Electrical trees have long been the interest of the electrical insulation community due to their role in power systems equipment failure at locations where high divergent fields might arise due to impurities, contaminants or voids. Even through trees take a long time to grow in real life, they can be grown experimentally in shorter times under various conditions so that their growth characteristics can be investigated. Different samples have been fabricated to investigate the effects of interfaces in electrical tree propagation. Initially, the impact of an interface perpendicular to the electric field, and the interface position, thickness and/or composition on the polymer’s lifetime was investigated. In the results acquired, the positive impact of interfaces positioned perpendicular to the electric field was evident: increasing the samples’ time to breakdown as well as the electrical tree inception time. Due to the encouraging results, further investigation has been focused on interface modification and how this might be used to control the electrical tree growth as well as the samples’ time to breakdown. Altering the interface’s surface roughness using a number of different methods was carried out. Results were graphically and statistically analysed so that the any conclusions are robust, and uncertainties clear. The statistical analysis used by generating regression model equations was a novel method to predict how different electrical tree parameters were affected/affecting by others. In this way the dielectric’s lifetime could be predicted with a certain level of confidence. The modification of the interface by coating the surface with either a thin layer of pure or nano-filled (hexagonal Boron Nitride) epoxy resin resulted in it being impervious thus preventing the electrical tree to propagate through it. This was a novel method that showed that specific modification methods can significantly enhance the dielectric’s lifetime when applied appropriately. Details of new sample fabrication techniques are described which enable better control of the materials and interfaces, and data on tree length growth characteristics are discussed.

This thesis describes the effects of climatic factors, particularly humidity and temperature on the properties of macromolecular substances, but also others, such as UV radiation, wind, water and oxygen. Furthermore, we introduce the definition and distribution of macromolecular substances. The next section describes the basic properties of dielectric materials. Much of the text is devoted to the description, production, curing, properties and utilization of epoxy resins. The last part deals with climate factors in general terms.

This thesis describes the effects of climatic factors, particularly humidity and temperature on the properties of macromolecular substances, but also others, such as UV radiation, wind, water and oxygen. Furthermore, we introduce the definition and distribution of macromolecular substances. The next section describes the basic properties of dielectric materials. Much of the text is devoted to the description, production, curing, properties and utilization of epoxy resins. The last part deals with climate factors in general terms.

This masters’s thesis study electric properties of nanocomposites based on epoxy resins, production of samples and measuring their electrical properties. In this thesis there are observed temperature dependences of the dissipation factor, relative permittivity and internal resistivity.

This work was performed under a cooporative research effort sponsored by the National Aeronautics and Space Administration (NASA) in conjunction with the aerospace industry and acedemia. One of the primary goals of NASA is to improve the safety and affordability of commercial air flight. Part of this goal includes research to reduce fuel consumption by developing lightweight carbon fiber, polymer matrix composites to replace existing metallic airframe structure. In the Twenty-first Aircraft Technology Program (TCAT) efforts were focused on developing novel processing methods to fabricate tailored composite airframe structure. The Vacuum Assisted Resin Transfer Molding (VARTM) processing technique offers a safer, more affordable alternative to manufacture large scale composite fuselages and wing structures. Vacuum assisted resin transfer molding is an infusion process originally developed for manufacturing of composites in the marine industry. The process is a variation of Resin Transfer Molding (RTM), where the rigid matched metal tooling is replaced on one side with a flexible vacuum bag. The entire process, including infusion and consolidation of the part, occurs at atmospheric pressure (101.5 kPa). High-performance composites with fiber volumes in the range of 45% to 50% can be achieved without the use of an autoclave. The main focus of the VARTM process development effort was to determine the feasibility of manufacturing aerospace quality composites with fiber volume fractions approaching 60%. A science-based approach was taken, utilizing finite element process models to characterize and develop a full understanding of the VARTM infusion process as well as the interaction of the constituent materials. Achieving aerospace quality composites requires further development not only of the VARTM process, but also of the matrix resins and fiber preforms. The present work includes an investigation of recently developed epoxy matrix resins, including the characterization of the resin cure kinetics and flow behaviors. Two different fiber preform architectures were characterized to determine the response to compaction under VARTM conditions including a study to determine the effect of thickness on maximum achievable fiber volume fraction. Experiments were also conducted to determine the permeabilities of these preforms under VARTM flow conditions. Both the compaction response and the permeabilities of the preforms were fit to empirical models which can be used as input for future work to simulate VARTM infusion using process models. Actual infusion experiments of these two types preforms were conducted using instrumented tools to determine the pressures and displacements that occur during VARTM infiltration. Flow experiments on glass tooling determined the fill-times and flow front evolution of preform specimens of various thicknesses. The results of these experiments can be used as validation of process model infusion simulations and to verify the compaction and permeability empirical models. Panels were infused with newly developed epoxy resins, cured and sectioned to determine final fiber volume fractions and part quality in an effort to verify both the infusion and compaction experimental data. The preforms characterized were found to have both elastic and inelastic compression response. The maximum fiber volume fraction of the knitted fabrics was dependent on the amount of stacks in the preform specimen. This relationship was found in the determination of the Darcy permeabilities of the preforms. The results of the characterization of the two epoxy resin systems the show that the two resins have similar minimum viscosities but significantly different curing behaviors. Characterization of the VARTM process resulted in different infusion responses in the two preform specimens investigated. The response of the saturated preform to a recompaction after infusion indicated that a significant portion of the fiber volume lost during infusion could be recovered. Fiber volume and void-content analysis of flat composite panels fabricated in VARTM using the characterized resins and preforms resulted in void-free parts with fiber volumes over 58%. Results in the idealized compaction tests indicated fiber volumes as high as 60% were achievable with the knitted fabric. The work over the presented here has led to a more complete understanding of the VARTM process but also led to more questions concerning its feasibility as an aerospace composite manufacturing technique. / Master of Science

The following thesis titled SPHERE OF INFLUENCE is about development. I discuss my efforts to develop as an artist addressing observation and awareness of the self and our surroundings. I will discuss how this relates to my approach with materials and process and will explain not only what the sculpture titled SPHERE OF INFLUENCE has come to represent for me, but also the reactions of viewers during the temporary installation of the SPHERE OF INFLUENCE at the Anderson Gallery at Virginia Commonwealth University from May 5th 2006 through May 14th, 2006. I will explain the SPHERE OF INFLENCE'S function as both an object meant to evoke an awareness of what and who surrounds its space and as a metaphor of my efforts to surpass personal and artistic boundaries.

Dans le cadre de cette thèse, nous rechercherons comment éliminer les opérations de non-valeur-ajoutée dans la fabrication des pièces en matériaux composites incluant la fixation des puces RFID directement dans les pièces en matériaux composites utilisées dans les industries aéronautiques et spatiales. Nous proposerons une nouvelle méthode innovante. Cette méthode industrielle utilise la technologie RFID pour aider éliminer les étapes de non-valeur-ajoutée qui empêchent des améliorations opérationnelles. En plus d’aider à éliminer des opérations de non-valeur-ajoutée, cette technologie peut permettre d’augmenter la communication transverse entre des processus opérationnels. L'utilisation appropriée de technologie RFID peut aussi aider à augmenter la visibilité des produits, des données et des outils dans la fabrication. Les étapes de contrôle inutiles qui induisent des délais de processus plus importants et des coûts additionnels plus élevés peuvent automatiquement être éliminées. De plus, cette méthode permet d’assurer une macro et micro traçabilité. La technologie RFID marche très bien tant avec la fibre de verre qu'avec les composés de fibre de carbone industriels. L’intégration de ces aides technologiques dans les pièces composites permet de créer des matériaux "intelligents" et de communiquer avec d'autres systèmes industriels qui sont voisins, ou dans un autre pays via le logiciel. Et cette capacité peut aider à réduire la documentation et améliorer la traçabilité pendant les phases industrielles transverses de l'entreprise. Les Informations peuvent être stockées sur la puce à l’avance ou bien après chaque processus. Ceci permet aussi d’élaborer de nouveaux processus et des occasions de traitement de la part de la société pour les parties qui sont en service. De cette façon, la puce peut permettre une communication entre le fabricant et le client. Les informations sur l'Étiquette RFID permettent aux pièces d'être gérées plus rapidement et à distance pendant tout le cycle de vie de la pièce. Les informations enregistrées sur la puce pendant la fabrication de la pièce composite peuvent même être lues, avec un ajout d’information, pendant que la pièce est en service. La méthode que nous proposons est la fixation la puce RFID dans les pièces en matériaux composites. Le dépistage et le contrôle automatiques de ces parties permettra à nos processus industriels d'être plus efficaces et visibles pendant la fabrication, aussi bien que le support après la livraison du produit. Dans un proche avenir, des entreprises nationales et internationales transformeront leur ingénierie et procédés de fabrication en appliquant cette méthode novatrice qui accélère les cycles de vie, maximise l'efficacité et élimine des étapes inutiles dans le processus. En conséquence, ces entreprises seront dans une bien meilleure position pour maximiser leur productivité et des nouvelles occasions de produit/marché aussi bien que la documentation de produit efficace et les processus de production aideront des entreprise ou les clients à abaisser leurs coûts d'exploitation, à augmenter la productivité des salariés, à améliorer la conformité, le délai de diminution et à faire des progrès plus rapides dans le domaine de la durabilité. En résumé, le fait de diminuer le délai de livraison à chaque étape dans le processus "On-Target" soutiendra) grandement la performance de " On-Cost" et " On-Quality". En utilisant cette méthode, les fabricants deviendront capables de diminuer considérablement leurs coûts, d’améliorer de façon significative les améliorations de processus, d’augmenter l’innovation à chaque étape du processus et de lancer dans l’entreprise des actions qui lui conféreront une vaste excellence opérationnelle. / The main objective of this thesis is to improve the traditional manufacturing processes in the company and to replace the traditional manufacturing methodology by new method in order to improve the manufacturing efficiency (time, cost, quality, safety of the products etc.). In the frame of this thesis, we will focus on how to eliminate the non-value added operations in the manufacturing by the embedding RFID tags directly in the composite parts used in aerospace companies. We will propose a new innovative state of the art composite manufacturing method that uses RFID technology to help eliminate non-value added manual steps that impede operational improvements. This technology can help to eliminate non-value added operations and increase the communication across operational processes. The appropriate use of RFID technology can also help increase the visibility of the products, data, and tools in manufacturing. The unnecessary control steps which induce higher process lead-times and higher additional costs can automatically be eliminated. The macro and micro traceability of processes and products (such as the part information, lifecycle, movement history and location) can all be automated and digitized with less manual intervention and less paper documentation. Carefully using this technology across our production processes, we can rapidly transform operational processes and improve their accuracy, control and efficiency. This is a lean, innovative and value adding innovative approach that significantly increases the visibility and monitoring of processes. RFID technology works very well with both glass and carbon fibre composites’ manufacturing. This technology helps makes the composite parts “smart” and communicate with other manufacturing systems that are nearby or in another country via software. And this capability can help reduce documentation and improve traceability during the manufacturing phases and across the company. Information can be stored on the tag before and/or after each process. This also enables new process and company service opportunities for parts that are in-service. In this way, the tag can enable a communication between the manufacturer and customer. The information on the RFID Tag enables the parts to be managed faster and remotely across the full lifecycle of the part. The information recorded on the RFID Tag during the manufacturing of the composite parts can even be read and more information can be read during in-service. This information can create an advantage for any modification of the parts, repair, and maintenance in the future. In this way, RFID based processes can reduce unnecessary steps across the whole supply chain and reduce the high workload of manual processes and documentation. Furthermore, costs can be minimized due to increased visibility and elimination of unnecessary steps across processes. Using RFID technology by direct embedding of the RFID Tag in the composite parts intends to measure and reduce “Process Variation”. The idea here is not to move the tasks, but to optimize and eliminating the non-value added tasks by using RFID based production method “embedding of RFID Tag in Composite parts”. The method that we propose is embedding the RFID tag in the composite parts. Automatically tracking and monitoring these parts will enable our industrial processes to be more efficient and visible during manufacturing as well as in service-processes that occur after delivery of the product. As mentioned previously, the intention here to enable our composite parts to be “smart” so they can be communicated to automatically across their lifecycle. This will help create an industrial "Internet of Things”. [...]

Neste trabalho foi realizado o estudo térmico, cinético e dielétrico durante a cura de um compósito constituído de uma matriz de resina epóxi-anidrido e de talco como carga modificadora das características dielétricas e mecânicas da matriz polimérica. Foram analisadas também as propriedades dinâmicas mecânicas e morfológicas dos compósitos completamente curados. O interesse na investigação das características térmicas, cinéticas e dielétricas visou encontrar correlação entre essas características e as propriedades dinâmicas mecânicas finais dos compósitos. Foram estudados os compósitos com diferentes concentrações de carga, variando de 0 a 10% m/m, utilizando as técnicas de calorimetria exploratória diferencial (DSC), de análise dielétrica (DEA), análise termomecânica dinâmica (DMTA) e análise por microscopia eletrônica de varredura (MEV). Os resultados da análise DSC foram analisados por método isotérmico (modelo de Sourour-Kamal modificado) e por método dinâmico (modelo isoconversional). Os resultados da análise da cura dos compósitos mostraram que a concentração da carga retarda o processo de cura, conforme observado pela análise dielétrica; a temperatura de transição vítrea do compósito curado apresentou valores mínimos nas concentrações de 7 e 10%, enquanto que a análise térmica dinâmica previu que a energia de ativação aumenta com o grau de conversão. Os resultados da análise termomecânica dinâmica mostraram o aumento no módulo de armazenamento a 25ºC de 2,1 GPa (0% talco) a 3,3 GPa (10% talco), indicando haver o efeito reforçador do talco sobre a matriz polimérica. As micrografias dos compósitos foram um excelente recurso para estudar suas morfologias e se correlacionam com os resultados cinéticos e mecânicos. / In this work we performed the thermal, kinetics, dielectrical and morphological studies on the curing of a hybrid composite material composed of epoxy-anhydride matrix and talc as modifier agent of the dielectrical and mechanical properties of the polymer matrix. It also was studied the dynamic mechanical properties of the full-cured composite materials. This investigation aimed to correlate the thermal, kinetics, and dielectrical characteristics of the curing material with their final mechanical properties. Composite materials with different talc concentrations were studied in the range from 0% up to 10% w/w, employing the Differential Scanning Calorimetry (DSC), the Dielectric Analysis (DEA), Dynamic Mechanical Thermal Analysis (DMTA) and Microscopy Electron Scanning (SEM) techniques. The DSC experimental results were analyzed through the isothermal method (Modified Sourour-Kamal model) and the dynamic method (Isoconversional model). The cure analysis results of the composite specimens showed the talc acting as a cure retardant as observed from DEA results; the glass transition temperature of the full-cured composite materials showed minimum values at talc concentrations of 7 and 10%, while the dynamic thermal analysis predicted the activation energy is increasing with the conversion degree. The DMTA results exhibited the storage modulus at 25ºC increases from 2.1 GPa for the matrix without talc up to 3.3 GPa at 10% talc concentration composite, thus indicating the reinforcement role of the talc on the polymer matrix. The composites micrographs were an excellent resource for study their morphologies and for correlation of kinetics and mechanical results.

Nas extremidades dos dutos flexíveis utilizados na indústria petroleira offshore são instalados os end fittings, ou conectores. Uma parte fundamental deste componente é o sistema de ancoragem, que consiste nos arames de aço da armadura de tração embebidos em resina epóxi, onde seu propósito é transmitir os esforços que provêm do duto. Este estudo tem como objetivo apresentar uma avaliação de três diferentes resinas epóxi (Huntsman: SW404/HY404, AW4804/HW4804 e XAW1395/HY950) comparando as propriedades mecânicas e a influência do ambiente de serviço, a fim de definir qual melhor se adequa para este fim. As propriedades mecânicas das resinas epóxi foram determinadas através de ensaios de compressão, tração, cisalhamento, pullout e medições de dureza. Os denominados ensaios de pullout representam um modelo simplificado do sistema de ancoragem e possibilitam o estudo da interface entre a resina e o aço da armadura de tração. Para avaliar o efeito da exposição do polímero às condições ambientais de serviço, amostras foram envelhecidas numa solução de água marinha na temperatura constante de 60°C, durante um período de 6 meses. Após este período, realizaram-se ensaios de compressão, cisalhamento e pullout, cujos resultados foram comparados com os obtidos de amostras sem nenhum período de exposição. A influência das elevadas temperaturas sobre a propriedade de adesão nas diferentes resinas foi avaliada mediante ensaios de pullout realizados à temperatura de 100°C. Além disto, foi realizada uma análise térmica através de ensaios de TGA e DMTA. Por fim, às propriedades determinadas nos diferentes ensaios e medições lhes foram atribuídas um peso quantitativo de acordo com sua importância dentro do sistema de ancoragem. Os valores das propriedades e seus pesos foram introduzidos a uma matriz de análise de multicritérios, que permitiu selecionar a resina epóxi com a melhor combinação de propriedades para ser aplicada em end fittings. Finalmente, é proposta a determinação de alguns parâmetros adicionais das resinas epóxi para complementar o estudo realizado / End fittings are components that are installed at the ends of flexible pipes used in the offshore oil industry. A fundamental part of this component is the anchoring system, which consists of the steel wires of the tensile armour embedded in epoxy resin, which its purpose is to transmit the loads that come from the pipe. This study aims to present an evaluation of three different epoxy resins (Huntsman: SW404/HY404, AW4804/HW4804 e XAW1395/HY950), comparing the mechanical properties and studying the influence of the service environment, in order to define which material is best suited for this application. The mechanical properties of the epoxy resins were determined by tests such as compression, tensile, shear and pullout tests and hardness measurements. The pullout tests represent a simplified model of the anchoring system and they allow the study of the interface between the resin and the steel of the tensile armour. To evaluate the effect of the exposition of the polymer material to environmental conditions found in service, some samples were immersed in a bath of sea water at a constant temperature of 60°C during a period of 6 months. After this period, compression, shear and pullout tests were performed and the results were compared with those obtained from samples without degradation. The influence of the high temperatures on the adhesion property of the different epoxy resins was evaluated with pullout tests performed at a temperature of 100°C. Furthermore, a thermal analysis was realized through TGA and DMTA tests. Finally, to the properties determined in the different tests and measurements were given a quantitative weight according to their importance within the anchoring system. The values of the properties and their weights were introduced into a matrix of multicriterial analysis that allowed selecting the epoxy resin with the best combination of properties to be applied in end fittings. Finally, it was proposed the determination of other epoxy resins parameters to complement this study.

High-voltage (HV) outdoor composite insulators used in transmission lines are made of two polymers, comprising the core and housing, bonded together with metallic end-connections. The interface between these polymers is parallel to the electric field, which makes the insulators more prone to interfacial problems at these common points [1]. If interfacial ageing occurs, degradation and catastrophic breakdown can result [2]. Therefore, the design reliability of outdoor composite insulators depends on the high-strength bond between the core and the housing [3],[4]. Research findings by Kutil and Froshlic [5] indicate that delaminated areas, cavities and/or micro cracks in the medium are enough to initiate streamer discharges along the interface that are capable of degrading both insulating materials. The heat, UV radiation, and high-energy electrons produced from such discharge activity resulted in the growth of carbon paths along the interface, known as ‘tracking’, ultimately causing failure [6]. This investigation focuses on the development of tracking between silicone rubber and epoxy resin, with a view to replicating the tracking phenomena seen within composite insulators in service. A fine wire is placed between the dielectrics materials to enhance the local electric field magnitude and initiate discharge processes. The resulting partial discharge (PD) activity has been monitored. This Information has been used to understand the inception and propagation of the interfacial tracking. A strong relationship was found between maximum PD magnitude and track length. PD patterns and unique detailed images of the interfacial tracking development, allowed identification of the growth characteristics of interfacial channels and phases of tracking growth. Furthermore, a correlation in the mechanisms of interfacial degradation was found between the lab-fabricated samples and commercial composite rods. Finally, a growth model of interfacial ageing has been developed with the information from FEA models, PD patterns and the detailed images of tracking growth. The physical structure and chemical analysis of interfacial tracking is also disclosed to provide an insight into interfacial ageing mechanisms that occur in the composite insulators under electrical stress.