O presente trabalho objetivou desenvolver e implementar, em escala laboratorial, uma rotina experimental com base em Imageamento por Ressonância Magnética Nuclear (IRMN) de modo a verificar seu potencial como metodologia não-destrutiva aplicável à inspeção quali- e quantitativa de água e hidrocarbonetos líquidos aprisionados no interior de células de núcleos-colméia utilizados na confecção de painéis-sanduíche compósitos estruturais de grau aeronáutico. Tentativas foram também realizadas no sentido de se observarem e caracterizarem danos por amassamento de núcleos-colméia, assim como de se detectar a presença de resina polimérica na forma sólida, visando, desta feita, verificar o uso do IRMN na inspeção de componentes previamente reparados e/ou contendo excesso de resina por falha do processo de manufatura. Concluiu-se que IRMN é uma poderosa ferramenta para a detecção e a quantificação de líquidos puros e compostos, ricos em hidrogênio, contidos nas células de núcleos de amostras extraídas de painéis-sanduíche compósitos. O potencial do IRMN na identificação, e, portanto, na discriminação entre os diversos fluidos se mostrou bastante promissor, desde que se empreguem ferramentas de processamento e análise computadorizada de imagens a partir de programas computacionais de reconhecimento de padrões via redes neurais artificiais e/ou sistemas com base em conhecimento. A técnica de IRMN utilizada neste estudo não permitiu a captura de imagens de resina polimérica sólida, nem mesmo quando à esta foram adicionadas cargas de elementos intensificadores de sinais de RMN, tais como ferro e gadolíneo. Danos no núcleo-colméia tão pequenos quanto 1,0 mm de profundidade e 1,8 mm de diâmetro foram clara e inequivocamente imageados e delineados pela técnica IRMN, desde que estivessem permeados por fluido hidrogenado (ex. água). A quantificação de líquidos nos núcleos-colméia por intermédio de ferramentas computacionais simples (processadores e analisadores de imagens) foi muito bem sucedida no caso dos líquidos com relativamente alto ponto de fulgor, pois as massas fluidas se mantiveram constantes por períodos de tempo significativamente longos no interior das células analisadas. / This work intended to develop and implement in laboratorial scale an experimental routine funded in Nuclear Magnetic Resonance Imaging (NMRI) in order to verify its potential as a non-destructive methodology for quali- and quantitative inspection of liquid water and hydrocarbons entrapped in honeycomb core cells utilized to build up aeronautical grade structural composite sandwich panels. Attempts were also carried out to observe and characterize crush damage of honeycomb core, as well as to detect solid polymer resin towards the use of NMRI to assess previously repaired components and/or containing in excess resin amount due to manufacturing process faults. It has been concluded that NMRI is a powerful tool in detecting and quantifying hydrogen-rich pure and compound liquids contained in core cells of composite sandwich samples. The NMRI potential in identifying and, therefore, discriminating several fluids has shown very promising as long as computed image processing and analysis tools are employed from pattern recognition software via artificial neural networks and/or knowledge-based systems. The utilized NMRI technique failed in imaging solid polymer resin, even when the latter was loaded with NMR-signal intensifier elements such as iron and gadolinium. Honeycomb core damages as small as 1.0 mm in depth and 1.8 mm in diameter were clearly and unambiguously imaged and delineated by the NMRI technique since they were permeated with hydrogenated fluid (ex., water). The quantification of liquids in honeycomb cores by means of simple computational tools (image processor and analyzer) was very successful in case of relatively high flash point fluids, insofar as their masses remained constant within the analyzed cells for significantly long periods of time.

Painéis sanduíche são largamente utilizadas em diversas aplicações de engenharia e o estudo de suas propriedades é fundamental para a ampliação de sua utilização. Neste trabalho, foram estudados painéis sanduíche com núcleo de poliuretano e faces de fibra de vidro fabricados pelo processo de laminação contínua. Na primeira configuração, as faces do painel foram fabricadas com manta de fibra de vidro e resina poliéster, com 39% de teor de vidro em massa e espessura de 1,9 mm. Na segunda configuração, as faces do painel foram fabricadas com tecido de fibra de vidro e resina poliéster, com 54% de teor de vidro em massa e espessura de 1,2 mm. Realizou-se o cálculo das propriedades mecânicas de cada compósito no programa MECH-Gcomp. As propriedades do núcleo foram retiradas, inicialmente, da literatura. Então, foi possível realizar a avaliação dos painéis pelo método dos elementos finitos utilizando elementos sólidos, comparando o comportamento dos dois tipos de painéis em relação aos carregamentos de compressão de núcleo, de compressão longitudinal e de flexão. Foram realizados ensaios nas faces isoladas e também nos painéis sanduíche completos. Para as faces, os ensaios foram de teor mássico de fibra de vidro, tração, compressão e cisalhamento Iosipescu, conforme as normas ASTM D5630, D3039/D3039M, D6641/D6641M e D7078/D7078M, respectivamente. Já para os painéis sanduíche, foram realizados os ensaios de compressão de núcleo, compressão longitudinal (edgewise) e cisalhamento do núcleo utilizando flexão, conforme as normas ASTM C365/C365M, C364/C364M e C393/C393M, respectivamente. Após os ensaios, foram calibrados os modelos do MEF, permitindo que os mesmos possam calcular outras configurações similares de painel sanduíche. Foi utilizado o programa Autodesk Simulation Composite Design para realizar a validação do ensaio de cisalhamento do núcleo. Concluiu-se que a análise de elementos finitos foi confiável em representar de forma realista o comportamento dos painéis sanduíche e a redução na espessura das faces do painel pode ser compensada com o aumento da sua resistência mecânica e rigidez por meio do aumento no teor mássico de reforço e trabalhando com a orientação do mesmo. / Sandwich panels are widely used in a variety of engineering applications and the study of their properties is fundamental for the expansion of their use. In this work, we studied sandwich panels with polyurethane core and fiberglass faces manufactured by the continuous lamination process. In the first configuration, the panel faces were made of fiberglass and polyester resin, with 39% glass content by mass and 1.9 mm thickness. In the second configuration, the panel faces were fabricated from fiberglass fabric and polyester resin, with 54% glass content by mass and 1.2 mm thickness. The mechanical properties of each composite were calculated in the MECH-Gcomp software. The properties of the core were initially taken from the literature. Then, it was possible to evaluate the panels by the finite element method using solid elements, comparing the behavior of the two types of panels in relation to the core compression loads, edgewise compression and bending. Tests were performed on the faces and also on the complete sandwich panels. For the faces, the tests were fiberglass mass content, tensile, compression and Iosipescu shear, according to ASTM D5630, D3039/D3039M, D6641/D6641M and D7078/D7078M, respectively. For sandwich panels, core compression, edgewise compression and core shear using bending tests were performed according to ASTM C365/C365M, C364/C364M and C393/C393M, respectively. After the tests, the FEM models were calibrated, allowing them to calculate other similar sandwich panel configurations. It was used Autodesk Simulation Composite Design software to validate the core shear test. It was concluded that the analysis of finite elements was reliable in realistically representing the behavior of the sandwich panels and the reduction in the thickness of the panel faces can be compensated with the increase of its mechanical resistance and stiffness by increasing the mass content of reinforcement and working with the orientation of the same.

A lightweight carbon fiber reinforced polymer (CFRP) sandwich panel has been developed for floor use in commercial office building construction. CFRP laminate skins were combined with low-density rigid polyurethane foam to create a composite sandwich panel suitable for floor use. The CFRP sandwich panel was optimized to withstand code prescribed office-building live loads using a 3D finite element computer program called SolidWorks. The thickness of the polyurethane foam was optimized to meet both strength and serviceability requirements for gravity loading. Deflection ultimately was the controlling factor in the design, as the stresses in the composite materials remained relatively low. The CFRP sandwich panel was then subjected to combined gravity and lateral loading, which included seismic loads from a fictitious 5-story office building located in a region of high seismic risk. The results showed that CFRP sandwich panels are a viable option for use with floors, possessing sufficient strength and stiffness for meeting code prescribed design loads, while providing significant benefits over traditional construction materials.

Painéis sanduíche são largamente utilizadas em diversas aplicações de engenharia e o estudo de suas propriedades é fundamental para a ampliação de sua utilização. Neste trabalho, foram estudados painéis sanduíche com núcleo de poliuretano e faces de fibra de vidro fabricados pelo processo de laminação contínua. Na primeira configuração, as faces do painel foram fabricadas com manta de fibra de vidro e resina poliéster, com 39% de teor de vidro em massa e espessura de 1,9 mm. Na segunda configuração, as faces do painel foram fabricadas com tecido de fibra de vidro e resina poliéster, com 54% de teor de vidro em massa e espessura de 1,2 mm. Realizou-se o cálculo das propriedades mecânicas de cada compósito no programa MECH-Gcomp. As propriedades do núcleo foram retiradas, inicialmente, da literatura. Então, foi possível realizar a avaliação dos painéis pelo método dos elementos finitos utilizando elementos sólidos, comparando o comportamento dos dois tipos de painéis em relação aos carregamentos de compressão de núcleo, de compressão longitudinal e de flexão. Foram realizados ensaios nas faces isoladas e também nos painéis sanduíche completos. Para as faces, os ensaios foram de teor mássico de fibra de vidro, tração, compressão e cisalhamento Iosipescu, conforme as normas ASTM D5630, D3039/D3039M, D6641/D6641M e D7078/D7078M, respectivamente. Já para os painéis sanduíche, foram realizados os ensaios de compressão de núcleo, compressão longitudinal (edgewise) e cisalhamento do núcleo utilizando flexão, conforme as normas ASTM C365/C365M, C364/C364M e C393/C393M, respectivamente. Após os ensaios, foram calibrados os modelos do MEF, permitindo que os mesmos possam calcular outras configurações similares de painel sanduíche. Foi utilizado o programa Autodesk Simulation Composite Design para realizar a validação do ensaio de cisalhamento do núcleo. Concluiu-se que a análise de elementos finitos foi confiável em representar de forma realista o comportamento dos painéis sanduíche e a redução na espessura das faces do painel pode ser compensada com o aumento da sua resistência mecânica e rigidez por meio do aumento no teor mássico de reforço e trabalhando com a orientação do mesmo. / Sandwich panels are widely used in a variety of engineering applications and the study of their properties is fundamental for the expansion of their use. In this work, we studied sandwich panels with polyurethane core and fiberglass faces manufactured by the continuous lamination process. In the first configuration, the panel faces were made of fiberglass and polyester resin, with 39% glass content by mass and 1.9 mm thickness. In the second configuration, the panel faces were fabricated from fiberglass fabric and polyester resin, with 54% glass content by mass and 1.2 mm thickness. The mechanical properties of each composite were calculated in the MECH-Gcomp software. The properties of the core were initially taken from the literature. Then, it was possible to evaluate the panels by the finite element method using solid elements, comparing the behavior of the two types of panels in relation to the core compression loads, edgewise compression and bending. Tests were performed on the faces and also on the complete sandwich panels. For the faces, the tests were fiberglass mass content, tensile, compression and Iosipescu shear, according to ASTM D5630, D3039/D3039M, D6641/D6641M and D7078/D7078M, respectively. For sandwich panels, core compression, edgewise compression and core shear using bending tests were performed according to ASTM C365/C365M, C364/C364M and C393/C393M, respectively. After the tests, the FEM models were calibrated, allowing them to calculate other similar sandwich panel configurations. It was used Autodesk Simulation Composite Design software to validate the core shear test. It was concluded that the analysis of finite elements was reliable in realistically representing the behavior of the sandwich panels and the reduction in the thickness of the panel faces can be compensated with the increase of its mechanical resistance and stiffness by increasing the mass content of reinforcement and working with the orientation of the same.

Painéis sanduíche são largamente utilizadas em diversas aplicações de engenharia e o estudo de suas propriedades é fundamental para a ampliação de sua utilização. Neste trabalho, foram estudados painéis sanduíche com núcleo de poliuretano e faces de fibra de vidro fabricados pelo processo de laminação contínua. Na primeira configuração, as faces do painel foram fabricadas com manta de fibra de vidro e resina poliéster, com 39% de teor de vidro em massa e espessura de 1,9 mm. Na segunda configuração, as faces do painel foram fabricadas com tecido de fibra de vidro e resina poliéster, com 54% de teor de vidro em massa e espessura de 1,2 mm. Realizou-se o cálculo das propriedades mecânicas de cada compósito no programa MECH-Gcomp. As propriedades do núcleo foram retiradas, inicialmente, da literatura. Então, foi possível realizar a avaliação dos painéis pelo método dos elementos finitos utilizando elementos sólidos, comparando o comportamento dos dois tipos de painéis em relação aos carregamentos de compressão de núcleo, de compressão longitudinal e de flexão. Foram realizados ensaios nas faces isoladas e também nos painéis sanduíche completos. Para as faces, os ensaios foram de teor mássico de fibra de vidro, tração, compressão e cisalhamento Iosipescu, conforme as normas ASTM D5630, D3039/D3039M, D6641/D6641M e D7078/D7078M, respectivamente. Já para os painéis sanduíche, foram realizados os ensaios de compressão de núcleo, compressão longitudinal (edgewise) e cisalhamento do núcleo utilizando flexão, conforme as normas ASTM C365/C365M, C364/C364M e C393/C393M, respectivamente. Após os ensaios, foram calibrados os modelos do MEF, permitindo que os mesmos possam calcular outras configurações similares de painel sanduíche. Foi utilizado o programa Autodesk Simulation Composite Design para realizar a validação do ensaio de cisalhamento do núcleo. Concluiu-se que a análise de elementos finitos foi confiável em representar de forma realista o comportamento dos painéis sanduíche e a redução na espessura das faces do painel pode ser compensada com o aumento da sua resistência mecânica e rigidez por meio do aumento no teor mássico de reforço e trabalhando com a orientação do mesmo. / Sandwich panels are widely used in a variety of engineering applications and the study of their properties is fundamental for the expansion of their use. In this work, we studied sandwich panels with polyurethane core and fiberglass faces manufactured by the continuous lamination process. In the first configuration, the panel faces were made of fiberglass and polyester resin, with 39% glass content by mass and 1.9 mm thickness. In the second configuration, the panel faces were fabricated from fiberglass fabric and polyester resin, with 54% glass content by mass and 1.2 mm thickness. The mechanical properties of each composite were calculated in the MECH-Gcomp software. The properties of the core were initially taken from the literature. Then, it was possible to evaluate the panels by the finite element method using solid elements, comparing the behavior of the two types of panels in relation to the core compression loads, edgewise compression and bending. Tests were performed on the faces and also on the complete sandwich panels. For the faces, the tests were fiberglass mass content, tensile, compression and Iosipescu shear, according to ASTM D5630, D3039/D3039M, D6641/D6641M and D7078/D7078M, respectively. For sandwich panels, core compression, edgewise compression and core shear using bending tests were performed according to ASTM C365/C365M, C364/C364M and C393/C393M, respectively. After the tests, the FEM models were calibrated, allowing them to calculate other similar sandwich panel configurations. It was used Autodesk Simulation Composite Design software to validate the core shear test. It was concluded that the analysis of finite elements was reliable in realistically representing the behavior of the sandwich panels and the reduction in the thickness of the panel faces can be compensated with the increase of its mechanical resistance and stiffness by increasing the mass content of reinforcement and working with the orientation of the same.

Des panneaux sandwichs en nid d'abeilles sont largement utilisés, notamment dans l’industrie aérospatiale et aéronautique, à cause du très bon rapport entre rigidité en flexion et poids. Concernant leur modélisation, ils sont considérés classiquement comme de milieux homogénéisés équivalents afin d'éviter des modèles numériques prohibitifs en coûts de calculs. Cependant, des travaux précédents ont montré que, si le comportement dynamique en membrane des sandwichs peut être correctement représenté par des modèles homogénéisés classiques dans une large gamme de fréquences, ces mêmes modèles ne permettent malheureusement pas de bien décrire le comportement en flexion dans le domaine de hautes fréquences (HF). En effet, la couche centrale en nid d'abeilles joue un rôle important dans le comportement en flexion du sandwich, il est donc indispensable de la modéliser de manière appropriée. Or, lorsque les longueurs d’onde impliquées deviennent aussi petites que les longueurs caractéristiques des cellules du nid d’abeilles, cette microstructure cellulaire interagit fortement avec les ondes et génère des effets d’interaction non négligeables, qui ne sont malheureusement pas pris en compte par des modèles homogénéisés classiques. Dans le cadre de cette thèse, on s’intéresse donc à l'amélioration de l’analyse théorique et numérique de la propagation d’ondes élastiques HF dans ces panneaux composites. On exploite les caractéristiques périodiques du nid d'abeilles en utilisant sur une approche numérique basée sur la théorie des ondes de Bloch. En effet, en décomposant des solutions non périodiques sur une base composée de modes périodiques de Bloch, il est possible de développer des modèles numériques, qui considèrent des phénomènes de propagation des ondes à l’intérieur d’une seule cellule de base et captent toutes les interactions. Ces modèles numériques sont donc de taille raisonnable, par rapport aux dimensions souvent très importantes des structures industrielles. Des analyses théoriques et des outils de modélisation ont été développés pour des milieux périodiques composés de structures minces : poutres ou plaques. Notre approche a été développée et validée pour des structures périodiques uni- puis bi-dimensionnelles composées de poutres. Pour les cas 2D, la forme de la cellule est hexagonale ou rectangulaire. Nous avons aussi considéré des plaques sandwichs en nid d’abeilles. Pour toutes ces structures, en identifiant les valeurs propres et les modes propres de Bloch sur une cellule primitive pour tous les vecteurs d’onde de Bloch situés dans la première zone de Brillouin dans l’espace de phase, la relation de dispersion entre le vecteur d'onde de Bloch et la valeur propre est calculée. En analysant cette relation de dispersion, les résultats importants sont obtenus, tels que les bandes de fréquences passantes et bloquantes et les caractéristiques d'anisotropie et dispersives des structures périodiques, la comparaison quantitative entre les premiers modes de Bloch et ceux des modèles homogénéisés classiques en vue d’une définition précise du domaine validation en fréquence de ceux-derniers et la mise en évidence des modes de Bloch « rétro-propagatifs » munis d’une vitesse de groupe négative. / Honeycomb core sandwich panels are widely used in the aeronautic industry due to their excellent flexural stiffness to weight ratio. Generally, classical homogenized model is used to model honeycomb core sandwiches in order to have an efficient but not expensive numerical modeling. However, previous works have shown that, while the homogenized models could correctly represent the membrane waves’ behavior of sandwiches in a large frequency range, they could not give satisfying simulation results for the flexural waves’ behavior in the high frequency range (HF). In fact, the honeycomb core layer plays an important role in the propagation of the flexural waves, so that when the involved wavelengths become close to the characteristic lengths of honeycomb cells, the cellular microstructure starts interacting strongly with the waves and its effect should no longer be neglected, which is unfortunately not the case of the homogenized models. In the present work, we are interested in improving the theoretical and numerical analysis of HF elastic waves’ propagation in honeycomb core sandwich panels by a numerical approach based on the Bloch wave theorem, which allows taking into account the periodic characteristics of the honeycomb core. In fact, by decomposing non-periodic wave solutions into their periodic Bloch wave basis modes, numerical models are defined on a basic cell and solved in a efficient way, and provide a better description and so a better understanding of the interaction between HF wave propagation phenomena and the periodic structures. Our numerical approach is developed and validated in the cases of one-dimensional periodic beam structures, of two-dimensional periodic hexagonal and rectangular beam structures and of honeycomb core sandwich plates. By solving the eigenvalue problem of the Bloch wave modes in one primitive cell of the periodic structure for all the wave vectors located in the corresponding first Brillouin zone in the phase space, the dispersion relation between the wave vector and the eigenvalue is calculated. The analysis of the dispersion relation provides important results such as: the frequency bandgaps and the anisotropic and dispersive characteristics of periodic structures, the comparison between the first Bloch wave modes to those of the classical equivalent homogenized models and the existence of the retro-propagating Bloch wave modes with a negative group velocity.

O presente trabalho objetivou desenvolver e implementar, em escala laboratorial, uma rotina experimental com base em Imageamento por Ressonância Magnética Nuclear (IRMN) de modo a verificar seu potencial como metodologia não-destrutiva aplicável à inspeção quali- e quantitativa de água e hidrocarbonetos líquidos aprisionados no interior de células de núcleos-colméia utilizados na confecção de painéis-sanduíche compósitos estruturais de grau aeronáutico. Tentativas foram também realizadas no sentido de se observarem e caracterizarem danos por amassamento de núcleos-colméia, assim como de se detectar a presença de resina polimérica na forma sólida, visando, desta feita, verificar o uso do IRMN na inspeção de componentes previamente reparados e/ou contendo excesso de resina por falha do processo de manufatura. Concluiu-se que IRMN é uma poderosa ferramenta para a detecção e a quantificação de líquidos puros e compostos, ricos em hidrogênio, contidos nas células de núcleos de amostras extraídas de painéis-sanduíche compósitos. O potencial do IRMN na identificação, e, portanto, na discriminação entre os diversos fluidos se mostrou bastante promissor, desde que se empreguem ferramentas de processamento e análise computadorizada de imagens a partir de programas computacionais de reconhecimento de padrões via redes neurais artificiais e/ou sistemas com base em conhecimento. A técnica de IRMN utilizada neste estudo não permitiu a captura de imagens de resina polimérica sólida, nem mesmo quando à esta foram adicionadas cargas de elementos intensificadores de sinais de RMN, tais como ferro e gadolíneo. Danos no núcleo-colméia tão pequenos quanto 1,0 mm de profundidade e 1,8 mm de diâmetro foram clara e inequivocamente imageados e delineados pela técnica IRMN, desde que estivessem permeados por fluido hidrogenado (ex. água). A quantificação de líquidos nos núcleos-colméia por intermédio de ferramentas computacionais simples (processadores e analisadores de imagens) foi muito bem sucedida no caso dos líquidos com relativamente alto ponto de fulgor, pois as massas fluidas se mantiveram constantes por períodos de tempo significativamente longos no interior das células analisadas. / This work intended to develop and implement in laboratorial scale an experimental routine funded in Nuclear Magnetic Resonance Imaging (NMRI) in order to verify its potential as a non-destructive methodology for quali- and quantitative inspection of liquid water and hydrocarbons entrapped in honeycomb core cells utilized to build up aeronautical grade structural composite sandwich panels. Attempts were also carried out to observe and characterize crush damage of honeycomb core, as well as to detect solid polymer resin towards the use of NMRI to assess previously repaired components and/or containing in excess resin amount due to manufacturing process faults. It has been concluded that NMRI is a powerful tool in detecting and quantifying hydrogen-rich pure and compound liquids contained in core cells of composite sandwich samples. The NMRI potential in identifying and, therefore, discriminating several fluids has shown very promising as long as computed image processing and analysis tools are employed from pattern recognition software via artificial neural networks and/or knowledge-based systems. The utilized NMRI technique failed in imaging solid polymer resin, even when the latter was loaded with NMR-signal intensifier elements such as iron and gadolinium. Honeycomb core damages as small as 1.0 mm in depth and 1.8 mm in diameter were clearly and unambiguously imaged and delineated by the NMRI technique since they were permeated with hydrogenated fluid (ex., water). The quantification of liquids in honeycomb cores by means of simple computational tools (image processor and analyzer) was very successful in case of relatively high flash point fluids, insofar as their masses remained constant within the analyzed cells for significantly long periods of time.

Ce travail de thèse porte sur l'étude de l'influence des micro-perforations sur la réponse vibratoire d'une structure cellulaire de type panneau sandwich NIDA (nid d'abeille). Les réflecteurs d'antenne de satellites placés sur les satellites de télécommunication, comme beaucoup d'autres éléments, sont fabriqués avec ce type de matériaux. Lors du décollage du lanceur pour la mise en orbite du satellite, les sollicitations mécaniques appliquées au système sont de nature acoustique et solidienne. La sollicitation acoustique liée au champ acoustique diffus et de très fort niveau présent dans la coiffe du lanceur est la plus importante. Elle joue un rôle important dans le dimensionnement et la conception du réflecteur d'antenne. L'enjeu de la thèse est d'évaluer le potentiel d'un traitement de ce panneau par micro-perforations pour en réduire les vibrations. L'effet des micro-perforations sur la réponse vibratoire du réflecteur d'antenne est double. D'une part, le chargement acoustique que constitue la pression excitatrice est réduit par un mécanisme d'absorption du à la présence des micro-perforations, couplées aux cavités formées par les cellules NIDA du matériau. Cet effet, connu dans la littérature est décrit notamment par le modèle d'impédance acoustique de D.-Y. Maa, couplé à un modèle d'impédance de la cavité NIDA et prenant en compte les rayonnements interne et externe à la micro-perforation. D'autre part, un effet, de nature vibro-acoustique est induit par le couplage entre les vibrations du panneau et les mouvements acoustiques dans les micro-perforations. La modélisation de cet effet, mal décrit dans la littérature constitue un élément original du travail : un modèle discret construit à partir de l'impédance acoustique d'un orifice permet le calcul d'une force d'amortissement élémentaire, puis, après homogénéisation, à une estimation de l'amortissement modal du panneau micro-perforé. Les modélisations proposées pour la réduction de chargement acoustique et de l'amortissement ajouté par micro-perforation montrent que la réponse vibratoire du panneau est faiblement réduite dans la plage de fréquence d'intérêt, ce que confirment plusieurs tests expérimentaux : comparaison de réponse de panneau micro-perforé ou non en chambre réverbérante et en chambre à bruit. La modification de chargement acoustique apportée par la micro-perforation des deux faces du panneau sandwich NIDA est modélisée dans le dernier chapitre et donne lieu à une augmentation de l'effet dans la gamme de fréquence visée. / This thesis work is about the study of the microperforations influence on the vibratory response of a cellular structure as a honeycomb sandwich panel. Satellites' antenna's reflectors placed on telecommunication satellites, as many satellites' elements, are manufactured in this kind of materials. During the launcher take-off for putting satellite into orbit, the mechanical stresses applied to the system are acoustical and vibration borne stress. The acoustic stress, linked to the high level diffuse acoustic field inside the launcher fairing is the most important. It plays a part in the antenna's reflector size and conception. The issue of the thesis is to evaluate the potential of a treatment using microperforations on this panel in order to reduce its vibration. The microperforations effect on the vibration response of the antenna's reflector is double. On one hand, the acoustic loading applied by the exciter pressure is reduced by an absorption mechanism due to the presence of microperforations, coupled to cavities formed by honeycomb cells. This effect, well known in the litterature, is for instance described by the acoustic impedance model developped by D.-Y. Maa, coupled to an impedance model of honeycomb cavity and taking into account the inner and outer radiations of the microperforation. On the other hand, a vibro-acoustical effect is induced by the coupling between panel vibrations and acoustic movements inside microperforations. The modelling of this effect, not well described in the litterature, constitutes an original element of the thesis work: a discrete model constructed using the acoustic impedance of an orifice, allows the computation of an elementary damping force and then leads, after an homogenisation, to an estimation of the modal damping of the microperforated panel. Both modellings proposed for the acoustic loading reduction and the damping added by microperforations, show that the panel vibration response is weakly reduced in the frequency band of interest, which confirms experimental tests like: response comparison of non microperforated and microperforated panels placed in reverberant room and noise chamber. The acoustic loading modification induced by the microperforation of both sides of the honeycomb sandwich panel is modelling in the thesis last chapter and allows an increase of the effect on the frequency band aimed.

The subject of this thesis is the design and assessment of steel sports hall in the town of Krnov. The main structural material is steel S355JR. The ground plan dimensions of the object is 48,0 metres to 36,0 metres, the height of the object is 16,78 metres. There is a sport facilities unit adjusted to the construction . The dimension of such an object is 30,0 metres to 8,0 metres. The support system consists of columns and an arched trussed rafter. The axial distance of cross-links is 8,0 m. The spatial rigidity is ensured by the transverse and longitudinal bracings. The hall is founded on reinforced concrete strip footings. The perimeter and roof cladding consists of sandwich panels. In this work is processed a static calculation of structural elements including connections and drawing documentation.

Lightweight design in rail vehicles has been important for quite some time. Structures have been optimised to fulfill their purpose and cut unnecessary weight to reach allowable axle loads. Classically this is done by using steel, thin-walled structures, throughout the car body, or, alternatively, power-pressed aluminum profiles. The use of composites and sandwich structures has, however, been somewhat limited in the railway industry, especially when considering High-Speed trains. The anticipated weight savings, and reduced complexity of this type of structure are believed to have great potential in the future. This thesis covers the development of methods for structural stiffness design of lightweight, load carrying, sandwich panels for high-speed rail vehicles. Focusis on reducing the weight of the vehicles while simplifying the construction to reduce manufacturing costs and assembly times. Significant work is put into understanding the dynamic influence this type of structure has on the car body. / QC 20110516 / Multifunctional body panels