Inspeção de materiais compósitos utilizando ondas acústicas guiadas

Pós-graduação em Engenharia Elétrica - FEIS

Estudo comparativo de pás para aerogeradores de grande porte fabricadas em materiais compósitos reforçadas com fibra de carbono ou fibra de vidro

The research and development of wind turbine blades are essential to keep pace with worldwide growth in the renewable energy sector. Although currently blades are typically produced using glass fiber reinforced composite materials, the tendency for larger size blades, particularly for offshore applications, has increased the interest on carbon fiber reinforced composites because of the potential for increased stiffness and weight reduction. In this study a model of blade designed for large generators (5 MW) was studied on a small scale. A numerical simulation was performed to determine the aerodynamic loading using a Computational Fluid Dynamics (CFD) software. Two blades were then designed and manufactured using epoxy matrix composites: one reinforced with glass fibers and the other with carbon fibers. For the structural calculations, maximum stress failure criterion was adopted. The blades were manufactured by Vacuum Assisted Resin Transfer Molding (VARTM), typical for this type of component. A weight comparison of the two blades was performed and the weight of the carbon fiber blade was approximately 45% of the weight of the fiberglass reinforced blade. Static bending tests were carried out on the blades for various percentages of the design load and deflections measurements were compared with the values obtained from finite element simulations. A good agreement was observed between the measured and calculated deflections. In summary, the results of this study confirm that the low density combined with high mechanical properties of carbon fibers are particularly attractive for the production of large size wind turbine blades

Projeto e Construção de um Veleiro Autónomo, utilizando materiais compósitos, Impressão a 3D e Aprendizagem Máquina

Este trabalho consistiu no projeto e construção de um veleiro autónomo de pequena escala. No início do trabalho, é feito um estudo acerca dos diferentes tipos de veículos autónomos, dando mais enfase aos veleiros. Em seguida, é iniciado o projeto do casco do veleiro, aplicando conceitos básicos de Arquitetura Naval. A forma do casco é desenhada com recurso ao programa DELFT Ship Free, onde são realizados estudos hidrodinâmicos do mesmo. Posteriormente é retratado a construção do casco projetado, com recurso a materiais compósitos e impressão 3D de componentes do veleiro. São ainda descritos os sensores, controladores, atuadores e programação desenvolvida para o veleiro. É também realizado um estudo sumário da estimativa de consumos e autonomia do sistema. No final, encontram-se os resultados obtidos das provas de mar efetuadas ao veleiro.

Fabrico híbrido em grande escala de materiais compósitos

As tecnologias de fabrico aditivo e subtrativo têm vindo a desenvolver-se no sentido de permitir a produção de peças com melhores rigor dimensional, características mecânicas, físicas e químicas, utilizando ainda materiais completamente novos desenvolvidos a pensar nos requisitos em determinadas aplicações. A fabricação híbrida, um processo que utiliza dois ou mais processos de fabrico com características diferentes na mesma unidade de fabrico aproveitando assim as vantagens de cada processo, tem vindo a aparecer como meio de melhorar a qualidade e complexidade dos produtos a serem desenvolvidos. O desenvolvimento de processos de grande escala tem também vindo a verificar-se, sendo estes uma ampliação e aplicação dos processos já existentes para a produção a uma escala maior. Os compósitos de matriz polimérica são os materiais em foco neste trabalho. Alguns polímeros derivam de fontes não renováveis como o petróleo, o que tem levado ao crescimento da indústria de reciclagem deste tipo de materiais para a sua reutilização. Acresce o facto de que a incorporação de resíduos industriais é vista como uma vantagem, quer em termos de custos, quer em termos de sustentabilidade. O presente trabalho teve com objetivo o desenvolvimento de tecnologias de fabricação híbrida, aplicadas a materiais compósitos provenientes, em parte, do reaproveitamento de resíduos industriais. Assim, foi desenvolvido um sistema de extrusão de grandes dimensões - um braço robot com uma extrusora acoplada no seu último eixo, com uma variante híbrida combinando extrusão e maquinação - uma máquina fresadora com uma extrusora acoplada na sua árvore (Eixo Z); e foram desenvolvidos materiais compósitos aplicando o reprocessamento com incorporação de resíduos, por forma a originar produtos de materiais reciclados, contribuindo para a conservação do ambiente. Foi efetuada a validação de um dos conceitos através do desenvolvimento de peças extrudidas com os materiais reciclados e posterior estudo de parâmetros de processamento que conduzem a melhores resultados em temos de geometria. Esta avaliação foi efetuada com recurso a técnicas de engenharia inversa. Foi possível identificar tendências que permitirão melhorar a aplicabilidade deste tipo de processos no fabrico de peças de grandes dimensões.

Compósitos poliméricos a base de fibras de licuri: efeitos da hibridização e do envelhecimento ambiental acelerado

The gradual replacement of conventional materials by the ones called composite materials is becoming a concern about the response of these composites against adverse environmental conditions, such as ultraviolet radiation, high temperature and moist. Also the search for new composite using natural fibers or a blend of it with synthetic fibers as reinforcement has been studied. In this sense, this research begins with a thorough study of microstructural characterization of licuri fiber, as a proposal of alternative reinforcement to polymeric composites. Thus, a study about the development of two composite laminates was done. The first one, involving only the fiber of licuri and the second comprising a hybrid composite based of fiber glass E and the fiber of licuri, in order to know the performance of the fiber when of fiber across the hybridization process. The laminates were made in the form of plates using the tereftálica ortho-polyester resin as matrix. The composite laminate made only by licuri fiber had two reinforcing fabric layers of unidirectional licuri and the hybrid composite had two reinforcing layers of unidirectional licuri fabric and three layers of fiber short glass-E mat. Finally, both laminates was exposed to aging acceleration in order to study the influence of environmental degradation involving the mechanical properties and fracture characteristics thereof. Regarding the mechanical properties of composites, these were determined through uniaxial tensile tests, uniaxial compression and three bending points for both laminates in original state, and uniaxial tensile tests and three bending points after accelerated aging. As regards the study of structural degradation due to aging of the laminates, it was carried out based on microscopic analysis and microstructure, as well as measuring weight loss. The characteristics of the fracture was performed by macroscopic and microscopic (optical and SEM) analysis. In general, the laminated composites based on fiber licuri showed some advantages in their responses to environmental aging. These advantages are observed in the behavior related to stiffness as well as the microstructural degradation and photo-oxidation processes. However, the structural integrity of this laminate was more affected in case the action of uniaxial tensile loads, where it was noted a lower rate of withholding his last resistance property

Laminados compósitos de PRFV: efeitos da descontinuidade geométrica e do envelhecimento ambiental acelerado

The growing demand in the use of composite materials necessitates a better understanding of its behavior related to many conditions of loading and service, as well as under several ways of connections involved in mechanisms of structural projects. Within these project conditions are highlighted the presence of geometrical discontinuities in the area of cross and longitudinal sections of structural elements and environmental conditions of work like UV radiation, moisture, heat, leading to a decrease in final mechanical response of the material. In this sense, this thesis aims to develop studies detailed (experimental and semi-empirical models) the effects caused by the presence of geometric discontinuity, more specifically, a central hole in the longitudinal section (with reduced cross section) and the influence of accelerated environmental aging on the mechanical properties and fracture mechanism of FGRP composite laminates under the action of uniaxial tensile loads. Studies on morphological behavior and structural degradation of composite laminates are performed by macroscopic and microscopic analysis of affected surfaces, in addition to evaluation by the Measurement technique for mass variation (TMVM). The accelerated environmental aging conditions are simulated by aging chamber. To study the simultaneous influence of aging/geometric discontinuity in the mechanical properties of composite laminates, a semiempirical model is proposed and called IE/FCPM Model. For the stress concentration due to the central hole, an analisys by failures criteria were performed by Average-Stress Criterion (ASC) and Point-Stress Criterion (PSC). Two polymeric composite laminates, manufactured industrially were studied: the first is only reinforced by short mats of fiberglass-E (LM) and the second where the reinforced by glass fiber/E comes in the form of bidirectional fabric (LT). In the conception configurations of laminates the anisotropy is crucial to the final mechanical response of the same. Finally, a comparative study of all parameters was performed for a better understanding of the results. How conclusive study, the characteristics of the final fracture of the laminate under all conditions that they were subjected, were analyzed. These analyzes were made at the macroscopic level (scanner) microscope (optical and scanning electron). At the end of the analyzes, it was observed that the degradation process occurs similarly for each composite researched, however, the LM composite compared to composite LT (configurations LT 0/90º and LT ±45º) proved to be more susceptible to loss of mechanical properties in both regarding with the central hole as well to accelerated environmental aging

Compósitos poliméricos a base de fibras de licuri: efeitos da hibridização e do envelhecimento ambiental acelerado

The gradual replacement of conventional materials by the ones called composite materials is becoming a concern about the response of these composites against adverse environmental conditions, such as ultraviolet radiation, high temperature and moist. Also the search for new composite using natural fibers or a blend of it with synthetic fibers as reinforcement has been studied. In this sense, this research begins with a thorough study of microstructural characterization of licuri fiber, as a proposal of alternative reinforcement to polymeric composites. Thus, a study about the development of two composite laminates was done. The first one, involving only the fiber of licuri and the second comprising a hybrid composite based of fiber glass E and the fiber of licuri, in order to know the performance of the fiber when of fiber across the hybridization process. The laminates were made in the form of plates using the tereftálica ortho-polyester resin as matrix. The composite laminate made only by licuri fiber had two reinforcing fabric layers of unidirectional licuri and the hybrid composite had two reinforcing layers of unidirectional licuri fabric and three layers of fiber short glass-E mat. Finally, both laminates was exposed to aging acceleration in order to study the influence of environmental degradation involving the mechanical properties and fracture characteristics thereof. Regarding the mechanical properties of composites, these were determined through uniaxial tensile tests, uniaxial compression and three bending points for both laminates in original state, and uniaxial tensile tests and three bending points after accelerated aging. As regards the study of structural degradation due to aging of the laminates, it was carried out based on microscopic analysis and microstructure, as well as measuring weight loss. The characteristics of the fracture was performed by macroscopic and microscopic (optical and SEM) analysis. In general, the laminated composites based on fiber licuri showed some advantages in their responses to environmental aging. These advantages are observed in the behavior related to stiffness as well as the microstructural degradation and photo-oxidation processes. However, the structural integrity of this laminate was more affected in case the action of uniaxial tensile loads, where it was noted a lower rate of withholding his last resistance property

Estudo do comportamento de vigas de betão simples e reforçadas com CFRP, sujeitas a envelhecimento

Dissertação para obtenção do Grau de Mestre em Engenharia Civil, Perfil de Estruturas

Um modelo analítico e computacional para consideração de efeitos de envelhecimento em estruturas de material compósito

Os materiais compósitos reforçados por fibras apresentam vantagens quando comparados aos materiais de construção mais tradicionais como concreto e aço. Por outro lado, devido ao fato destes materiais serem relativamente recentes no mercado, questões a respeito de sua durabilidade são ainda objeto de discussão e faz-se necessária intensa pesquisa sobre o envelhecimento dos compósitos. Como conseqüência, recentemente têm surgido inúmeros trabalhos à respeito da degradação dos compósitos considerando efeitos como temperatura, oxidação, radiação UV, condições de carregamento, etc. A maioria destas pesquisas, no entanto, são realizadas a nível de material e não são diretamente aplicáveis à situações de projeto. Desta forma, existe grande demanda por novos estudos e dados compatíveis com aplicações estruturais. Neste trabalho apresenta-se um modelo analítico-numérico adequado para, interpretação e aplicação destes dados experimentais em análise e projeto de estrutural. A formulação proposta inclui relações constitutivas elásticas anisotrópicas com envelhecimento, relações constitutivas viscoelásticas anisotrópicas com envelhecimento em termos de variáveis de estado, análise de falhas com critério de degradação ajustado à idade do material e considera-se grandes deslocamentos e pequenas deformações. As diferenças essenciais entre os processos de envelhecimento em endurecimento e amolecimento são descritos juntamente com as relações constitutivas para cada caso. Estas equações são deduzidas na forma adequada para análise numérica via método dos elementos finitos usando uma solução incremental-iterativa com consideração de efeitos pos-críticos. Vários exemplos são apresentados, incluindo análises elásticas, viscoelásticas e de falha com envelhecimento.

Envelhecimento ambiental acelerado em PRF a base de tecidos híbridos kevlar/vidro: propriedades e instabilidade estrutural

There are a number of damaging mechanisms that various materials can suffer in service. However, when working with polymer composite materials, this is something that requires analysis, especially when exposed to adverse environmental conditions. Thus, the objective of the present thesis is the study of the direct influence of environmental aging and the form of hybridization of the reinforcement woven on the structural stability, surfacedegradation and fracture process of polymer composites laminates. For this, the development of two polymer composite laminates was necessary, where one of them was reinforced with a bi-directional woven with hybrid strandsofkevlar-49/glass-Efibers, and the other also with a bi-directionalwoven, however with weft and warpformed of alternating strandsof Kevlar-49 fibers and glass-E fiber The reinforcementwoven are industrially manufactured. Both laminates use a polyester resin as a matrixand are made up of four layers each. All laminates were industrially prepared by the hand lay-up method of manufacturing. To do this, test specimens were manufactured of the respective laminates and submitted to environmental aging accelerated through the aging chamber. They were exposed to alternating cycles of UV radiation and moisture (heated steam) for a standard defined period. At the end of the exposure period the specimens were subjected to mechanical tests of uniaxial tensile and bending in three points and to the characterizationsof the fracture and surface deterioration. In addition, they were submitted to a structural degradation assessment by the measurement of mass variation technique (MMVT) and the measurement of thickness variation technique (MTVT), this last technique being developed in this thesis. At the end of the analysis it was observed that the form of hybridization of the reinforcement woven and the aging process directly influence with losses or gain in mechanical properties, with losses in the structural degradation and in the formation and propagation of damage mechanism of the developedcomposite laminates

Efeitos da radiação uv, temperatura e vapor aquecido nos compósitos poliméricos: monitoramento, instabilidade estrutural e fratura

The application of composite materials and in particular the fiber-reinforced plastics (FRP) has gradually conquered space from the so called conventional materials. However, challenges have arisen when their application occurs in equipment and mechanical structures which will be exposed to harsh environmental conditions, especially when there is the influence of environmental degradation due to temperature, UV radiation and moisture in the mechanical performance of these structures, causing irreversible structural damage such as loss of dimensional stability, interfacial degradation, loss of mass, loss of structural properties and changes in the damage mechanism. In this context, the objective of this thesis is the development of a process for monitoring and modeling structural degradation, and the study of the physical and mechanical properties in FRP when in the presence of adverse environmental conditions (ageing). The mechanism of ageing is characterized by controlled environmental conditions of heated steam and ultraviolet radiation. For the research, it was necessary to develop three polymer composites. The first was a lamina of polyester resin reinforced with a short glass-E fiber mat (representing the layer exposed to ageing), and the other two were laminates, both of seven layers of reinforcement, one being made up only of short fibers of glass-E, and the other a hybrid type reinforced with fibers of glass-E/ fibers of curaua. It should be noted that the two laminates have the lamina of short glass-E fibers as a layer of the ageing process incidence. The specimens were removed from the composites mentioned and submitted to environmental ageing accelerated by an ageing chamber. To study the monitoring and modeling of degradation, the ageing cycles to which the lamina was exposed were: alternating cycles of UV radiation and heated steam, a cycle only of UV radiation and a cycle only of heated steam, for a period defined by norm. The laminates have already undergone only the alternating cycle of UV and heated steam. At the end of the exposure period the specimens were subjected to a structural stability assessment by means of the developed measurement of thickness variation technique (MTVT) and the measurement of mass variation technique (MMVT). Then they were subjected to the mechanical tests of uniaxial tension for the lamina and all the laminates, besides the bending test on three points for the laminates. This study was followed by characterization of the fracture and the surface degradation. Finally, a model was developed for the composites called Ageing Zone Diagram (AZD) for monitoring and predicting the tensile strength after the ageing processes. From the results it was observed that the process of degradation occurs Abstract Raimundo Nonato Barbosa Felipe xiv differently for each composite studied, although all were affected in certain way and that the most aggressive ageing process was that of UV radiation, and that the hybrid laminated fibers of glass-E/curaua composite was most affected in its mechanical properties

Avaliação da delaminação após furação em compósitos laminados

As características excepcionais dos materiais compósitos de matriz polimérica têm conduzido à sua crescente utilização em todos os domínios. A necessidade de ligar estas peças entre si obriga à realização frequente de operações de furação que, embora devidamente adaptada, pode provocar diferentes tipos de dano nas peças a ligar. Desses, o dano mais grave é a delaminação pelas suas consequências na perda das propriedades mecânicas. Neste trabalho é apresentado um estudo comparativo da extensão do dano em função da geometria de ferramenta utilizada. Para tal as placas foram radiografadas após furação e a imagem resultante segmentada para medição das áreas associadas. Os resultados mostram a importância de uma adequada geometria de ferramenta na redução do dano causado pela furação em compósitos laminados.

Avaliação de ferramentas na furação de laminados compósitos

Drilling of polymeric matrix composite structures

Estudo e caracterização mecânica de compósitos reforçados com fibras naturais

As crescentes preocupações ambientais e a necessidade de um desenvolvimento sustentável tem proporcionado um grande interesse no estudo e desenvolvimento de materiais mais ecológicos e amigos do ambiente. No caso particular da indústria dos materiais compósitos, a utilização de fibras naturais de origem vegetal, em substituição das tradicionais fibras de vidro, tem aumentado significativamente nos últimos anos. Para além dos claros benefícios ecológicos, a utilização de fibras naturais em detrimento das fibras de vidro, possibilita também o fabrico de componentes com baixo peso, boas propriedades mecânicas, baixo custo, pouco abrasivos às ferramentas de produção e com boas propriedades de isolamento térmico e acústico. Contudo, existem também algumas limitações decorrentes da utilização de fibras naturais como reforço de materiais poliméricos, como exemplo, a possibilidade de emitirem odores e absorverem água, a falta de adesão entre as fibras e as matrizes e o facto de possuírem baixa resistência à temperatura. No presente trabalho, foram estudadas e analisadas as propriedades mecânicas de laminados de matriz termoendurecível de epóxido e poliéster, reforçados com várias camadas de tecido bidireccional de fibras de juta. Para além dos referidos laminados, foram também produzidos e estudados compósitos de matriz termoplástica biodegradável de PLA (ácido poliláctico), reforçados com fibras curtas de juta. Todos os compósitos produzidos foram sujeitos a ensaios de tracção e flexão e as suas propriedades foram comparadas. O tecido de juta utilizado como reforço dos compósitos fabricados, foi caracterizado através de vários ensaios, utilizados tipicamente na indústria têxtil. As propriedades extraídas destes ensaios, foram úteis para a previsão das propriedades mecânicas dos materiais compósitos fabricados.Por fim, foi realizada uma análise critica sobres todos os resultados extraídos dos ensaios efectuados.

Fundição centrífuga de compósitos alumínio/sic com gradiente funcional de propriedades: processamento e caracterização

Dissertação apresentada para a obtenção do Grau de Doutor em Ciência dos Materiais Especialidade de Materiais Compósitos pela Universidade Nova de Lisboa, Faculdade de Ciências e Tecnologia