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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Structure et propriétés physiques de composites à matrice biosourcée/fibres naturelles continues pour applications aéronautiques / Structure and physical properties of bio-based matrix/continuous natural fibers composites for aeronautic applications

Haddou, Geoffrey 11 December 2017 (has links)
L'objectif de ce travail est de proposer des composites totalement biosourcés à application potentielle pour l'aménagement cabine et conforme aux exigences REACh. L'utilisation de fibres végétales comme renforts de matrices polymères est une voie prometteuse qui permet de réduire l'impact environnemental, tout en diminuant la masse. Une nouvelle matrice polyamide biosourcée synthétisée par Arkema - Polyamide méta-xylylène diamine 10 - a été utilisée pour cette étude. Une étude préliminaire de composites Polyamide 11/poudre de bambou a montré que l'introduction du renfort ne perturbait pas la structure physique de la matrice. De plus, l'optimisation des propriétés mécaniques s'effectue en l'absence d'agent de couplage. Les composites fibres continues de bambou/PA mXD 10 qui sont également mis en œuvre sans agent de couplage, ont des modules de cisaillement supérieurs à ceux des composites synthétiques de référence fibre de verre/matrice phénolique, avec un gain de masse de l'ordre de 50%. / The aim of this work is to propose fully bio-based composites for a potential application in the cabin interior, and compliant with the REACh regulations. The use of vegetable fibers as reinforcement into polymeric matrices is an encouraging way to decrease the environmental impact, end the weight as well. A new bio-based polyamide matrix, synthetized by Arkema - Polyamide meta-xylylene diamine 10 - was used in this work. A preliminary study on Polyamide 11/bamboo powder showed the introduction of the fillers did not modified the physical structure of the matrix. Moreover, the optimization of the mechanical properties occurs with no coupling agent. The continuous bamboo fibers/PA mXD 10 composites, which were also processed without coupling agent, present shear moduli superior than the one of the synthetic reference glass fibers/phenolic, with a gain of weight about 50%.
12

Étude du vieillissement hygrothermique des composites renforcés de fibres naturelles : approche expérimentale et modélisation / Study of the hygrothermal aging of natural fibers reinforced composites : an experimental and numerical approach

Freund, Ludovic 20 June 2018 (has links)
Les composites sont devenus des matériaux courants dans l’industrie dès lors que la performance est recherchée. Les matrices polymères renforcées de fibres de verre ou de carbone sont utilisées dans l’aéronautique, l’automobile et le sport pour leurs propriétés spécifiques très élevées. Depuis peu, les fibres naturelles sont envisagées comme renforts pour les matériaux polymères pour concilier performance et écologie. Cependant, l’utilisation de pièces structurales utilisant des fibres végétales se heurte à un inconvénient majeur : leur vieillissement rapide causé par une forte sensibilité à l’humidité. Dans ce mémoire, nous avons cherché à estimer la durée de vie de ces composites à travers une caractérisation de l’endommagement en atmosphère humide du matériau, et une modélisation de son absorption d’humidité. Parmi les différentes fibres végétales disponibles, le lin a été choisi pour renforcer une matrice acrylique de la gamme « Elium ». Cette acrylique de nouvelle génération est un thermoplastique dont la polymérisation peut s’effectuer à froid par ajout d’un catalyseur au même titre que la plupart des thermodurcissables, et permet donc une bonne imprégnation des fibres, et évite tout endommagement thermique des fibres de lin. L’impact du vieillissement hygrothermique du composite sur ses propriétés mécaniques a été étudié en sollicitant le matériau à des cycles d’humidité. Ce protocole a permis de différencier deux effets du vieillissement : la plastification du composite causée par la présence de molécules entre les chaînes polymériques, et l’endommagement de la structure par fragilisation de l’interface fibre/matrice et l’oxydation de la cellulose. Le premier effet est réversible par séchage alors que le second est permanent, et est le plus dommageable pour la structure. Une loi de comportement hydromécanique a pu être déduite de ces essais, et sera utilisée en parallèle d’un modèle de diffusion par éléments finis afin de déterminer l’évolution à long terme des propriétés du composite soumis à un environnement réel. Le modèle prédit une baisse de plus de 50% du module élastique, et 60% de la contrainte à rupture après un temps d’utilisation de seulement un an. Néanmoins, le modèle utilisé se base sur de nombreuses hypothèses, notamment concernant la sensibilité de l’endommagement hydrique à la température. Une étude complémentaire est donc nécessaire afin de définir une réelle durée de vie de ces matériaux / Today, when high performance is required, composite materials are a common solution. Glass fibers or carbon fibers reinforced polymers are mostly used in aeronautic, automotive and sport industries where specific properties are needed. Recently, natural fibers have been considered as a reinforcement for polymers in order to conciliate performance and ecology. However, the production of structural parts with natural fibers face a major drawback: their fast aging caused by a high water sensitivity. In this thesis, we tried to estimate their lifetime through the characterization of the composite water damaging and the modeling of the moisture absorption. Among all the natural fibers available, flax was chosen to reinforce an acrylic matrix from the range Elium®. This new generation acrylic is a thermoplastic whose polymerization can be carried out at room temperature by adding a catalyst, like thermoset polymer are commonly produced. It allows a good fiber impregnation and avoid any thermal damage of the flax fibers during the process. The effect of the hydrothermal aging of the composite on its mechanical properties has been studied by exposing the material to moisture cycles. This protocol allowed us to distinguish two several aging effects: the composite yielding induced by the presence of water molecules into the polymer network and the structure’s damage by weakening the fiber/matrix interface and oxidizing the cellulose. The first effect is reversible by drying the composite, while the second one cause permanent decrease of mechanical properties. An hydromechanical model has been determined from these experiments and has been used with a finite element model of diffusion in order to determine the long-term evolution of the composite’s mechanical properties submitted to a reel environment. The model predicts more than 50% decrease of the composite’s stiffness, and more than 60% decrease of its strength after only one year of use. Therefore, without a proper treatment of the flax fiber for purpose of limiting its water damage, the flax/acrylic composite cannot be used as a structural part
13

Nanocompósitos de poli(glicerol sebacato) reforçados com nanowhiskers de caroá (Neoglaziovia variegata) e macambira (Bromelia laciniosa)

Macêdo, Murilo José Pereira de 17 September 2013 (has links)
Made available in DSpace on 2015-04-01T12:17:40Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2177616 bytes, checksum: bad1b5abac746f9000b37ffd93fc28e9 (MD5) Previous issue date: 2013-09-17 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Natural fibers were studied to investigate possibilities and better treatment techniques for the development of nanocomposites with poly(glycerol sebacate) (PGS). In this study, the potential of plants such as caroá (Neoglaziovia variegata) and macambira (Bromelia laciniosa) was investigated as sources of natural fibers to obtain whiskers by acid hydrolysis. Fibers were obtained from plant leaves of each species were pre-treated with alcohol and water to remove impurities, treated with aqueous sodium hydroxide (mercerization) and then with sodium chlorite (bleaching) before hydrolyzing with sulfuric acid in order to obtain cellulose whiskers. Fibers and whiskers were characterized thermogravimetric analysis (TGA), X-ray diffraction (XRD) and the morphology was analyzed by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Polymers and composites reinforced with whiskers were characterized by TGA, DSC, mechanical (tensile) tests and Fourier Transform Infrared Spectroscopy (FTIR). Results show that it was possible to extract whiskers from both natural and macambira and composite properties were dependent on whisker content. / O objetivo desta pesquisa foi estudar técnicas de obtenção e tratamento de fibras naturais para o desenvolvimento de nanocompósitos com o poli(glicerol sebacato). Nesse trabalho foram investigadas as potencialidades das plantas caroá (Neoglaziovia variegata) e macambira (Bromelia laciniosa) como fontes de fibras naturais para obtenção de whiskers a partir de hidrólise ácida. As fibras foram obtidas das folhas de ambas, separadas por processamento manual, pré tratadas com água e álcool (lavagens) para retirada de impurezas, tratadas com soluções aquosas de hidróxido de sódio (mercerização) e em seguida tratadas com clorito de sódio (branqueamento), onde se obteve uma massa com alto teor de celulose e então foi tratada com ácido sulfúrico em procedimento de isolamento para a obtenção de whiskers de celulose. As fibras foram caracterizadas por análise química, análise termogravimétrica (TGA), a cristalinidade foi investigada por difratometria de raios-X (DRX) e a morfologia foi investigada através de microscopia eletrônica de varredura (MEV). Os whiskers obtidos das fibras foram caracterizados por microscopia de força atômica (AFM), por TGA e por DRX. As reações de síntese do poli(glicerol sebacato) (PGS) se deram em temperaturas relativamente baixas (120ºC), através da policondensação e em atmosfera inerte de argônio ou nitrogênio, sem o uso de catalisadores externos. Os polímeros e compósitos reforçados com whiskers foram caracterizados por TGA, calorimetria exploratória diferencial (DSC), caracterização mecânica em ensaios de tração e por espectroscopia na região do infravermelho por transformada de Fourier (FTIR). As superfícies fraturadas nos ensaios de tração foram observadas por MEV. Os nanocompósitos apresentaram uma grande variação nas propriedades mecânicas com os teores de fibras, indicando a influência dos whiskers na matriz, aumentando o módulo e a resistência e diminuindo a elasticidade.
14

Compósitos reforçados com fibras naturais para a indústria automobilística / Natural fiber reinforced composites for automotive applications

Nestor Pedro Giacomini 28 February 2003 (has links)
Este trabalho tem como finalidade o desenvolvimento de compósitos a base de resina de poliéster insaturado reforçados com fibras naturais visando aplicações na indústria automotiva. Foram obtidas amostras em escala semi-industrial de compósitos reforçados com fibra de curauá, sisal e vidro, com teores variando de 15 a 40% em massa, com e sem a adição de carga mineral na matriz polimérica, através do processo de prensagem a frio. Os efeitos de cada um dos fatores foram analisados sobre a resistência à tração, módulo de elasticidade, alongamento na ruptura, resistência à flexão e ao impacto. Além disso, foi determinado o comportamento dos materiais com diferentes composições com relação à absorção de umidade. A variação da resistência à flexão como função do tempo de imersão e do teor de umidade absorvido pelos diferentes materiais foi determinada. Foram analisadas as propriedades superficiais como brilho, neblina (haze), ondulância (long-waviness) para as amostras produzidas e submetidas a ensaios de envelhecimento térmico, câmara de condensação e envelhecimento artificial. Todos os resultados obtidos foram baseados em normas da indústria automobilística para verificar conformidade com as exigências do setor. / The purpose of this work is to develop unsaturated polyester based composites reinforced with natural fibers of automotive applications. Samples have been obtained in a semi-industrial scale of composites reinforced with curauá, sisal and glass fiber, with contents varying from 15 to 40% in weight, with and without mineral filler incorporation to the polyester matrix. The molding technique employed was compression molding. The effects of these variables have been investigated over the tensile strenght, young\'s modulus, strain at rupture, flexural and impact strenght of the materials. The behavior of each sample has been investigated concerning water absorption. The variation of flexural strenght as a function of water absorption and immersion time has been determined for each formulation studied. Surface properties such as gloss, haze, long and short-waviness have been determined for all samples obtained just after painting and after artificial weathering, thermal aging and water absorption tests. All results have been performed based on automotive standards in order to evaluate the conformance of the materials to the requirements of the industry.
15

Pesquisa e criação: desenvolvimento de coleção de fios de fibras de paina / Research and design: development of yarns collection with kapok fibers

Rayana Santiago de Queiroz 16 October 2013 (has links)
Das lógicas vigentes de produção e consumo mais recorrentes no sistema da moda, emergem problemáticas ambientais e sociais de escala mundial. Ao longo da sua evolução, a produção têxtil, uma das atividades humanas mais antigas e elementares, tornou-se uma importante responsável pelo consumo em grande escala e uso indevido de recursos naturais e, associada aos valores de consumo da sociedade urbano-industrial, a sazonalidade da moda é mais um agravante. Fruto de uma visão de mundo fragmentada, intrínseca ao paradigma moderno, o design têxtil e de moda, assim como outras áreas do conhecimento, se desenvolveram orientados a sustentar um padrão de desenvolvimento econômico e tecnológico compatíveis com estas lógicas, de forma que no Brasil, importantes saberes sobre processos tecnológicos e o uso de matérias-primas inerentes a nossa cultura popular foram levados a um processo de desuso e esquecimento. Saberes estes intimamente associados à biodiversidade e tidos como de extrema importância dentro das políticas nacionais e internacionais de desenvolvimento ambiental e social. Neste contexto, este trabalho se desenvolveu com o objetivo de propor uma coleção de fios, produzidos a partir de fibras de paina, da espécie nativa Chorisia speciosa, e de técnicas têxteis artesanais, associando à criação as pesquisas teórica e experimental. O método que delineamos para o desenvolvimento da coleção de fios abrange: i) pesquisa teórico-conceitual, em que foram levantados os principais conhecimentos sobre as matérias primas e técnicas no âmbito da cultura têxtil popular brasileira e as principais tendências de moda e consumo no Brasil e no mundo; ii) pesquisa técnico-experimental, fase da pesquisa em que foi testada a viabilidade técnica de transformar as fibras de paina e diferentes misturas destas com fibras de algodão e lã em um fio, bem como o seu tingimento, utilizando as técnicas artesanais pesquisadas na etapa anterior; iii) desenvolvimento da coleção de fios propriamente dita. A partir dos dados obtidos na pesquisa, foi identificado que o vasto conhecimento popular a cerca das técnicas têxteis demonstra imenso potencial ao incorporá-lo no processo criativo têxtil. Além disso, a pesquisa técnico-experimental apontou a viabilidade de fiação da paina com misturas de algodão e lã, bem como o seu tingimento natural. Por meio deste trabalho foi possível então ratificar a importância e potencial de aliar a pesquisa científica à criação de moda tanto para o desenvolvimento de um novo material, como na proposição de formas distintas de produção e consumo de moda. As tendências de moda pesquisadas demonstraram que uma parcela da sociedade vive na atualidade uma intensa e acelerada redefinição de conceitos, valores e estilo de vida que contrariam a configuração do mercado de moda e a lógica de consumo predominante inerente a este, e se projetam gradativamente em transformações nos comportamentos de consumo e consequentemente no mercado e economia. Assim, elas apenas reafirmam a valia da presente pesquisa para o mercado de moda e a propensão deste à aceitação de produtos como o que propusemos aqui. / Social and environmental issues have emerged in global scale from the prevailing logics of production and consumption recurrent in the fashion system. The textile production, one of the oldest elementary human activities, has become a major factor in large scale consumption and in the misuse of natural resources throughout its evolution. Another aggravating factor is the urban-industrial society consumption values and the seasonality of fashion. As a result of a fragmented worldview, intrinsic to the modern paradigm, the textile and fashion design as well as other areas of knowledge - have been developed towards the sustainability of economic and technological development patterns compatible to these logics. In Brazil, important knowledge about technological processes and the use of raw materials, inherent in our popular culture, feel in disuse and oblivion. This knowledge is closely associated with biodiversity and taken with paramount importance for national and international environmental and social development policies. In this context, this work was developed aiming to propose a yarn collection produced with kapok fibers - from the native specie Chorisia speciosa - and textile craft techniques, linking creation to theoretical and experimental research. The outlined method for the development of the yarn collection includes: i) theoretical and conceptual research, in which we analyzed the main knowledge on raw materials and techniques in Brazilian popular textile culture and main fashion and consumption trends in Brazil and the world, ii) technical and experimental research, the phase in which we tested the technical feasibility of kapok fibers transformation and different mixtures of these fibers with cotton and wool on a yarn, as well as its dyeing, using the handmade techniques surveyed in the previous step, iii) development of yarn collection. From the data obtained in the research, we identified that the vast popular knowledge on technical textiles have immense potential to be incorporated in creative textile process. In addition, technical experimental research demonstrated the feasibility of kapok spinning with mixtures of cotton and wool, as well as its natural dyeing. Throughout the work, it was possible to confirm the potential importance of linking scientific research to fashion creation for both the development of new material and for proposing different forms of fashion production and consumption. Fashion trend research showed that part of the society is experiencing an intense and accelerated redefinition of concepts, values and lifestyle that contradicts the fashion market configuration and its consumer logic. Results of this process have gradually been projected as changes in consumer behavior, and consequently, in the market and the economy. Therefore, they reaffirm this research value for the fashion market and its propensity to accept the proposed products.
16

Reciclagem de rejeitos de polietileno de baixa densidade provenientes de uma cooperativa de catadores na forma de madeira plástica / Recycling of low-density polyethylene waste from pickers\' cooperatives in the form of wood-plastic composite

Camila Cezar Grillo 03 June 2016 (has links)
No mundo atual é possível observar uma produção crescente de resíduos sem uma destinação adequada, tendo como destino principal o descarte em aterros sanitários. Esse agravante é maior quando se refere aos polímeros, que são baratos, disponíveis em grande quantidade e com pouco valor agregado após o uso. O estudo proposto em parceria com a cooperativa de catadores de materiais recicláveis da cidade de Lorena teve como foco principal a reciclagem de rejeitos de polietileno de baixa densidade no sentido de obter um produto com valor comercial, a madeira plástica, visando contribuir no desenvolvimento técnico da reciclagem destes rejeitos, bem como nos aspectos sociais e ambientais relacionados. Foram produzidos compósitos de polietileno de baixa densidade com fibra natural de coco verde com o agente de reforço com porcentagem de 5 a 30% m/m. Para melhorar a adesão interfacial entre a fibra e polímero foi utilizado o compatibilizante polietileno graftizado com anidrido maléico a 2,5%. Os resultados mostraram que é possível obter êxito na reciclagem dos rejeitos de filmes de PEBD na forma de madeira plástica, sendo que o compósito de rejeito branco com 15% em massa de fibra de coco e o compósito de rejeito transparente com 30% de fibra de coco foram os materiais que apresentaram o melhor desempenho de propriedades mecânicas em termos de resistência ao impacto e à tração, obtendo valores superiores aos de madeiras comerciais. Portanto, a produção de madeira plástica a partir dos rejeitos de polietileno é uma maneira de aumentar a fonte de renda dos cooperados e promover ganhos ambientais com a redução do descarte de rejeitos plásticos poluentes no meio ambiente. / In today\'s world has being observed an increasing production of waste without adequate location, whose main destination is in landfills. This is a more serious aggravating when it refers on the polymers, that are inexpensive, available in large quantities and with little value after use. The present work, in partnership with pickers cooperatives of recyclable materials from the Lorena city, had mainly focused on recycling of low-density polyethylene waste in order to obtain a product with commercial value: a wood-plastic composite, to contribute to technical development recycling of waste as well as the social and environmental aspects. The composites were produced from low-density polyethylene with natural coconut fiber as a reinforcing agent at 5 to 30 wt%. For interfacial adhesion between the fiber and polymer was used a compatibilizer agent maleic anhydride grafted polyethylene (PE-g-MA) at 2.5 wt%. The results showed that it is possible to succeed in recycling LDPE film waste in the form of wood-plastic. The LDPE/coconut fiber composites from white polymeric waste containing 15wt% of fiber and LDPE/coconut fiber composites from transparent polymeric waste containing 30wt% were the materials with the highest mechanical performance related to impact resistance and tensile strength, reaching values higher than commercial woods. Therefore, the production of plastic wood from polyethylene waste is an alternative for improve the source of income of the cooperative and promote environmental gains by reducing the disposal of the polluting plastic waste in the environment.
17

Fibras naturais como matéria-prima para a produção de carvão ativado / Natural fibers as raw material for the production of activated carbon

Rombaldo, Carla Fabiana Scatolim, 1983- 17 June 2015 (has links)
Orientador: Antonio Carlos Luz Lisboa / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-27T17:27:40Z (GMT). No. of bitstreams: 1 Rombaldo_CarlaFabianaScatolim_D.pdf: 2818147 bytes, checksum: eb790e05e31dc621e11ca7ea1a4eb2d7 (MD5) Previous issue date: 2015 / Resumo: As fibras obtidas diretamente de fonte animal, mineral e vegetal são definidas como fibras naturais, sendo as mais comuns: a lã, o linho, o rami, o sisal, a juta, entre outras. Essas fibras têm uma importância social muito forte em países tropicais, especialmente na geração de empregos na zona rural e em áreas economicamente deprimidas. As fibras naturais, em sua maioria, são leves, resistentes, não abrasivas, renováveis, biodegradáveis e recicláveis, características que permitem competir com outros materiais artificiais que tenham problemas de disponibilidade ou ambientais. Além dos compósitos desenvolvidos com fibras naturais, existem ainda os carvões ativados que se destacam como um material com elevada porosidade e alta capacidade de adsorção, tanto em fase liquida quanto em fase gasosa. Visando o aproveitamento de recursos naturais disponíveis no território nacional e buscando alternativas que sejam economicamente viáveis para a produção de carvão ativado (CA), o presente trabalho teve como objetivo geral utilizar as fibras de juta e as fibras de sisal como matérias-primas para a produção de CA. Os CAs produzidos foram testados para a remoção de benzeno em solução aquosa. A produção do CA foi baseada na carbonização e na ativação física com CO2 e vapor d¿água. Para avaliar a evolução da estrutura porosa dos CAs obtidos foi utilizada a técnica de adsorção de N2 a 77K. Os resultados indicaram a possibilidade de produzir um material poroso com uma combinação de estrutura micro e mesoporosa, dependendo dos parâmetros utilizados nos processos de carbonização e ativação. Foram realizados alguns ensaios de adsorção das frações solúveis da gasolina em água, tanto com os CAs provenientes das fibras naturais, juta e sisal, como em CAs comerciais. Foi possível observar que o CA proveniente da fibra de juta se mostrou tão eficiente quanto o CA comercial. / Abstract: The fiber obtained directly from animal, mineral and vegetable are defined as natural fibers, and the most common are: wool, linen, ramie, sisal, jute, and others; which have very strong social importance at tropical countries, especially for job creation in rural and economically poor areas. These fibers are lightweight material, resistant, non-abrasive, renewable, biodegradable and recyclable. Features that allow it compete with other artificial materials, which have availability or environmental problems. In addition to the natural fiber composites there are activated carbons which stand out as high porosity material with high adsorption capacity of liquid and gas phases. Aiming at the use of natural resources available in the country and seeking for alternatives that are economically viable for activated carbon production, this study has investigated the possibility of using jute fiber and sisal fiber as precursors for the production of activated carbon (AC). The produced AC were characterized and tested for benzene adsorption in aqueous solution. The AC production of was based on the carbonization and physical activation with CO2 and steam. To evaluate the porous structure of the produced activated carbon N2 adsorption at 77K was used. The adsorption results indicated the possibility of producing a porous material having a combination of micro and mesoporous structure, depending on the parameters used in the carbonization and activation processes. The water-soluble gasoline fraction adsorption experiments using natural fibers and commercial AC showed that both are equally efficient / Doutorado / Engenharia de Processos / Doutora em Engenharia Quimica
18

Pultruze biokompozitu na bázi lněných vláken / Pultrusion process of composite based on flax fibres

Hahn, Filip January 2015 (has links)
Theoretical part of master's thesis is focused on chemical treatments of natural fibers and their use as reinforcement material in polymer composites. Flax fibers were treated with two different silane coupling agents to improve their adhesion with polymer matrix. Nature of treatment was studied by using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Composites based on both treated and untreated flax fibers were prepared by pultrusion.technique. Mechanical properties and water absorption of prepared composites were evaluated.
19

Production Process for Tunnel Modeling : An Analysis of Composites for Water Applications

Ghaderidosst, Melody, Hurtigh Grabe, Vilma, Norman, Rebecka, Rosvall, Adam, Wiksten, Evelina January 2021 (has links)
Hydroelectric power is a leading source of renewable energy where large turbines convert the kinetic energy of water into electricity. In order to not exceed the capacity limit of the turbine, excess water in the dams needs to be diverted away through spillways. In order to do in-house testing of the water flow, a 1:30 scale tunnel manufactured by an external supplier is used. The production of the tunnels is however preferred to be done in-house. In this thesis different material options and methods for the tunnel modeling production are examined. This has been achieved by a thorough literature study following practical experiments. Polymers are known for their strength and stiffness to weight ratio as well as low cost and availability. To further enhance its material properties for given applications, polymers can be reinforced with different fibers creating a composite. Several fibers were considered, however in order to support the set strategy of Vattenfall AB regarding environmental and sustainability goals, natural fibers, specifically hemp and flax deemed to be a good fit using epoxy as the matrix material. Based on the material properties tested for the composites, flax with epoxy was the resulting material used to model the tunnels. The final method for the production process using said material was based on three different methods that were tested. The conclusion was that using a flax-epoxy composite with a hand lay-up method using a negative mold made of Styrofoam gave the best results. It should, however, be noted that a definite production process for the tunnel could not be determined due to time limitations. A theoretical production process for tunnel modeling was nevertheless composed.
20

Mechanical and thermal behavior of multiscale bi-nano-composites using experiments and machine learning predictions

Daghigh, Vahid 01 May 2020 (has links)
The mechanical and thermal properties of natural short latania fiber (SLF)-reinforced poly(propylene)/ethylene-propylene-diene-monomer (SLF/PP/EPDM) bio-composites reinforced with nano-clays (NCs), pistachio shell powders (PSPs), and/or date seed particles (DSPs) were studied using experiments and machine learning (ML) predictions. This dissertation embraces three related investigations: (1) an assessment of maleated polypropylene (MAPP) coupling agent on mechanical and thermal behavior of SLF/PP/EPDM composites, (2) heat deflection temperature (HDT) of bio-nano-composites using experiments and ML predictions, and (3) fracture toughness ML predictions of short fiber, nano- and micro-particle reinforced composites. The first project (Chapter 2) investigates the influence of MAPP on tensile, bending, Charpy impact and HDT of SLF/PP/EPDM composites containing various SLF contents. The second project (Chapter 3) introduces two new bio-powderditives (DSP and PSP) and characterizes the HDT of PP/EPDM composites using experiments and K-Nearest Neighbor Regressor (KNNR) ML predictions. The composites contain various contents of SLF (0, 5, 10, 20, and 30wt%), NCs (0, 1, 3, 5wt%), micro-sized PSPs (0, 1, 3, 5wt%) and micro-sized DSPs (0, 1, 3, 5wt%). The third project (Chapter 4) characterizes the fracture toughness of the same composite series used in the second project, by applying Charpy impact tests, finite element analysis, and a ML approach using the Decision Tree Regressor (DTR) and Adaptive Boosting Regressor (ABR). 2wt% MAPP addition enhanced the composite tensile/flexural moduli and strength up to 9% compared with the composites with zero MAPP. In addition, energy impact absorption was profoundly increased (up to78%) and HDT (up to 4 Co) was improved upon MAPP addition to the composites. SLF, NC, DSP and PSP could separately and conjointly increase HDT and fracture toughness values. The KNNR ML approach could accurately predict the composite’s HDT values and, Decision Tree Regressor (DTR) and Adaptive Boosting Regressor ML algorithms worked well with fracture toughness predictions. Pictures taken through a transmission electron microscope, scanning electron microscope and X-Ray proved the NC dispersion and exfoliation as one of the factors in HDT and fracture toughness improvements.

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