A necessidade de recuperação e reforço em estruturas de madeira, concreto e aço exigiu da construção civil uma procura por métodos mais eficientes que pudessem cumprir esse papel. Com este objetivo vários estudos estão sendo realizados utilizando fibras reforçadas com polímeros (FRP). Dentre estas fibras, as que vêm apresentando melhores resultados como reforço para peças estruturais de madeiras são as fibras de carbono e as fibras de vidro. Dentro deste escopo, este trabalho tem como objetivo estudar o comportamento estrutural de vigas de madeira de espécies nacionais reforçadas com fibras de carbono e com fibras de vidro, verificando a eficiência deste reforço e adequando modelos de cálculo para avaliação da resistência e da rigidez das vigas reforçadas, e também verificar a eficiência de uma formulação de adesivos à base de mamona e do adesivo Cascophen, para fixação das respectivas fibras na madeira, em substituição ao adesivo epóxi, normalmente utilizado. Foram efetuados ensaios de vigas de madeira reforçadas com polímeros, em modelo reduzido, e em protótipos, para diversas configurações de geometria e quantidade de fibras utilizadas. Os resultados obtidos indicam uma boa concordância entre os modelos teóricos para avaliar a resistência e a rigidez das vigas reforçadas, e os resultados experimentais, e a eficiência do reforço. Também foram conduzidos ensaios de tração em corpos-de-prova de fibras laminado com os adesivos, caracterizando a sua resistência e elasticidade e comparando o comportamento dos adesivos estudados. Os resultados indicaram o melhor comportamento do adesivo epóxi. / The necessity of rehabilitation and reinforcement in wood structures, concrete and steel demanded a search for more efficient methods that could to carry this paper. With this objectives several studies are using fibers reinforced polymers (FRP). These fibers which presenting better results in structural reinforcement for structural pieces of wood are the fibers of carbon and the glass fibers. This work has as objective studies the structural behavior of wood beams of national species reinforced with carbon fibers and with glass fibers, verifying the efficiency of this reinforcement and adapting calculation models for evaluation of the strength and stiffness of the reinforced beams, and also to verify the efficiency of a formulation of adhesives to the castor oil and of the adhesive Cascophen, for fixation of the respective fibers in the wood, in substitution the adhesive epoxy, usually used. Experimental work was made with wood beams reinforced with polymeric, in reduced model, and in prototypes, for several geometry configurations and amount of used fibers. The obtained results indicate a good agreement among the theoretical models to evaluate the strength and stiffness of the reinforced beams, and the experimental results, and the efficiency of the reinforcement. Traction rehearsals were also led in body-of-proof of fibers laminated with the adhesives, characterizing your strength and elasticity and comparing the behavior of the studied adhesives. The results indicated the best behavior of the adhesive epoxy.

While there is a substantial amount of information regarding the electrochemical behavior of fuel cells and there components little to no information is available regarding the mechanical properties of fuel cell materials in stack setups. This set of experiments was set up to test mechanical properties of gas diffusion layer and bipolar plate materials in a one cell setup. Samples were clamped to specified pressures and deformation properties were observed and measured. Measurements were taken of impingements of the gas diffusion layers into the gas flow channels. A limit for compression of cell configurations was found to be approximately 300psi. Upon reaching the compression limit bipolar plates collapse and materials between plates show signs of breakage. Under compression diffusion media showed impingement into the gas flow channels as well as substantial compression of the three layer stack.

Submitted by MARCELO MAJEWSKI null (marcelomajewski@bol.com.br) on 2017-03-20T20:40:04Z No. of bitstreams: 1 Marcelo [v13-03-2017vFINAL].pdf: 3845690 bytes, checksum: c51d5240a6bf0ae87ee09592959712cc (MD5) / Rejected by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br), reason: Solicitamos que realize uma nova submissão seguindo as orientações abaixo: No campo “Versão a ser disponibilizada online imediatamente” foi informado que seria disponibilizado o texto completo porém no campo “Data para a disponibilização do texto completo” foi informado que o texto completo deverá ser disponibilizado apenas 6 meses após a defesa. Caso opte pela disponibilização do texto completo apenas 6 meses após a defesa selecione no campo “Versão a ser disponibilizada online imediatamente” a opção “Texto parcial”. 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Agradecemos a compreensão. on 2017-03-22T13:50:06Z (GMT) / Submitted by MARCELO MAJEWSKI null (marcelomajewski@bol.com.br) on 2017-03-23T01:46:44Z No. of bitstreams: 1 Marcelo [v13-03-2017vFINAL].pdf: 3845690 bytes, checksum: c51d5240a6bf0ae87ee09592959712cc (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-03-23T16:39:23Z (GMT) No. of bitstreams: 1 majewski_m_me_guara.pdf: 3845690 bytes, checksum: c51d5240a6bf0ae87ee09592959712cc (MD5) / Made available in DSpace on 2017-03-23T16:39:23Z (GMT). No. of bitstreams: 1 majewski_m_me_guara.pdf: 3845690 bytes, checksum: c51d5240a6bf0ae87ee09592959712cc (MD5) Previous issue date: 2017-02-06 / O aumento do uso de compósitos estruturais tem levado a uma preocupação constante com a confiabilidade destes materiais. Em particular, o processo de cura das resinas na fabricação é citado como um dos problemas mais significativos no processamento de compósitos estruturais. Assim, para que essa classe de materiais possa ser economicamente viável e atender às exigências dos padrões de qualidade do setor aeronáutico, tecnologias de processamento automatizado e novas formas de matéria-prima estão sendo desenvolvidas e implantadas na fabricação. Desta forma, o objetivo da presente pesquisa foi estudar a influência das propriedades térmicas dos materiais de moldes, utilizados no processamento de compósitos via RTM, nas propriedades finais dos laminados. Foram processadas três placas de compósitos com reforço não dobrável (NCF-non-crimp fabric) biaxial [+45°/-45°] via RTM: em molde de aço 1020, laminado 1; e em liga de alumínio 5052-F, laminados 2 e 3. Para verificar a influência dos materiais dos moldes nas propriedades finais, foram analisadas a tenacidade à fratura interlaminar em modo I e investigação das superfícies de fratura pelo Microscópio Eletronico de Varredura (MEV). O comportamento térmico estudado via análise térmica dinâmico-mecânica (DMA), que avaliou as diferenças no grau de cura dos laminados 1, 2 e 3 com a análise da Tg. Nos processamentos, evidenciou-se que o molde de alumínio apresentou maior controle e estabilidade térmica, enquanto que o molde de aço apresentou maior estabilidade dimensional. Pelo modo I, observou-se maior energia de iniciação de trinca (GIc) para o laminado 1 em relação aos laminados 2 e 3. Nas imagens de fratura no MEV constatou-se a influência da fração volumétrica de fibras e a quantidade de fiber bridging. No laminado 1, observou-se mechas de fibra sobre a costura e fibras rompidas originadas do fiber bridging, que foram responsáveis pela energia adicional exigida na propagação da trinca (GI). No laminado 2 observou-se acúmulo de resina e menor quantidade de fiber bridging, consequentemente, valores intermediários de GI, já no laminado 3 notou-se a ausência de fiber bridging, o que proporcionou a propagação da trinca no domínio da matriz, apresentando o menor valor GI entre os laminados. Nos dois últimos laminados a diminuição de GIc foi atribuida ao grau de cura da resina. Na qual observou-se as transições vítreas (Tg) próximas entre os laminados 1 e 3, e para o laminado 2 a Tg foi inferior, o que demonstrou efetiva correlação entre as características térmicas dos moldes com as propriedades físicas e mecânicas finais dos laminados compósitos obtidos via RTM. / The increase use of structural composites has led to a constant concern on the reliability of these materials. In particular, curing process of resins during manufacturing are cited as one of the most significant problems in the structural composites. Therefore, in order to this class of materials can be economically viable and meet the requirements of quality in the aeronautic industry standards, automated processing technologies and new materials have been developed and implemented in manufacturing sector. Thus, this research aimed to investigate the influence of thermal properties of the mold, which was used in the processing of composites via RTM, on the final properties of the laminates. Three composite plates comprised with NCF (non-crimp fabric) reinforcement, which has biaxial [+45°/-45°] configuration, and epoxy matrix. Two molds were employed for this investigation: steel 1020, for laminate 1, and aluminum alloy 5052-F, for laminates 2 and 3, all laminates with the same fiber stacking sequence. The influence of the materials of the molds in the final properties were verified with interlaminar fracture toughness in mode I (GIc), and their images of the fractured surfaces investigated by Scanning Electron Microscope (SEM). The thermal analysis conducted with Dynamic Mechanical Thermal Analysis (DMA), which evaluated the differences in the degree of cure of laminate 1, 2 and 3 by vitreous temperature transitions (Tg). It was evidenced that the aluminium mold showed better thermal conductivity and temperature stability, while the steel mold showed higher dimensional stability. Mode I showed higher energy crack initiation (GIc) for laminate 1 than for laminates 2 and 3. In the SEM images, it was verified a change in fiber volume fraction and the amount of fiber bridging. Laminate 1 showed fiber tows on the stitch regions and ruptured fibers originated from the fiber bridging, which were responsible for the additional energy of propagation (GI). Laminate 2 showed resin accumulation and less loose fibers, and consequently, intermediate values of GI, Laminate 3 no fiber bridging occured, which showed the propagation of the crack in the matrix domain, presenting the lowest GI value between the laminates. In laminates 2 and 3, the decrease in GIc can be attributed to the degree of cure, in which correlated to the glass transitions (Tg) results. Overall, the tests demonstrated a good correlation between the thermal characteristics of the molds with the final physical and mechanical properties of the laminates obtained via RTM.

Ce travail de thèse consiste à caractériser l’endommagement subi par une mèche de carbone au cours des procédés de transformation textile, et plus particulièrement au cours du tissage des préformes pour les matériaux composites. Un protocole de caractérisation mécanique sur mèche sèche, ainsi qu’une méthode non-destructive d’analyse d’images, ont été mis au point pour quantifier cet endommagement. / This aim of this work is to characterize the damage suffered by a carbon tow in textile processing methods, and more particularly during preforms weaving for composites materials. A mechanical characterization protocol on dry tow tensile test and a non-destructive method of image analysis, have been developed to quantify this damage.

Postes tubulares pré-moldados de concreto armado foram instalados no Brasil pelas empresas de telefonia móvel ao implantar ou ampliar áreas de cobertura do sistema a partir de 1996. A grande maioria desses postes, da ordem de duas mil unidades, foi fabricada por uma mesma empresa, pelo processo de centrifugação. As alturas desses postes variam de 20 a 60 m. Alguns desses postes colapsaram depois de três ou quatro anos de utilização, tendose conhecimento de quatro deles, nos estados de São Paulo, Espírito Santo, Rio de Janeiro e Rio Grande do Sul. Todos os colapsos conhecidos desses postes, ocorreram com ruptura na emenda entre o módulo tubular 1, engastado ao solo, e o seguinte módulo. Após extenso trabalho de investigação e diagnóstico do problema, levado a cabo em 40 postes demolidos e estocados na cidade de Santana do Parnaíba/SP, ficou demonstrado que o problema patológico mais relevante encontrado era a emenda entre módulos. O diagnóstico apontou fadiga da emenda por traspasse devido ao excesso de armadura, com taxas variando de 8,5% a 18,2%. Essas taxas efetivas de armadura superaram em muito o limite máximo permitido por norma e recomendável do ponto de vista de transmissão de esforços nessa região. O objetivo principal desta tese é demonstrar que é possível aproveitar esses postes, sem necessidade de sua substituição, através de um procedimento de reforço, original e seguro, que corrija as deficiências iniciais do projeto. Várias alternativas foram propostas pelo meio técnico aos proprietários desses postes para solução do problema, mas nenhuma conseguiu satisfazer às necessidades operacionais, econômicas e técnicas requeridas. A solução estudada minuciosamente nesta tese, consiste, sucintamente, em preencher o fuste do poste na região do traspasse com graute de elevada resistência mecânica e realizar confinamento passivo com uma camada de fibra de carbono, reduzindo as taxas de armadura a níveis adequados e assegurando confinamento da emenda. Essa solução foi ensaiada em laboratório, utilizando-se postes já removidos, ou seja, em escala real, de forma a comprovar a eficiência do reforço proposto. Todos os ensaios com módulos de postes não reforçados mostraram ruptura por falha na transferência de esforços na região do traspasse de armaduras, apresentando mecanismo de ruptura muito próximo ao encontrado na prática, em postes que colapsaram. Todas as rupturas ocorridas em postes reforçados na região do traspasse com a solução proposta ocorreu por flexão no domínio III, sem nenhuma deterioração por fadiga da região do traspasse de armaduras, comprovando a eficiência do reforço proposto. O custo da reabilitação desenvolvida nesta tese é, em média, de um terço à metade do valor da substituição do poste por uma torre metálica , o que a torna uma alternativa altamente atrativa para as empresas do setor, contribuindo para a solução de um grave problema nacional de engenharia (ciência aplicada). / Precast reinforced concrete posts were installed in Brazil by mobile telephone companies when implanting and enlarging service areas of the system starting in 1996. The great majority of these posts were manufactured by a single company, using a centrifugal process. Approximately two thousand units of posts were produced of heights ranging between 20m [60 ft] and 60 m [197 ft]. Some of those posts collapsed after three or four years of use, reportedly being known of four cases, located in the states of São Paulo, Espírito Santo, Rio de Janeiro and Rio Grande do Sul. All of the known collapses happened with rupture in the reinforcement development length between the first module (the one fixed to the ground) and the second module. After an extensive investigation work and diagnosis of the problem, carried out in 40 dismounted posts that had been previously stocked in the city of Santana do Parnaíba/SP, it was demonstrated that the most relevant problem found was in the development length of the reinforcement between the modules. The diagnosis pointed the fatigue due to the elevated reinforcement area at the joint area, which ranged between 8,5% to 18,2%. Those rates exceed considerably the maximum limit allowed by standards in order to guarantee adequate conditions for stress transfer in that area. The main objective of this dissertation is to demonstrate that it is possible to use the posts without need of their substitution, through a reinforcement procedure, original and safe, that corrects the initial deficiencies of the project. Several alternatives were proposed by the technical community for the solution of the problem, but none of them could satisfy the operational, economical and technical needs requested by the owners of the posts. The proposed solution consists in filling the section of the posts in the joint area with a high mechanical strength grout and a layer of carbon fiber reinforcement in order to accomplish passive confinement, therefore reducing the reinforcement rates to appropriate levels. This solution was tested in laboratory, using real scale posts already removed in order to confirm the efficiency of the proposed reinforcement procedure. All of the tests with non reinforced posts showed rupture due to failure of stress transfer in the joint area, presenting a very close rupture mechanism to the one found in practice in the posts that collapsed. All of the ruptures occurred in the reinforced posts were due to flexure in the Section III domain without any deterioration of the joint area, proving so the efficiency of the proposed reinforcement. The rehabilitation cost of the solution developed on this dissertation varies, on average, between a third and a half of the cost of replacing the structure for a metallic tower, thus providing an attractive alternative for the companies in this business, contributing to the solution of a serious national problem of engineering (applied science).

Ultramicroelectrodes (UMEs) (limiting dimensions <~25 μm) and nanoelectrodes (<~100 nm) exhibit enhanced electrochemical properties compared to macroscopic electrodes. Their small sizes and enhanced properties make them well-suited for various interesting and important applications such as measuring redox-active species in nonaqueous solvents, studying intermediates of fast electrochemical reactions, and investigating electrochemical and electrocatalytic properties of single nanoparticles. While UMEs are commercially available, nanoelectrode fabrication is still largely confined to research labs. Various methods for constructing nanoelectrodes have been reported and continue to be developed, but most require considerable expertise, and comparisons between different fabrication processes are lacking. In this work, a comparison of laser-assisted pulling and chemical vapor deposition (CVD) methods of electrode fabrication is made with the aim of optimizing production of carbon nanoelectrodes for single nanoparticle electrochemical measurements. By examining effects of pulling parameters, post-pulling treatments, and CVD processing, electrodes as small as ~50 nm were successfully produced.

As the aerospace industry continues to incorporate composites into its aircraft, there will be a need for alternative solutions to the current autoclaving process. Liquid composite molding (LCM) has proven to be a promising alternative, producing parts at faster rates and reduced costs while retaining aerospace grade quality. The most important factor of LCM is controlling the resin flow throughout the fiber reinforcement during infusion, as incomplete filling of fibers is a major quality issue as it results in dry spots or voids. Void formation occurs at the resin flow front due to competition between viscous forces and capillary pressure. The purpose of this work is to characterize capillary pressure in vacuum infusion, and develop a model that can be incorporated into flow simulation. In all tests performed capillary pressure was always higher for the carbon fiber versus fiberglass samples. This is due to the increased fiber packing associated with the carbon fabric. As the fabric samples were compressed to achieve specific fiber volumes an increase in capillary pressure was observed due to the decrease in porosity. Measured values for capillary pressure in the carbon fabric were ~2 kPa, thus the relative effects of Pcap may become significant in flow modeling under certain slow flow conditions in composite processing.

In the current thesis, the 4-probe electrical resistance of carbon fiber-reinforced polymer (CFRP) composites is utilized as a metric for sensing low-velocity impact damage. A robust method has been developed for recovering the directionally dependent electrical resistivities using an experimental line-type 4-probe resistance method. Next, the concept of effective conducting thickness was uniquely applied in the development of a brand new point-type 4-probe method for applications with electrically anisotropic materials. An extensive experimental study was completed to characterize the 4-probe electrical resistance of CFRP specimens using both the traditional line-type and new point-type methods. Leveraging the concept of effective conducting thickness, a novel method was developed for building 4-probe electrical finite element (FE) models in COMSOL. The electrical models were validated against experimental resistance measurements and the FE models demonstrated predictive capabilities when applied to CFRP specimens with varying thickness and layup. These new models demonstrated a significant improvement in accuracy compared to previous literature and could provide a framework for future advancements in FE modeling of electrically anisotropic materials. FE models were then developed in ABAQUS for evaluating the influence of prescribed localized damage on the 4-probe resistance. Experimental data was compiled on the impact response of various CFRP laminates, and was used in the development of quasi- static FE models for predicting presence of impact-induced delamination. The simulation-based delamination predictions were then integrated into the electrical FE models for the purpose of studying the influence of realistic damage patterns on electrical resistance. When the size of the delamination damage was moderate compared to the electrode spacing, the electrical resistance increased by less than 1% due to the delamination damage. However, for a specimen with large delamination extending beyond the electrode locations, the oblique resistance increased by 30%. This result suggests that for damage sensing applications, the spacing of electrodes relative to the size of the delamination is important. Finally CT image data was used to model 3-D void distributions and the electrical response of such specimens were compared to models with no voids. As the void content increased, the electrical resistance increased non-linearly. The relationship between void content and electrical resistance was attributed to a combination of three factors: (i) size and shape, (ii) orientation, and (iii) distribution of voids. As a whole, the current thesis provides a comprehensive framework for developing predictive, resistance-based damage sensing models for CFRP laminates of various layup and thickness.

Wheelchair-bound individuals who have limited or no upper-limb usage have difficulty with picking and placing of objects, opening doors, and other activities of daily living (ADLs), such as turning on a light switch or drinking from a cup. A wheelchair-mounted robot arm (WMRA) would aid individuals with completing ADLs and increase their independence, therefore an improved WMRA has been designed. Building upon previous WMRA research and incorporating research from industrial robot arms, carbon fiber tubing is the main component for the structure of the arm, a novel development for WMRAs. Factors that go into WMRA design include weight, speed, safety, robustness, cost, and the anticipated tasks. Many of these factors, such as weight, speed, and cost, can be improved upon compared to previous WMRAs by using carbon fiber materials. The use of carbon fiber enables the arm to be strong, but also lighter weight than other WMRAs. Testing was conducted on the pultruded carbon fiber tubing to ensure that the structure of the arm could withstand the necessary bending and tensile forces for the arm to hold up to 3.85kg, the standard weight of a gallon of milk, at the end effector. The arm's carbon fiber frame also allows the motor and sensor wiring to run internally, which improves the arm's safety and aesthetics, while protecting it from the arm's external environment. Lightweight high-torque motors, harmonic drives, newly designed carbon fiber frame, and a stand-alone 8-axis motion-control board, allow the arm to weigh less, have a longer overall length, be more robust, and be safer electronically than the previous University of South Florida WMRA, which was shown through prototype testing.

The efficacy of dispersed reduced graphene oxide (rGO) as a nucleation site for the growth of mesophase in an isotropic pitch was investigated and quantified in this study. Concentrations of rGO were systematically tested in an isotropic petroleum and coal-tar pitch during thermal treatments and compared to pitch without rGO. The mesophase content of each thermally treated pitch was quantified by polarized light point counting. Further characterization of softening temperature and insolubles were quantified. Additionally, the pitches with and without rGO were melt spun, graphitized, and tensile tested to determine the effects of rGO on graphitized fiber mechanical properties and fiber morphology.