Orientador: Carlos Alberto Soufen / Banca: Luís Augusto Sousa Marques da Rocha / Banca: Ivaldo de Domenico Vallarelli / Resumo: Os laminados de compósitos poliméricos possuem um valor já consagrado dentro das aplicações mecânicas e industriais. Sua versatibilidade aliado a suas propriedades mecânicas, estimula o aumento da aplicação, devido em partes pela facilidade de construção, tornando-os competitivos com relação a outros materiais. O conhecimento sobre a matriz polimérica, que possui inúmeras variações e aplicações e sobre o reforço, que neste estudo utilizou tecidos de fibra de carbono em sarja, formaram o prelúdio do trabalho. A análise de compósitos laminados com tecidos bidirecionais em ângulo de 90º, e a variação de três tipos de matriz polimérica, sendo duas do grupo epóxi e uma do grupo epóxi éster vinil, constituíram os laminados. O processo de corte por jato dágua e por fresagem CNC, influenciaram diretamente a rugosidade da superfície de corte dos laminados. Os ensaios mecânicos de tração e flexão, colaborou para identificar qual das três matrizes possui o melhor desempenho. As técnicas de caracterização por microscopia óptica, possibilitou identificar as camadas dos tecidos, a matriz, modos de falhas e a impregnação entre matriz e reforço. A microscopia confocal 3D além de formar imagens em 3D, demonstrou a diferença de rugosidade entre os processos aplicados, sendo confirmados posteriormente pelo ensaio de rugosidade ficando claro que o processo de corte por fresagem CNC é a melhor opção, pois, o processo de corte por jato dágua demonstrou não ser tão eficiente devido a formação de uma superfície com maior rugosidade em virtude da existência de substâncias abrasivas no fluido de corte, provocando micro trincas nos laminados. Os resultados apontaram que a resina epóxi SQ 2004 é a que possui melhores propriedades mecânicas, seguida da resina SQ 2001 da resina epóxi éster vinil Derakane 470 / Abstract: The laminated polymer composites have a value already established within the mechanical applications and industries. Its versatility coupled with their mechanical properties, stimulates increased use due in part by the ease of construction, making them competitive with respect to other materials. Knowledge of the polymeric matrix that has numerous variations and applicatons on the reinforcement in this study utilized fabrics of carbon fiber twill formed a prelude to the work. The analysis of laminated composites with woven bi-directional angle of 90º, and the variation of three types of polymer matrix, two of the epoxy groups and the epoxy group, vinyl ester, were the laminates. The process of cutting water jet and CNC milling, directly influenced the roughness of the cut surface of the laminate. The tensile test and bending, collaborated to identify which of the three matrices has the best performance. The techniques of characterization by optical microscopy, enabled us to identify the layers of tissue, the matrix failure modes and impregnation betweeen matrix and reinforcement. Confocal microscopy 3D besides forming 3D images showed the difference in roughness between the cutting processes applied, and later confirmed by testing roughness became clear that the process of cutting CNC milling is the best option because the process cutting water jet proved not to be as effective due to the formation of a surface with increased roughness due to the presence of abrasives in the cutting fluid, causing micro-cracks in the laminate. The results showed that the epoxy resin SQ 2004 is the one that has better mechanical properties, then the resin SQ 2001 and the epoxy vinyl ester Derakane 470 / Mestre

Orientador: Edson Cocchieri Botelho / Coorientadora: Lília Müller Guerrini / Banca: Mirabel Cerqueira Rezende / Banca: Silvia Sizuka Oishi / Resumo: Nos últimos anos, reforços constituídos de nanoestruturas em carbono, tais como nanotubos de carbono, fulerenos, grafenos e nanofibras de carbono, vêm sendo muito pesquisados devido às suas elevadas propriedades mecânicas, elétricas e térmicas. Uma vez que, as nanofibras de carbono consistem em um reforço contínuo (ou na forma de mantas) de elevada área superficial específica, associado ao fato de que estas podem ser obtidas a um baixo custo e em grandes quantidades, estas vêm se mostrando vantajosas quando comparadas aos tradicionais nanotubos de carbono. Assim, as nanofibras de carbono são ótimas candidatas para a obtenção de materiais avançados, podendo estas serem utilizadas como reforços em compósitos com diversas aplicações, tais como em implantes neurológicos e ortopédicos, como suportes de catalisadores, artefatos para aplicações aeroespaciais, dentre outras. Desta forma, o objetivo principal deste trabalho é a produção de nanofibras de carbono, empregando como precursora a manta de poliacrilonitrila (PAN) obtida pelo processo de eletrofiação via solução polimérica, com posterior utilização como reforço em compósitos poliméricos. Neste trabalho, uma manta de poliacrilonitrila com nanofibras de diâmetro de aproximadamente (375 ± 85) nm foi obtida por eletrofiação, sendo esta posteriormente carbonizada. A massa residual resultante do processo de carbonização foi de aproximadamente 38% em massa, com uma redução de 50% nos diâmetros das nanofibras após a queima das mantas de PAN, sendo que as mesmas apresentaram um rendimento de 25%. Na análise da estrutura cristalina do material carbonizado, verificou-se que o material apresentou uma desorganização estrutural. E a partir do ensaio de condutividade elétrica da manta carbonizada, concluiu-se que o material se comporta como um ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In recent years, reinforcement consisting of carbon nanostructures, such as carbon nanotubes, fullerenes, graphenes, and carbon nanofibers has been very researched due to its mechanical, electrical and thermal properties, besides having good thermal conductivity, mechanical resistance and high surface area. Since the carbon nanofibers comprise a continuous reinforcing with high specific surface area, associated with the fact that they can be obtained at a low cost and in large amounts, they have shown to be advantageous compared to traditional carbon nanotubes. Thus, the carbon nanofibers are excellent candidates in order to obtain advanced materials, and these can be used as reinforcements in composites with several applications such as for example, neurological and orthopedic implants, integrates in catalysts systems, devices for aerospace applications, among others. So, the main objective of this work is the processing of carbon nanofibers, using PAN as a precursor, obtained by the electrospinning process via polymer solution, with subsequent use for applications as reinforcement in polymer composites. In this work, PAN nanofibers were produced by electrospining with a diameter of approximately (375 ± 85) nm. The resulting residual weight after carbonization was approximately 38% in mass, with a diameters reduction of 50%, and the same showed a yield of 25%. From the analysis of the crystallinity structure of the carbonized material, it was found that the material presented a disordered structure. From the electrical conductivity results of the specimens, it was concluded that the material behaves as a semi-conductor. The epoxy resin/carbon nanofiber composite presented an elastic modulus value of (3.79 ± 0.48) GPa, a glass transition temperature (Tg) in the range from 108.9 to 135 5 ° C and a linear thermal expansion coefficient within the range of 68 x 10-6 /°C and 408 x 10-6 /°C / Mestre

Made available in DSpace on 2014-10-09T12:26:27Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:31Z (GMT). No. of bitstreams: 0 / A utilização de materiais compósitos poliméricos em elementos estruturais requer o conhecimento do comportamento durante a vida em serviço. A garantia da integridade destes elementos estruturais de compósitos demanda um estudo do comportamento dependente do tempo, por causa da sua resposta viscoelástica e das inúmeras possibilidades de configurações de fabricação. No presente estudo, foram realizados ensaios de fluência e ruptura por fluência em tração em compósitos unidirecionais fabricados com resina epoxídica e fibra de carbono de alta resistência, com os ângulo das fibras a 60º e 90º em relação à direção do carregamento, nas temperaturas de 25 e 70 ºC. A caracterização viscoelástica do compósito foi realizada por meio das curvas de fluência a vários níveis de carregamento constante em períodos de 1000 h, obtenção do envelope de ruptura por fluência pelas curvas de ruptura por fluência, a determinação da transição do comportamento linear para não linear pelos gráficos isócronos e ainda a comparação das curvas de flexibilidade à fluência com um modelo de predição de comportamento viscoelástico fundamentado na equação de Schapery. Pelos ensaios foi constatada uma modificação no comportamento do material, com relação à resistência, rigidez e deformação, demonstrando que estas propriedades foram afetadas pelo tempo e nível de tensão, especialmente em temperatura de trabalho acima da ambiente. O modelo de predição foi capaz de representar o comportamento à fluência, entretanto deve ser considerada a determinação dos termos das equações, além da variação destes com a tensão aplicada e o tempo decorrido de ensaio. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:55:41Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:07Z (GMT). No. of bitstreams: 0 / Em um cenário nacional de grandes dificuldades orçamentárias, soluções criativas que conjuguem os esforços de instituições em prol de uma finalidade comum são sempre desejáveis. Neste trabalho, analisa-se o desenvolvimento de fibras de carbono de alto desempenho para aplicação em ultracentrífugas nucleares e o projeto de Pesquisa Cooperativa que o viabilizou. A fibra de carbono com as características necessárias a empreendimentos desse tipo é um insumo de grande complexidade tecnológica. A produção é concentrada em alguns poucos produtores mundiais e seu comércio é alvo de restrições e salvaguardas internacionais. Não há produção no Brasil. É considerada material de uso dual, ou seja, pode ter tanto aplicações exclusivamente civis, como militares. A Marinha do Brasil utiliza essa fibra na fabricação de ultracentrífugas nucleares, nas quais materiais que conjuguem leveza, rigidez e resistência de alto nível são extremamente desejáveis, pois aumentam a eficiência na separação isotópica. Sua fibra de carbono, importada, é baseada na poliacrilonitrila (PAN), comercialmente mais difundida, mais barata e utilizada em aplicações similares. A necessidade de desenvolvimento nacional é decorrência de dificuldades em sua aquisição. Para tanto, foi organizada uma parceria de pesquisa entre o Centro Tecnológico da Marinha (CTMSP), a UNICAMP, a USP e a empresa RADICIFIBRAS, com apoio financeiro de uma agência governamental (FINEP), para a produção nacional de fibra de carbono baseada na PAN. A pesquisa realizada identificou as práticas de sucesso alcançadas, bem como os referenciais teóricos de Projetos de Pesquisa Cooperativa. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Ph.D. (Chemistry) / Please refer to full text to view abstract

Orientadores: Derval dos Santos Rosa, Armando Moreno Lopes Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-18T11:05:11Z (GMT). No. of bitstreams: 1 Marini_MarcioVinicius_M.pdf: 3583126 bytes, checksum: 5e4af10aedd8586c476507d633cf6c75 (MD5) Previous issue date: 2011 / Resumo: O reforço de estruturas de concreto armado ou protendido têm sido necessário na construção civil devido às falhas causadas por erros em projetos e execuções de obras, corrosões de armaduras, reabilitação após incêndios ou mudanças na utilização das estruturas projetadas. Os métodos convencionais para reforço de estruturas de concreto estão relacionados ao reforço pela adição de barras de aço e de concreto na estrutura ou, ainda, pela instalação de chapas de aço. O uso de fibras de carbono para reforços estruturais é recente, apresentando vantagens em relação aos métodos tradicionais, tais como: fácil manuseio na aplicação, alta aderência entre as fibras de carbono e o concreto e aumento na resistência à corrosão. Sendo assim, o objetivo deste trabalho é avaliar a aderência entre o sistema de reforço com as fibras de carbono e concretos com resistência à compressão de 15 MPa, 40 MPa e 60 MPa. A aderência concreto/fibra foi avaliada por meio de ensaios pull-out em pequenas placas de concreto com fibras de carbono aplicada superficialmente. Do concreto, foram obtidos resultados de sua porosidade e rugosidade; por meio de estereomicroscópia, foram avaliadas características como a textura superficial. Os resultados demonstraram que os concretos com menor relação água/cimento (a/c), ou seja, com maior resistência à compressão apresentaram maior aderência entre si e o sistema de reforço com fibras de carbono e menores valores de porosidade e rugosidade com maior homogeneidade superficial. Em relação aos concretos com maior relação água/cimento (a/c), observou-se o comportamento inverso nas propriedades citadas. De acordo com esses resultados, pôde-se concluir que a resistência à compressão do concreto (substrato) alterou a resistência de aderência com o sistema de reforço com fibras de carbono e também a porosidade; a rugosidade e a característica de superfície não influíram significativamente nestas propriedades / Abstract: Strengthening of conventional or prestressed concrete structures has been used due to failure occurred by design errors, erroneous methods and executives process, corrosion of steel bars of concrete pieces, rehabilitation after damages caused by fire or variations of structure type utilization. Conventional strengthening methods of concrete structure are used adding new steel bars to structure or installing steel plates. However more recent reinforcement methods based on carbon fiber use had been demonstrated advantages, such as: easy and fast application to substrate, high adhesion between carbon fiber and concrete and method to increase corrosion of bars of concrete structures. Thus, this work aims to evaluate adhesion process between strengthening concrete system employing carbon. In the experimental study was used concrete specimens with compressive strength of 15 MPa, 40 MPa and 60 MPa. The interface adherence of concrete/fiber was evaluated through pull-out test type on concrete slabs, where carbon fiber was superficially applied. Results of concrete porosity and roughness were obtained through a stereo microscope that assesses characteristics as the superficial texture. The obtained results showed that concretes with lower water/cement ratio (w/c) had higher values of adhesion between carbon fiber and concrete, lower porosity values and higher superficial homogeneity. Opposite behavior was observed in concretes with higher water/cement ratio (w/c). According to the obtained results was possible to note that the compressive strength concrete (substrate) modified the adherence resistance between concrete and carbon fiber, where higher compression strength increased adherence between concrete and carbon fiber. Also the results indicated that both the concrete surface characteristics and the roughness were not influenced significantly / Mestrado / Estruturas / Mestre em Engenharia Civil

No description available.

The effect of surface pretreatment on the adhesive bonding and bond durability of carbon fiber/epoxy and carbon fiber/bismaleimide matrix composites was studied. Methyl ethyl ketone (MEK) wipe, peel ply, grit blast and gas plasma treatments were the pretreatments of interest. Chemical and physical changes which occurred in the cured composite surfaces following pretreatment were characterized with x-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), contact angle analysis, diffuse reflection infrared spectroscopy (DRIFT), profilometry and scanning electron microscopy (SEM). Double lap shear and Boeing wedge configurations were used to evaluate the strength as well as the durability of the composites bonded with an epoxy film adhesive. Fluoropolymer residues which were found on the composite surfaces were fully removed by grit blasting and oxygen plasma treatments, but not by an MEK wipe. The use of a peel ply prevented fabrication contamination from depositing on the bonding surfaces. In addition to its cleaning effect, oxygen plasma was also capable of incorporating additional polar functionality into the composite surface. The presence of the fluoropolymer contamination on the MEK-wiped surface resulted in low surface energy and wettability, whereas peel ply, grit blast and oxygen plasma improved both the surface energy and the wettability of the composite surfaces. The grit blasted and peel ply surfaces were observed to have a significant degree of roughness, as measured by profilometry and seen by SEM. A rubber-toughened epoxy film adhesive was used for the bonding studies. Lap shear strengths were evaluated under ambient conditions as well as at 82°C, both dry and following a 30 day/71°C water exposure. Wedge durability testing was carried out in a dry 75°C oven, 75°C water, 100°C water and aircraft de-icing fluid. Relative to the MEK-wiped controls, lap shear strength as well as hot/wet durability was improved by the peel ply and oxygen plasma treatments for both epoxy and bismaleimide composites. Grit blasting was seen to have some utility for the epoxy composites at room temperature, but was generally observed to be detrimental to strength and durability, particularly in the case of the bismaleimide composites. In order to separate the effect of surface chemistry from the effect of surface roughness on composite bond strength, a study was carried out in which surface functionality was varied while the topography remained constant. For this purpose, peel ply surfaces, which have a consistent and reproducible degree of roughness, were treated with fluoropolymer compounds and gas plasmas, as well as left untreated. It was found that the removal of fluoropolymer contamination was the main contributor to the observed bond strength improvement following plasma treatment; however, highly functionalized oxygen plasma-treated surfaces showed evidence of improved durability in a hot aqueous environment. The effect of elapsed time following oxygen plasma treatment of epoxy composites was also studied. XPS atomic concentration, wettability by water and a liquid epoxy resin, and lap shear strengths were plotted as a function of time following removal from the plasma reactor. Changes which occurred in the chemistry and wettability of an oxygen plasma-treated surface had a subsequent negative effect on the lap shear strengths of the bonded specimens. A study was carried out using model epoxy and bismaleimide compounds in thin film form, for the purpose of studying surface chemistry and interfacial reactions following an oxygen plasma treatment. XFS and infrared reflection-absorption spectroscopy (IR-RAS) were used to probe the reactions which occurred. Close correspondence was found between the XPS and IR-RAS analysis of functional groups incorporated into the surface of the films by the plasma treatment. IR-RAS analysis of the model surfaces following exposure to a neat, liquid epoxy resin revealed that, while adsorption of the liquid epoxy occurred on both plasma-treated and nonplasma-treated surfaces, the oxygen plasma treated surface alone was capable of initiating ring-opening reactions in the epoxy. However, this effect was not observed unless immediate contact was made between the plasma-treated surface and the liquid epoxy resin. / Ph. D.

A series of RF plasmas was chosen to modify the surface chemical composition of Hercules IM7 carbon fibers. A two-liquid tensiometric method was used to determine the surface energy parameters y(ds) and I(psf) of the fibers. An XPS analysis of air and argon plasma treated fibers indicated a significant surface oxidation of the fibers which translated into low y(ds) values and high I(psf)values. An ammonia plasma was shown to remove an outer layer from the surface of the fibers. It also increased y(ds) compared to as-received fibers without affecting the non-dispersion (IPsf) XPS results indicated that methane and ethylene plasmas deposited a layer of low surface energy hydrocarbon on the fiber surface. A trifluoromethane plasma and a tetrafluoromethane plasma introduced a significant amount of fluorine containing groups in the fiber surface in the form of a fluorinated plasma polymer in the first case and through direct attack of the fiber surface by fluorine atoms in the second case. The surface chemical composition and the surface energy parameters of two series of commercially treated carbon fibers were also determined and compared to the results on IM7 carbon fibers. The adhesion of carbon fibers to polyethersulfone (PES) was measured by using the microbond pull-out test, and compared to the adhesion of the same fibers to an epoxy resin. The load required to debond the microdroplet was used as a measure of the bond strength. The data were also analyzed in terms of interfacial fracture energy accordIng to the model developed by Jiang and Penn (1992). The microbond pull-out test results showed no significant relation between the fiber surface chemical composition or the fiber surface energy, and the adhesion to PES. However, plasmas which have a strong ablative character such as the ammonia and the tetrafluoromethane plasmas did improve the fiber-PES adhesion, when compared to as-received fibers. The study of the fiber-epoxy systems revealed that a chemical effect contributed to the adhesion improvement but to a lesser extent than the "cleaning" effect of the surface treatment. The results support the two part mechanism proposed by Drzal and extend its application to carbon fiber-thermoplastic systems, but in this case the chemical effect is minimal. / Ph. D.

The use of fiber reinforced plastics (FRP) in repairing and strengthening bridges has been researched in recent years. In particular, attaching unidirectional FRP to the tension face of reinforced concrete beams has provided an increase in stiffness and load capacity of the structure. However, due to the brittle nature of the unidirectional FRP, the ductility of the beam decreases. One possible solution to this problem is the use of cross-ply or off-axis FRP laminates. This thesis focuses on the investigation of the flexural behavior of reinforced concrete beams strengthened with one of two different FRP orientations (0°/90° and ±45°). More particularly, the change in strength and ductility of the beams as the number of FRP layers are altered is investigated. Seven under-reinforced concrete beams were constructed and tested to failure. With the exception of the control beam, each specimen was applied with two, three, or four layers of either 0°/90° and ±45° FRP orientations. To predict the flexural behavior of the specimens, a theoretical model was derived using basic concepts, past research, and the tested properties of the concrete, steel reinforcement, and FRP. Also, two methods were used to analyze the ductility of the tested beams. Along with the test details of each specimen; the moment, deflection, CFRP strain, crack patterns, and mode of failure are discussed. The results included an increase in load capacity with respect for the number of CFRP layers applied for both orientations. Also, the ductility of the beams were reduced by adding CFRP orientations. / Master of Science