D.Ing. (Civil Engineering) / Polypropylene (PP) fibre is one of the most widely used fibres for reinforcing concrete. Due to its unique material properties such as economic production cost, relatively high melting point and alkaline resistance, PP fibres in concrete are found to increase the toughness, provide restrained plastic and drying shrinkage cracking resistance, increase impact resistance and flexural loading capacity (especially during the post-crack stage) of concrete structures and components. The wettability of PP fibre surfaces is poor due to the hydrophobic surface nature of polypropylene. The bonding between the PP fibre and the concrete matrix is recognized as poor and currently the PP fibre / concrete interfacial bonding depends upon interlocking and keying (mechanical bonding). As the interfacial bond strength between the PP fibre and the concrete is much smaller than the tensile strength of PP fibre and concrete, in order to fully explore the reinforcing effect of PP fibres in concrete, further improvement of interfacial bonding is necessary. In this investigation, the research work was conducted on the surface oxyfluorinated PP fibre newly developed by the Atomic Energy Corporation of South Africa Limited. Examining the feasibility of using this fibre in concrete, as well as evaluating its superiority over unmodified PP fibres, is the key task of this investigation. This new type of oxyfluorinated PP fibre shows a large increase in interfacial bond strength compared to the unmodified PP fibres. The surface free energy concept and Lewis acid-base interfacial interaction theory were innovatively used to examine the interfacial bonding between the PP fibre and the concrete matrix. The purpose of this study was to develop the background of such oxyfluorinated PP fibres, to establish the mechanism of the increase in interfacial bonding and to investigate the basic properties of the concrete incorporating oxyfluorinated PP fibres. The experimental results on the properties of oxyfluorinated PP fibre reinforced concrete compared with those of unmodified PP fibre reinforced concrete and plain concrete are presented, with some field test results focused on the improvement in shrinkage cracking control capacity. It is concluded in this investigation that the surface oxyfluorinated PP fibres possess significantly increased PP fibre / concrete interfacial bonding due to the chemical bond arising from the acid base interfacial interaction and the intimate interfacial contact arising from the improved fibre surface wettability. When combining oxyfluorinated pp fibre with concrete, a general improvement in the physical and mechanical properties of fibrous concrete compared to that created with unmodified PP fibres, is obtained.

Les interactions fluide-structure sont d'un grand intérêt en ingénierie et pour des applications industrielles et médicales. Comprendre les interactions entre des particules aux formes complexes et des écoulements peut mener à de nouveaux projets pour l'administration ciblée de médicaments, pour des micro capteurs de débit et à une meilleure compréhension du comportement des micro-organismes. Dans cette thèse, nous étudions l'interaction fluide-structure de particules chirales de taille microscopique à bas nombres de Reynolds. Les particules sont rigides et confinées dans une géométrie 2D ou flexibles avec une forme hélicoïdale. Combiner des techniques de microfabrication, comme des méthodes d'assemblage multi-échelles et la microfluidique, permet d'avoir un excellent contrôle à la fois sur les propriétés géométriques et mécaniques des fibres et aussi sur les caractéristiques de l'écoulement comme ses propriétés Newtoniennes et non Newtoniennes, sa vitesse et sa géométrie. Dans un premier temps, nous avons étudié des fibres rigides, 2D et asymétriques, i.e. des fibres en L. Les confinements latéral et transversal ont été étudiés tout comme la forme de la fibre. Lorsque la particule est transportée dans un écoulement visqueux, elle tourne jusqu'à atteindre une orientation d'équilibre. Dans cette orientation particulière, la fibre se décale vers les murs latéraux du canal. Une étude complète des trajectoires de la fibre a été réalisée et des comparaisons avec des particules symétriques ont été faites. Ce sujet de recherche pourrait aider à concevoir des dispositifs pour trier des particules à des fins médicales. Dans un second temps, nous avons étudié des fibres hélicoïdales flexibles de taille micrométrique. La dynamique de formation de l'hélice a été analysée. Les hélices se forment à partir de rubans droits 2D qui, de façon spontanée, s'enroulent quand ils sont libérés dans l'eau. La forme hélicoïdale est obtenue seulement quelques minutes après la libération des rubans mais l'hélice continue à rétrécir pendant plusieurs heures jusqu'à ce qu'elle atteigne une courbure préférentielle. Deux temps caractéristiques sont identifiés dans cette dynamique de formation. Un modèle a été développé pour comprendre le complexe équilibre entre les forces élastiques, de tension de surface et visqueuses aux temps courts. Après avoir analysé plusieurs hypothèses, comme l'impact d'une couche sacrificielle, une possible modification du module du matériau et la présence de fluage, l'évolution du rayon de l'hélice aux temps longs s'explique probablement par du fluage. La dynamique d'extension et de relaxation de la fibre flexible a aussi été étudiée dans des fluides Newtonien et non Newtonien. L'étude dans des solutions de polymères est pertinente et intéressante car la taille des micro hélices est comparable à celle des flagelles des micro-organismes et à celle de chaînes de polymères de grande masse moléculaire. Il s'agit donc d'un problème mutli-échelles complexe car la viscosité locale au niveau du ruban pourrait être différente de la viscosité globale de l'écoulement. / Fluid-structure interactions are of wide interest in engineering, industrial and medical applications. Understanding the interactions between complex shaped particles and flows might lead to new designs for targeted delivery, microflow sensors and to a better understanding of the behavior of microorganisms. In this thesis, we study the fluid-structure interaction of microscale chiral particles at low Reynolds numbers. The particles are rigid and confined in a 2D geometry or flexible with a helical shape. The combination of microfabrication techniques, such as multiscale assembly methods and microfluidics, enables to have a perfect control on both the geometrical and mechanical properties of the fibers and the flow features such as Newtonian or non Newtonian properties, the flow velocity and the flow geometry. First we studied asymmetric 2D rigid fibers, i.e. L-shaped fibers. Both lateral and transversal confinements have been investigated, as well as the shape of the fiber. When the particle is transported in viscous flows, it rotates until reaching an equilibrium orientation. In this specific orientation, the fiber drifts towards the lateral walls of the channel. A full investigation on the trajectories of the fiber has been performed and comparisons with symmetric particles have been done. Such research may help design devices to sort particles for medical purposes. Secondly we studied flexible microscale helical fibers. The dynamics of the helix formation has been investigated. The helices are formed from straight 2D ribbons, which spontaneously coil when released in water. The helical shape is reached only several minutes after the release but the helix keeps shrinking during several hours until reaching a preferred curvature. Two different timescales are identified in this formation dynamics. A model has been developed to understand the complex balance between elastic, surface tension and viscous forces at short times. After investigating several assumptions such as the impact of a sacrificial layer, a possible change in the modulus of the material and a creep behavior, the evolution of the radius at long times is most likely explained by creep. The extension and relaxation dynamics of the flexible fiber has also been studied in Newtonian and non Newtonian fluids. The study in polymer solutions is relevant and interesting because the size of the microhelix is comparable to the flagella of microorganisms and to the chains of high molecular weight polymers. Complex multiscale problems are then involved as the local viscosity at the scale of the ribbon might differ from the global viscosity at the scale of the flow.

Sustainability through replacement of non-renewable fibers with renewable fibers is an ecological need. Impact of transportation costs from South-east Asia on the life cycle analysis of the composite is detrimental. Kenaf is an easily grown crop in America. Farm based processing involves placing the harvested crop in rivers and ponds, where retting of the fibers from the plant (separation into fibers) can take 2 weeks or more. The objective of this thesis is to analyze industrially viable processes for generating fibers and examine their synergistic impact on mechanical performance, surface topography and chemistry for functional composites. Comparison has been made with commercial and conventional retting process, including alkali retting, enzymatic retting, retting in river and pond water (retting occurs by natural microbial population) with controlled microbial retting. The resulting kenaf fibers were characterized by dynamic mechanical analysis (DMA), Raman spectroscopy (FT-Raman), Fourier transform infrared spectroscopy (FT-IR), polarized optical microscopy (POM), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) optical fluorescence microscopy, atomic force microscopy (AFM) and carbohydrate analysis. DMA results showed that pectinase and microbe treated fibers have superior viscoelastic properties compared to alkali retting. XPS, Raman, FT-IR and biochemical analysis indicated that the controlled microbial and pectinase retting was effective in removing pectin, hemicellulose and lignin. SEM, optical microscopy and AFM analysis showed the surface morphology and cross sectional architecture were preserved in pectinase retting. Experimental results showed that enzymatic retting at 48 hours and controlled microbial retting at 72 hours yield uniform and superior quality fibers compared to alkali and natural retting process. Controlled microbial retting is an inexpensive way to produce quality fibers for polymer composite reinforcement.

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This document only includes an excerpt of the corresponding thesis or dissertation. To request a digital scan of the full text, please contact the Ruth Lilly Medical Library's Interlibrary Loan Department (rlmlill@iu.edu).

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Call number: LD2668 .T4 1984 C52 / Master of Science

Orientador: Cristiano Monteiro de Barros Cordeiro / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-02T14:50:23Z (GMT). No. of bitstreams: 1 Osorio_JonasHenrique_D.pdf: 57449332 bytes, checksum: 92f06bf0e96b31630478243a818a7fd6 (MD5) Previous issue date: 2017 / Resumo: Nesta tese, fibras ópticas especiais são estudadas para fins de sensoriamento. Primei-ramente, propomos a estrutura denominada fibra capilar com núcleo embutido (embedded-core capillary fibers) para realização de sensoriamento de pressão. Estudos numéricos e analíticos foram realizados e mostraram que altas sensibilidades a variações de pressão poderiam ser al-cançadas com esta estrutura simplificada, que consiste de um capilar dotado de um núcleo, dopado com germânio, em sua parede. Experimentos permitiram medir uma sensibilidade de (1.04 ± 0.01) nm/bar, que é um valor alto quando comparado a outros sensores de pressão ba-seados em fibras microestruturadas. Ademais, estudamos fibras do tipo surface-core, que são fibras cujos núcleos são colocados na superfície externa da fibra. Nesta abordagem, redes de Bragg foram utilizadas para obter sensores de índice de refração ¿ fazendo-se uso da interação entre o campo evanescente do modo guiado no núcleo e o ambiente externo à fibra ¿ e de cur-vatura ¿ ao se explorar o fato de que, nestas fibras, o núcleo se encontra fora do centro geomé-trico da mesma. As sensibilidades a variações de índice de refração e curvatura medidas, 40 nm/RIU em torno de 1.41 e 202 pm/m-1 comparam-se bem a outros sensores baseados em redes de Bragg. Outrossim, fibras capilares poliméricas foram investigadas como sensores de temperatura e pressão. Para a descrição do sensor de temperatura, usou-se um modelo analítico para simular o espectro de transmissão dos capilares e a sua dependência com as variações de temperatura. No que tange à aplicação de sensoriamento de pressão, variações nas espessuras dos capilares devido à ação da pressão foram calculadas e relacionadas à sensibilidade da me-dida de monitoramento. Nestas duas aplicações, realizações experimentais também são repor-tadas. Finalmente, oportunidades adicionais de sensoriamento ao se utilizar fibras ópticas es-peciais são apresentadas, a saber, um sensor de pressão para dois ambientes baseados em fibras de cristal fotônico, um sensor de três parâmetros baseado em redes de Bragg, fibras afinadas e interferência multimodal, um sensor de nível de líquido baseado em redes de Bragg e interfe-rência multimodal e um sensor de temperatura baseado em fibras embedded-core preenchidas com índio. Os resultados aqui reportados demonstram o potencial das fibras ópticas em forne-cerem plataformas de sensoriamento para alcançar medidas de diferentes tipos de parâmetros com alta sensibilidade e resolução adequada / Abstract: In this thesis, specialty optical fibers for sensing applications are investigating. Firstly, we propose the embedded-core capillary fiber structure for acting as a pressure sensor. Analyt-ical and numerical studies were performed and showed that high pressure sensitivity could be achieved with this simplified fiber structure, which consists of a capillary structure with a germanium-doped core placed within the capillary wall. Experiments allowed measuring a sensitivity of (1.04 ± 0.01) nm/bar, which is high when compared to other microstructured optical fiber-based pressure sensors. Moreover, we studied the so-called surface-core optical fibers, which are fibers whose cores are placed at the external boundary of the fiber. In this approach, Bragg gratings were used to obtain refractive index ¿ making use of the interaction between the guided mode evanescent field and the external medium ¿ and directional curva-ture sensors ¿ by exploring the off-center core position. The measured refractive index and the curvature sensitivities, respectively 40 nm/RIU around 1.41 and 202 pm/m-1, compares well to other fiber Bragg grating-based sensors. Additionally, antiresonant polymer capillary fibers were investigated as temperature and pressure sensors. For the temperature sensing descrip-tion, one used an analytical model to simulate the transmission spectra of such fibers and the dependence on temperature variations. Regarding the pressure sensing application, pressure-induced capillary wall thickness variations were analytically accounted and related to the sys-tem pressure sensitivity. In both these applications, experimental data were presented. Finally, additional opportunities using specialty optical fibers were presented, namely, a photonic-crystal fiber-based dual-environment pressure sensor, a three parameters sensor using Bragg gratings, tapered fibers and multimode interference, a liquid-level sensor based on Bragg grat-ings and multimode interference, and a temperature sensor based in an embedded-core fiber filled with indium. The results reported herein demonstrates the potential of optical fibers for providing sensing platforms to attain measurements of different sort of parameters with highly sensitivity and improved resolutions / Doutorado / Física / Doutor em Ciências / 152993/2013-4 / CNPQ