Com desenvolvimento significativo da indústria aeronáutica, naval e automotiva a partir de 1960, houve a necessidade de diminuir peso, juntamente com a melhora de propriedades como resistência mecânica, controle de vibrações, aumento de resistência a agentes químicos, etc. É neste contexto que surgem os materiais compostos por laminados modernos, utilizados como uma primeira tentativa para projetar novos materiais a partir da combinação em escala macroscópica de duas ou mais matérias simples. Juntamente com o desenvolvimento de materiais de alto desempenho, obtidos por empilhamento de compostos laminados, tornou-se necessário o desenvolvimento de novas teorias capazes de modelar adequadamente as tensões cisalhantes responsáveis pelos acoplamentos interlaminares. Neste sentido as novas teorias aplicadas a modelos macro mecânicos, como, a FSDT (First shear deformation theory) e as teorias cinemáticas cúbicas TSDT (Third shear deformation theory), são as mais adequadas para prescrever o comportamento anisotrópico severo e falhas por delaminação do que a teoria clássica da laminação (TCL) inicialmente desenvolvida para abordar este tipo de problemas. A utilização destas teorias chamadas de alta ordem remonta dos anos oitenta e há inúmeros trabalhos publicados em problemas de placas retangulares e cascas sem restrições cinemáticas ao deslocamento. A partir do exposto este trabalho traz estudos de problemas estáticos de placas circulares e cascas de revolução ortotrópicas obtidas por material composto por laminados. Os modelos numéricos são obtidos utilizando o método de elementos finitos (MEF) com elementos lagrangeanos de alta ordem do tipo ( 0C ) juntamente com as teorias cinemáticas de primeira ordem FSDT (Reissner-Mindlin) e teorias de cinemática cúbica TSDT propostas por Reddy (1984) e Kant et al. (1982). Os estudos apresentados neste trabalho trazem o desempenho das teorias supracitadas na abordagem de problemas como: travamento de cisalhamento e membrana; fenômenos de camada limite e capacidade de aproximar soluções em deslocamento de modelos numéricos tridimensionais. Dentro deste contexto será utilizado para uma das análises um problema motivador que consiste de um reservatório cilíndrico submetido a pressões elevadas. Os resultados apresentados concordam com os exemplos benchmarking trazidos no desenvolvimento do trabalho, representando suas características. / Submitted by cmquadros@ucs.br (cmquadros@ucs.br) on 2018-02-16T14:16:35Z No. of bitstreams: 1 Dissertacao Daniel Alves de Andrade.pdf: 3540400 bytes, checksum: fd548646ca4f58220c72ff64c34f117d (MD5) / Made available in DSpace on 2018-02-16T14:16:35Z (GMT). No. of bitstreams: 1 Dissertacao Daniel Alves de Andrade.pdf: 3540400 bytes, checksum: fd548646ca4f58220c72ff64c34f117d (MD5) Previous issue date: 2018-02-16 / With significant development of the aeronautical, naval and automotive industry from 1960, there was a need to reduce weight, along with the improvement of properties such as mechanical resistance, vibration control, increased resistance to chemical agents, etc. It is in this context that the materials composed of modern laminates appear, used as a first attempt to design new materials from the combination on a macroscopic scale of two or more simple materials. Along with the development of high performance materials obtained by stacking laminated compounds, it became necessary to develop new theories capable of adequately modeling the shear stresses responsible for interlaminar couplings. In this sense, the new theories applied to macro mechanical models, such as the First Shear Deformation Theory (FSDT) and the TSDT (Third Shear Deformation Theory) cubic kinetic theories, are the most appropriate to prescribe severe anisotropic behavior and delamination failures The classical lamination theory (TCL) initially developed to address this type of problem. The use of these so-called high-order theories dates back to the 1980s and there are numerous published works on problems of rectangular plates and shells without kinematic restrictions on displacement. From the above, this work presents studies of static problems of circular plates and orthotropic shells obtained by material composed of laminates. Numerical models are obtained using the Finite Element Method (MEF) with high-order lagrangean elements of type ( 0 C ) along with the first-order kinematic theories FSDT (Reissner-Mindlin) and TSDT cubic kinematics theories proposed by Reddy (1984) and Kant et al. (1982). The studies presented in this work bring the performance of the aforementioned theories in the approach of problems such as: shear locking and membrane; Boundary layer phenomena and the ability to approximate solutions in displacement of three-dimensional numerical models. Within this context, a motivating problem consisting of a cylindrical reservoir subjected to high pressures will be used for one of the analyzes. The presented results agree with the benchmarking examples brought in the development of the work, representing its characteristics

Submitted by DANY ARNOLDO HERNÁNDEZ BALTODANO (danyhdzb@hotmail.com) on 2017-04-18T19:13:44Z No. of bitstreams: 1 Thesis Dany Hernandez.pdf: 2171039 bytes, checksum: 8f2efded7710ccbd5aed9274952116a7 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-04-18T20:27:33Z (GMT) No. of bitstreams: 1 hernandezbaltodano_da_me_bauru.pdf: 2171039 bytes, checksum: 8f2efded7710ccbd5aed9274952116a7 (MD5) / Made available in DSpace on 2017-04-18T20:27:33Z (GMT). No. of bitstreams: 1 hernandezbaltodano_da_me_bauru.pdf: 2171039 bytes, checksum: 8f2efded7710ccbd5aed9274952116a7 (MD5) Previous issue date: 2017-03-15 / Outra / Considerando as amplas aplicações de materiais compósitos para melhorar estruturas de obras em engenharia, é importante estudar a dependência do comportamento do material em função da velocidade de deformação aplicada aos materiais compósitos e aos epóxis adesivos. Propriedades mecânicas do material Sikacarbodur S512 e materiais adesivos mostram comportamentos diferentes quando analisados utilizando diferentes razões de deformação. Os resultados obtidos mostram que o Sikacarbodur S512 não é um material dúctil devido à ausência de capacidade de experimentar deformações inelásticas porque o domínio elástico domina seu comportamento mecânico. Os aditivos epóxis não têm domínio plástico considerável, e o intervalo visco elástico domina o seu comportamento mecânico sob forças de tração. As análises de microscopia eletrônica de varredura (MEV) das amostras de Sikacarbodur S512 mostram que o comportamento de fratura acontece na zona de interface (zona de contato entre as fibras e a resina) que é afetada pela concentração de tensões e propagações de trincas. As análises de MEV antes e depois dos testes de tração das amostras de Sikadur 30 e Sikadur 330 mostram que ambos os materiais possuem uma fase contínua e uma fase granular. Nas duas resinas as ligações covalentes são quebradas durante os testes embora o Sikadur 30 tem o comportamento mais crítico. O Sikadur 330 tem melhor comportamento mecânico do que o sikadur 30 e esse melhor comportamento é mais bem entendido quando compara-se suas deformações de ruptura em tensão e suas capacidades para absorver energia. / Considering the wide application range of composite materials for retrofitting civil engineering structures, it is found important to study the strain rate dependent behavior of both composite materials and some structural adhesive epoxies. Mechanical properties of Sikacarbodur S512 and adhesives bonding materials show different behavior when analyzed at different strain rates. Moreover, it was found that Sikacarbodur S512 is not a ductile material since it cannot sustain inelastic deformation because an elastic range governs its mechanical behavior. Epoxies adhesive do not have a significant plastic range; a viscoelastic range governs their main mechanical behavior under tensile loads. Sikacarbodur S512 analyses using scanning electron microscopy (SEM) shows that the fracture behavior is addressed by the interphase zone (contact zone between fiber and resin) which is affected by tensile stress concentration and cracks propagations. SEM analyses before and after tensile tests of both Sikadur 30 and Sikadur 330 shows that they have a continuous phase and a granular phase. In both resins, covalent bonds are broken, however sikadur 30 shows the most critical behavior. Sikadur 330 has better mechanical behavior under uniaxial tensile test than sikadur 30, and this better behavior is realized when their tensile strain to break and absorbed energy capacity are compared.

Submitted by Adrielly Hokama Razzini null (adrielly91100@aluno.feis.unesp.br) on 2017-06-08T18:25:27Z No. of bitstreams: 1 Razzini_AH_me_iha.pdf: 17122324 bytes, checksum: 018bdb7d8435fdfe61da7f226c07a068 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-06-13T13:40:20Z (GMT) No. of bitstreams: 1 razzini_ah_me_ilha.pdf: 17122324 bytes, checksum: 018bdb7d8435fdfe61da7f226c07a068 (MD5) / Made available in DSpace on 2017-06-13T13:40:20Z (GMT). No. of bitstreams: 1 razzini_ah_me_ilha.pdf: 17122324 bytes, checksum: 018bdb7d8435fdfe61da7f226c07a068 (MD5) Previous issue date: 2017-05-08 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Materiais compósitos têm sido cada vez mais utilizados na indústria aeronáutica, devido a inúmeras vantagens que serão apresentadas nesse trabalho. Entretanto, impactos podem comprometer significativamente a estrutura. Tais impactos podem ocorrer a “baixa velocidade”, através de ferramentas derrubadas e contato com veículos/equipe de manutenção, e também a “alta velocidade”, como colisões com aves, raios elétricos, detritos de pneus ou pequenas pedras na pista. Conhecer a ocorrência e localização dos mesmos, assim como o progresso de danos subsequentes, permite realizar inspeções mais focadas e otimizar o custo e eficiência de manutenção. Este trabalho propõe a utilização de transdutores piezelétricos em formato de rosetas piezelétricas para localização de impacto em estruturas de materiais compósitos. As rosetas são compostas de transdutores retangulares de Macro-Fiber Composite (MFC), que apresentam uma resposta altamente diretiva para ondas ultrassonoras, o que foi explorado para determinar a localização da onda emitida, independente da velocidade de propagação da onda na estrutura. A acuracidade do mé- todo foi demonstrada experimentalmente em uma placa de fibra de carbono/ resina epóxi de dimensões 1060 ×1100×2mm, formada de 13 camadas plain-weave com duas rosetas piezelétricas coladas à superfície via adesivo cianoacrilato. Os impactos foram conduzidos utilizando um pequeno martelo com ponta metálica, simulando impactos realísticos sofridos por uma estrutura em serviço. O ponto de impacto foi determinado pelo método proposto e comparado com a localização real do impacto. / The usage of composite materials has been experiencing a continuous growth in aeronautic industry, due to countless advantages. However, impacts can significantly compromise the structure. These impacts can occur at "low velocity", by tools dropped, contact with maintenance vehicles or personnel and also at "high velocity", by bird/hail strikes, runaway debris from tires os lightnings. Knowing the occurrence and location of the impacts, as well as the progression of any subsequent damage, allows performing focused follow-up inspections, which can optimize maintenance cost and effectiveness. This work proposes using piezoelectric transducers arranged as rosettes to locate impacts on composite materials structures. The rosettes are comprised of rectangular transducers of Macro-Fiber Composite (MFC), which exhibit an highly directive response to ultrasonic waves that will were explored to determine the source of the incoming wave, regardless of the wave velocity. The accuracy of this method is experimentally demonstrated on a 1060x1100x2mm carbon/epoxy plate, formed by 13 plain-weave layers with two piezoelectric rosettes bounded to the surface via cyanoacrylate. The impacts were carried out using a small hammer with hardened steel tip, simulating realistic impacts suffered by an in-service structure. The impact point is determined by the proposed method and compared with the actual location of impact. / CNPq: 131152/2015-7

Orientador: Edson Cocchieri Botelho / Coorientadora: Michelle Leali Costa / Banca: Luiz Cláudio Pardini / Banca: Rogério Lago Mazur / Resumo: O consumo de eletricidade tem aumentado de forma significativa nas últimas décadas. Isso, aliado com a dificuldade em construir novas linhas de transmissão, principalmente devido aos requisitos ambientais estabelecidos pelo Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis (IBAMA), trouxe um grande desafio no atendimento da crescente demanda por eletricidade. Os cabos condutores de alumínio com alma de compósito (ACCC) foram designados para ter alta resistência à tração, baixo coeficiente de expansão térmica e baixa flecha entre as torres. No entanto, o uso desses novos materiais pode criar uma série de problemas com relação à sua aplicabilidade que precisa ser avaliada. Os polímeros estão sujeitos à degradação por exposição a altas temperaturas, umidade e radiação ultravioleta, entre outros. Dentre os polímeros termorrígidos atualmente disponíveis, a resina fenol formaldeído é uma das mais comuns no mercado, com excelente desempenho em altas temperaturas, resistência à chama e isolação mecânica. Dessa forma, o uso de compósitos de resina fenol formaldeído reforçados com fibras de carbono podem ser excelentes substitutos para os aços tradicionais que vêm sendo atualmente utilizados como núcleos de cabos de transmissão, reduzindo a flecha entre as torres e melhorando a eficiência de transmissão de energia elétrica. Nesse contexto, este trabalho avaliou a aplicabilidade do sistema pultrudado de resina fenol formaldeído reforçada com fibras de carbono em núcleo de cabos condutores em linhas de transmissão. Os resultados mostraram que a temperatura de início de decomposição é de 363 °C e a temperatura de transição vítrea é de 165 °C. Esses limites de temperatura são suficientes para aplicação do compósito como núcleo de cabos de transmissão, dada a demanda ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Consumption of electricity has been increasing significantly in the last decades and the difficulty in building new transmission lines brought a great challenge to supply electricity, mainly due the environmental requirements established by the Brazilian Institute of Natural and renewable resources (IBAMA) and the raising in demand for electricity. The Aluminum Conductor Composite Core cables (ACCC) have been developed due to their high tensile strength, low thermal expansion coefficient and low sag between the transmission towers. Nevertheless, the use of new materials in transmission lines may bring a series of problems in relation to its employment, which needs to be assessed. The use transmission cables with composite core may promotes degradation of polymeric matrix due high temperatures expositions, humidity, ultraviolet radiation, and so forth. The phenol-formaldehyde resin presents excellent performance in high temperatures, flame resistance and mechanical isolation. Composites with carbon fiber and phenol-formaldehyde matrix might be excellent replacements to the traditional steel applied in conductor cables cores. This study evaluated the suitability of carbon fiber-reinforced polymer with phenol-formaldehyde matrix to transmission lines. The results showed that thermal decomposition of material initiates in 363 ºC and the glass transition temperature is 165 ºC, which is sufficient to be applied in transmission cables with nowadays demand. The mechanical results were favorable: all samples showed higher ultimate strength superior to the specified to ASCR transmission cables. The specific modulus of is 26.3 m2/s2 for steel and 102.3 m2/s2 for the pultruded system, which indicates a significant advantage in replacement of the traditional steel for the pultruded system, although it is necessary to apply a coating in the composite to avoid decomposition and galvanic corrosion / Mestre

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2010. / Hybrid polymeric composites (HPC) are widely used for the design of aerospace, automobile and civil engineering structures. One of the major challenges posed by these materials and structures is their brittle nature. When subjected to impact and dynamic loads, the polymeric composite structures undergo micro cracking. The cracks coalesce, propagate and can lead to catastrophic failure of the material and structures. In this thesis, an intelligent hybrid polymeric composite (IHPC) beam with healing ability was developed and tested. The IHPC beam developed consisted of a 3% prestrained 1mm diameter Ni-Ti shape memory alloy (SMA) wire actuator embedded in the polymeric host matrix. The function of the embedded Ni-Ti shape memory alloy was to enhance intelligence and healing ability to the IHPC beam. Upon electric current resistance heating, the Ni-Ti SMA actuator responds by contracting as a result of detwinned martensite → austenite phase transformation. Contraction of the SMA in the IHPC beam was utilized to stiffen and enhance healing by retarding crack growth and recovery of the strain induced in the loaded IHPC beam. This can result to increase of the flexural stiffness EI (defined as the product of the Young’s Modulus E of the material and the moment of inertia I of the geometry of the beam) and mode I fracture stress intensity factor KIC of the IHPC beam. One (1) mm diameter Ni-Ti SMA wire was used in the experimental work in this thesis. The wire was cut into 35 pieces, 200 mm long each. Ni-Ti SMA wires were heated in the furnace to a temperature of 250ºC for ten (10) hours then were left to cool in the ambient air. The heat treatment was aimed to release any residual stress and to stabilize the austenite start (AS) and austenite finish (Af) transformation temperatures of the Ni-Ti SMA. After heat treatment, the Ni-Ti SMA wires were prestrained by 3% (based on a gauge length of 150mm) on a tensile testing machine. Prestraining of the Ni-Ti SMA wires was aimed to induce detwinned martensite volume fraction in them hence increasing the transformation strain and recovery force of the Ni-Ti SMA actuator. Intelligent hybrid polymeric composite (IHPC) beams and polymeric virgin (PV) beams, all of dimensions 150mmx25mmx10mm were manufactured by casting 60D polyurethane thermosetting epoxy resin in a silicon mould. transformation strain and recovery force of the Ni-Ti SMA actuator.

In many engineering applications, it is desirable to know the behaviour of structures and systems under loading conditions. One reason is to help optimize the design and prevent damage and failure which might occur during in service and operation. Damage represents a serious problem which can cause catastrophic failure of structures, machines and systems. Therefore for safe operation, efficient and reliable methods for inspection and monitoring of damage are required. Different methods for health monitoring of structures such as non destructive testing (NDT) and strain gauges are widely used. These methods have proven to be efficient in terms of resolution and response. However, some disadvantages associated with them include the vicinity of the area under inspection which must be well known, equipment to acquire the necessary information is expensive and in many cases high skills are required for operation. On the other hand, advances in materials science and MEMS systems has promoted the use of new materials with piezoelectric properties. This include mainly polymeric and ceramic materials which after processed can be used for structural health monitoring. These materials offer a number of advantages such as lightweight, sensitivity, toughness, durability, and low cost. The present research work investigates the feasibility of using a polymeric material, Polyvinylidene Fluoride (PVDF) as a sensor for deformation and defect detection in structures. The sensors are embedded in composite cantilevered type beams to detect defects at distinct locations along the beam’s length. The defect detection method proposed is based on experimental tests and Finite Element simulations. Experimental tests on defect free and beams with manufactured internal flaws were conducted. Numerical (FEM) simulations of defect free and flawed beam models containing sections of reduced elastic modulus to represent the damage were conducted using ANSYS software. The experimental tests have been used for the validation of the numerical solution. Results have shown that the defect location changes the stiffness and indeed the frequency of vibration. For flaws near the fixed end of the beams, lower frequencies are obtained as compared to flaws away from the fixed end. PVDF sensors were used to acquire the natural frequencies of the beams for the first mode of vibration. Good agreement was verified between experimental and numerical simulation results. The work has demonstrated that PVDF film sensors can be used as possible candidates for defect detection. The analysis of the behaviour embedded PVDF sensors near the fixed end of cantilever beams, represents an initial and important step towards the application of measuring static and dynamic behaviour of structures as part of a health monitoring process.

Orientador: Edson Cocchieri Botelho / Coorientador: Luis Rogerio de Oliveira Hein / Banca: Mirabel Cerqueira Rezende / Banca: José Maria Fernandes Marlet / Resumo: O desenvolvimento da tecnologia dos compósitos poliméricos avançados tem como uma de suas funções a união de materiais que combinem características como: elevada resistência mecânica e rigidez aliadas à baixa massa específica. Um dos problemas principais de utilização de compósitos poliméricos em aplicações estruturais consiste em sua união efetiva para a integração de componentes. Neste sentido, estudos recentes mostram que a técnica de soldagem por resistência elétrica é um dos processos mais promissores para união de compósitos, por ser um método rápido e por necessitar de pouca preparação de superfície. Este trabalho tem como objetivo avaliar os melhores parâmetros de soldagem por resistência elétrica para laminados de PPS (poli(sulfeto de fenileno)) reforçados com fibras contínuas (vidro e carbono) e híbrido com aplicações aeronáuticas. Para esta finalidade, são avaliados os parâmetros mais adequados quanto ao tempo, corrente elétrica e pressão a serem utilizados no processo de soldagem. A caracterização dos materiais soldados é realizada por meio de ensaios mecânicos (lap shear), análises térmicas (DMA e TMA) e análise morfológica (microscopias óptica e eletrônica de varredura). Com a utilização do planejamento de experimentos, foi encontrado o melhor valor da variável resposta para cada laminado estudado, e desse modo a melhor combinação dos parâmetros de soldagem, sendo para o PPS/fibras de carbono (37,0A, 3,0MPa, 50,0s), para o PPS/fibras de vidro (32,0A, 1,85MPa, 175,0s) e para o laminado híbrido (38,5ª, 3,0MPa, 50,0s). Com relação à temperatura de transição vítrea dos compósitos, esta não foi afetada significativamente pelo processo de soldagem, viabilizando o método de soldagem estudado para a integração de componentes aeronáuticos / Abstract: The technology improvement of advanced polymeric composites has as one of its functions the junction of materials that present unique properties such as high strength and stiffness allied with low density. One of the major problems of using polymer composites in structural application consists in the effective joint for integrating components. In this behalf, recent studies demonstrate that the technique of electrical resistance welding is one of the most promising for bonding composites, as a rapid method because it does not require much surface preparation. This work aims to evaluate the more appropriate parameters of electrical resistance welding for PPS (poly (phenylene sulfide)) laminates reinforced with fabric continuous fibers (glass and carbon) designed for aeronautical applications. For this purpose, the parameters will be evaluated leading into account time, electric current and pressure to be used in the welding process. The welded material characterization will be accomplished through mechanical testing (lap shear), thermal (DMA and TMA) and morphological analysis (using optical and scanning electron microscopes). Through the procedure of design of experiments, it was found the best value of the response variable for each laminate studied here, and thus the best combination of welding parameters, being for the PPS/carbon fibers (37.0 A, 3.0 MPa, 50.0s) for the PPS/glass fibers (32.0 A, 1.85 MPa, 175.0 s) and the hybrid laminate (38.5 A, 3.0 MPa, 50.0 s). In relation to the glass transition temperature of these composites, this was not significantly affected by the welding process, enabling the welding method for studying the integration of aeronautical components / Mestre

Made available in DSpace on 2014-06-11T19:30:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-10-19Bitstream added on 2014-06-13T19:39:42Z : No. of bitstreams: 1 muradorfilho_a_me_bauru.pdf: 1523059 bytes, checksum: b7492203fa42c21510e2cb2a14614f56 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O campo dos nanomateriais tem se expandido enormemente nas últimas décadas principalmente devido às suas propriedades especiais. As experiências descritas na literatura em grande gama de aplicações mostram propriedades elétricas, magnéticas, ópticas e outras, extremamente aperfeiçoadas com relação aos sisstemas macroscópios. A ciência e tecnologia trabalham atualmente com inúmeras técnicas químicas para a obtenção de óxidos e dentre elas destaca-se o Método Poliol por ser vantajoso e adequado na preparação de nanopartículas com variadas morfologias, dimensões e crisalinidade. Entretanto, poucos estudos foram realizados sobre a síntese e a caracterização de compósitos com o propósito de investigar as propriedades resultantes da possível sinergia obtida a partir da interação entre dois óxidos nanoestruturados. Este trabalho teve como objetivo a síntese e a caracterização de compósito nanoestruturado formado de dois óxidos multifuncionais: o óxido de zinco e o dióxido de titânio. Para a síntese foram utilizados o acetato de zinco dihidratado e o isopropóxido de titânio para a obtenção do ZnO e do TiO2, respectivamente. o compósito foi obtido pelo Método Poliol a partir da interrupção momentânea da síntese dos óxidos isolados seguido da mistura das soluções. O compósito, assim como os óxidos sintetizados isoladamente, foram caracterizados po9r difração de raios X (DRX), análise térmicas (TG/DTA), medidas de adsorção de gás nitrogênio (BET), microscopia eletrônica de varredura (MEV), espectroscopia de adsorção de luz na região do ultravioleta, visível e infravermelho, espectroscopia Raman. O compósito formado pelo Método Poliol apresentou o ZnO na forma aglomerado, porém nanoestruturado, e o TiO2 após tratamento térmico de 400º C. Foi verificada ainda a presença de resíduos orgânicos nos materiais como... (Resumo completo, clicar acesso / The field of nanomaterials has expanded greatly in recent decades mainly due to its special propoerties. The experiments described in the literature in a wide variety of applications show electrical properties, magnetic, optical and others, extremely improvement properties with respect to macroscopic systems. Science a technology are currently working with numerous chemical techniques to achieve oxides and them stands out the Polyol Method to be advantageous and appropriate in the preparation of nanoparticles with various morphologies, size and crystallinity. However, few studies have been done on the synthesis and characterization of composites in order to investigate the resultants properties from possible synergy obtained from the interaction between two nanoestructured oxides. This work aimed to the synthesis and characterization nanostructured composites formed by two multifunctional oxides, zinc oxide and titanium dioxide. For the synthesis were used zinc acetate dihydrate and titanium isopropoxide to obtain the ZnO and TiO2, respectively. The composite was obtained by Polyol from the interruption of the synthesis of single oxides followed by mixing the solutions. The composite, as weell as oxides separately synthesized, were characterized by X-ray diffraction (XRD), thermal analysis (TG/DTA), meassurements of nitrogen gas adsorption (BET), scanning electron microscopy (SEM), YV-VIS and IR absorption spectroscopy and Raman spectroscopy. The composite obtained by the Polyol Method presented ZnO as agglomerate, however nanostructured, and TiO2 after heat treatment of 400ºC. It was also verified the presence of organic waste in the materials as synthesized and titanium glycolate as an intermediate in the reaction of titanium dioxide. A comparison of optical behavior, as synthesized composite formed by ZnO and titanium... (Complete abstract click electronic access below)

abstract: Although high performance, light-weight composites are increasingly being used in applications ranging from aircraft, rotorcraft, weapon systems and ground vehicles, the assurance of structural reliability remains a critical issue. In composites, damage is absorbed through various fracture processes, including fiber failure, matrix cracking and delamination. An important element in achieving reliable composite systems is a strong capability of assessing and inspecting physical damage of critical structural components. Installation of a robust Structural Health Monitoring (SHM) system would be very valuable in detecting the onset of composite failure. A number of major issues still require serious attention in connection with the research and development aspects of sensor-integrated reliable SHM systems for composite structures. In particular, the sensitivity of currently available sensor systems does not allow detection of micro level damage; this limits the capability of data driven SHM systems. As a fundamental layer in SHM, modeling can provide in-depth information on material and structural behavior for sensing and detection, as well as data for learning algorithms. This dissertation focusses on the development of a multiscale analysis framework, which is used to detect various forms of damage in complex composite structures. A generalized method of cells based micromechanics analysis, as implemented in NASA's MAC/GMC code, is used for the micro-level analysis. First, a baseline study of MAC/GMC is performed to determine the governing failure theories that best capture the damage progression. The deficiencies associated with various layups and loading conditions are addressed. In most micromechanics analysis, a representative unit cell (RUC) with a common fiber packing arrangement is used. The effect of variation in this arrangement within the RUC has been studied and results indicate this variation influences the macro-scale effective material properties and failure stresses. The developed model has been used to simulate impact damage in a composite beam and an airfoil structure. The model data was verified through active interrogation using piezoelectric sensors. The multiscale model was further extended to develop a coupled damage and wave attenuation model, which was used to study different damage states such as fiber-matrix debonding in composite structures with surface bonded piezoelectric sensors. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2012

Cette thèse s'inscrit dans le cadre des méthodes de couplage non-intrusives qui permettent de concilier deux types de logiciels : logiciels commerciaux généralistes et logiciels dédiés. L'objectif est d'appliquer un tel couplage pour le traitement des assemblages de plaques stratifiées.En effet, le comportement aux environs des zones critiques de ces matériaux composites nécessite une prise en compte fine (3D) des phénomènes en jeu alors que la pratique industrielle consiste à représenter les structures par des modèles simplifiés de plaques ou de coques.La méthode non-intrusive développée ici permet ainsi de « patcher » virtuellement le modèle plaque par des modèles 3D locaux, de coupler fortement le modèle global avec les patchs, sans modifier les maillages ni les modèles.Diverses stratégies de raccords sont envisagées, ainsi que des améliorations à la technique de couplage. / This thesis is part of the nonintrusive coupling methods framework which allow to merge to kind of software : general commercial software and dedicated software.The aim is to apply such coupling for the analysis of assembly of laminated plates.In fact, the behavior in composite material around critical zones requires to take in account complex phenomena (in 3D), whereas the industrial way of work is to simplify the structure with plate or shell model in order to handle very large structures.The nonintrusive coupling method developed here allow to virtually apply a 3D patch to the plate model in order to enriched the global description without any modification of the global meshes, models, or solver.Various methods of coupling and improvement to the classical nonintrusive coupling are proposed.