Orientador: Maria Odila Hilário Cioffi / Coorientador: Herman Jacobus Cornelis Voorwald / Banca: Mirabel Cerqueira Rezende / Banca: Carlos Alberto Cimini Junior / Resumo: A indústria aeronáutica nacional tem intensificado sua busca por materiais alternativos, com características e propriedades que permitam a substituição segura do material metálico. Com o objetivo de ganhar competitividade no mercado internacional e contribuir para o desenvolvimento tecnológico no país, o presente trabalho apresenta a técnica de processamento de moldagem por transferência de resina (RTM), utilizada na fabricação de materiais compósitos estruturais e ainda pouco estudada no Brasil. Os compósitos processados por essa técnica apresentam maior fração volumétrica de fibras, melhor acabamento superficial e pouca ou nenhuma necessidade de acabamento do componente produzido. Este trabalho compreende o processamento e a caracterização de compósitos produzidos com resina epóxi monocomponente Cycom 890 e dois tipos de tecidos, plain weave e twill 2x2, ambos de fibra de carbono. Para a determinação dos parâmetros de processamento, a resina foi caracterizada quanto aos seus comportamentos térmico e viscoso. Com base nos resultados e testes preliminares foi determinada a temperatura mais adequada de injeção em 100°C, a pressão de injeção entre 0,2 e 0,4 MPa e de vácuo em 250 mPa.s. Os compósitos produzidos foram analisados pela técnica de ultrassom C-Scan e os resultados mostraram que os laminados processados estão homogêneos quanto à impregnação. Testes de tração mostram que os laminados com tecido tipo Twill apresentam maior média de resistência à tração, enquanto que a diferença de trama não influencia significativamente às propriedades de flexão e cisalhamento, que se mostraram superiores as propriedades de compósitos produzidos em autoclave com maiores porcentagens de reforço. Em fadiga, ambos os laminados apresentaram um curto intervalo, com tensões próximas à de tração, no entanto, o laminado PW/Cycom apresentou maior... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The national aeronautical industry has intensified your search for alternative materials, with characteristics and properties that allow the safety replacement of metallic material. The goal is to gain competitiveness on international market and contribute with technological development in the country. This work presents a processing technique of resin transfer molding (RTM), used on manufacture of structural composites and understudied in Brazil. Composites processed by this method have a higher fibers volume fraction, better surface finish and little or no finishing require of produced component. This work includes the processing and characterization of composites made with monocomponent epoxy resin Cycon 890 and two types of carbon fiber fabrics, plain weave and twill 2x2. To determine processing parameters, the resin was characterized regarding thermal behavior and viscosity. Based on this results and preliminary tests, it was determined the most appropiate injection temperature at 100°C, the injection pressure between 0.2 and 0.4 MPa and vacuum pressure in 250 mPa.s. Composites produced were analyzed by C-scan ultrasound technique showing a homogeneous impregnation of processed panels. Tensile and flexural tests characterized mechanically composites, allowing seeing that Twill fabric has higher medium tensile performance, while the difference of weft does not influence significantly the flexural and shear properties, that are superior than properties of composites made by autoclaving with higher reinforced volume. In fatigue, both composites showed short interval, close to ultimate tensile strength (uts), however, the PW/Cycom laminated showed higher fatigue resistance, with an interval between 85-92% of uts. About the thermal behavior, it was observed an improvement in properties with the addition of carbon... (Complete abstract click electronic access below) / Mestre

Orientador: Maria Odila Hilario Cioffi / Banca: Tessie Gouvea da Cruz / Banca: Mirabel Cerqueira Rezende / Resumo: A indústria de transporte como um todo tem intensificado sua busca por materiais e processos de fabricação que atendam as necessidades de redução de custo e peso. Esta busca entretanto deve estar correlacionada ao aumento da resistência mecânica e da produtibilidade de peças cada vez mais complexas. Desta forma, o processo de infusão de resina líquida como a Moldagem por Transferência de Resina Assistida por Vácuo (VARTM) vem se destacando, em especial na indústria aeronáutica, como um meio de produção destas peças. O presente trabalho visa avaliar comparativamente laminados processados pelo método VARTM polimerizados de diferentes formas, onde um dos laminados foi polimerizado em uma estufa e outro polimerizado por meio do aquecimento do molde de infusão. Cada um dos laminados possuía três espessuras, e foram produzidos com resina epóxi bi-componente e tecido plain weave de fibra de carbono. Para a determinação dos parâmetros de processamento, a resina foi caracterizada quanto ao comportamento térmico. Para avaliar a presença de defeitos (poros e vazios) foi utilizada a inspeção por ultrassom, a digestão ácida e a porosimetria de mercúrio. Para a caracterização mecânica, foram utilizados os ensaios de resistência à tração, cisalhamento no plano e cisalhamento interlaminar, com posterior análise fractográfica. Os laminados produzidos tiveram suas propriedades térmicas avaliadas pela análise dinâmico-mecânica. Os resultados destas análises mostraram uma baixa influência do processo de cura sobre as propriedades dos compósitos produzidos e uma limitação na utilização do VARTM para produção de laminados com elevada espessura / Abstract:The transportation industry has intensified materials research and manufacturing processes development in order to reduce cost and weight, linked to increase mechanical strength and reproducibility of complex parts. In this regarding the liquid resin infusion process such as Vacuum Assisted Resin Transfer Molding (VARTM) has been highlighting, specially for the aircraft components. The present work aims to compare two composites laminates processed in different cure program. One of them was cured in an oven and other one by heating the manufacturing mold using electrical resistance. Each laminate was manufactured with three thickness using a bi-component epoxy resin and plain weave carbon fiber fabric, processed by VARTM. For choose process parameters the resin thermal behavior was conducted. In order to evaluate the presence of defects (voids and poros) ultrasonic inspection, acid digestion evaluation and mercury porosimetry technique were used. For the mechanical characterization tensile, in-plane shear and interlaminar shear tests were used, with subsequent fractographic analysis by SEM. Laminates also had its thermal behavior evaluated by a dynamic mechanical analysis. Results showed a low influence of curing process over laminate properties and a limitation of VARTM process application to manufacture parts with a high number of plies / Mestre

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The problem with which this investigation is concerned is that of identifying and prioritizing the competencies required to design and implement manufacturing systems for advanced composite structures. The classical Delphi procedure is the research method used for the conduct of this study. A five-member advisory board developed a list of seventeen categories under which the competencies would reside. In the first-round questionnaire, the seventeen categories were presented to a Delphi panel of experts who provided up to five competencies required in each category. The first-round returns provided two new categories and 973 competency statements. Duplications were eliminated and 366 competency statements remained in nineteen categories. The second, third, and fourth rounds were a reiterative rating process. The panel was asked to rate the items in the questionnaire based on their relative importance to the intent of the study. The importance rating scale included "very important," "important," "slightly important," and "unimportant." The means and interquartile ranges were calculated for each statement and provided as feedback in the successive round. Kendall's coefficient of concordance W for tied ranks was used to validate the panel consensus. The W was significant at the .01 level for each of the three rounds where rating was performed. The data were presented in rank order within categories by importance level. Eighteen percent of the competency statements were rated "very important," 77 percent "important, and 5 percent "slightly important." No statements were rated "unimportant" by the panel. It was concluded that, as indicated by the 19 categories and 366 competencies, the scope of the requirements for designing and implementing manufacturing systems for advanced composite structures represent a broad range of knowledge and skill requirements. The breadth of the range of the requirements indicated the need for the development of areas of specialization within the subject field to adequately address the requirements.

Understanding the mechanical behavior of composite materials requires extensive knowledge of fracture behavior as a crack approaches an interface between the bulk material and the reinforcement structure. Overall material toughness can be greatly influenced by the propensity of an impinging crack to propagate directly through the substrate or deflect along an interface boundary. As the basis for this thesis; the assertion that an impinging crack may encounter a reinforcement structure at various incident angles is explored. This requires the ability to predict crack penetration/ deflection behavior not only normal to the reinforcement, but at various incident angles. Previous work in the area of interface fracture mechanics has used a stress or energy based approach, with recent advances in the field of a combined cohesive-zone method. Work presented here investigates the interaction between strength and toughness when using the cohesive-zone method on the problem of an impinging crack not normally incident to the interface of a composite material. Computational mechanics methods using Abaqus and user-define cohesive elements will be applied to this angled incident crack problem. A circular model based on the displacement field equations for mode-I fracture loading is introduced and verified against well-established LEFM solutions. This circular model is used to study the effects of incident crack angle on the penetration vs. deflection behavior of an impinging crack at various angles of incidence. Additionally, the effects of angle on the load applied to the model at fracture are explored. Finally, a case study investigating how the interaction between strength and toughness found using the cohesive-zone method helps to explain some of the inconsistencies seen in the interface indentation fracture test procedure. / Graduation date: 2013

This study develops new quantitative thermoelastic stress analysis (TSA) techniques for fracture and fatigue damage analysis of composite materials. The first part deals with the thermo-mechanical derivation of two quantitative TSA techniques applied to orthotropic composites with and without a transversely-isotropic surface coating layer. The new TSA test procedures are derived in order to relate the thermal infrared (IR) images with the sum of in-plane strains multiplied by two newly defined material constants that can be experimentally pre-calibrated. Experiments are performed to verify the TSA methods with finite element (FE) numerical results along with available anisotropic elasticity solution. The second part of this study applies the quantitative TSA techniques together with the Lekhnitskii's general anisotropic elasticity solution to calculate mixed-mode stress intensity factors (SIFs) in cracked composite materials. The cracked composite coupons are subjected to off-axis loadings with respect to four different material angles in order to generate mixed-mode SIFs. A least-squares method is used to correlate the sum of in-plane strains from the elasticity solution with the measured TSA test results. The mode-I and mode-II SIFs are determined from eccentrically loaded single-edge-notch tension (ESE(T)) composite specimens. The FE models and virtual crack closure technique (VCCT) are utilized for comparisons. In the third part, a new stochastic model is proposed to generate S-N curves accounting for the variability of the fatigue process. This cumulative damage Markov chain model (MCM) requires a limited number of fatigue tests for calibrating the probability transition matrix (PTM) in the Markov chain model and mean fatigue cycles to failure from experiments. In order to construct the MCM stochastic S-N curve, an iterative procedure is required to predict the mean cycles to failure. Fatigue tests are conducted in this study to demonstrate the MCM method. Twenty-one open-hole S2-glass laminates are fatigue-cycled at two different stress levels. The coupon overall stiffness and surface-ply TSA damage area have been used as two damage metrics. The MCM can satisfactorily describe the overall fatigue damage evolution for a limited number of coupons (less than 6) subjected to a given specific stress level. The stochastic S-N curve can be constructed using at least two sets of fatigue tests under different stress levels. Three available fatigue tests for different E-glass laminates from the literature are also investigated using the proposed MCM approach. The results show the MCM method can provide the stochastic S-N curves for different composite systems and a wide range of fatigue cycles.