Ao se estudar problemas de impacto de estruturas deformáveis, a consideração dos efeitos térmicos se faz muito importante, pois além de se observar a transformação de energia mecânica em calor pode-se considerar, ao longo do processo de análise, as mudanças das propriedades mecânicas do material envolvido devido ao aquecimento do meio. Neste sentido, o objetivo principal deste trabalho é o desenvolvimento de uma formulação termodinamicamente consistente e sua implementação computacional, baseada no potencial de energia livre de Helmholtz e na primeira e segunda leis da termodinâmica, para se analisar, via elementos finitos, o impacto entre estruturas com comportamento termo-elástico e termo-plástico. O problema mecânico será tratado com formulação posicional desenvolvida em projetos de pesquisa anteriores e que podem ser classificados como Lagrangeano total com cinemática exata. Para a modelagem do impacto utilizar-se-á a técnica do multiplicador de Lagrange associada à teoria potencial para previsão do impacto, técnica de retorno geometricamente definida e algoritmo de integração temporal de Newmark adequadamente adaptado para problemas gerais de impacto. / It becomes quite important study the thermal effects when considering impact in structures, because besides the mechanical energy changing into heat, one may consider the changes in the material properties due overheating. In this sense, the main goal of this work is develop a thermodynamic formulation and its implementation, based in the Helmholtz free-energy and in the first and second law of thermodynamics, to analyze structures under impact. The mechanical problem will be solved by a positional finite element application developed in past researches and it can be classified as a total Lagrangean with exact kinematics. In order to consider the impact, the Lagrangean multiplier will be associated to the potential theory of impact prevision, technique geometrically defined and an adapted technique based on the time integration of Newmark, modified to impact problems.

Introdução - Estudos mostram maior ocorrência de complicações cardiovasculares na população HIV/aids. Alguns estudos envolvendo animais e indivíduos saudáveis ou com outras doenças observaram benefícios no consumo de chocolate e erva mate na função endotelial e vasodilatação. Objetivo Avaliar o efeito da ingestão de chocolate e erva mate na elasticidade arterial de indivíduos com HIV/aids em terapia antirretroviral. Métodos Ensaio clínico cruzado, aleatorizado e duplo-cego, envolvendo 89 indivíduos com HIV/aids entre 19 e 59 anos, em tratamento regular com antirretrovirais por no mínimo 6 meses, e carga plasmática do HIV <500 cópias/ml. Os indivíduos receberam suplementação diária com aproximadamente 65g de chocolate amargo, 3g de erva mate ou respectivos placebos por 15 dias, com washout de igual tempo entre as intervenções. A aferição da elasticidade arterial foi realizada por análise do formato da onda de pulso com o equipamento HDI/PulseWaveTM CR-2000®. Também foram avaliados: composição corporal, glicemia, perfil lipídico, proteína C-reativa e concentração plasmática de espécies reativas ao ácido tiobarbitúrico (TBARS). As respostas entre tratamentos foram avaliadas por ANOVA e por teste t de Student pelo Stata® 11.0, considerando-se p< 0,005. Resultados A população foi composta principalmente por homens (62,9 por cento) caucasianos (46,1 por cento) com idade média de 44,6 ± 7,1 anos. O tempo médio de diagnóstico de HIV/aids foi de 13,2 ± 4,8 anos com 10,6 ± 5,1 anos de terapia antirretroviral. Não foram encontradas diferenças significantes na elasticidade arterial dos pequenos e grandes vasos após as suplementações. Conclusão Este é o primeiro estudo a avaliar o efeito da ingestão de erva mate e chocolate na elasticidade arterial de indivíduos com HIV/aids. Apesar das evidências positivas desses alimentos na saúde cardiovascular de animais e indivíduos com outras doenças, os mesmos efeitos não foram observados neste estudo. Provavelmente o tempo de suplementação, a biodisponibilidade das substâncias bioativas e o metabolismo alterado desses indivíduos interferiram nos resultados obtidos, sugerindo a necessidade de melhor investigação desses fatores / Introduction There has been an increase on cardiovascular diseases occurrence in the HIV/aids population. Some studies involving animals and healthy individuals or individuals with other pathologies have shown benefits on endothelial function and vasodilation under use of chocolate and yerba maté. Objective To evaluate the effect of chocolate and yerba maté intake on HIV/aids patient´s arterial elasticity. Methods Double-blind crossover trial including 89 HIV/aids patients, 19 to 59 years of age, on antiretroviral therapy for at least six months, and with viral load <500copies/ml. The individuals consumed daily approximately 65g of dark chocolate, 3g of yerba maté or placebo during 15 days, followed by a 15-day washout period after each intervention. Arterial elasticity was measured using the HDI/PulseWaveTM CR-2000 CardioVascular Profiling System®, which provides a pulse wave contour analysis. Body composition, glicemic index, lipid profile, C-reactive protein and thiobarbituric acid reactive substances (TBARS) were also assessed. The crossover analysis was performed using analysis of variance (ANOVA) on Stata®. The paired Students t-test was also applied. A p value <0.05 was considered significant. Results Most of the individuals were men (62.9 per cent), caucasian (46.1 per cent) aging 44.6 ± 7.1 years. The mean time of HIV/aids diagnosis was 13.2 ± 4.8 years, with 10.6 ± 5.1 years of antiretroviral therapy. There were no significant alterations on elasticity of either large or small arteries after chocolate and yerba maté intake. Conclusion This is the first research to evaluate the effect of chocolate and yerba maté intake on HIV/aids patient´s arterial elasticity. Despite of the positive evidence of these foods on cardiovascular health of animals and populations with other pathologies, the same effects were not observed in this study. Most probably the time of intervention, the bioavailability of the bioactive substances and the altered metabolism of this individuals interfered on the results, which indicates the need for further investigation

Made available in DSpace on 2016-04-26T20:52:39Z (GMT). No. of bitstreams: 1 Luiz Maia de Gutierrez Ballester.pdf: 784047 bytes, checksum: 930f3b9647c62b57506441525e8d6c95 (MD5) Previous issue date: 2015-03-23 / Currently the Brazilian energy market undergoes major challenges. In the present paper the evolution of the energy market has been evaluated with some concepts of competition and monopoly in order to compare the Brazilian market with other more mature markets in terms of evolution of the electricity sector, such as California, the Nord Pool and the United Kingdom. This new Brazilian electrical energy market brings, inevitably, risks for the generating agents. These risks can be analyzed and quantified, as literature, through a series of indicators such as VAR, CVAR, Ebitda at Risk and Profit at Risk. However, these metrics use volatile pricing scenarios and directly influenced by the consumption of energy. In this way we evaluate econometrically whether the variable is elastic with the income and the rate of energy, which can constitute a potentializing factor of risk in case of presenting a great elasticity / Atualmente o mercado de energia brasileira passa por grandes desafios. No presente trabalho a evolução do mercado de energia foi avaliado com alguns conceitos de competitividade e monopólio a fim de podermos comparar o mercado brasileiro com outros mercados mais maduros em termos de evolução do setor elétrico, tais como a Califórnia, o Nord Pool e o Reino Unido. Este novo mercado de energia elétrica brasileiro traz inevitavelmente riscos para estes agentes de geração. Estes riscos podem ser analisados e quantificados, conforme literatura, através de uma série de indicadores como VAR, Ebitda at Risk, CVAR e Profit at Risk. Porém estas métricas utilizam cenários de preços voláteis e diretamente influenciados pelo consumo de energia. Desta forma avaliamos econometricamente se a variável é elástica com a renda e com a tarifa de energia, o que pode constituir um fator potencializador do risco no caso de apresentar uma elasticidade grande

Les nanocomposites présentent des propriétés uniques dont l'origine est sujette à débat. Dans ce travail, nous cherchons à déterminer quel est l'impact de la morphologie de la charge et de son état de distribution sur les propriétés des matériaux. Pour cela, nous avons étendu un modèle théorique que nous résolvons numériquement.Nous avons étudié l'effet de la distribution des charges dans la matrice. Nous montrons qu'un état de distribution fortement hétérogène conduit à un renforcement plus important qui s'étend dans une plus large gamme de températures, mais augmente aussi la dissipation d'énergie. Ensuite, nous étudions l'effet de la structure des charges. Des particules parfaitement sphériques sont comparées à des agrégats fractals plus ou moins finement définis. Nous montrons que des objets finement définis peuvent s'imbriquer au sein de la matrice et conduisent à une augmentation du renfort et de la dissipation dans ces matériaux.Puis, nous étudions la réponse de nos systèmes lorsqu'ils sont soumis à une première élongation de forte amplitude. Nous montrons alors qu'un système hétérogène se plastifie localement progressivement au cours de la déformation alors qu'un système homogène présente une plastification catastrophique généralisée à partir d'une déformation critique. Enfin dans une dernière partie nous évaluons la possibilité d'étendre le modèle afin de simuler l'endommagement des nanocomposites. Nous introduisons pour cela un critère rupture local afin de prendre en compte l'endommagement du polymère entre les charges. Nous étudions ensuite comment se comportent les matériaux simulés en faisant varier la morphologie de la charge, son état de distribution et son taux.Ce travail constitue la première étude systématique de l'effet de la morphologie et de la distribution des charges sur les propriétés mécaniques des nanocomposites. Nous montrons que ces paramètres peu contrôlés sont pourtant des paramètres clés et peuvent servir à optimiser les propriétés d’usage d'un nanocomposite / Nano-filled elastomer composites are used in a very broad range of applications such as tires, damping materials and impact modifiers. The addition of nanoscale rigid particles in a polymer matrix induces nonlinear effects that are not yet fully understood far above the glass transition temperature of the pure matrix. A model of the reinforcement of nanocomposites based on the reduced mobility of the polymer confined between two spherical filler particles has been developed over the last ten years. In order to study the influence of the filler shape, structure, size, and dispersion state, we have extended the model were the morphology of the fillers is defined explicitly as spherical particles aggregated in the polymer matrix. The model is then solved by mesoscale numerical simulation in order to describe the mechanical properties of the nanocomposite. We study the mechanical response of nanocomposite filled with aggregates of different shapes and distribution state to deformations of various amplitudes in the reinforcement regime. We show that the mechanical behavior of nanocomposites strongly depends on the filler morphology and we propose that stress-relaxation mechanisms in the material are related to the disorder (particle size, aggregation number, distribution state) in the filler population. In a second part of this work, we study the mechanical response at larger amplitude in both a non-destructive and destructive regime. For that matter, the model has been extended in order to account for damaging of the polymer between filler particles.Our model opens the path for the development of systems with tailored properties by adjusting the fillers morphology and distribution.

A gestão eficaz de recursos computacionais em nuvem está diretamente ligada a gerir corretamente o desempenho das aplicações hospedadas na Máquina Virtual (Virtual Machine - VM), criando um ambiente capaz de controlá-la e redimensionar recursos de Memória, Disco, CPU e outros que se façam necessários, individualmente em resposta a carga de trabalho. Neste trabalho considera-se também a gestão eficaz a qual é possível realizar o retorno sobre o investimento realizado para a contratação do serviço de IaaS. Nesta pesquisa de mestrado, foi proposto o gerenciamento da infraestrutura computacional em nuvem, através de dois modelos que facilitam o provisionamento auto-adaptativo de recursos em um ambiente virtualizado: alocação de recursos utilizando modelo para previsão da carga de trabalho futura e a gestão auto-adaptativa de capacidade utilizando agentes computacionais para monitorarem constantemente as VMs. Além disso, é proposto o retorno do investimento, que trata a relação entre o valor que o cliente contratou do serviço de IaaS e o quanto efetivamente ele está utilizando. Desta forma, a cada período é contabilizado a taxa do valor gasto em unidades monetárias. Para contemplar esta proposta, foram desenvolvidos algoritmos que são o núcleo de todo gerenciamento. Também foram realizados experimentos e os resultados mostram a capacidade do autogerenciamento das máquinas virtuais, com reconfiguração dinâmica da infraestrutura através de previsões baseadas em histórico e também da reconfiguração e monitoramento com o uso de agentes computacionais. Após a análise e avaliação dos resultados obtidos nos experimentos, é possível afirmar que houve uma significativa melhora da reconfiguração dos recursos com agentes computacionais se comparado a reconfiguração com previsão de carga futura. / The efficient management of computational resources in the cloud is directly linked to correctly manage the performance of the applications hosted in the virtual machine (Virtual Machine - VM), creating an environment able to control it and resize features Memory, Disk, CPU and others resources, individually in response to workload. This work is also considered effective management which is possible to realize the return on investment for hiring the IaaS service. This Master thesis, is proposed the management of computing infrastructure in the cloud, using two models that facilitate self-adaptive resource provisioning in a virtualized environment using resource allocation model to predict the future workload and adaptive self-management capacity utilizing computational agents to continuously monitor the VMs. Furthermore, it is proposed return on investment, which is the ratio between the value that the client hired the IaaS service and how effectively it is using. Thus, each period is accounted for the rate of the amount spent in monetary units. To address this proposal, were developed algorithms that are the core of all management. Experiments were also conducted and the results show the ability of self-management for virtual machines with dynamic reconfiguration of infrastructure through predictions based on historical and also the reconfiguration and monitoring with the use of computational agents. After the analysis and evaluation of the results obtained in the experiments, is possible say that there was a significant improvement in reconfiguration of resources with computational agents compared with the workload forecast.

A teoria de elasticidade não-linear é apropriada para a investigação de instabilidades materiais relacionadas ao amolecimento e à formação de bandas de cisalhamento. Estes fenômenos podem surgir em compósitos constituídos de fases que, isoladamente, não apresentam tais fenômenos sob as mesmas condições de carregamento. O objetivo principal desta tese de doutorado é utilizar métodos computacional e de homogeneização na investigação do comportamento de laminados bifásicos compostos de lâminas elásticas não-lineares. Em particular, utilizam-se o método dos elementos finitos (MEF) clássico e os métodos de homogeneização assintótica (MHA) e de segunda ordem tangencial para gerar resultados computacionais e analíticos que possam ser comparados entre si. Com este objetivo em mente, estuda-se primeiramente o comportamento efetivo de bilaminados compostos por distribuições periódicas de lâminas elástico-lineares, homogêneas e isotrópicas. Os bilaminados estão em equilíbrio na ausência de forças de corpo. Gera-se uma sequência de bilaminados com número crescente de lâminas e simulam-se ensaios de tração uniaxial no regime de pequenas deformações utilizando malhas de elementos finitos refinadas. Resultados destas simulações computacionais são comparados a resultados analíticos obtidos de ensaio de tração uniaxial similar de um sólido homogeneizado via MHA. Os resultados computacionais tendem aos resultados analíticos à medida que o número de lâminas na sequência de bilaminados tende ao infinito. Em seguida, investiga-se o comportamento efetivo de bilaminados compostos por distribuições periódicas de lâminas elásticas não-lineares, homogêneas, quase-incompressíveis e isotrópicas submetidos a condições de deformação impostas em seus contornos. Utilizando-se o método de homogeneização de segunda ordem tangencial, determinam-se as propriedades efetivas dos bilaminados. Estas propriedades são utilizadas na condição de Legendre-Hadamard para predizer perda de elipticidade das equações governantes. A violação desta condição está relacionada à formação de bandas de cisalhamento no compósito. Utilizando malha de elementos finitos refinada, simula-se numericamente o problema de equilíbrio de um bilaminado com número elevado de lâminas na ausência de força de corpo e sujeito a deformações impostas no contorno. Os resultados computacionais predizem perda de elipticidade para um nível de deformação próximo ao nível de deformação da perda de elipticidade predita pelo método de homogeneização. Os resultados analíticos e computacionais indicam que a perda de elipticidade é fortemente influenciada pelo contraste de heterogeneidade entre as fases e pelas condições de contorno. / The theory of nonlinear elasticity is suitable for the investigation of material instabilities related to softening and formation of shear bands. These phenomena can arise in composites consisting of phases which, taken separately, do not exhibit such phenomena under the same loading conditions. The main objective of this thesis is to use both computational and homogenization methods in the investigation of the behavior of two-phase laminates composed of nonlinear elastic laminae. In particular, we use the finite element method (FEM) and both the asymptotic homogenization method (AHM) and the tangent second-order homogenization method to generate computational and analytical results that can be compared to each other. With this goal in mind, we study first the effective behavior of bilaminates composed of periodic distributions of linearly elastic, homogeneous, and isotropic laminae. The bilaminates are in equilibrium in the absence of body forces. A sequence of bilaminates with increasing number of laminae is used to numerically simulate uniaxial tensile tests in the small strain regime using refined finite element meshes. Computational results are then compared with analytical results obtained from a similar tensile test of a solid homogenized via MHA. The computational results tend to the analytical result as the number of laminae in the sequence of bilaminates tends to infinity. Next, we investigate the effective behavior of bilaminates composed of periodic distributions of nonlinearly elastic, homogeneous, isotropic, and quasi-incompressible laminae that are subjected to deformation conditions on their boundaries. Using the tangent second-order homogenization method, the effective properties of the bilaminates are determined. These properties are used in the Legendre-Hadamard condition to predict loss of ellipticity of the governing equations. Violation of this condition is related to the formation of shear bands in the composite. Using refined finite element meshes, we simulate numerically the problem of equilibrium of a bilaminate with a high number of laminae in the absence of body force and subjected to deformation conditions on the boundary. The computational results predict loss of ellipticity at a deformation level close to the deformation level for which loss of ellipticity is predicted by the homogenization method. The computational and analytical results indicate that the loss of ellipticity is strongly influenced by both the heterogeneity contrast between the phases and the boundary conditions.

Este trabalho teve por objetivo o desempenho de misturas asfálticas densas utilizando um ligante convencional (CAP-20) e o mesmo ligante modificado com polímeros tipo SBS, produzido sob o nome comercial de BETUFLEX B 65/60, através dos ensaios Marshall, fluência por compressão uniaxial estática e dinâmica, resistência à tração por compressão diametral e módulo resiliente pro compressão diametral dinâmica, em misturas compactadas com uma mesma faixa granulométrica e diferentes teores de ligantes. O ensaio Marshall apresentou, para as misturas preparadas com asfalto modificado, valores maiores de estabilidade para a maioria dos teores, apesar de valores elevados de fluência em todos os teores analisados. Os resultados de deformação do ensaio de fluência por compressão uniaxial não distinguiram claramente o efeito da adição de polímeros em misturas asfálticas, ao contrário do observado no ensaio dinâmico, onde as deformações foram consideravelmente menores para a maioria dos teores analisados. Os resultados do ensaio de resistência à tração por compressão diametral mostram um desempenho superior da mistura modificada. O ensaio de módulo resiliente por compressão diametral dinâmica indicou, à temperatura de 25ºC, valores menores para a mistura com asfalto modificado, não sendo notada, entretanto, uma diferenciação de desempenho nas temperaturas de 5ºC e 40ºC. A modelação matemática das curvas de fluência e de recuperação às equações constitutivas de alguns modelos visco-elásticos básicos detectou uma diferenciação entre os valores de alguns elementos constitutivos, tanto do ensaio dinâmico, quanto do estático. / The purpose of this study is to evaluate the performance of asphalt mixes using conventional binder and the same binder modified with SBS polymer (Betuflex B 65/60) based on Marshall test, static and dynamic creep tests, indirect tensile strength test and resilient modulus by indirect tensile test, with the same granulometric composition and different binders contents. In Marshall test, polymer modified asphalt mixes presented better stability performance than conventional asphalt mixes in most of binders contents, despite of the higher flow values obtained for all binders contents. The static creep test results indicated that this test does not clearly distinguish the effect of polymer in asphalt mixes while the results of dynamic creep test indicated the opposite, i. e., polymer modified asphalt mixes deformations are smaller for most of the asphalt binders contents studied. The indirect tensile strength test results showed a better performance of modified asphalt. The results of resilient modulus by indirect tensile test at 25°C showed smaller values for modified asphalt, while the results at 5ºC and 40ºC did not show differences between the asphalt mixes. The mathematics modelling of the creep and recovering curves according to constitutive equations of some basic visco- elastic models showed a difference between the values of some constitutive elements in both cases, dynamic and static tests.

"The effect of bacterial surface biopolymers on bacterial adhesion to surfaces was studied through experiments and modeling. Atomic Force Microscopy (AFM) provided the tool to measure the interaction forces between different bacterial cells and silicon nitride tips under different chemical conditions at a nanoscopic level. Two bacterial strains were considered: Pseudomonas putida KT2442 and Escherichia coli K-12 JM109. This study addressed the following issues: 1) the effect of solution ionic strength and solvent polarity on adhesion between Pseudomonas putida KT2442 and the silicon nitride AFM tip, 2) role of heterogeneity of bacterial surface biopolymers on bacterial adhesion, 3) role of lipopolysaccharides (LPS) on adhesion at three different scales: continuous, batch, and nanoscale, and 4) nature of interactions between E. coli JM109 and a model surface (silicon nitride tip). To address the first issue, formamide, water, and methanol were used to investigate the effect of polarity on surface characteristics of biopolymers on the bacterial surface while a range of salt concentrations between that of water to 1 M KCl were used to study the effect of ionic strength. The adhesion increased with decreasing polarity of the solvent, indicating that the polymers on the bacterial surface are hydrophilic in nature. The adhesion was slightly affected by ionic strength variations up to a concentration of 0.1 M KCl; this may have been due to the fact that the ionic concentration in the solution did not counterbalance the ionic concentration in the biopolymer brush on the bacterial surface. However, a dramatic increase in the adhesion magnitude was observed when the salt concentration increased above 0.1 M KCl. This transition in adhesion with ionic strength from a low to high value induced a transition in the elasticity of the bacterial surface biopolymers. The biopolymer brush layer did change from rigid to soft with increasing the ionic strength. The elasticity was quantified mainly by the use of the freely jointed chain (FJC) model. Our interest in investigating the role of heterogeneity on adhesion developed from the results of the first study. The bacterial surface polymers were thought to be different in their chemical and physical nature since they were found to span a range of segment lengths. Analyzing the adhesion forces for P. putida KT2442 showed that the bacterial surface is heterogeneous. The heterogeneity was evident on the same cell surface and between different cells from the same population. To resolve the third issue, approximately, 80% of the surface LPS of E. coli K-12 JM109 were removed by treating the cells with 100 mM ethylenediaminetetraacetic acid (EDTA). The effect of LPS removal on the adhesion of the cells to the silicon nitride tip was studied in water and phosphate buffered silane (PBS). The adhesion results from the AFM experiments were compared to batch retention experiments with glass as the substratum and column attachment experiments with columns packed with quartz sand. LPS controlled bacterial adhesion to the different surfaces in the study at three scales: batch, continuous, and nano-scale. Finally, the nature of interactions between E. coli JM109 and a model surface (silicon nitride tip) were investigated in solvents of varying polarity (formamide, water, and methanol). The Young’s modulus of elasticity for the bacterial surface was estimated by fitting of the Hertzian model to the force-indentation curves. Young’s modulus values increased as the solvent polarity decreased, indicating a stiffer bacterial surface in lower polarity solvents. The average adhesion force in each solvent was negatively correlated with the dielectric constant of the solvent, suggesting hydrophilic biopolymers. Specific and non-specific interaction forces between the AFM tip and the biopolymers were further characterized by applying a Poisson statistical analysis to the discrete adhesion data. The specific and non-specific interaction forces were the highest in methanol (-4 and -1.48 nN respectively). These values are in accordance with the high adhesion magnitude values measured with AFM in methanol. The results of my different studies emphasized the important role of AFM in studying biological interactions to different surfaces and in characterizing bacterial surface biopolymers."

Le dioxyde d'uranium irradié (UO2), combustible nucléaire des réacteurs à eau pressurisée, contient deux populations de cavités saturées par des gaz de fission : i. des cavités intergranulaires plutôt lenticulaires, dont la taille varie de quelques dizaines à plusieurs centaines de nanomètres, ii. des cavités intragranulaires plutôt sphériques, dont la taille est de l'ordre du nanomètre. Des travaux récents ont montré qu'il existe un effet de surface à l'échelle des cavités nanométriques qui modifie le comportement élastique effectif du combustible. Ce travail vise à proposer un modèle micromécanique analytique capable de tenir compte de cette microstructure hétérogène ainsi que de l'effet de surface afin de décrire le comportement élastique macroscopique de l'UO2 irradié. La démarche mise en oeuvre est fondée sur une modélisation multi-échelles et s'appuie sur des techniques d'homogénéisation en mécanique des matériaux. L'UO2 irradié est décrit comme un matériau poreux contenant des nanocavités sphériques (cavités intragranulaires) et sphéroïdales (cavités intergranulaires), sous pression et orientées aléatoirement. L'effet de surface présent à l'échelle nanométrique est pris en compte via un modèle d'interface imparfaite cohérente entre la matrice et les cavités. Un modèle original fondé sur l'approche par motifs morphologiques représentatifs a été développé afin de décrire le comportement élastique effectif de ce milieu hétérogène. Le modèle analytique proposé repose sur des hypothèses simplificatrices dont la pertinence est évaluée à partir de simulations numériques par éléments finis qui s'appuient sur une formulation spécifique afin de tenir compte de la présence d'interfaces imparfaites cohérentes. / The irradiated uranium dioxide (UO2), which is the nuclear fuel of pressurized water reactors, contains two populations of cavities saturated by fission gaz: i. intergranular cavities almost lenticular in shape whose size ranges between few tens to several hundred nanometers, ii. intragranular cavities, almost spherical in shape whose size is of the order of the nanometer. Recent studies have shown the existence of a surface effect at the scale of nanometric cavities, which influences the effective elastic behavior of the nuclear fuel. In this work, an analytical micromechanical model, which is able to take into account this heterogeneous microstructure and the surface effect at the nanometric scale, is proposed to describe the macroscopic behavior of the irradiated UO2. The approach is based on a multiscale modeling and homogenization techniques in mechanics of materials. The irradiated UO2 is described as a porous media, which contains pressurized spherical nanocavities (intragranular cavities) and randomly oriented pressurized spheroidal cavities (intergranular cavities). The surface effect is taken into account with imperfect coherent interfaces between the matrix and the cavities. A novel model based on the morphologically representative pattern approach has been developed to describe the effective elastic behavior of this heterogeneous medium. The proposed model relies on assumptions whose relevance is evaluated with finite element simulations which require a specific formulation to take into account the imperfect coherent interfaces.

Made available in DSpace on 2017-07-24T19:22:09Z (GMT). No. of bitstreams: 1 Cristian Higashi.pdf: 1616679 bytes, checksum: a243cd9970614325c2c06ab7c7f592d1 (MD5) Previous issue date: 2008-02-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The aim of this study was to assess the hardness and elastic modulus of resin-dentin bonding area formed by an ethanol/water-based (Adper TM Single Bond 2 [SB]) and an acetone-based system (One Step Plus [OS]), under different moisture conditions and application methods. On 24 human molars, a flat superficial dentin surface was exposed by wet abrasion. Two coats of SB or OS adhesive were applied on either a dry (D) or rewetted surface (W), under active (AA) or inactive (IA) application. After polymerization of the adhesives (600 mW/cm2/20 s), composite build-ups were constructed incrementally and specimens were stored in water (24 h). They were cross-sectioned perpendicular to the resin-dentin interface to obtain slices of 1.5 mm thickness that were embedded and polished before the test. Nanoindentations were made on composite resin, adhesive system, hybrid layer and dentin regions. The results of hardness and elastic modulus (GPa) of adhesive system and hybrid layer were analyzed by a three-way ANOVA and Tukey’s multiple comparison tests (α=0.05). The mean and standard deviation of hardness and elastic modulus values of composite resin were (1.02 ± 0.07) and (14.94 ± 0.67) respectively. In dentin, the hardness was (0.69 ± 0.10) and the elastic modulus (17.94 ± 1.84). In the adhesive layer, the highest hardness (0.38 ± 0.06) and elastic modulus (6.93 ± 0.93) of SB were obtained in W group. In this same area, the elastic modulus of OS (5.91 ± 1.12) was lowest in AA group. In the hybrid layer, the hardness of both adhesive systems was highest in AA group, however statistically significant just for OS (0.51 ± 0.2). In D group the highest hardness (0.47 ± 0.24) and elastic modulus (10.98 ± 4.65) of hybrid layer were obtained with AA. It was concluded that the active application of both adhesives in dry dentin resulted in higher hardness and elastic modulus values in the hybrid layer and the moisture increased hardness and elastic modulus values of Adper TM Single Bond 2 in the adhesive layer. / O objetivo deste trabalho foi avaliar a dureza e módulo de elasticidade da interface de união resina-dentina formado por adesivos convencionais de 2 passos à base de água/etanol (Adper TM Single Bond 2 [SB]) e à base de acetona (One Step Plus [OS]), variando a umidade dentinária e forma de aplicação dos mesmos. 24 terceiros molares humanos foram lixados para a obtenção de uma superfície dentinária plana. Duas gotas do adesivo SB ou OS foram aplicadas de forma ativa (AA) ou inativa (AI) sobre uma dentina seca (S) ou reumedecida (U). Após a fotopolimerização dos adesivos (600 mW/cm2 / 20 s) os dentes foram restaurados incrementalmente e armazenados em água destilada por 24 h. Cortes perpendiculares à interface de união foram realizados para obtenção de fatias de aproximadamente 1,5 mm de espessura, que foram embutidas e polidas previamente ao teste. Nanoindentações foram realizadas nas regiões da resina composta, sistema adesivo, camada híbrida e dentina. Os valores de dureza e módulo de elasticidade (GPa) do sistema adesivo e camada híbrida foram submetidos a uma análise de variância de 3 fatores de medidas repetidas e ao teste de comparações múltiplas de Tukey (α=0,05). A média e desvio padrão dos valores de dureza e módulo de elasticidade da resina composta (GPa) foram (1,02 ± 0,07) e (14,94 ± 0,67), respectivamente. Na dentina, a dureza foi (0,69 ± 0,10) e o módulo de elasticidade (17,94 ± 1,84). Na camada de adesivo, os maiores valores de dureza (0,38 ± 0,06) e módulo de elasticidade (6,93 ± 0,93) do SB foram obtidos no grupo U. Nesta mesma região, o módulo de elasticidade do OS (5,91 ± 1,12) foi menor para o grupo AA. Na região da camada híbrida, a dureza de ambos os sistemas adesivos foi maior no grupo AA, porém significativamente somente para o OS (0,51 ± 0,2). No grupo S os maiores valores de dureza (0,47 ± 0,24) e módulo de elasticidade (10,98 ± 4,65) da camada híbrida foram obtidos com AA. Concluiu-se que a aplicação ativa de ambos os sistemas adesivos em substrato dentinário seco resultou nos maiores valores de dureza e módulo de elasticidade na região da camada híbrida e a umidade dentinária influenciou positivamente nos valores de dureza e módulo de elasticidade do sistema adesivo Adper TM Single Bond 2 na região da camada de adesivo.