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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.
1

Epoxy/Single Walled Carbon Nanotube Nanocomposite Thin Films for Composites Reinforcement

Warren, Graham 2009 May 1900 (has links)
This work is mainly focused upon the preparation, processing and evaluation of mechanical and material properties of epoxy/single walled carbon nanotube (SWCNT) nanocomposite thin films. B-staged epoxy/SWCNT nanocomposite thin films at 50% of cure have been prepared for improving conductivity and mechanical performance of laminated composites. The SWCNTs were functionalized by oxidation and subsequent grafting using polyamidoamine generation 0 dendrimers (PAMAM-G0). The epoxy nanocomposites containing SWCNTs were successfully cast into thin films by manipulating degree of cure and viscosity of epoxy. The first section of this study focuses on the covalent oxidation and functionalization of single-walled carbon nanotubes (SWCNTs), which is necessary in order to obtain the full benefit of the SWCNTs inherent properties for reinforcement. In the second section of this work the preparation of B-staged epoxy/SWCNT nanocomposite thin films is discussed and what the purposes of thin films are. Additionally, the morphology as well as mechanical properties is evaluated by numerous means to obtain a clear picture as to the mechanisms of the epoxy/SWCNT nanocomposites. Furthermore, the effects of using sulfanilamide as a more attractive surface modifier for improved dispersion and adhesion and the effects of nylon particles for improved toughening on epoxy/SWCNT nanocomposites are discussed which displays improvements in numerous areas. Finally, based on these findings and previous studies, the B-staged epoxy/SWCNT nanocomposite thin films can be seamlessly integrated into laminated composite systems upon heating, and can serve as interleaves for improving conductivity and mechanical strengths of laminated fiber composite systems.
2

Conductive Coating Materials

Cakar, Ilknur 01 July 2006 (has links) (PDF)
In this study, electrically conductive coating materials composed of epoxy resin and carbon black (CB) were prepared by applying two different mixing techniques (Grinding and Mechanical Mixing). The effect of carbon black addition, ultrasonication, mixing type and surface modification of carbon black on the morphologies, electrical and mechanical properties of the composites were investigated. According to test results, Grinding Method is much more efficient and for this method, percolation concentration was found as 2 vol %. The electrical resistivity value obtained at this composition is around 107 ohm.cm. Also, for the samples prepared by Grinding Method, the hardness increased by adding conductive filler, but the impact energy and adhesive strength decreased with increasing carbon black content. Ultrasonication was applied to the samples containing 2 vol % CB obtained by Grinding Method to reduce the electrical resistivity further. Three different ultrasonic mixing times were tried, however, no positive effect was observed on electrical and mechanical properties. Since the addition of carbon black has a negative effect on the processability of the mixture, it was aimed to obtain desired conductivity value at lower percolation concentration by modifying carbon black surface with different silane coupling agents and formamide. The best result in terms of electrical conductivity was obtained for the materials produced with formamide treated carbon black by Grinding Method. At 1 vol % concentration, the electrical resistivity was found as approximately 106 ohm.cm which is three orders smaller than the resistivity of materials prepared with untreated carbon black.
3

Étude et modélisation de la polymérisation dynamique de composites à matrice thermodurcissable / Analysis and modeling of the dynamic polymerization of thermosetting matrix composites

Paris, Christophe 28 November 2011 (has links)
La cuisson rapide de préimprégnés est une problématique d'actualité qui sous entend les nécessités de rentabilité dans l'industrie aéronautique. Cette étape est basée sur la maîtrise du degré d'avancement de réaction du système thermodurcissable au cours du cycle qui régit l'ensemble des propriétés finales des pièces composites. La caractérisation et la modélisation cinétique du préimprégné aéronautique M21/T700 sont réalisées en vue d'appliquer des dynamiques de mise en oeuvre rapides applicables sur une installation de thermocompression dotée d'un moule chaué par induction de technologie Cage System de Roctool. La construction de diagrammes Temps Température Transformation et la réalisation d'un couplage thermo-cinétique par éléments finis permettent de proposer des cycles optimisés d'une durée de moins de 2 heures (au lieu de 4h30 en cuisson autoclave), en préservant la présence de particules de thermoplastiques dans la matrice. L'étude des propriétés des plaques fabriquées montre des résultats comparables à ceux obtenus pour des pièces mises en oeuvre lors de cycles standards de fabrication à l'aide du procédé autoclave. / The increase of composite content in aerospace structures requires an improvement of profitability through high curing processes. The curing step is based on the control of the degree of cure of the thermosetting system that governs the final properties of the composite parts. The Cage System technology from the Roctool company enables high curing rates thanks to induction heating system. Thus, the characterization and the kinetic modeling of the M21/T700 aeronautical prepreg have been realized for such sollicitations (i.e. high heating rates). To provide a better temperature control, the thermal and kinetic interactions are also considered by finite element modeling of composite thickness. Time Temperature Tranformation diagrams have been set up to build short curing cycle of less than 2h (instead of 4h30 in autoclave curing), considering the presence of thermoplastic particules. Finally, the part properties are in good agreement with the autoclave cycle recommended by the material supplier.
4

Influence de charges carbonées sur la dissipation thermique de nouveaux composites diélectriques / Influence of carbon fillers on the heat dissipation of new dielectric composites

Diaz Chacon, Lurayni 09 December 2016 (has links)
La plupart des équipements électroniques et électriques sont enrobés ou encapsulés par de la résine epoxy, choisie pour ses qualités physiques, chimiques et surtout diélectriques. Cependant, ce matériau présente un inconvénient majeur : sa faible conductivité thermique (0.2 W/mK). Dans ce contexte, nous avons élaboré et caractérisé des composites epoxy / carbone dans le but d’améliorer la conductivité thermique de ce type de résine tout en conservant ses propriétés diélectriques. Nous avons ainsi testé le potentiel d’une large gamme de charges carbonées, de structures, formes et tailles variées (sphères, tubes et plaquettes), telles que des micro-sphères de carbone et des nanotubes multi-parois synthétisées par CVD et PECVD, mais aussi des charges industrielles : nano-plaquettes de graphite (graphite exfolié), du coke de pétrole, du graphite synthétique et naturel. Des échantillons de matériaux composites massifs (50 x 50 x 4 mm) ont été préparés à partir d’une résine industrielle DGEBA de viscosité élevée 8.5-15 Pa.s, en faisant varier le taux de charge. Les propriétés thermiques des composites ont été mesurées à partir de la technique du hot disk (source plane instationnaire). Les meilleurs résultats ont été obtenus à partir des nano-plaquettes de graphite : les conductivités thermiques des composites ont atteint (0.55 W/mK) pour une charge admissible maximale de 2.67 vol.%. L’accroissement relatif de conductivité thermique a été de 66 % pour 1 vol.%. Cet accroissement est particulièrement élevé dans la mesure où les meilleurs résultats reportés sont de 20 % / vol.% dans le cas de résines à viscosité plus faible de type DGEBF (2.5 - 4.5 Pa.s). La concentration de charge admissible (1.3 vol.%) pour conserver une résistivité électrique suffisamment élevée (> 105 ohm.m) nous a permis d’atteindre une conductivité thermique de 0.37 W/mK (soit une augmentation de 100% par rapport à la résine initiale). Ces résultats sont interprétés en termes de transport des phonons acoustiques dans un système composite bi-phasique. Les nano-plaquettes de graphite sont caractérisées par une morpholigie anisotrope, d’ une surface d’environ 26 x 26 microns dont l’épaisseur est de l’ordre de 6 nm. Elles combinent une structure lamellaire périodique bien ordonnée dans les plans de graphène (caractérisation par XPS, EDX et DRX), et des rapports d’acicularité élevés ( 4300), estimés à partir de différentes techniques : TEM, SEM et BET. Nous montrons qu’accroitre l’acicularité des nano-plaquettes de graphite par exfoliation, en préservant une grande surface des plans de graphène, et sans générer de défauts de structure, constitue un défi. Cette morphologie 2D particulière permet d’une part de conserver voire augmenter la conductivité intrinsèque des charges, favorisée dans les plans de graphène, et d’autre part, en raison de leur grande surface spécifique, de garantir après leur dispersion dans la résine, un meilleur transport des phonons acoustiques dans le composite. / Most electronic and electrical equipment are coated or encapsulated by epoxy resin due to its physical, chemical and dielectric properties. However, this material has a major drawback: its low thermal conductivity ( 0.2 W / mK). In this context, we have developed and characterized epoxy / carbon composites in order to improve the thermal conductivity of this type of resin while maintaining its dielectric properties. We have tested the potential of a wide range of carbonaceous fillers, structures, shapes and sizes (spheres, tubes and plates), such as carbon micro-spheres and multi-walled carbon nanotubes synthesized by CVD and PECVD, but also industrial fillers: graphite nano-platelets (exfoliated graphite), petroleum coke, synthetic and natural graphite. Large composite samples (50 x 50 x 4 mm) were prepared from a DGEBA engineering resin of high viscosity 8.5-15 Pa.s, by varying the charge vol%. The thermal properties of the composites were measured from the transient plane source technique (hot disk). The best results are obtained from graphite nano-platelets: the thermal conductivity reach (0.55 W / mK) for a maximum load of 2.67 vol%.. The relative increase of thermal conductivity is 66% to 1 vol.%. This increase is particularly high to the extent that the best results reported so far is 20% / vol% for resins with lower viscosity, type DGEBF (2.5 - 4.5 Pa.s). The allowable concentration (1.3 vol.%) to maintain a sufficiently high electrical resistivity (> 105 ohm.m) permits to increase of the thermal conductivity to 100% (0.37 W / mK) compared to the initial resin. These results are interpreted in terms of transport of acoustic phonons in the composite two-phase system. Graphite nano-platelets are characterized by anisotropic shapes with a surface of about 26 x 26 microns whose thickness is of the order of 6 nm. They combine an ordered periodic structure in graphene planes (characterization by XPS, EDX and XRD), and a high aspect ratio ( 4300), estimated using various techniques: TEM, SEM and BET. We show that graphite exfoliation permit to increase the aspect ratio of graphite nanoplatelets, maintaining large micronic graphene surface, and without generating structural defects is a challenge. This peculiar 2D morphology allows on one hand, to retain or even increase the intrinsic filler conductivity, favored in the graphene planes, and on another hand, due to their high surface area, to ensure after their dispersion in the resin, a better transport of acoustic phonons through the composite.

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