Este trabalho aborda o comportamento de dois solos (uma argila e uma areia), reforçados com fibras plásticas de polipropileno. Os solos foram compactados no teor de umidade ótimo e peso específico seco máximo e foram misturados com fibras de diferentes teores e comprimentos. Os resultados dos ensaios de compressão simples foram usados para selecionar os teores e comprimentos ótimos de fibras. Os resultados mostraram que a resistência do solo arenoso cresceu com o aumento do teor e comprimento das fibras e o solo argiloso apresentou acréscimo de resistência, com o aumento do teor até o comprimento de fibra de 10 mm. As curvas tensão-deformação dos ensaios triaxiais, para solos com e sem reforço foram similares, com uma resistência de pico definida e pequena redução de queda de tensão pós pico. As amostras de solo arenoso apresentaram considerável aumento de resistência, com o aumento do teor e comprimento das fibras. Pequenos painéis, fabricados com o solo argiloso (300 x 300 x 100) mm, mostraram que a presença da fibra pode reduzir a magnitude das trincas quando comparados com o solo sem reforço. / This work presents the behavior of two soils (clay and sandy) reinforced with polypropylene plastic fibers. The soils were compacted at the optimum moisture content and maximum dry unit weight and were mixed with fibers of different lengths and contents. Unconfined compressive tests results were used to select the optimum fiber length and content. The results showed that the granular soil strength increased with increasing fiber length and content. The cohesive soil, on the other hand, showed strength up to fiber length of 10 mm. Stress - strain curves from triaxial tests for both reinforced and unreinforced cohesive soil were similar with a defined peak strength and small post peak reduction. Granular soil samples presented considerable strength increases with the increases of length and fiber content. Small panels fabricated with the reinforced cohesive soil (300 x 300 x 100) mm, showed that the presence of fiber can reduce crack magnitude when compared with the unreinforced soil.

Orientador: Cristiano Monteiro de Barros Cordeiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica "Gleb Wataghin" / Made available in DSpace on 2018-08-14T18:48:20Z (GMT). No. of bitstreams: 1 Chesini_Giancarlo_M.pdf: 4393028 bytes, checksum: cd402e08666717100399e5c4d9465306 (MD5) Previous issue date: 2009 / Resumo: Neste trabalho de mestrado apresentamos o estudo e desenvolvimento de dispositivos óticos totalmente à fibra. Para isso, exploramos as novas possibilidades trazidas pelo advento das fibras de cristal fotônico (PCF's, do inglês Photonic Crystal Fibers). As PCF's são uma classe especial de fibras óticas que apresentam uma estrutura regular de buracos de ar na sua seção transversal, semelhante a um cristal fotônico. As fibras de cristal fotônico, além de apresentarem as vantagens inerentes às fibras óticas tradicionais, possuem novos graus de liberdade intrínsecos. Entre eles, o mais importante é a possibilidade de alterar fortemente as características da fibra através, apenas, do arranjo de buracos. Aqui, desenvolvemos uma fibra de cristal fotônico com dois buracos externos à microestrutura para integração de eletrodos. Posteriormente, um desses eletrodos foi exposto, polindo-se a lateral da fibra, e contato elétrico foi realizado. O elemento de controle do dispositivo ótico é a corrente elétrica que, aplicada ao eletrodo, o esquenta e o faz expandir via efeito Joule. O aumento de temperatura e a compressão causada pela expansão do eletrodo alteram o índice de refração e, portanto, a birrefringência da fibra. Foram realizadas, ainda, simulações utilizando o software comercial Comsol Multiphysics com o objetivo de entender a influência da temperatura e da compressão mecânica no modo ótico guiado pela fibra, bem como encontrar maneiras de otimizar o dispositivo em questã / Abstract: In this work we present a study and the development of all-fiber optical devices. For this purpose we exploited the new possibilities brought by the development of Photonic Crystal Fibers. PCF's are special kind of optical fibers with a regular pattern of air holes in their transverse section, resembling a photonic crystal. Photonic Crystal Fibers not only have the inherent advantages of traditional optical fibers but they have new intrinsic degrees of freedom. Among them, we can quote the possibility of strongly altering the fiber characteristics through the design of the air holes pattern. Here, we developed a photonic crystal fiber with two extra holes for electrode integration. One of these electrodes was exposed by side polishing the fiber and electrical contact to an external circuit was made. The contrai element of the optical device is the electrical current which, when applied to the electrode, heats it up and make it expand by Joule effect. The temperature increase and the compression caused by the electrode expansion alter the refractive index and, consequently, the fiber birefringence. We algo numerically studied the problem through Com sol software. The objective here was to understand the influence of temperature and stress on the light guided mode. In conclusion, we demonstrated in this work the creation of an all-fiber device based on the integration of electrodes to photonic crystal fibers where the element of contrai is the electrical current applied to the electrodes. We algo studied how to improve the parameters concerning the device operation / Mestrado / Física Geral / Mestre em Física

Orientadores: Luiz Carlos Barbosa, Cristiano Monteiro de Barros Cordeiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T19:12:29Z (GMT). No. of bitstreams: 1 Santos_ElianeMourados_M.pdf: 4020531 bytes, checksum: 57766702771129e7f4bfe1d0c7852f67 (MD5) Previous issue date: 2007 / Resumo: Este trabalho apresenta estudos de como inserir fluidos (líquidos e gases) em fibras ópticas microestruturadas, especialmente fibras de cristal fotônico, também conhecidas como PCF¿s (do inglês Photonic Crystal Fibers). Estas fibras possuem buracos de ar que percorrem todo seu comprimento. Elas podem ser divididas em dois grandes grupos: as de núcleo sólido que guiam luz por reflexão interna total e as de núcleo oco que guiam luz por um mecanismo conhecido como photonic bandgap. Ambos os tipos de fibras permitem várias aplicações em áreas como óptica e fotônica e nos dedicamos aqui à área de sensoriamento a fibra. Nesta área, usamos os microburacos para inserir fluido e dessa maneira manipular as propriedades de guiamento (em fibras de núcleo líquido), deixar a fibra mais sensível a algum parâmetro externo ou para sensoriar o fluido em questão. Nos três casos, precisamos estudar os processos de preenchimentos de fibras microestruturadas. Para este fim, estudamos e desenvolvemos maneiras de inserir fluidos em fibras de núcleos sólidos ou ocos. Usando preenchimento seletivo, produzimos fibras com núcleo líquido, criando uma região de alta interação entre luz e material. Neste trabalho, estudamos diferentes técnicas de preenchimento. A primeira, para fibras de núcleo líquido, é um preenchimento seletivo que pode ser feito usando uma máquina de emendas (splicer) ou um polímero para bloquear os microburacos. O outro consiste em manter as pontas das fibras livres (para medidas ópticas) enquanto o preenchimento é feito. Por fim, usamos o conhecimento desses processos em aplicações como sensoriamento de fluidos ou parâmetros externos e manipulação de propriedades de guiamento da luz / Abstract: This work presents studies of how to insert fluids (liquid and gas) into microstructured optical fibers, especially photonic crystal fibers, also known as PCF¿s. These optical fibers possess air holes that run along its entire length. They can be divided into two major groups: solid core fibers that guide light by total internal reflection and hollow core fibers that guide light by photonic bandgap. Both types of fibers allow several applications in areas such as optics and photonics and we dedicated this work to the fiber-sensing field. In this area we use the micro holes to insert fluids and in this way to manipulate the guidance properties in liquid core fibers, to leave the fiber more sensitive to some external parameter or to sensing the fluid. In these three cases we need to study the filling procedures in microstructured fibers. For this purpose, we studied and developed ways of inserting fluids in hollow and solid core fibers. We produced liquid core fibers, creating a high light-material overlap, using a selective filling technique. In this work we studied different filling techniques. The first one, for liquid core fibers, is a selective filling, which can be done by using a splicer machine or a polymer to block the fiber micro holes. The last one consists of keeping the fiber tips free (for optical measurements) while the filling is done. And finally we used the filling process knowledge in applications like sensing of fluids or external parameters and manipulation of guidance properties / Mestrado / Física Geral / Mestre em Física

Made available in DSpace on 2016-03-15T19:38:07Z (GMT). No. of bitstreams: 1 Alexandre Bozolan dos Santos.pdf: 2799601 bytes, checksum: 413a15ac3509d4fa1aa645d287b876c6 (MD5) Previous issue date: 2008-01-22 / Photonic crystal fibers (PCFs) are optical fibers whose core is surrounded by a regular matrix of holes that is responsible for light confinement and guidance. This new architecture opens new perspectives in the development of nonlinear applications, many of which are based upon the high efficiency with which nonlinearity-driven spectral broadening known supercontinuum generation is obtained in solid-core PCFs. Another asset of PCFs is that their structure can be filled with liquids or gases, which then efficiently interact with the guided light. The possibility of obtaining supercontinuum generation in a PCF whose core is filled with highly nonlinear liquids has been recently theoretically studied. The insertion of liquids in PCFs introduces a new degree of freedom with which the efficiency of nonlinear effects can be maximized. This dissertation describes experimental work, in which the generation of a supercontinuum spectrum is demonstrated in a PCF whose hollow core was selectively filled with distilled water. A maximum broadening of 503nm, measured at -20dB, was obtained with femtosecond pulse pumping at λ=976nm. The comparison with spectra obtained with a 800nm pump and with bulk samples demonstrate that both a low dispersion at the pump wavelength and pump guidance are crucial for the broad output spectrum obtained. Numerical simulations and analyses were also undertaken to complement the study. / Fibras de cristal fotônico (PCF s) são fibras ópticas cujo núcleo é cercado por uma matriz regular de buracos, responsável pelo confinamento e guiamento da luz. Esta nova arquitetura abre novas perspectivas no desenvolvimento de aplicações não-lineares, muitas das quais são baseadas na alta eficiência com que o alargamento espectral não-linear conhecido como geração de supercontínuo é obtido em PCF s de núcleo sólido. Outra característica das fibras de cristal fotônico é que sua estrutura pode ser preenchida com líquidos e gases, que então interagem eficientemente com a luz guiada. A possibilidade de se obter a geração de supercontínuo em uma fibra de cristal fotônico cujo núcleo é preenchido com líquidos altamente não-lineares foi teoricamente estudado recentemente. A inserção de líquidos nas PCF s introduz um novo grau de liberdade, aumentando a eficiência com que os efeitos não-lineares podem ser gerados. Esta dissertação descreve um trabalho experimental no qual é demonstrada a geração de supercontínuo em uma PCF cujo núcleo foi preenchido seletivamente com água destilada. Obteve-se um alargamento máximo de 503nm medido, a -20dB, com o bombeio de pulsos de femtossegundos em 976nm. A comparação com o espectro obtido com o bombeio em 800nm e em amostras volumétricas demonstram que tanto a baixa dispersão no comprimento de onda de bombeio quanto o guiamento dos pulsos são cruciais para a obtenção do largo espectro observado. Simulações e análises numéricas foram também realizadas para complementar o estudo.

Orientador: Newton de Oliveira Pinto Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-08T03:07:34Z (GMT). No. of bitstreams: 1 Fernandes_Andrea_M.pdf: 3789790 bytes, checksum: 3995163d23effcb84c04682718a55ef9 (MD5) Previous issue date: 2005 / Resumo: O reforço do concreto através da utilização de fibras de aço vem se mostrando, ao longo dos anos, como alternativa econômica e tecnicamente viável para diversos tipos de aplicações . Sua ampla utilização na indústria da construção mundial, em diversos casos de sucesso, despertou interesse também do segmento tuneleiro moderno. Passou-se a utilizar fibras para reforçar o concreto das aduelas dos anéis montados por tuneladoras (TBM- Tunnel Boring Machines ¿ máquina de escavar túneis) nas principais obras ao redor mundo. Desta forma, após diversos anos sem obras importantes de túneis metroviários no Brasil, a construção da linha 4 (Amarela) do Metrô de São Paulo, utilizará uma destas máquinas de escavar túneis, sendo do tipo EPBM (Earth Pressure Balanced Machine), cujo revestimento será feito com anéis segmentados (aduelas) de concreto. O projeto básico desta obra (década de 60) prevê armação das aduelas de forma tradicional (em desuso) com gaiolas de aço. Em virtude dos benefícios que o reforço com fibras oferece, e ainda, baseando-se no sucesso da experiência mundial, surgiu a necessidade de um estudo no Brasil sobre esta tecnologia. Assim, tomando como base os dados do projeto básico do projeto da linha 4 (cargas, geometrias, etc.), iniciou-se um estudo comparativo do reforço com gaiolas e do reforço com fibras de aço. Este trabalho apresenta algumas etapas deste estudo, procura abordar aspectos relevantes do processo desde a fabricação até a instalação das aduelas no túnel, explica os benefícios possíveis de serem atingidos, resume alguns dos principais motivos que levaram a indústria tuneleira a adotar a tecnologia de reforço com fibras de aço, vantagens e desvantagens / Abstract: The reinforcement of the concrete using steel fibers became possible, through the years, by it¿s economical and technical viability. It¿s wide range of utilization in civil construction, in several success work cases, made the modern tunneling industry realize the necessity of studding it as well. Concrete Segmental Lining Rings placed by TBMs - Tunnel Boring Machines - have been produced with Steel Fiber in the ultimate reference jobs around the world. After several years without of Metro projects in São Paulo Brasil, the already under construction line 4 with total 12,8 km of tunnels, will use one EPBM - Earth Pressure Balanced Machine ¿ witch lining is being considered made by reinforced concrete. The Basic Project (from the 60¿s) primarily considered steel bars as cage reinforcement. To benefit from the steel fiber reinforcement concrete, still, based on successful practical cases world wide, became the necessity to study this technology locally, in Brasil. Thus, taking the basic data from the original Line 4 project (geometry, etc.) a comparative study between steel cages and steel fibers started. This work contents some of the steps from this study and intents to evaluate key aspects from the whole process, since production phase at the segment plant, transport, installation and maintenance of the tunnel. Also explains the basic reasons of migration to the steel fiber reinforcement, including the benefits for the whole tunneling industry and society / Mestrado / Edificações / Mestre em Engenharia Civil

The aim with this master thesis was to investigate the potential of using non-wood fibers to enhance the paper strength. Abaca, sisal and banana fibers were added to conventional bleached chemical softwood pulp. The effect of refining was investigated, both as co-refining and as separate refining. The fiber properties were determined with a Fiber Tester and the drainage resistance was determined with Schopper-Riegler. Density, tensile index, tear index and burst index were determined on paper sheets made in a Rapid-Köthen sheet former. The results showed that abaca had longer fiber length than softwood, while sisal had slightly shorter fiber length compared with softwood. Sheet density was lowered with addition of all three fiber types, while the drainage resistance was increased for the same. It was also observed that the tensile index increased with additions of abaca, while additions of sisal and banana fibers gave lower tensile indexes. The same trend was observed for the tear index and burst index. Refining gave higher values of the drainage resistance, density, tensile index and burst index. However, the tear index was affected differently depending on the fiber type and fiber blend. For sisal and banana fibers, the tear index was first increased at lower refining degrees and were thereafter decreased with further refining. When studying abaca and softwood, a declining trend was observed over the entire refining interval. The conclusion was that addition of abaca fibers increased all investigated strength properties. Sisal and banana fibers gave higher values of the tear strength, when exposed to mild refining.

The commercial use of hemp fiber in the construction industry within the United States is non-existent. This lack of use is because of State and Federal laws forbidding the growth of hemp in the United States, which has led to a lack of research. Not having an established supply chain for hemp and coupled with limited research has put the United States behind other countries in finding viable options for these renewable resources. This is a study of the performance of raw hemp fibers and processed hemp twine in a cement past mixture subjected to tensile loading. Three water/cement ratios (0.66, 0.49, 0.42) were considered. Replacement of cement with fly ash is also part of the program to see if it affects the performance of the system. A detailed description of the method of applying the tensile load to the micro/macro fibers along with the fixture setup is part of this article. The results of this investigation show the hemp twine and fibers will bond to the cement matrix and they can carry higher tensile loads at higher w/c ratios. This study shows that 30 mm embedment length is best for hemp macro fibers and 20 mm embedment for hemp micro fibers. This study also includes a comparative investigation of the performance of hemp fibers to synthetic and steel fibers added to a concrete mix. This investigation examined the compressive strength of the fiber-reinforced concrete mixes, flexural capacity, ductility, flexural toughness and the effects the fibers have on Young’s modulus of elasticity. All fibers were introduced to the same mix design (w/c = 0.49) with replacement of 25% of cement with fly ash. Hemp micro fibers at the same dosing rate a synthetic micro fibers has a slightly higher toughness and equivalent flexural strength. Hemp macro fibers at a higher dosing rate as compared to synthetic fibers will have similar toughness and equivalent flexural strength. Steel fibers performed better than the synthetic and natural fibers at 28-day compressive strength.

In this work, a novel self-sensing technology is introduced for fiber-reinforced polymer (FRP) composites, offering an accurate and cost-effective solution for damage detection, localization, and fatigue life prediction. This dissertation implements an innovative approach, transforming structural carbon fiber tows into piezoresistive sensors that enable real-time structural health monitoring (SHM) without the need for additional sensor devices. The self-damage detection and memory (SDDM) hybrid composite material leverages the carbon fiber as a sensor network, with glass fiber providing electrical insulation. Damage detection capabilities are first introduced, demonstrated by tensile testing that revealed two distinct loading peaks and a sharp nonlinear increase in resistance at the point of carbon fiber failure, highlighting its capabilities for damage early warning. Progressive impact tests further confirmed the material's ability to permanently record microdamage, showcasing a self-memory function that could inform life-cycle predictions. Next, a practical sensor layout was developed, utilizing carbon fiber sensor tow branches connected in parallel each with varying resistances. This novel design can monitor large areas while minimizing the number of connections required to the DAQ circuit, significantly reducing manufacturing costs and complexities. Impact tests on carbon and glass fiber-reinforced composites validated the system’s ability to detect and precisely locate damage, with less than three percent error between the measured resistance and predicted damage location. These results highlight the effectiveness of the proposed damage localization framework, offering an efficient SHM solution for large-area composite structures. Lastly, this dissertation introduces a low-cost, real-time fatigue life prediction system that leverages the piezoresistive cumulative damage behavior of carbon fiber sensor tows. A Bidirectional Long Short-Term Memory (LSTM) neural network was implemented to predict fatigue life based solely on resistance time-history, with no need for explicit stress inputs. Fatigue tests conducted across various stress amplitudes were used to train and evaluate a LSTM model, with results indicating the model’s ability to accurately predict remaining life. Moreover, testing results showed a sharp increase in resistance before failure, demonstrating the carbon fiber sensor tow's damage early warning capabilities for both cyclic and quasistatic monotonic loading. This system presents a promising, cost-effective SHM method that not only ensures structural safety but also extends the service life of FRP composites through accurate fatigue life prediction.

Polyacrylonitrile (PAN) and its copolymers are used in a wide variety of applications ranging from textiles to purification membranes, packaging material and carbon fiber precursors. High performance polyacrylonitrile copolymer fiber is the most dominant precursor for carbon fibers. Synthesis of very high molecular weight poly(acrylonitrile-co-methyl acrylate) copolymers with weight average molecular weights of at least 1.7 million g/mole were synthesized on a laboratory scale using low temperature, emulsion copolymerization in a closed pressure reactor. Single filaments were spun via hybrid dry-jet gel solution spinning. These very high molecular weight copolymers produced precursor fibers with tensile strengths averaging 954 MPa with an elastic modulus of 15.9 GPa (N = 296). The small filament diameters were approximately 5 'm. Results indicated that the low filament diameter that was achieved with a high draw ratio, combined with the hybrid dry-jet gel spinning process lead to an exponential enhancement of the tensile properties of these fibers. Carbon fibers for polymer matrix composites are currently derived from polyacrylonitrile copolymer fiber precursors where solution spinning accounts for ~40 % of the total fiber production cost. To expand carbon fiber applications into the automotive industry, the cost of the carbon fiber needs to be reduced from $8 to ~$3-5. In order to develop an alternative melt processing route several benign plasticizers have been investigated. A low temperature, persulfate-metabisulfite initiated emulsion copolymerization was developed to synthesize poly(acrylonitrile-co-methyl acrylate) copolymers with acrylonitrile contents between 91-96 wt% with a molecular weight range of 100-200 kg/mol. This method was designed for a potential industrial scale up. Furthermore, water was investigated as a potential melting point depressant for these copolymers. Twenty-five wt% water lead to a decrease in the Tm of a 93/7 wt/wt % poly(acrylonitrile-co-methyl acrylate) of Mw = 200 kg/mol to 160 0C as measured via DSC. Glycerin, ethylene glycol and glycerin/water combinations were investigated as potential plasticizers for high molecular weight (~200,000 g/mol), high acrylonitrile (93-96 mole:mole %) content poly(acrylonitrile–co-methyl acrylate) statistical copolymers. Pure glycerin (25 wt %) induced crystallization followed by a reduced "Tm" of about 213 °C via DSC. However this composition did not melt process well. A lower MW (~35 kg/mol) copolymer did extrude with no apparent degradation. Our hypothesis is that the hydroxyl groups in glycerin (or water) disrupt the strong dipole-dipole interactions between the chains enabling the copolymer endothermic transition (Tm) to be reduced and enable melting before the onset of degradation. Additionally high molecular weight (Mw = 200-230 kg/mol) poly(acrylonitrile–co-methyl acrylate) copolymers with lower acrylonitrile content (82-85 wt %) were synthesized via emulsion copolymerization and successfully melt pressed. These materials will be further investigated for their utility in packaging applications. / Ph. D.

<p>High-performance fibers used for ballistic protection are characterized by having outstanding mechanical properties such high modulus and strength. These mechanical properties are granted by the fiber’s chemical and physical structure as well as their high degree of orientation. Twaron fibers are one of the most commonly used fibers on soft body armors such as bulletproof vests. They are made from poly (p-phenylene terephthalamide) (PPTA), a rigid-rod and highly crystalline polymer. Although these fibers are crystalline and have great mechanical properties, their performance can decrease when they are exposed to different degradation factors. Free volume is the unoccupied space between the polymer molecules. It is responsible for characteristics such as diffusion and viscosity. Hence, the free volume changes as the polymer degrades. This thesis focuses on the effects of sonication, pH changes, and sweat on the free volume of PPTA fibers. </p><p><br></p> <p>A non-destructive technique known as positron annihilation lifetime spectroscopy (PALS) was used to measure the free volume in PPTA. Changes in the free volume of fibers degraded under different conditions were compared to their mechanical performance. Degradation in DI water, pH 4 and pH 10 aqueous solutions was conducted for 10 weeks at 80^oC. Sweat degradation of PPTA fibers was also conducted for 10 weeks at 25^oC, 50^oC, and 100^oC. Fibers degraded in pH4 and sweat solutions had greater loss of mechanical performance and changes in the free volume. PALS was able to detect changes in the nanostructure of PPTA fibers at early stages of degradation. This data was supported by mechanical tests and is complementary to other characterization techniques such as small angle X-ray scattering (SAXS). Results of this research are a steppingstone for future studies on lifetime predictions of bulletproof vests and the development of the next generation of soft body armors. </p>