Carbon nanotubes have been studied for nearly two decades and their amazing properties continue to spur intense investigation in the area of polymer composites. In terms of potential commercialization, mutiwall carbon nanotubes (MWCNTs) are currently the most prevalent and economically viable form of nanotubes. Uncovering innovative means to take full advantage of their properties remains a fundamental issue. In this thesis, viability of their use to reinforce polymeric systems is reported. Acrylonitrilebutadiene- styrene (ABS) was used as the host matrix. MWCNTs were introduced to the ABS matrix via melt compounding. The resulting composite was thoroughly rheologically, thermally, and mechanically characterized. Several applications were also experimentally studied. The composites fatigue performance is measured and compared to a typical micron sized carbon fiber. These results indicate that both the nano and micron scale carbon fibers reduce the resistance to fatigue failure. The mechanism of failure in both cases appears to be different and is discussed. The use of microwave energy is investigated for the use of heating purposes. Results show a distinct advantage over conventional heating methods. Microwaves allow for volumetric, fast, selective, and controllable heating of the ABS system.

Orientador: César Renato Foschini / Coorientador: Gilberto de Magalhães Bento Gonçalves / Banca: Carlos Alberto Soufen / Banca: Avelino Alves Filho / Resumo: A exigência dos requisitos de desempenho em estruturas aeroespaciais, navais e automobilísticas vem proporcionando o desenvolvimento de novos materiais, bem como de novas técnicas de fabricação. Normalmente, elevados valores de resistência e rigidez específicas aliados ao baixo peso específico são procurados em projetos estruturais, obtendo-se soluções por meio da utilização de materiais compósitos, particularmente polímeros termo fixos dotados de reforços fibrosos. O entendimento do que é um material composto é necessário, pois trata-se da combinação de no mínimo dois materiais com fase heterogênea, que separados possuem propriedades e características distintas e sua combinação é desejada para a confecção de um material único, com a conformidade das propriedades de ambos os materiais, tornando atrativa sua aplicação. Para otimizar a confecção do laminado em cada projeto, é imprescindível a utilização do modelo em elementos finitos para a obtenção da faixa de tensões, pelo método do critério de falha, sofrida pela amostra e assim obter-se a melhor propriedade mecânica para o seu uso. O presente trabalho tem por objetivo elaborar um estudo comparativo entre os resultados obtidos experimentalmente e os obtidos virtualmente, para validar o uso do software de elementos finitos na execução de um projeto utilizando como material principal o compósito estrutural de fibra de carbono com resina epóxi. Para isso, foram realizados ensaios para obter as propriedades mecânicas, e a melhor... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The demand of requirements in performance of aerospace, naval and automotive structures has been providing the development of new materials as well as new manufacturing techniques. High values of specific strength and stiffness combined with low specific gravity are usually sought in blade designs for wind generators and other components of these systems, obtaining solutions using composite materials, particularly thermoset polymers endowed with fibrous reinforcements. The understanding of what is a composite material is necessary because it is a combination of at least two materials with heterogeneous phase, which have different properties and characteristics and their combination is desired for the manufacture of a single material with conformity of the properties of both materials, making its application attractive. To optimize the preparation of the laminate in each project, it is essential to use the finite element model to obtain the stress range, by the failure criterion method, and to obtain the best mechanical property for its use. The present work has the objective of elaborating a comparative study between the results obtained experimentally and those obtained virtually to validate the use of finite element software in the execution of a project using the structural material of carbon fiber with epoxy resin as its main material. For this, tests were carried out to obtain the mechanical properties and the best curing temperature of the SQ 2004 resin. Later, carbon f... (Complete abstract click electronic access below) / Mestre

The purpose of this study was to determine the effects, if any, of including varying amounts of fiberglass in Unidirectional Carbon Fiber Laminates. The focus was on strength, weight, and damage. A solution to the entrapment of air in thick unidirectional carbon fiber laminates under vacuum pressure was expected from this study. This study presents background, introduction, data, and results pertaining to the subject. Care was made to fully explain all procedures and terminology for complete comprehension of the subject matter. This study used Design of Experiments to formulate an adequate test population, and it used multiple specimens per Case to formulate an accurate representation of the results. This study used empirical results calculated from Compression After Impact data gathered on a Instron model 5585H at NRRI with a CAI frame, and a load cell capable of 56,250lbs, using Bluehill software for data collection, as well as results determined from nondestructive inspection using a PE + Pulse Echo ultrasonic machine, specifically a Flawinspecta from Diagnostic Sonar LTD with 128 element 67mm array and Flawinspecta version 1.3.6 software. A focus of this research was to create a method to manufacture thick unidirectional carbon fiber laminates solely under vacuum pressure. Currently the only way to manufacture suitable thick unidirectional laminates is through use of an autoclave; otherwise an abundance of entrapped air structurally weakens the part and will result in an inadequate specimen. This entrapped air not only weakens the piece by interrupting the stress handling characteristics of the fiber-matrix structure, but makes it near impossible to use ultrasound as a nondestructive inspection option to check for inconsistencies in the material. The second focus of the research was to understand the effects, if any of including fiberglass within a carbon composite panel. Both dry fiberglass veil and pre-preg fiberglass fabric were included in various samples to view any effects on strength, and damage tolerance. The samples were compared on thickness or bulk, weight, residual strength, and damage mitigation. Disclaimer: Certain information such as: Sources, Technical Data, Specific Names, etc. must be withheld due to Classification, and Business Interests.

Master of Science / Department of Civil Engineering / Asadollah Esmaeily / Engineers involved in construction face various challenges. One of them being dealing with cracks in concrete. Naturally, concrete is weak in tension defining its bristle characteristics. To compensate, fiber reinforcement is used in the concrete mixes. Popular fiber types are steel, glass, polypropylene, and carbon fibers. These types of fibers are used to reinforce concrete. These fibers all increase the tensile and flexural strength of concrete. Additionally, they all have their own advantages. This paper is oriented to briefly introduce basic properties of these fibers. This includes the composition, production, advantages, applications, and restrictions of the mentioned fibers.

Les matériaux composites à base de fibres de carbone (CF) sont actuellement très utilises dans le domaine de l’aérospatiale, de la construction et du sport grâce à leurs excellentes propriétés mécaniques, une faible densité et une haute stabilité thermique. Les propriétés des composites dépendent fortement de la nature et de la qualité de l’interface fibre/matrice. Une bonne adhérence interfaciale permet un meilleur transfert de charge entre la matrice et les fibres. Les CFs sans traitement sont chimiquement inertes et présentent donc une faible adhérence vis-à-vis de la résine époxyde. Par ailleurs, les faibles propriétés transversales et interlaminaires limitent sensiblement la performance et la durée de vie des composites. Par conséquent, un type de renfort à base de fibres traitées est fortement souhaité pour améliorer les propriétés globales des composites, en particulier l'adhésion interfaciale entre les fibres et la matrice. Dans cette thèse, trois types de traitement de surface, l’ensimage, le traitement thermique et la croissance de nanotubes (CNTs), ont été appliqués aux CFs. En particulier, les CFs greffées de CNTs, se combinant avec les deux autres traitements, montrent la meilleure adhérence interfaciale avec la matrice époxyde. L’ensimage proposé peut améliorer la performance du CNT-CF hybride et minimiser les dommages aux fibres lors de la manipulation ultérieure tels que le transport et la préparation de composites. Tout d’abord, l’ensimage a été réalisé sur la surface des fibres par dépôt de résine époxyde en solution. L’ensimage permet de protéger les filaments au cours de la mise en oeuvre et favorise également la liaison fibre/matrice. Différentes formulations d’ensimage selon les proportions époxy/durcisseur ont été utilisées. La quantité d'ensimage déposée sur les fibres de carbone a été contrôlée en faisant varier la concentration de la solution d’ensimage. Ensuite, un traitement thermique, effectué sous un mélange de gaz à 600-750 oC, a permis de modifier la surface des CFs. L'influence de la composition du gaz, du temps de traitement et de la température sur les propriétés interfaciales des composites CFs/époxy a été systématiquement quantifiée. Enfin, des CNTs ont été greffés sur les CFs par une méthode de dépôt chimique en phase vapeur en continu afin d’obtenir un nouveau type de renfort hybride multi-échelle. Les CNTs greffés permettent d’augmenter la surface de contact et d’améliorer l’accrochage mécanique de la fibre avec la résine. De plus, ils pourraient améliorer la résistance au délaminage, les propriétés électriques et thermiques des composites. Les CFs greffées de CNTs de différentes morphologies et densités ont été produites en faisant varier les conditions de croissance. Après le traitement de surface, les essais de fragmentation ont été menés afin d’évaluer la résistance au cisaillement interfacial (IFSS) des composites CFs/époxy. Par rapport aux fibres vierges, l’ensimage et le traitement thermique ont contribué à une augmentation de l'IFSS de 35% et de 75%, respectivement. L'adhésion interfaciale entre la matrice époxyde et les fibres greffées avec CNTs pourrait être adaptée en faisant varier la morphologie, la densité de nombre et la longueur de CNT. Les CFs greffées avec 2% en masse de CNTs (10nm de diamètre) ont entraîné une amélioration de l'IFSS de 60%. Un traitement thermique et un ensimage pourraient contribuer à une augmentation supplémentaire de 108%. Il convient de mentionner que la dégradation des fibres n’a pas été observée après les divers traitements précédemment évoqués. Les résultats de ces travaux pourraient mener au développement de ces techniques à plus grande échelle pour la conception de structures à base de composites CFs/époxy. / Carbon fiber (CF)-reinforced polymer composites are widely used in aerospace, construction and sporting goods due to their outstanding mechanical properties, light weight and high thermal stabilities. Their overall performance significantly depends on the quality of the fiber-matrix interface. A good interfacial adhesion provides efficient load transfer between matrix and fiber. Unfortunately, untreated CFs normally are extremely inert and have poor adhesion to resin matrices. Meanwhile, poor transverse and interlaminar properties greatly limit the composite performance and service life. Therefore, a new kind of fiber-based reinforcement is highly desired to improve the overall composite properties, especially the interfacial adhesion between fiber and matrix. In this thesis, three kinds of surface treatment, including sizing, heat treatment and carbon nanotube (CNT) growth, were applied to CFs. In particular, CFs grafted with CNTs, combining with the other two treatments demonstrate superior interfacial adhesion to the tested epoxy matrix. The proposed epoxy sizing can improve the CNT-CF hybrid performance and prevent fiber damage during the subsequent handling such as transport and composite preparation. Firstly, epoxy-based sizing was applied onto the CF surface by the deposition from polymer solutions. Sizing could not only protect the carbon fiber surface from damage during processing but also improve their wettability to polymer matrix. A detailed study was conducted on the influence of the ratio of epoxy and amine curing agent in the sizing formulation. The sizing level on the fiber surface was controlled by varying the concentration of polymer solutions. Secondly, heat treatment in a gas mixture at 600-750 oC was used to modify the carbon fiber surface. The effect of gas mixture composition, treatment time and temperature on the interface was evaluated systematically. Thirdly, CNTs were in-situ grafted on the carbon fiber surface by a continuous chemical vapour deposition (CVD) process to obtain hierarchical reinforcement structures. These hybrid structures have the potential to improve the interfacial strength of fiber/epoxy composites due to the increased lateral support of the load-bearing fibers. Meanwhile, the CNT reinforcement could improve the composite delamination resistance, electrical and thermal properties. The CF grown with CNTs of different morphologies and densities were produced by varying CVD conditions. After the surface treatment, single fiber fragmentation test was used to assess the interfacial shear strength (IFSS) of carbon fiber/epoxy composites. Compared with the as-received CFs, the epoxy sizing and the heat treatment contributed to an improvement in IFSS of up to 35% and 75%, respectively. The interfacial adhesion between epoxy matrix and CNT-grafted fibers could be tailored by varying the CNT morphology, number density and length. The CFs grafted with 2 wt% CNTs of 10 nm in diameter resulted in an improvement in IFSS of around 60%. A further heat treatment and epoxy sizing could contribute to an additional increase of 108%. It’s worth to mention that no significant strength degradation of the fibers was observed after the surface treatments. This work could support the development of large-scale approach to CF surface treatment, and throw light on the design of structurally efficient CF/epoxy composites.

Carbon fiber ultramicroelectrodes (CF-UMEs) are commonly used as electrochemical probes and sensors due to their small size, fast response, and high signal-to-noise ratio. Surface modification strategies are often employed on CF-UMEs to improve their selectivity and sensitivity for desired applications. However, many modification methods are cumbersome and require expensive equipment. In this study, a simple approach known as soft nitriding is used to prepare nitrogen-doped CF-UMEs (N-CF-UMEs). Nitrogen groups introduced via soft nitriding act as electrocatalytic sites for the breakage of O-O bonds during the reduction of peroxides like H2O2, a common target of biosensing strategies. Voltammetric studies confirm that, compared to CF-UMEs, N-CF-UMEs possess enhanced electrocatalytic activity towards H2O2 reduction as evidenced by an increase in current and positive shift in onset potential for the reaction. N-CF-UMEs also proved capable for amperometric detection of H2O2, exhibiting good linear response from 0.1 to 5.6 mM at -0.4 V vs. Ag/AgCl.

Corrosion of steel reinforcements is the leading causes of malfunction or even failures of reinforced concrete (RC) structures nationwide and worldwide for many decades. This arises up to substantial economic burden on repairs and rehabilitations to maintain and extend their service life of those RC public projects. The inherent natures of glass fiber-reinforced polymers (GFRP) bars, from their superior corrosion resistance to high strength-to-weight ratio, have promoted their acceptance as a viable alternative for steel reinforcement in civil infrastructures. Comprehensive understanding of the bond between GFRP bars and concrete, in particular under in-service conditions or extremely severe events, enables scientists and engineers to provide their proper design, assessment and long-term predictions, and ultimately to implement them toward the corrosion-free concrete products. This research aims to develop a holistic framework through an experimental, analytical and numerical study to gain deep understanding of the bond mechanism, behavior, and its long-term durability under harsh environments. The bond behavior and failure modes of GFRP bar to concrete are investigated through the accelerated aging tests with various environmental conditions, including alkaline and/or saline solutions, freezing-thawing cycles. The damage evolution of the bond is formulated from Damage Mechanics, while detailed procedures using the Arrhenius law and time shift factor approach are developed to predict the long-term bond degradation over time. Besides, the machine learning techniques of the artificial neural network integrated with the genetic algorithm are used for bond strength prediction and anchorage reliability assessment. Clearly, test data allow further calibration and verification of the analytical models and the finite element simulation. Bond damage evolution using the secant modulus of the bond-slip curves could effectively evaluate the interface degradation against slip and further identify critical factors that affect the bond design and assessment under the limit states. Long-term prediction reveals that the moisture content and elevated temperature could impact the material degradation of GFRP bars, thereby affecting their service life. In addition, the new attempt of the Data-to-Information concept using the machine learning techniques could yield valuable insight into the bond strength prediction and anchorage reliability analysis for their applications in RC structures. / ND NASA EPCoR (FAR0023941) / ND NSF EPSCoR (FAR0022364) / US DOT (FAR0025913)

Delamination is currently a largely undetectable form of damage in composite laminate materials. This thesis will develop a method to more easily detect delamination damage within composite materials. Using finite element analysis modeling and lab testing, a new method from interpreting the results obtained from existing structural health monitoring techniques is developed. Lamb waves were introduced and recorded through an actuator and sensors made of piezoelectric material. The data was then analyzed through a novel data reduction method using the Fast Fourier Transform (FFT). Using the data from FFT, the idea of covariance of energy change was developed. By comparing the covariance of energy change in beams with differing delamination size, thickness and depth, correlations were able to be developed. With these correlations, the severity and of damage was able to be detected.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21775号 / 工博第4592号 / 新制||工||1715(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 阿部 竜, 教授 作花 哲夫, 教授 安部 武志 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Reinforced fiber polymer composites are a class of materials that are composed of multiple constituents that work together to create a material specific for applications. By combining different fibers and matricies, laminates can be created that meet demands for high specific stiffness, damping specifications, and electrical resistance. However, their internal complexity subjects them to a number of internal failure modes that have the potential to fail the laminate. Those failure mechanisms are fiber breaking, microcracking in the matrix, debonding of the fibers from matrix, and delamination of ply layers. To assess these failures, nondestructive evaluation methods have been developed to detect internal damage before catastrophic failure occurs. This dissertation investigates an in-situ magnetostrictive based nondestructive method for monitoring delaminations in carbon fiber reinforced polymer laminates by using embedded Terfenol-D particles. The objective is to characterize how laminate ply count and delamination presence affect sensing through the mechanical and magnetic parameters that influence the induced voltage or sensing signal. In addition, the effect of magnetostriction on the formation and propagation of cracks on the sensor boundaries are also investigated. Methods used to characterize this behavior involve experimental testing, analytical, and numerical modeling. From the results, a threedimensional finite element analysis model reveals how the sensor interacts mechanically with the host structure through lower stresses in the delaminated region due to the absence of adhesive forces. The stress variation results in a local magnetic permeability change which influences the induced voltage. The experimental nondestructive testing show that the key parameter influencing the sensing signal for this setup was the particle density, which is controlled by fabrication process. An attempt to analytically model the experimental sensing signal with a first order differential equation using a multi-step process was successful, but there is poor correlation with the experimental results. Finally, analytical mechanics are developed to evaluate the interlaminar failure under a magnetostrictive stress of 55MPa, and was found to not cause interlaminar failure or delamination propagation in Section-A.