les outils de simulation électromagnétique existants. De plus, le rapport d'échelle entre les différents niveaux (système, boîtiers composites, cartes, circuits, composants) est trop important ; cette disparité d'échelle complexifie considérablement la discrétisation géométrique de l'ensemble. L'association de ces différentes contraintes conduisent à des difficultés réelles aux quelles les ingénieurs CEM sont confrontés. C'est pourquoi il est nécessaire de développer des modèles performants permettant de faciliter l'analyse 3D du système hôte complet. Ce travail de thèse s'est donc réparti sur deux volets :- dans un premier temps, nous présentons une méthodologie de calcul de l'efficacité de blindage des boîtiers en matériaux composites, afin d'évaluer la potentialité de ces matériaux en termes de blindage électromagnétique et de cerner les principaux facteurs qui y contribuent.- dans un second temps et dans l'objectif de fournir une approche permettant de mettre les systèmes électroniques complexes intégrant des boîtiers de blindage composites en conformité avec les exigences strictes de CEM, nous proposons une méthodologie de modélisation des rayonnements électromagnétiques. Cette modélisation (à base d’algorithmes génétiques) permet de remplacer les dispositifs ou les boîtiers rayonnants (composites notamment) par un ensemble de dipôles élémentaires. Le modèle équivalent, de type "boîte noire", est ainsi représentatif de l’ensemble de la structure en termes de rayonnement électromagnétique en hautes fréquences et est facilement intégrable dans le maillage de structures hôtes. Ce modèle multipolaire fournit des prédictions spatiales et fréquentielles du champ électrique et magnétique permettant entre autres de calculer l'efficacité de blindage du boîtier dans l'espace, donnant ainsi un moyen de quantifier son impact perturbateur sur son environnement. D'autre part, cette approche permet de simplifier l'analyse 3D d'un système complet abritant des boîtiers composites en contrôlant le comportement EM à tous les niveaux : système, boîtiers, cartes, circuits et composants. / The modeling of composite materials is a domain of study which benefits of increasingly interest. Indeed, the popularization of the use of such materials requires the development of new models in order to better understand their behavior. The automotive and aerospace industry strives to optimize material selection based on the specificities of each application in order to reduce the weight of the equipment and to provide better mechanical and thermal characteristics. Composite materials have been also presented as a potential alternative to metals for the role of electromagnetic shielding. Their generalization in this context is nevertheless hampered by a relative lack of knowledge of their electromagnetic behavior. For this purpose, it is necessary to have methodologies to evaluate the shielding effectiveness of composite enclosures and identify the different corresponding mechanisms and parameters.Moreover, the deployment of these alternative materials on a larger scale is hindered by other constraints related mainly to the difficulty of complete 3D analysis of complex systems including composite enclosures. In fact, the topological complexity of certain components greatly complicates their integration into existing electromagnetic simulation tools. Moreover, the scale ratio between the different levels (system, composite enclosures, electronic card, circuit, component) is too large ; This disparity of scale complexifies considerably the geometrical discretization of the entire system. The combination of these different constraints leads to real difficulties to which EMC engineers face. That is why it is necessary to develop efficient models to facilitate the 3D analysis of the complete host system.This work is therefore divided in two sections :- In a first time, we present a methodology to calculate shielding effectiveness of composite enclosures of electronic equipment. The goal is to evaluate the potential of these materials in terms of electromagnetic shielding and to identify the main contributing factors.- In a second time, and in order to ensure compliance of complex electronic systems incorporating composite shielding enclosures with the stringent requirements of EMC, we propose a modeling methodology of electronic devices radiation. This modeling (based on genetic algorithms) allows to replace the radiating devices and enclosures (especially composites) by a set of elementary dipoles. The equivalent model, "black box" type, is thus representative of the entire structure in terms of high frequency electromagnetic radiation and is easily integrable in the mesh of host structures. This multipolar model provides spatial and frequency predictions of the electric and magnetic field, enabling among others to calculate the shielding effectiveness of the radiating enclosure in space, thereby giving a way to quantify its disruptive impact on its environment. Moreover, this approach allow to simplify the 3D analysis of a complete system comprising composite enclosures by controlling the EM behavior at all levels: system, enclosures, cards, circuits and components.

We develop a dual-purpose damage model (DPDM) that can simultaneously model intralayer damage (ply failure) and interlayer damage (delamination) as an alternative to conventional practices that models ply failure by continuum damage mechanics (CDM) and delamination by cohesive elements. From purely computational point of view, if successful, the proposed approach will significantly reduce computational cost by eliminating the need for having double nodes at ply interfaces. At the core, DPDM is based on the regularized continuum damage mechanics approach with vectorial representation of damage and ellipsoidal damage surface. Shear correction factors are introduced to match the mixed mode fracture toughness of an analytical cohesive zone model. A predictor-corrector local-nonlocal regularization scheme, which treats intralayer portion of damage as nonlocal and interlayer damage as local, is developed and verified. Two variants of the DPDM are studied: a single- and two- scale DPDM. For the two-scale DPDM, reduced-order-homogenization (ROH) framework is employed with matrix phase modeled by the DPDM while the inclusion phase modeled by the CDM. The proposed DPDM is verified on several multi-layer laminates with various ply orientations including double-cantilever beam (DCB), end-notch-flexure (ENF), mixed-mode-bending (MMB), and three-point-bending (TPB). The simulation is executed in the platform of FOOF (Finite element solver based on Object-Oriented Fortran). The objective of FOOF is to develop a new architecture of the nonlinear multiphysics finite element code in object oriented Fortran environment. The salient features of FOOF are reusability, extensibility, and performance. Computational efficiency stems from the intrinsic optimization of numerical computing intrinsic to Fortran, while reusability and extensibility is inherited from the support of object-oriented programming style in Fortran 2003 and its later versions. The shortcomings of the object oriented style in Fortran 2003 (in comparison to C++) are alleviated by introducing the class hierarchy and by utilizing a multilevel programming style.

Solution processed circuits are expected to be the main components to achieve low cost, large area, flexible electronics. However, the commercialization of solution processed flexible electronics face several challenges. The passive component such as capacitors are limited in frequency range and operating voltage. The active component such as transistors suffer from low mobility ultimately leading to limited current-carrying capacity. Just as in traditional silicon technology, the fabrication process and material choices significantly impact the performance of the fabricated devices. My thesis focuses on the optimization of the performance of printed capacitors and transistors through investigation of several aspects of the device structure and fabrication process. The first part of this work focuses on the optimization of printed nanoparticle/polymer composite capacitors. Thin film metal oxide nanoparticle/polymer composites have enormous potential to achieve printable high-k dielectrics. The combination of high-k ceramic nanoparticle and polymer enables room temperature deposition of high dielectric constant film without the need of high temperature sintering process. The polymer matrix host fills the packing voids left behind by the nanoparticles resulting to higher effective dielectric permittivity as a system and suppresses surface states leading to reduced dielectric loss. Such composite systems have been employed in a number of flexible electronic applications such as the dielectrics in capacitors and thin film transistors. One of the most important properties of thin film capacitors is the breakdown field. In a typical capacitor system, the breakdown process leads to catastrophic failure that destroys the capacitor; however, in a nanoparticle/polymer composite system with self-healing property, the point of breakdown is not well-defined. The breakdown of the dielectric or electrodes in the system limits the leakage observed. It is possible, however, to define a voltage/field tolerance. Field tolerance is defined as the highest practical field at which the device stays operational with low failure rate by qualifying the devices with defined leakage current density. In my work, the optimization of the field tolerance of (Ba,Sr)TiO₃ (BST)/parylene-C composite capacitors is achieved by studying the influence of the electromigration parameter on leakage and field strength through the inherit asymmetrical structure of the fabricated capacitors. One approach to creating these composites is to use a spin-coated nanoparticle film together with vapor deposited polymers, which can yield high performance, but also forms a structurally asymmetric device. The performance of a nanoparticle BST/parylene-C composite capacitor is compared to that of a nanoparticle BST capacitor without the polymer layer under both directions of bias. The composite device shows a five orders of magnitude improvement in the leakage current under positive bias of the bottom electrode relative to the pure-particle device, and four orders of magnitude improvement when the top electrode is positively biased. The voltage tolerance of the device is also improved, and it is asymmetric (44 V vs. 28 V in bottom and top positive bias, respectively). This study demonstrates the advantage of this class of composite device construction, but also shows that proper application of the device bias in this type of asymmetrical system can yield an additional benefit. The dependence of the field tolerance of nanoparticle/polymer composite capacitors on the electromigration parameter of the electrodes is investigated using the symmetrical dielectric system. The breakdown is suppressed by selecting the polarity used in nanoparticle (Ba,Sr)TiO₃/parylene-C composite film-based capacitors. Metals including gold, silver, copper, chromium, and aluminum with comparable surface conditions were examined as the electrodes. The asymmetric silver, aluminum, gold, copper, and chromium electrode devices show a 64 %, 29 %, 28 %, 17 %, 33 %, improvement in the effective maximum operating field, respectively, when comparing bias polarity. The field at which filament formation is observed shows a clear dependence on the electromigration properties of the electrode material and demonstrates that use of electromigration resistant metal electrodes offers an additional route to improving the performance of capacitors using this nanoparticle/polymer composite architecture. The second part of my thesis focuses on the novel pneumatic printing process that enables manipulation of the crystal growth of the organic semiconductors to achieve oriented crystal with high mobility. Small molecule organic semiconductors are attracting immense attention as the active material for the large-area flexible electronics due to their solution processability, mechanical flexibility, and potential for high performance. However, the ability to rapidly pattern and deposit multiple materials and control the thin-film morphology are significant challenges facing industrial scale production. A novel and simple pneumatic nozzle printing approach is developed to control the crystallization of organic thin-films and deposit multiple materials with wide range of viscosity including on the same substrate. Pneumatic printing uses capillary action between the nozzle and substrate combined with control of air pressure to dispense the solution from a dispense tip with a reservoir. Orientation and size of the crystals is controlled by tuning the printing direction, speed, and the temperature of the substrate. The main advantages of pneumatic printing technique are 1) simple setup and process, 2) multi-material layered deposition applicable to wide range of solution viscosity, 3) control over crystal growth. The manipulation of crystal growth will be discussed in the next chapter. This method for performance optimization and patterning has great potential for advancing printed electronics. The dependence of the mobility of printed thin film 6,13-bis(triisopropylsilylethynyl) pentacene [TIPS-pentacene] and C8-BTBT on printing conditions is investigated, and the result indicates that the formation of well-ordered crystals occurs at an optimal head translation speed. A maximum mobility of 0.75 cm²/(Vs) is achieved with 0.3 mm/s printing speed and 1.3 cm²/(Vs) with 0.3 mm/s printing speed at 50C for TIPS-pentacene and C8-BTBT respectively. In summary, pneumatic printing technique can be an attractive route to industrial scale large area flexible electronics fabrication.

Este trabalho é uma contribuição à análise progressiva de falhas em materiais compósitos poliméricos. Esses materiais combinam as propriedades de seus constituintes (fibra, resina polimérica e interface) de forma a melhorar o desempenho frente à utilização das fases isoladamente. A combinação de fases permite obter características como baixa densidade e elevada rigidez, que são almejadas pelo segmento aeronáutico, pois podem proporcionar um aumento de autonomia ou da capacidade de carga das aeronaves. A anisotropia inerente aos compósitos torna possível projetá-los de forma a obter-se a rigidez e a resistência desejada. Por outro lado, a anisotropia dificulta a previsão precisa dos mecanismos de falha, e conseqüentemente, do comportamento global da estrutura. Apresenta-se, assim, com base numa revisão bibliográfica criteriosa, bem como, através de resultados experimentais, a avaliação de um modelo de material fenomenológico, onde se identificam modos de falhas intralaminares. Uma vez verificad a falha por algum critério, degradam-se as propriedades do material. O modelo de material foi implementado junto ao pacote de elementos finitos Abaqus através de uma sub-rotina UMAT (\"User Material\"), escrita em Fortran. Em seguida, estudou-se o problema de um laminado em duas configurações de empilhamento (\'[0º] IND.10\' e \'[0º/90º/0º/90º/0º] IND.S\') sob flexão 3-pontos. Os resultados das simulações foram comparados com resultados experimentais, observando erros da ordem de 10%. Sendo que estes foram obtidos em função de um estudo dos parâmetros associados a solução do problema não-linear, tais como: tamanho de incremento de iteração e parâmetros associados à lei de degradação de material. Por fim, concluiu-se que o modelo de material avaliado é adequado para previsão da falha da primeira camada, bem como, da redução da rigidez estrutural e da resistência residual. Sendo que, a resposta teórica obtida se manteve parcialmente dentro dos limites inferior e superior do envelope experimental. / This work is a contribution to the progressive failure analysis in polymer composite materials. These materials combine the properties of its constituents (fiber, resin and interface) in order to improve the performance against the use of phases alone. The combination of the phases can provide characteristics such as low density and high strength, which are desired in the aeronautical segment, because it can increase the autonomy or aircraft payload. The anisotropy inherent in composites turns possible to design the material for a desired stiffness and strength. Furthermore, it turns difficult the prediction of failure mechanisms, and consequently, the overall behavior of the structure. This study presents, based on a review and experimental results, the evaluation of a phenomenological material model, which identify intralaminar failure modes. Once verified the failure by any criterion, the material properties are reduced by a degradation law. The material model was implemented in a UMAT (User Material) subroutine which linked to the finite element package Abaqus. It was applied in the study of 3-point bending problem for two stacking sequences (\'[0º] IND.10\' e \'[0º/90º/0º/90º/0º] IND.S\'). The results were compared with experimental tests, presenting a error in the order of 10%. Since that these where obtained by a study of the parameters associated to the solution of the nonlinear problem, such as: time step, and parameters associated to the material degradation laws. Finally, it was concluded that the material model is judged suitable for predicting the failure of the first ply, the reduction of structural stiffness and the residual strength. Besides, a part of the theoretical response obtained is maintained within the lower and upper limits of the experimental tests envelope.

Este trabalho apresenta duas técnicas de ensaios não-destrutivos por ultra-som realizados em um tanque com água para determinar as constantes elásticas de materiais compostos de fibra de vidro/epóxi. A primeira técnica é a transmissão direta utilizando um par de transdutores. A segunda é a técnica de pulso-eco, utilizando um único transdutor. A água do tanque atua como um acoplante para transferir a energia mecânica do transdutor para a amostra. Como o transdutor não fica em contato direto com a amostra, pode-se garantir um acoplamento constante. O sistema de medição dota de um dispositivo que permite medir a velocidade da onda elástica sob diferentes ângulos de incidência, através da rotação manual da amostra. Devido ao fenômeno de conversão de modos com incidência oblíqua na interface amostra-água, ensaios por ultra-som em tanques com água fornecem as informações necessárias para o cálculo das constantes elásticas em amostras de materiais anisotrópicos, numa dada direção, a partir das medições das velocidades longitudinal e de cisalhamento. Numa dada direção de propagação em um meio anisotrópico, existem três ondas elásticas distintas: uma longitudinal e duas de cisalhamento. Se as constantes elásticas do material são conhecidas, é possível obter as três velocidades em uma dada direção bastando resolver a equação de Christoffel. Invertendo a equação de Christoffel, obtém-se as constantes elásticas a partir das velocidades medidas em uma dada direção. Os experimentos são realizados com amostras de fibra de vidro/epóxi unidirecionais e bidirecionais, utilizando transdutores com freqüências de 0,5 MHz, 1 MHz e 2,25 MHz. Os resultados experimentais obtidos utilizando ambas as técnicas são comparados com um modelo denominado “Regra das Misturas" e com resultados da literatura. / In this work, two ultrasonic non destructive techniques were implemented in a water tank and used to determine the elastic constants of glass-epoxy composites samples. The first is the through-transmission technique implemented with a pair of ultrasonic transducers. The second is the back-reflection technique that uses a single transducer in pulse-eco mode. The water acts as a couplant and transfers the mechanical energy from the transducer to the sample. As the transducer is not in direct contact with the sample, we can guarantee a good coupling with the immersion technique. With the system device, it is possible to measure the velocities of the elastic waves in different angles by manually rotating the sample. Due to wave mode conversion phenomenon at the sample-water interface with oblique incidence, ultrasonic immersion testing provides information to calculate the elastic constants of the specimen by measuring longitudinal and shear wave speeds. There are three different modes of waves, one longitudinal and two shear waves, for any given direction of propagation in an anisotropic medium. If the elastic constants of a medium are known, it is possible to obtain the three wave speeds in particular propagations directions by solving the Christoffel equation. Inverting the Christoffel equation, it is possible to obtain the elastic constants from the measured wave speed in several specific directions of the anisotropic material. Measurements were carried out on unidirectional and bidirectional glass-epoxy composite samples, using transducers with central frequency of 0.5 MHz, 1 MHz, and 2.25 MHz. The experimental results obtained with both techniques are compared with a model denominated “Rule of Mixture" estimation and with the literature.

Este trabalho tem como objetivo principal a otimização dos protótipos fabricados pelo processo FDM (Fused Deposition Modeling) em procedimento baseado na análise do comportamento estrutural dos protótipos variando as estratégias de preenchimento das camadas. Para atingir tal objetivo, corpos de prova com diferentes orientações de preenchimento foram ensaiados experimentalmente e os resultados foram verificados em análise estrutural por elementos finitos. Foram verificados o caráter ortotrópico do material do protótipo e a validade do uso da Teoria Clássica dos Laminados na simulação de seu comportamento. Os conceitos e metodologia de análise foram validados em estudos de casos, mostrando a viabilidade de sua aplicação na obtenção de protótipos funcionais / The objective of this work is to develop an optimization procedure for FDM prototypes. This procedure is based on the structural analysis of the prototypes within different slice filling paths. In order to reach this objective, experimental tests with different filling trajectories are conducted and the results are used in structural analysis by finite element method. The orthotropic behavior of the prototype material and the use of the Classical Laminate Theory in the numerical simulation were validated. The results were applied in different case studies, showing the viability of its application in the design of functional prototypes.

O presente trabalho tem por finalidade estudar e implementar um modelo numérico de análises cinemáticas de sólidos tridimensionais via método dos elementos finitos posicionais, com consideração de fibras longas ou curtas inseridas de maneira aleatória ou não no domínio da análise. O modelo numérico considera material isotrópico para a matriz e não linearidade geométrica. O domínio do sólido é discretizado por meio de elementos finitos tetraédricos de ordem qualquer, cujos parâmetros nodais são suas posições. A medida de deformação utilizada é a de Green, associada à lei constitutiva de Saint-Venant-Kirchhoff, referenciada pela configuração inicial do corpo, caracterizando o sistema de espaço como Lagrangiano total. O cálculo da posição de equilíbrio é baseado no princípio da mínima energia potencial total. Para a resolução do problema não linear geométrico, adota-se o método iterativo de Newton-Raphson. A inserção das fibras no domínio da análise é feita com a associação das mesmas com elementos finitos unidimensionais curvos de ordem qualquer, cujas posições nodais são dadas em função das posições dos nós dos elementos de sólido. Essa abordagem tem como vantagem o fato de não aumentar o número de graus de liberdade do sistema, ao mesmo tempo em que não limita as posições das fibras dentro do domínio por não ser necessária a coincidência das malhas. Exemplos são apresentados para validação dos desenvolvimentos e implementações realizadas. / This study aims to develop and implement a numerical model of kinematic enrichment, to analyze tridimensional solids based on positional finite element method, considering long and short fibers random distributed inside the domain. The numerical model considers isotropic material and geometric nonlinear behavior for both matrix and fibers. Tetrahedral finite elements with any order of approximation are used to discretize the solid domain, with positions as nodal parameters. Green strain and Saint-Venant-Kirchhoff constitutive law are used, referenced in initial configuration of the body, characterizing the developed formulation as total Lagrangian. The equilibrium is obtained with the application of Total Potential Energy Principle, adopting the Newton-Raphson method to solve the resulting nonlinear system of equations. The fibers are considered in the formulation using curved one-dimensional finite elements with any order of approximation, and the nodal positions of the fibers are related with the nodal positions of the solid elements. The coupling method adopted does not increase the number of degrees of freedom of the system, and does not limit the positions of the fiber nodes to be coincident with solid nodes. Examples are presented in order to validate the developed and implemented formulations.