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1
Carapella, Elissa E. "Micromechanics of crenulated fibers in carbon/carbon composites". Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09192009-040251/.
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Buchanan, Fraser James. "Oxidation and protection of carbon-carbon composites". Thesis, University of Cambridge, 1993. https://www.repository.cam.ac.uk/handle/1810/283685.
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Dillon, Frank. "Pitch for carbon composites". Thesis, University of Newcastle Upon Tyne, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315565.
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Matzinos, Panagiotis D. "Coal-tar pitch as the matrix carbon precursor in carbon-carbon composites". Thesis, Loughborough University, 1995. https://dspace.lboro.ac.uk/2134/28083.
Testo completoAbstract (sommario):
Coal-tar pitch is a promising carbon matrix precursor for carbon-carbon composites. It has a suitable viscosity, high carbon yield, and it forms graphitic structures. In addition, pitch is a relatively cheap raw material. This thesis is a study on the use of coal-tar pitch as carbon matrix precursor in carbon–carbon composites.
5
Crocker, Philippa. "Structural effects of oxidation of carbon/carbon composites". Thesis, University of Bath, 1991. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293204.
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Allen, Abraham Keith. "A method for winding advanced composites of unconventional shapes using continuous and aligned fibers /". Diss., CLICK HERE for online access, 2004. http://contentdm.lib.byu.edu/ETD/image/etd639.pdf.
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Obst, Andreas W. "Thermal stresses in coatings on carbon-carbon composites". Diss., Virginia Tech, 1995. http://hdl.handle.net/10919/39111.
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Huang, Y. Y. S. "Carbon nanotube composites and networks". Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604698.
Testo completoAbstract (sommario):
Strong interactions are present in as-grown carbon nanotube. When carbon nanotubes are used in macroscopic forms of composites, the properties of the ensemble are often governed by the characteristic interaction and the morphology of the percolating nanotube networks, while the intrinsic attributes associated with a single, individual nanotube become less apparent. Experiments and theoretical models were developed to study this interaction, and ultimately to optimize the fabrication of carbon nanotube composites and networks. Short carbon nanotubes can be produced via sonication cutting. The same process can be applied to determine the strength of nano-filaments of different natures. Rheometry was found to be useful to provide qualitative information about the spatial distribution and orientation of carbon nanotubes in a liquid medium. In all, the choice of dispersion and processing techniques determines the final microstructure, there it plays a critical role in varying the physical properties and subsequent applications of the carbon nanotube/ polymer composites. The studies presented here have also paved new ways to tailor the electrical properties of generic carbon nanotube-polymer composites, and to create structures for soft electrodes and conductive networks for transparent flexible coatings.
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Samalot, Rivera Francis J. "Processing, characterization and modeling of carbon nanofiber modified carbon/carbon composites". Birmingham, Ala. : University of Alabama at Birmingham, 2007. https://www.mhsl.uab.edu/dt/2008r/rivera.pdf.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--University of Alabama at Birmingham, 2007.Additional advisors: Krishan K. Chawla, Derrick Dean, Yogesh Vohra, Mark Weaver. Description based on contents viewed Feb. 13, 2009; title from PDF t.p. Includes bibliographical references (p. 174-186).
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Brender, Patrice. "Etude de l'influence de la température sur les réactions tribochimiques des matériaux carbonés : Application au freinage aéronautique de composites Carbone/Carbone". Thesis, Mulhouse, 2012. http://www.theses.fr/2012MULH5872.
Testo completoAbstract (sommario):
L’objectif de ce travail est d’étudier quantitativement l’évolution des propriétés de surface des matériaux carbonés et leur réactivité dans les conditions proches de celles rencontrées lors du taxiage des avions. Les essais de freinage ont été réalisés à l’aide d’un Banc d’Essai Tribométrique à Simulation Inertielle. Les composites C/C frottés et les débris d’usure sont caractérisés par des techniques non-conventionnelles multi-échelles. Les composites frottés (dans leur totalité) et les débris d’usure sont caractérisés par thermo-désorption programmée et chimisorption d’oxygène. Ces analyses permettent de déterminer la nature et la quantité de groupes fonctionnels et la teneur en sites actifs, caractéristique de la réactivité intrinsèque du carbone et responsable de l’interaction avec les espèces gazeuses de l’environnement. Ces caractérisations sont complétées par des analyses morphologiques, structurales et texturales par microscopies, diffractions des rayons X, adsorption de gaz. L’analyse des caractéristiques physico-chimiques des débris d’usure et des disques frottés permet de remonter aux réactions tribochimiques ayant eu lieu dans le contact : des réactions chimiques entre l’oxygène ou l’eau et les liaisons C-C rompues ont été mises en évidence. Un modèle permettant de justifier les différences de propriétés tribologiques lors des essais de taxiage a été proposé. Ce modèle, basé sur la réactivité du système et sur les propriétés de l’interface de frottement, permet d’élucider les problématiques liées à la température dans ce type de systèmeThe objective of this work is to study quantitatively the evolution of carbon materials surface properties and reactivity under breaking conditions similar to those encountered during taxiing. The breaking tests were carried out using a Tribometric Test Bench. The rubbed C/C composites and the wear debris collected are then characterized by mutiscale unconventional techniques. The whole rubbed composites and the wear debris are characterized by Temperature-Programmed Desorption and by oxygen chemisorption. These analyzes are used to determine the nature and amount of functional groups and the content of active sites that is characteristic of the reactivity of the carbon material and also responsible of its interaction with the surrounding environment. The characterizations are completed by morphological, structural and textural analysis, such as Electron Microscopy, X-Ray Diffraction and gas adsorption. The analysis of the physic-chemical characteristics of wear debris and of the rubbed discs enables to evidence the tribochemical reactions occurring in the mechanical contact: chemical reactions between oxygen or water and the broken C-C bonds have been evidenced. A model is finally proposed, justifying the differences in the tribological properties during taxiing tests. The later is based on the carbon reactivity and on the interface properties and justify the temperature dependence of this system
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Liu, Wenjiao. "Electromechanical response of carbon nanotube/carbon fibre epoxy composites". Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123267.
Testo completoAbstract (sommario):
Carbon fibre (CF) reinforced polymers have become the most widely used composites in theaerospace industry. However, ensuring the integrity of composite structures remains one of themain challenges. By measuring the change in electrical resistance of these materials, it is feasibleto monitor strains and damage initiation and accumulation in-situ and in real-time. The objectiveof this work is to investigate the potential of adding carbon nanotubes (CNTs) to existing CFpolymersto improve strain self-sensing. First, the DC and AC conductivities of epoxy containingdifferent CNT weight concentrations are measured in order to characterize the percolationthreshold. Second, the variation in electrical resistance as a function of electrode distance isinvestigated for CF-epoxy and CF-CNT-epoxy composites. The results show that the addition ofCNTs increases through-thickness conductivity by primarily reducing CF-CF contact resistancerather than increasing the number of CF-CF contacts. In addition, the presence of CNTsengenders a more homogeneous CF-CF contact resistance distribution. Third, theelectromechanical behaviours of CF-epoxy and CF-CNT-epoxy composites are compared viatension, compression, and flexure experiments while simultaneously monitoring electricresponses. The addition of CNTs results in: 1) improved sensitivity under compression due to thecreation of more CF-CF contacts; 2) better linearity under tension due to a more gradual changein CF-CF contact resistance; 3) better electric response reproducibility and repeatability due tomore homogeneous distribution of CF-CF contact resistance. Finally, an existing analyticalmodel is modified to estimate the change in surface resistance on both the tension andcompression sides of flexural specimens using the results of tension- and compression-only testsas inputs. The modelling data is then compared with the measured change in surface resistanceunder flexural load and shows good agreement. The model advances CF-CF contact as thedominating mechanism in the change of surface resistance under mechanical loading—especiallyin compression.Les polymères à fibre de carbone (FC) sont de nos jours les composites les plus largementutilisés dans le domaine aéronautique. Cependant, assurer l'intégrité de ces structures compositesreste l'un des principaux défis. En mesurant la variation de la résistance électrique descomposites polymère-FC, il est possible de surveiller les déformations et les dommages in-situen temps réel. L'objectif de ce travail est d'étudier l'influence de l'addition de nanotubes decarbone (NTCs) dans des polymère-FC sur la capacité d'auto-détection des déformations et desendommagements structurels. Premièrement, les conductivités continues et alternatives derésines époxy contenant différentes concentrations en poids de NTC sont mesurées afin decaractériser le seuil de percolation. Deuxièmement, la variation de la résistance électrique enfonction de la distance de l'électrode est étudiée pour les composites époxy-FC et époxy-CFNTC. Les résultats démontrent que l'ajout de NTC augmente la conductivité à travers l'épaisseur,en réduisant principalement la résistance de contact FC-FC plutôt que d'augmenter le nombre decontacts FC-FC. De plus, l'ajout de NTC permet une répartition plus homogène de la résistancedes contacts FC-FC. Troisièmement, les comportements électromécaniques peuvent êtrecomparés en mesurant les réponses électriques d'échantillons en temps réel soumis à des tests detraction, compression, et flexion. L'ajout de NTC conduit à: 1) une amélioration de la sensibilitésous contraintes de compression due à davantage de contacts FC-FC créés, 2) une meilleurelinéarité de la résistance électrique sous contraintes de traction due à un changement plusprogressif de la résistance de contact FC-FC, 3) une meilleure reproductibilité et répétabilité desréponses électriques grâce à une répartition plus homogène de la résistance de contact FC-FC.Enfin, un modèle analytique est modifié pour estimer la variation de la résistance de surface enflexion en utilisant les résultats des essais de traction et de compression comme donnéesd'entrée. Les données obtenues par le modèle sont ensuite comparées avec la variation de larésistance de surface mesurée lors des essais en flexion, et présentent une bonne corrélation. Cemodèle démontre en plus que la variation des contacts FC-FC domine la variation de résistancede surface sous chargement mécanique, en particulier la compression.
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Ibarra, Gonzalez Nagore. "Carbon nanotube staple yarn/carbon composites in fibre form". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708995.
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Leigh, Benjamin David. "Strength degradation of carbon-carbon composites for aircraft brakes". Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285332.
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Avery, William Byron. "A study of the mechanical behavior of a 2-D carbon-carbon composite". Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/76091.
Testo completoAbstract (sommario):
The objective of this study was to observe and characterize the out-of-plane fracture of a 2-D carbon-carbon composite and to gain an understanding of the factors influencing the stress distribution in such a laminate. The experimental portion of this study consisted of performing an out-of-plane tensile test in a scanning electron microscope and determining the modes of failure. Failure was found to be interlaminar, with cracks propagating along the fiber-matrix interface.
Finite element analyses of a two-ply carbon-carbon composite under in-plane, out-of-plane, and thermal loading were performed. Stress distributions were studied as a function of stacking sequence, undulation aspect ratio, and undulation offset ratio. The results indicated that under out-of-plane loading σx and τxz were strongly dependent on the geometric parameters studied, but σz and σy were relatively independent of geometry. Under in-plane loading all components of stress were strong functions of the geometry, and large interlaminar stresses were predicted in regions of undulation. The thermal analysis predicted the presence of large in-plane normal stresses throughout the laminate and large interlaminar stresses in regions of undulation.
An elasticity solution was utilized to analyze an orthotropic fiber in an isotropic matrix under uniform thermal load. The analysis reveals that the stress distributions in the fiber are singular when the radial stiffness Crr is greater than the hoop stiffness C₀₀. Conversely, if Crr < C₀₀ the maximum stress in the composite is finite and occurs at the fiber-matrix interface. In both cases the stress distributions are radically different than those predicted assuming the fiber to be transversely isotropic (Crr = C₀₀).Ph. D.
15
Diaz, Chacon Lurayni. "Influence de charges carbonées sur la dissipation thermique de nouveaux composites diélectriques". Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT320/document.
Testo completoAbstract (sommario):
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 compositeMost 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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Gao, Feng-Ge. "Structure of 2-D carbon/carbon composites and its dependence on processing". Thesis, Loughborough University, 1993. https://dspace.lboro.ac.uk/2134/31871.
Testo completoAbstract (sommario):
Carbon fibre reinforced carbon (C/C) composites are advanced materials which exhibit good performance in high temperature inert environments. These materials are generally produced from carbon fibre reinforced polymers (CFRP) by carbonisation and a long series of densification treatments using chemical vapour deposition (CVD) or polymer impregnation. The carbonisation of CFRP results in a highly porous structure with low strength and stiffness so that the aim of the densification is to fill the voids to improve mechanical properties. It is however known that an understanding of void structure in the composites and its relation to raw materials, processing conditions and mechanical properties is important.
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Pardini, Luiz Claudio. "The structure & properties of SiC-modified carbon fibre reinforced carbon composites". Thesis, University of Bath, 1994. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359217.
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Charron, Morgan. "Modélisation basée images du comportement thermomécanique de composite C/C". Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0670/document.
Testo completoAbstract (sommario):
Les composites C/C sont principalement utilisés dans les applications à très haute température et notamment dans le domaine du spatial. Savoir concevoir ces matériaux est essentiel pour améliorer leurs performances et diminuer les coûts de production. Ce mémoire présente le développement d’un modèle multiéchelle basé images du comportement thermomécanique d’un composite C/C à renfort 3Daiguilleté. L’utilisation de méthodes classiques ne permet pas de décrire correctement cette architecture très complexe. La méthode CEPI (Computing Effective Properties using Images) présentée s’appuie d’une part sur les propriétés des constituants, dont certaines ont été caractérisées au laboratoire, etd’autre part sur l’architecture de ces matériaux, qui a été obtenue à partir d’une image tomographique.Les propriétés mesurées des constituants ont été directement utilisées dans un modèle microscopique de fil idéal, le modèle macroscopique étant lui directement basé sur l’image de tomographie. Les paramètres des calculs aux différentes échelles ont ensuite été étudiés et discutés pour en déterminer l’influence et permettre de valider certaines hypothèses. La comparaison des résultats numériques et expérimentaux a enfin permis de valider la méthode CEPI sur le comportement mécanique linéaire et de mettre en avant les principaux axes d’améliorations pour le comportement en dilatation des ces compositesC/C composites are used in very high temperature applications, especially in space activities. The ability to design these materials is essential in order to enhance their performances and lower their production costs. This work introduces an images-based multiscale modeling of the thermomechanical behavior of a C/C needled composites. Standard methods cannot describe this very complex architecture.The CEPI model (Computing Effective Properties using Images) is based on one hand on the components properties, some of them having been characterized in the laboratory, and on the other hand on the architecture of the material which is directly obtained using tomography images. The components properties were used on a microscopic model of an idealistic yarn, while the macroscopic model was based on the CT scan data itself. The influence of the internal parameters of the method was studied and discussed, and allowed validating some hypotheses. Finally, the comparison between the numerical and experimental results validates the CEPI model on the linear mechanical behavior and stressed the key axes of improvement for the thermal expansion behavior of these composites
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Cantwell, W. J. "Impact damage in carbon fibre composites". Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/7834.
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Savage, Gary. "Mechanical properties of carbon/graphite composites". Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38153.
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Tahhan, May. "Carbon nanotubes and conducting polymer composites". Intelligent Polymers Research Institute - Faculty of Science, 2004. http://ro.uow.edu.au/theses/407.
Testo completoAbstract (sommario):
A nanocomposite is defined as a material of more than one solid phase, where at least one dimension falls in the nanometer range. The combination of carbon nanotubes (CNT) and conducting polymers offers an attractive route for the production of novel compounds that can be used in a variety of application such as sensors, actuators, and molecular scale electronic devices. The ultimate goal of this work is to develop and investigate CNT composites that provide a structural functionality together with one or more other key functions. A variety of novel CNT dispersions were prepared using commercially available CNT systems such as Rice single-walled carbon nanotubes (RCNT), HiPco single-walled carbon nanotubes (HCNT), and Multi-walled carbon nanotube (MWCNT). This study explored the application of novel functional dispersing agents. Deoxyribose Nucleic Acid (DNA) a biological molecule, N- sopropylacrylamide 2-acrylamido-2-methyl-1-propanesulfonic acid (NIPPAm-AMPS) a polyelectrolyte, Didodecyldimethyl ammonium bromide (DDAB) a polymerizable compound, Poly(methoxyaniline-5-sulfonic acid) (PMAS) an inherently conducting polymer, and PVA an insulating polymer were some of the agents used to disperse the CNT. These dispersions were then evaluated in term of their stability and ability to effectively disperse the CNT. Solid-state CNT composites (mats) were then prepared by means of pressure filtration of the CNT/dispersant solutions. These mats were characterized using a variety of different techniques to determine their viability to be used as mechanical actuators or electrochemical devices. The characterization methods included cyclic voltammetry, conductivity, capacitance, atomic force microscopy, scanning electron microscopy, Young’s modulus, and actuation measurements. Abstract RCNT/conducting polymer composites were prepared by the electropolymerization of Pyrrole with a range of different dopant anions in the presence of different RCNT dispersions. In these composites, the RCNT were completely covered by the polymer, consequently the electrochemical responses of these composites were dominated by the electrochemistry of the polymers with the CNT functioning as a conductor element. Polypyrrole was also electropolymerized using functionalized multi-walled carbon nanotubes (FMWCNT) as dopant. Electropolymerization was carried out using galvanostatic and potentiostatic techniques on gold-coated Mylar and ITO-glass. It was determined that PPy/FMWCNT composites deposited on either electrode using potentiostatic deposition exhibited redox peaks. This redox behavior was not observed when the galvanostatic deposition was employed. HCNT/Polyaniline (PAn) composites were prepared by either casting a film from a solution of HCNT and PAn in 1,2-Dichlorobenzene, or by casting a film of PAn onto an existing HCNT mat. The latter exhibited the highest conductivity. The actuation behavior of these CNT composites was investigated and it was determined that the PAn component contributes to the actuation strain while the HCNT component contributes to Young’s modulus. The combination of the HCNT (with their mechanical properties) and PAn (with its actuator behavior) offers and attractive route not only to reinforce the polymer film but also to introduce new electronic properties based on morphological modifications or electronic interactions between the two components giving a robust blend of optimum properties. These results open the door for these composites to be used in a variety of applications that require a combination of the above characteristics such as mechanically reinforced actuator devices, robotics, optical fiber switches, prosthetic devices, and anti-vibration systems. In addition, PPy with a range of dopant anions was electrodeposited galvanostatically, potentiostatically, and potentiodynamically on the surface of four different carbon electrodes, RCNT mat (unannealed), RCNT mat (annealed), glassy carbon, and carbon foil. It was found that the method of electrodeposition was crucial to the electroactivity of the deposited polymers, particularly when deposited onto a RCNT mat due to the different interaction between the deposited polymer and the RCNT mat. Finally, HCNT/SDS, HCNT/PMAS, and HCNT/DNA fibers were prepared using the Particle Coagulating Spinning method (PCS). The annealing process resulted in a dramatic increase in conductivity of up to 2600 times higher compared to the unannealed fibers. However, the annealing process did not play any role in keeping the fibers together or modifying the alignment of the carbon nanotubes ropes within the fibers. The HCNT/DNA fibers, with their biocompatibility, high conductivity, and good mechanical properties can be used as artificial muscles, bioelectronic sensors, or even as platforms to support the growth of nerve cells. This thesis delineates the methods of successful production of solid sate CNT mats and fibers, utilizing traditional polymeric and more novel multi- functional dispersant materials. Thereby, providing a series of new framework for which future device structures can be fabricated.
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Kortschot, Mark Timothy. "Damage mechanics of carbon fibre composites". Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293010.
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Hawtin, Benjamin Charles. "Defect criticality of carbon fibre composites". Thesis, University of Bath, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425875.
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Clancy, Adam Richard Justin. "Innovative routes to carbon nanotube composites". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/56217.
Testo completoAbstract (sommario):
Single-walled carbon nanotubes (SWCNTs) have superlative properties, but applications which can exploit these on a macroscopic scale have been hindered due to damage from processing, impurities, heterogeneity, and agglomeration. The creation of reduced nanotubes (nanotubide) allows SWCNTs to dissolve as individualised species using Columbic repulsion in a non-damaging manner. The synthesis of nanotubide solutions is accelerated through the use of sodium naphthalide in dimethylacetamide, which simultaneously reduces and dissolves SWCNTs. The system creates high concentration solutions and can be modified to facilitate efficient, mild, kinetically driven purification. Nanotubide undergoes reductive functionalisation and reaction variables were investigated to increase grafting density, including charging stoichiometry, nanotube concentration, reagent sterics, SWCNT purity and anionic leaving group. An intermediate sodium concentration (25 mM) is necessary to balance insufficient charge at low concentrations and counterion condensation at high concentrations. Functionalisation of nanotubide with oligomeric species terminated with bulky aryl groups allows individualised SWCNTs to remain in solution after the functionalisation. Coagulation fibre spinning of SWCNT composites requires high concentrations and well dispersed species, making nanotubide an ideal candidate. By coagulating nanotubide into poly(vinyl chloride) the reactivity of nanotubide was utilised, forming a cross-linked composite. Altering the SWCNT source, polymer molecular weight and coagulant concentration led to strain hardening composite fibres with strengths up to 482 MPa. Alternatively, poly(vinyl acetate) (PVAc) can be used to form fibres that can be deprotected to form poly(vinyl alcohol) composites. The dispersion of nanotubes can be improved through functionalisation of SWCNTs, although the final fibre mechanical properties are dominated by the fibre macrostructure. Notwithstanding, nanotubide has been shown to be a versatile route to novel hierarchy composites and has potential for many other applications.
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Erland, Samuel. "Characterisation of uncured carbon fibre composites". Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715265.
Testo completoAbstract (sommario):
The weight saving benefits of carbon fibre composites have been keenly adopted by civil aviation, with over 50% of the weight of modern designs coming from the carbon fibre components. The rapid rise in demand for this new material has led to the development of fully automated manufacturing techniques, improving rate of production and repeatability of manufacture. However, this rapid development, combined with a constant drive for increased rate of manufacture from industry can result in the formation of critical defects in the more complicated structural components. Manufacturing complex aeronautical structures from carbon fibre leads to a number of interesting mechanical problems. Forcing a multi-layered laminate to conform to a curved geometry requires individual layers to move relative to one another in order to relieve various forming-induced stresses. If the layers are constrained the dissipation of these stresses in the form of interply shear is prevented and a wide range of defects can occur, compromising the integrity of the final component. One of the most important of these is fibre wrinkling, which is effectively the buckling of one or more layers within an uncured laminate. This buckle results in a localised change in fibre orientation, which can result in a significant knockdown in part strength. A large amount of research has been conducted on carbon fibre in its cured state, when it exists as elastic fibres in an elastic matrix. Manufacturing occurs when the material is uncured however, with modern processes typically using fibres which are pre-impregnated with resin in order to reduce void content and aid fibre placement. A ply of uncured material therefore consists of stiff elastic fibres suspended in a very weak liquid viscoelastic material, whose properties are hugely influenced by temperature and rate of deformation. This thesis builds a better understanding of the mechanics involved in forming, using a series of characterisation techniques developed drawing from techniques in the literature. Part of the process involves the fitting of a one-dimensional viscoelasto-plastic model to experimental test data in order to represent the material response when shearing two plies about their interface. This model shows the material response to be dominated by the viscoelastic resin at low temperatures, before becoming frictional and fibre dominated at higher temperatures. In terms of optimum formability, a region exists in the transition from the viscous to frictional behaviour at which resistance to forming is minimised. With this data alone, optimum forming parameters such as rate of deformation, pressure and temperature can be suggested based on the material being used, along with design parameters such as stacking sequence. Another important characteristic which must be understood when considering ply wrinkling is the bending stiffness of uncured prepreg, both as a single ply and when combined to form a small laminate. A wrinkle is in effect the buckling of a single or small number of plies within a laminate, therefore by understanding the bending stiffness and process-induced loading we can begin to predict whether or not wrinkles are likely to occur for a particular manufacturing regime. In order to assess bending stiffness, a modified Dynamic Mechanical Analysis process is employed, replacing the standard Engineers Bending Theory calculations with a Timoshenko element to capture the large degree of intraply shear experienced in the bending of uncured prepreg. Finally, a small laminate scale demonstrator is considered in which a 24-ply laminate is consolidated into a female tool in such a way as to induced maximum shear strain between the plies, in order that the optimum forming parameters predicted by the characterisation tests might be validated. A simple energy minimisation model is used to predict the variation in consolidation strain around the part due to resistance to shear, using material parameters from the model describing the inter-ply shear test data. These parameters are also used to inform a novel modelling technique which has been developed parallel to this thesis, which is validated against the experimental results, and shows how the characterisation techniques can be used to advance simulation methods aimed at reducing the development time for new carbon fibre components. This work provides a set of tests and methodologies for the accurate characterisation of the behaviour of uncured carbon fibre during forming. The models developed alongside these tests allow for a detailed interrogation of the results, providing valuable insight into the mechanics behind the observed material behaviour and enabling informed decisions to be made regarding the forming process in order that the occurrence of defects might be minimised. The primary aim has been to provide a set of vital input parameters for novel, complex process modelling techniques under development, which has been achieved and validated experimentally.
26
Shaffer, Milo Sebastian Peter. "Carbon nanotubes : dispersions, assemblies and composites". Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624476.
Testo completo
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Watts, Paul CristoÌir Patrick. "Electrically conducting carbon nanotube polystyrene composites". Thesis, University of Sussex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288865.
Testo completo
28
Yue, Liang. "EPOXY COMPOSITES WITH HYBRID CARBON FILLERS". Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1387167480.
Testo completo
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Whittaker, A. J. "Thermal transport properties and microstructure of a series of carbon/carbon fibre composites". Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375729.
Testo completo
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Zhang, Ying. "Thermal diffusivity evaluation for carbon-carbon composites using infrared thermography /". Available to subscribers only, 2007. http://proquest.umi.com/pqdweb?did=1456294291&sid=1&Fmt=2&clientId=1509&RQT=309&VName=PQD.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Southern Illinois University Carbondale, 2007."Department of Mechanical Engineering and Energy Processes." Includes bibliographical references (leaves 95-102). Also available online.
31
Zheng, Yishan. "Activated carbon & carbon-cryogel composites for haemoperfusion based applications". Thesis, University of Brighton, 2013. https://research.brighton.ac.uk/en/studentTheses/daf37d00-4da8-4b0d-8bb5-a91941fed23d.
Testo completoAbstract (sommario):
A number of pathological conditions are associated with the build up of toxic substances within the systemic circulation. For example, renal and hepatic failure can lead to the accumulation of metabolites which are usually processed by these organs. There has been much interest over a number of years in techniques such as haemoperfusion that could help clear these toxins from the body and improve patient outcome. Haemoperfusion is an extracorporeal blood purification technique in which a patient’s blood is passed over a column containing a material designed to adsorb a board spectrum of biological toxic molecules. Direct blood contact with the adsorbent requires a material that is able to display good haemocompatibility whilst maintaining adsorption efficiency. Activated carbons (AC) have great adsorption capacity and have previously been used as haemoadsorbents. However the haemocompatibility of carbons has been questioned and they are often coated with biocompatible polymers that increase their haemocompatibility but also act as a barrier to the removal of larger toxins and middle molecules.
32
Joshi, Ninad Milind. "Study of the Effect of Unidirectional Carbon Fiber in Hybrid Glass Fiber / Carbon Fiber Sandwich Box Beams". University of Dayton / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1386188162.
Testo completo
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Tual, Nicolas. "Durability of carbon/epoxy composites for tidal turbine blade applications". Thesis, Brest, 2015. http://www.theses.fr/2015BRES0057/document.
Testo completoAbstract (sommario):
Les matériaux composites sont utilisés dans de nombreuses structures marines et de nouvelles applications sont en cours de développement telles que les pales d’hydroliennes. La fiabilité de ces composants dans un environnement très sévère est cruciale pour la rentabilité de ces systèmes récupérateurs d’énergie des courants marins. Ces structures sont sujettes à de nombreuses forces, telles que les courants marins, les vagues, tempêtes mais également diverses agressions marines telles que l’eau de mer et la corrosion. Une compréhension approfondie du comportement au long terme de ces parties mobiles est donc essentielle. La majorité des développeurs d’hydroliennes ont préféré des pales en carbone. Ainsi il est nécessaire de comprendre comment une longue immersion dans l’océan affecte ces composites. Dans cette étude, le comportement au long terme de différents composites carbone/époxy a été étudié en utilisant des essais de vieillissement accéléré. Une diminution significative des résistances des composites a été observée après saturation en eau de mer. Pour des temps d’immersion plus longs, seulement peu de changements des propriétés apparaissent. Peu d’effets significatifs ont été observés tant sur les modules que sur la ténacité. Ces changements de propriétés sont initialement dus à la plastification de la matrice, suivis par un affaiblissement de l’interface fibre/matrice. L’endommagement peut affecter le comportement au long terme des structures composites et créer de nouveaux chemins préférentiels pour la diffusion de l’eau. En conséquence un modèle basé sur un critère couplé résistance/ténacité a été proposé pour décrire le seuil d’endommagement et basé sur un critère en ténacité pour décrire la cinétique d’endommagement. Il permet de reproduire d’une manière correcte le seuil et la cinétique d’endommagement pour des matériaux vieillis et non vieillis. L’évolution de l’entrée d’eau dans les composites a été suivie dans le but de développer un modèle de diffusion prenant en compte le nature anisotrope des composites. Ainsi le modèle de diffusion a été utilisé sur pale d’hydrolienne. Finalement des premières investigations sur le couplage entre le modèle de diffusion et l’endommagement ont été réalisées. Cette étude a contribué au développement d’outils pour quantifier la durabilité au long terme des pales d’hydroliennes en compositesComposite materials are used in many marine structures and new applications are being developed such as tidal turbine blades. The reliability of these components, in a very severe environment, is crucial to the profitability of tidal current energy systems. These structures are subject to many forces such as ocean tides, waves, storms but also to various marine aggressions, such as sea water and corrosion. A thorough understanding of the long term behavior of the moving parts is therefore essential. The majority of tidal turbine developers have preferred carbon blades, so there is a need to understand how long immersion in the ocean affects these composites. In this study the long term behavior of different carbon/epoxy composites has been studied using accelerated ageing tests. A significant reduction of composite strengths has been observed after saturation of the material in seawater. For longer immersions only small further changes in these properties occur. No significant changes have been observed for moduli nor for composite toughness. Changes in properties are initially due to matrix plasticization, followed by reductions due to fibre/matrix interface changes. Damage can affect the long term behavior of composites structures and create new pathways for water diffusion. As a consequence a damage model has been proposed based on a coupled strength/toughness criterion to describe the threshold of damage and on a toughness criterion to describe the crack development kinetics. It describes in a correct manner the damage threshold and kinetics for the as-received material and for material after sea water ageing. The evolution of the rate of water ingress into composite materials has been followed, in order to develop a diffusion model taking into account the anisotropic nature of composites. Then the diffusion model has been applied on a tidal turbine blade. Finally a first investigation of the coupling between the diffusion model and damage has been performed. This study has contributed to the development of tools to quantify long term durability of composite tidal turbine blades
34
Baxter, Robert Ian. "The erosion and structural characterisation of low density carbon-carbon composites". Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.481775.
Testo completo
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Hutton, Toby. "The friction and wear of carbon-carbon composites for aircraft brakes". Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760692.
Testo completo
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Steiner, Stephen Alan III. "Carbon nanotube growth on challenging substrates : applications for carbon-fiber composites". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/71272.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, February 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
"December 2011." Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 305-315).
Nanoengineered hierarchal fiber architectures are promising approaches towards improving the inter- and intralaminar mechanical properties (e.g., toughness and strength) and non-mechanical properties of advanced fiber-reinforced composites such as graphite/epoxy. One fiber architecture of particular interest is carbon fiber coated with radially-aligned arrays of carbon nanotubes (CNTs), which can enable through-thickness and interply matrix reinforcement of carbon-fiber-reinforced composites while simultaneously providing additional multifunctional benefits such as electrical and thermal conductivity enhancement. Growth of CNTs on carbon fibers can be achieved by chemical vapor deposition (CVD) techniques, however previous processes for doing so have resulted in a significant reduction in the tensile strength and stiffness of the carbon fibers. This thesis aims to develop an understanding of catalyst-substrate and CVD environment-substrate interactions relevant to maintaining fiber mechanical properties in the growth of CNTs on carbon fibers by CVD and to use this understanding to develop practical approaches for growing CNTs on carbon fibers that simultaneously preserve fiber properties. Novel oxide-based catalysts are demonstrated for the first time to be effective for both CNT growth and graphitization of amorphous carbon and are characterized using in situ metrology. These catalysts show promise for use on substrates that exhibit sensitivity to conventional metal catalysts (such as carbon fibers). New CVD processing techniques based on materials properties unique to this class of catalysts are presented and explored. Coatings for enabling growth of aligned CNTs on carbon fibers, coatings for improving adhesion of materials to carbon fibers, and coatings for facilitating low-temperature growth of CNTs on carbon fibers are developed. The mechanochemical responses of carbon fibers to high-temperature processing, exposure to CVD gases relevant for CNT growth, and in situ tensioning during CVD growth at high temperatures are investigated. Methods for growing CNTs on carbon fibers that enable aligned CNT morphologies and that preserve fiber properties are presented. A new system for optimizing CNT growth on carbon fibers with special considerations for oxide-based catalysts is described. Finally, recommendations for manufacturing hierarchal carbon fibers for composites in an industrially practical way are made.
by Stephen Alan Steiner III.
Ph.D.
37
Mohammad, F. Z. "Novel oxidation protection system for carbon-carbon composites at high temperature". Thesis, Cranfield University, 2005. http://dspace.lib.cranfield.ac.uk/handle/1826/11433.
Testo completoAbstract (sommario):
Carbon-carbon composite materials have been identified as one of the most
potential materials for light weight and high temperature applications. Mechanical
properties of carbon-carbon composites do not degrade even at temperature as high as
2000°C. However the main problem in their use in high temperature oxidizing
environment is their tendency to oxidize at temperatures of 400°C and above. Therefore
some oxidation protection mechanism is mandatory to make these materials available for
high temperature applications.
It is the purpose of the current research to develop a viable high temperature
oxidation protection system for carbon-carbon composites. It has been shown that such a
coating system must have at least two layers; a gradient porous SiC layer aimed to
redistribute the stress produced due to CTE (coefficient of thermal expansion) mismatch
and a dense top layer of a suitable material meant to protect carbon-carbon composite
substrate from oxidation. Materials for the top layer experimented during the current
research were SiC, ShN4 and HfC. Pack cementation technique was used to develop the
gradient SiC layer while top dense layers were deposited by using the reactive sputtering
technique. To improve the oxidation protection and crack resistance of the top dense
coating multilayering approach was adopted.
During the current research basically four different coating systems were
produced, characterized and then tested at high temperature for their oxidation
performance. These coating systems were, gradient SiC layer plus dense sputtered SiC
layer, gradient SiC layer plus dense sputtered ShN 4 layer, gradient SiC layer plus dense
sputtered SiC/ShN 4 layers, gradient SiC layer plus dense sputtered SiClHfC layers.
Oxidation testing of these coatings in atmosphere showed that these coatings are
thermodynamically stable at all test temperatures studied (1300-1575°C), except coatings
with a ShN 4 layer. ShN4 becomes thermodynamically unstable at 1575°C. These coatings
remained mechanically stable (no spallation) except the coatings with HfC layers.
Coatings with HfC layers spalled off at all temperatures. Investigation into the causes of
spallation indicated that the thickness (20-25 flm) of the converted SiC gradient layer was
insufficient, plus the processing conditions during the deposition of HfC were the main
causes for their failure.
38
Heisey, Cheryl L. "Adhesion of novel high performance polymers to carbon fibers : fiber surface treatment, characterization, and microbond single fiber pull-out test /". Diss., This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-02052007-081244/.
Testo completo
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Mohd, Kamal Azhari Nurul Khaliesah. "Development of metal-organic framework carbon composites for carbon dioxide and methane separation". Thesis, Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2020. http://www.theses.fr/2020IMTA0201.
Testo completoAbstract (sommario):
Le dioxyde de carbone (CO2), principal contaminant des gaz naturels bruts et du biogaz doit être extrait en vue d’un enrichissement en méthane (CH4) compatible avec les spécifications d’injection en réseaux de gaz naturel. Au cours des dernières années, une famille de matériaux poreux de type réseaux organométalliques à base de magnésium (Mg-MOF-74) a ouvert une nouvelle perspective à cet effet en raison d’une excellente affinité des sites métalliques exposés au sein de la structure cristalline pour l’adsorption du CO2. Ce matériau est un adsorbant potentiellement bon candidat pour l’enrichissement en CH4 de gaz naturel et de biogaz par des procédés opérant en modulation de pression. La présente étude propose d’examiner l’amélioration des performances d'adsorption du CO2 en mélange avec le CH4 par dopage du matériau Mg-MOF-74 avec des nanotubes de carbone et de l'oxyde de graphène. L'objectif est d'améliorer les propriétés texturales pour favoriser la diffusion des molécules des gaz dans les micropores et leur accessibilité aux sites d'adsorption. Les matériaux ont été synthétisés sous réaction solvothermique et caractérisés par DRX, IRTF, MEB, ATG et physisorption d’azote à 77K. Les équilibres et énergies d'adsorption ont été mesurées suivant une méthode manométrique dans une gamme de pression allant jusqu'à 35 bar et à 25°C, 50°C et 75°C. La cinétique de sorption a été étudiée à partir d’expériences de manométrie et de la méthode dite « Zero Length Column » à 25°C, 50°C et 75°C. A une teneur optimisée à 0,3% en masse d’agent dopant, le modèle de Brunauer–Emmett–Teller montre que la surface spécifique des matériaux dopés est augmentée de plus de 21% par rapport à celle du matériau non-dopé. Les données d'équilibre indiquent que la capacité d’adsorption en CO2 est sensiblement améliorée pour les matériaux dopés dans toute la gamme opératoire étudiée, tandis qu’ils démontrent une sélectivité comparable ou améliorée, dépendante de la températureCarbon dioxide (CO2), which is the major contaminant present in raw natural gas and biogas need to be extracted to increase their methane (CH4) content and match the standards of pipeline injection. In recent years, a family of porous materials, magnesium-based Metal Organic Framework (Mg-MOF-74), has opened new perspectives for this purpose thanks to strong adsorption affinity of CO2 with exposed metallic sites in the crystalline network. This material is a potential good adsorbent candidate for the enrichment in CH4 of natural gas and biogas by Pressure Swing Adsorption processes. The present study proposes to examine the CO2 adsorption performances and separation ability from CH4 of Mg-MOF-74 materials doped with carbon nanotubes and graphene oxide. The objective is to improve the texture of the materials to promote the diffusion of gas molecules into micropores and their accessibility to adsorption sites. The materials were synthesized under solvothermal reaction and characterized by PXRD, FTIR, FESEM, TGA and physisorption of nitrogen at 77K. The adsorption equilibria and energies were measured using manometric method in a pressure range up to 35 bar and at 25°C, 50°C and 75°C. The sorption kinetics of CO2 and CH4 on the materials were studied from manometric experiments and using the Zero Length Column method at 25°C, 50°C and 75°C. At an optimized content of the doping agents of 0.3 wt%, Brunauer–Emmett–Teller model shows that the specific surface area is increased for both composites, by more than 21% compared to the pristine material. The equilibrium data indicates that the CO2 adsorption capacity is significantly improved in the whole range of operating conditions for both composites compared to the pristine material, whereas the CO2/CH4 adsorption selectivity appears either comparable or better as a function of temperature
40
Broughton, William Richard. "Shear properties of unidirectional carbon fibre composites". Thesis, University of Cambridge, 1990. https://www.repository.cam.ac.uk/handle/1810/250965.
Testo completo
41
McClory, Caroline. "Studies on multiwalled carbon nanotube polymer composites". Thesis, Queen's University Belfast, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486255.
Testo completoAbstract (sommario):
A novel thennoset polyurethane (TPU), two amorphous thennoplastics, poly(methyl methacrylate) (PMMA), high impact poly(styrene) (HIPS) and a semi-crystalline polymer, medium density poly(ethylene) (MDPE) were used in the fonnation of a range of polymer/carbon nanotube composites for commercial and development research purposes.· Composites of thennoplastic polymers were produced by melt-processing due to the immediate compliance of the melt-mixing process with current industrial practices and the scarcity of literature pertaining to the subject. In the case ofTPU, multi-walled carbon nanotubes (MWCNTs) were used as the filler material and composites were produced using a specifically designed solution based process. A true nanoscale reinforcing effect was obtained, in that stiffness, strength and relative toughness of the TPU matrix was greatly enhanced on addition of as little as 0.1wt.% MWCNTs. A range of arc discharge MWCNTs, CVD-MWCNTs and f-MWCNTs were used in the fabrication of a range of PMMAlMWCNT composites in order to determine the effect of aspect ratio, physical structure and functionalisation of MWCNTs on the morphology and end 1roperties of the composite material. Carboxyl functionalisation of the MWCNT end-caps promoted homogeneous and anisotropic dispersion and distribution off-MWCNTs within the PMMA matrix, evident from morphological analysis although reducing the intrinsic conductivity of the nanotubes. A lower screw speed than is norinally practised during the twin screw extrusion of nanocomposites achieved the highest degree of nanotube dispersion and distribution in the HIPS studied. Single screw extrusion successfully produced homogeneous MDPE/CVD-MWCNT composites with an electrical percolation threshold of 2wt.% MWCNTs. For all systems, the extent of interfacial interactions between the polymer and MWCNTs was studied using Raman spectroscopy. The formation of a percolated network of MWCNTs in the polymer matrices was also examined in tenns ofrheological and electrical behaviour.
42
Costa, Elisabete Fernandez Reia Da. "Liquid moulding of carbon nanoparticle filled composites". Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/7276.
Testo completoAbstract (sommario):
This thesis focuses on the incorporation of carbon nanoparticles within continuous fibre reinforcements by liquid composite moulding processes, in order to provide enhanced electrical and delamination properties to the multiscale composites. The mechanisms controlling the flow and filtration of these nanoparticles during liquid composite moulding are studied, in order to develop a predictive 1-D model which allows design of the processing of these composite materials. Five different carbon nanoparticles at 0.25 wt% loading, three unmodified and one surface modified carbon nanotube systems and one carbon nanofibre system, were utilised to modify a commercial two-component epoxy resin utilised to impregnate carbon and glass reinforcements at high fibre volume fraction by resin transfer moulding. The dispersion of the nanofillers in the prepolymer was carried out by ultrasonication, high shear mixing or triple roll milling or a combination of the three. Electrical conductivity measurements of the carbon nanoparticle liquid suspensions during dispersion, alongside optical microscopy imaging and rheological analysis of these allowed the selection of the concentration of nanofiller and the appropriate dispersion technique for each nanoparticle system. The resin transfer moulding process required adaptation to incorporate the dispersion and modify degassing steps, especially when utilising unmodified carbon nanoparticles suspensions, due to their higher viscosity and tendency to be filtered. Nanoparticle filtration was identified by electrical conductivity measurements and microscopy of specimens cut at increasing distances from the inlet. Cake filtration was observed for some of the unmodified systems, whereas deep bed filtration occurred for the surface modified CNT material. Property graded composites were obtained due to filtration, where the average electrical conductivity of the carbon and glass composites produced increased by a factor of two or one order of magnitude respectively. The effect of filler on the delamination properties of the carbon fibre composites was tested under mode I. The results do not show a statistically significant improvement of delamination resistance with the presence of nanoparticles, although localised toughening mechanisms such as nanoparticle pull-out and crack bridging as well as inelastic deformation have been observed on fracture surfaces. Particle filtration and gradients in concentration resulted in non-linear flow behaviour. An 1-D analytical and a finite difference model, based on Darcy’s law accompanied by particle mass conservation and filtration kinetics were developed to describe the flow and filtration of carbon nanoparticle filled thermosets. The numerical model describes the non-linear problem by incorporating material property update laws, i.e. permeability, porosity and viscosity variations on concentration of retained and suspended particles with location and time. The finite difference model is consistent and converges to the analytical solution. The range of applicability of the analytical model is limited to lower filtration coefficients and shorter filling lengths, providing an approximate solution for through thickness infusion; whereas the numerical model presents a solution outside this range, i.e. in-plane filling processes. These models allow process design, with specified carbon nanoparticle concentration distributions achieved via modifying the nanofiller loading at the inlet as a function of time.
43
Hughes, M. "Composites of carbon nanotubes and conducting polymers". Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604735.
Testo completoAbstract (sommario):
Carbon nanotubes and conducting polymers are both interesting for their unique electrochemical properties that make them well suited to use in electrochemical capacitors (sources of high power pulses of electrical energy) and actuators (artificial muscles). In the case of carbon nanotube films, it is their high surface area and electrical conductivity that makes them attractive, particularly in terms of their fast response times. In contrast, the redox chemistry of conducting polymers enables them to achieve large charge storage capacities and dimensional changes in response to potential cycling (often several orders of magnitude larger than those of carbon nanotubes). This thesis reports on the structure and electrochemical properties of composites of multi-walled nanotubes and conducting polymers (polypyrrole and poly(3-methylthiophene)) in addition to their performance in electrochemical capacitors and actuators. The composite film growth conditions were manipulated so as to merge the desirable properties of multi-walled nanotubes with those of conducting polymers. The results composite films were capable of charge storage capacitances, response times and cycle lives superior to those of pre conducting polymer films produced and tested using similar conditions. The alignment, concentration, production route, dimensions and chemical treatment of the carbon nanotubes were all found to play an important role in determining the nanostructure, doping and electrochemical behaviour of the composite films produced. The electrochemical capacitors tested illustrated the power and energy gains that are possible when using carbon nanotube-conducting polymer composite films. Composite film actuators made from multi-walled nanotubes and polypyrrole demonstrated the importance of orienting the nanotubes perpendicular to the desired direction of actuation in order to improve actuation kinetics (through increased electrical conductivity) without constraining actuation of the conducting polymer.
44
Sun, Xinxin. "Conductive behaviour of carbon nanotube based composites". Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/6280.
Testo completoAbstract (sommario):
This project was basically exploratory in the electrical properties of carbon nanotube (CNT) based materials. The direct current (DC) conductivity of CNT/polymer composites was computed by using equivalent circuit method and a three dimensional (3-D) numerical continuum model with the consideration of tunneling conduction. The effects of the potential barrier of polymer and the tortousity of CNTs on the conductivity were analyzed. It was found that both of percolation threshold and DC conductivity can be strongly affected by the potential barrier and the tortousity. The influence of contact resistance on DC conductivity was also computed, and the results revealed that contact resistance and tunneling resistance had significant influences on the conductivity, but did not affect the percolation threshold. The microstructure-dependent alternating current (AC) properties of CNT/polymer composites were investigated using the 3-D numerical continuum model. It was found that AC conductivity and critical frequency of CNT/polymer composites can be enhanced by increasing the curl ratio of CNTs. In the mid-range CNT mass fraction, with increasing curl ratio of CNTs, AC conductivity, interestingly, became frequency-dependent in low frequency range, which cannot be explained by reference to the percolation theory. A proper interpretation was given based on the linear circuit theory. It was also found that the critical frequency can also be affected by the size of CNT cluster. Series numerical formulas were derived by using a numerical capacitively and resistively junction model. In particular, this work introduced an equivalent resistor-capacitor (RC) circuit with simple definitions of the values of contact resistance and average mutual capacitance for CNT/polymer nanocomposites. Theoretical results were in good agreement with experimental data, and successfully predicted the effect of morphology on the AC properties of CNT/polymer composites. DC and AC conductivities of multi-walled carbon nanotube (MWCNT)/graphene oxide (GO) hybrid films were measured for selected MWCNT mass fractions of 10%, 33.3%, 50%, 66.7%, and 83.3% using four-probe method. The experimental results were fitted using scaling law, and relatively high percolation threshold was found. This high percolation threshold was understood in terms of the potential energy and intrinsic ripples and warping in the freestanding graphene sheets. The capacitance of these hybrid films were measured using the voltmeter-ammeter-wattmeter test circuit with different voltages and heat treatments. The MWCNT/GO film showed relatively high specific capacitance (0.192F/cm3 for the mass fraction of 83.3%) and power factor compared to conventional dielectric capacitors. Both of measured capacitance and power factor can be enhanced by increasing testing voltages. The capacitance of MWCNT/GO films rapidly decreased after heat treatments above 160 ℃. This decrease was caused by redox reaction in the GO sheets. The capacitive behaviour of MWCNT/GO hybrid films was also interpreted by using the equivalent circuit model. Single-walled carbon nanotube (SWCNT) and SWCNT/Poly(vinyl alcohol) (PVA) films were used to form a piezoresistive strain sensor. Both of static and dynamic strain sensing behaviours of SWCNT and SWCNT/PVA films were measured. It was found that the sensitivities of these films decreased with increasing their thicknesses. The SWCNT film with a thickness of 1900 nm and SWCNT/PVA film exhibited viscoelastic sensing behaviour, because van der Waals attraction force allowed axial slippages of the smooth surface of nanotubes. A numerical model was derived based on the dynamic strain sensing behaviour. This model could be useful for designing CNT strain sensors. Finally, thermoelectric power (TEP) of deformed SWCNT films with various thicknesses was measured. It was observed that positive TEP of SWCNT films increased with increasing stain above the critical point. The experimental results were fitted by using a numerical model in terms of a variation of Nordheim-Gorter relation and fluctuation induced tunneling (FIT) model. From the numerical model, it was found that the increase of TEP above the critical strain resulted from the positive term of the contribution from the barrier region, and the effect of barrier regions decreases with increasing the thickness of the film.
45
Sun, Ying. "Mechanical properties of carbon nanotube/metal composites". Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4611.
Testo completoAbstract (sommario):
Carbon nanotubes (CNTs) have captured a great deal of attention worldwide since their discovery in 1991. CNTs are considered to be the stiffest and strongest material due to their perfect atomic arrangement and intrinsic strong in-plane sp[super]2--sp[super]2 covalent bonds between carbon atoms. In addition to mechanical properties, CNTs have also shown exceptional chemical, electrical and thermal properties. All these aspects make CNTs promising candidates in the development of novel multi-functional nanocomposites. Utilizing CNTs as fillers to develop advanced nanocomposites still remains a challenge, due to the lack of fundamental understanding of both material processing at the nanometer scale and the resultant material properties. In this work, a new model was developed to investigate the amount of control specific parameters have on the mechanical properties of CNT composites. The new theory can be used to guide the development of advanced composites using carbon nanotubes, as well as other nano-fibers, with any matrices (ceramic, metal, or polymer). Our study has shown that the varying effect based on changes in CNT dimensions and concentration fit the model predictions very well. Metallic CNT composites using both single-walled carbon nanotubes (SWNT) and multi-walled carbon nanotubes (MWNT), have been developed through a novel electrochemical co-deposition process. Copper and nickel matrix composites were developed by using pulse-reverse electrochemical co-deposition. Uniaxial tensile test results showed that a more than 300% increase in strength compared to that of the pure metal had been achieved. For example, the ultimate tensile strength of Ni/CNTs composites reached as high as about 2GPa. These are best experimental results ever reported within this field.; The mechanical results are mainly attributed to the good interfacial bonding between the CNTs and the metal matrices and good dispersion of carbon nanotubes within the matrices. Experimental results have also shown that the strength is inversely dependent on the diameter of carbon nanotubes. In addition to the mechanical strength, carbon nanotube reinforced metallic composites are excellent multifunctional materials in terms of electrical and thermal conduction. The electrical resistivity of carbon nanotube/copper composites produces electrical resistivity of about 1.0~1.2 x10[super]-6ohm-cm, which is about 40% less than the pure copper. The reduced electrical resistivity is also attributed to the good interfacial bonding between carbon nanotubes and metal matrices, realized by the electrochemical co-deposition.ID: 028916756; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 95-105).
Ph.D.
Doctorate
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
46
Harper, Lee Thomas. "Discontinuous carbon fibre composites for automotive applications". Thesis, University of Nottingham, 2006. http://eprints.nottingham.ac.uk/10246/.
Testo completoAbstract (sommario):
Increasingly stringent emissions targets are encouraging vehicle manufacturers to prioritise reduction of vehicle mass. The falling cost of carbon fibre is increasing the viability of lightweight carbon-based body panel systems across a broad range of production volumes. In the present work an automated process has been developed for the manufacture of random fibre preforms at medium volume production levels (30-50,000ppa). This thesis seeks to understand the influence of key microstructural parameters on the mechanical and physical properties of carbon fibre laminates produced by directed fibre preforming. The principal parameters studied are fibre length, tow filament count and laminate thickness. A statistical process simulation has been developed to predict preform density variation and the results are compared with experimental tensile properties. Experimental studies have shown that there is a notable reduction in areal density variation and consequently an increase in tensile properties with shorter fibres (115mm to 6mm) and thicker laminates (1.5mm to 4mm for a constant volume fraction). Shorter lengths improved preform coverage and gave higher tensile strength, whilst thicker laminates reduced the presence of unreinforced areas which cause stress concentrations. Tow filamentisation has been induced by pneumatic means to reduce the mean filament count and maximise the mechanical performance when using inexpensive, 24K bundles. By maximising the level of filamentisation both stiffness and strength can be increased by 20% and 45% respectively. An analytical stiffness model is presented to predict the effect of tow filament count on the in-plane elastic constants. Filament count and out-of-plane fibre orientation distributions are determined from optical microscopy and are incorporated into a multi-level Mori-Tanaka based model. Predictions are within 8% of the experimental data for laminates containing large fibre bundles and 10% for laminates with highly filamentised bundles. An expression for critical bundle length has been developed for more accurate strength prediction, based on the number of filaments within the bundle. Experimental results confirm that the critical tow length is proportional to the tow filament count. Directed fibre preforming has been benchmarked against other competing processes in respect of mechanical properties, weight saving potential and cost. A full-scale demonstrator component has been manufactured using a variety of carbon composite solutions, which can all provide 40 to 50% weight saving for an equivalent bending stiffness to steel and greatly improved dent resistance. Directed fibre preforming has shown great promise for both semi-structural and structural components for medium volume applications, particularly when aligned fibres are introduced. The results from this work can be directly scaled for industrial application to provide a cost effective, lightweight alternative to steel.
47
Green, Philip Charles. "Impact damage characteristics of carbon-epoxy composites". Thesis, University of Hertfordshire, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332277.
Testo completo
48
Jennings, Tracy Michelle. "Thermal fatigue of carbon fibre-bismaleimide composites". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290903.
Testo completo
49
Shyha, Islam Saad Elsayed Mohamed. "Drilling of carbon fibre reinforced plastic composites". Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/1353/.
Testo completoAbstract (sommario):
Following an extensive literature survey focusing on the machinability of carbon fibre reinforced plastics (CFRP), three main phases of experimental work were undertaken to evaluate the drilling of CFRP and associated stack materials. Phase 1 and 2 involved small diameter holes (1.5 mm) in thin CFRP laminates (3 mm thick) while Phase 3 addressed the feasibility of one-shot drilling (6.35 mm diameter holes) in multilayer workpiece stacks comprising titanium, CFRP and aluminium. Machinability was assessed in terms of tool life/wear, force/torque, hole size and geometrical accuracy, workpiece surface integrity and chip morphology.
50
Qian, Connie Cheng. "Structural optimisation of discontinuous carbon fibre composites". Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/14542/.
Testo completoAbstract (sommario):
There has been a growing interest in using discontinuous carbon fibre composites for semi-structural applications within the automotive industry. The main advantages of discontinuous fibres are low material costs, low wastage and low touch labour compared with processes using carbon fibre textiles. Directed Carbon Fibre Preforming (DCFP) is an automated process for producing complex 3D preforms for liquid moulding. DCFP offers the potential for producing highly optimised structures, with local control over tow size, fibre length and volume fraction within the component. The execution of this is challenging however, as confidence in the current library of material properties is low and existing structural optimisation packages only consider a very limited number of design variables, which are restricted to more conventional composite materials. This thesis aims to establish a structural design tool to exploit the design freedom offered by the DCFP process. A large number of parameters associated with the fibre architecture can be controlled to meet a range of design criterions such as performance, weight and cost. The optimisation tool is capable of generating locally varied fibre areal mass and thickness maps that are suitable for manufacture by the robot controlled process. The developed model adopts a multi-scaled finite element approach. Meso-scale simulations are performed to establish size effects in discontinuous fibre composites, to quantify the level of stochastic variability and to determine the representative volume element for a given fibre architecture. A DCFP material database is generated to facilitate macro-scale modelling at the component level. The macro-scale model iteratively redistributes material in order to minimise the total strain energy of the model under prescribed loading conditions. The optimised model is segmented into areas of uniform areal mass, where the zone geometries are tailored to achieve representative material properties according to the meso-scale results, whilst ensuring the design is fit for manufacture. An automotive spare wheel well has been chosen as a demonstrator component, enabling two DCFP architectures to be compared against a continuous glass/carbon fibre NCF design. The first case offers a high performance (high specific stiffness) solution and the second offers a low cost option using high filament count tows. Following optimisation, results suggest that a 3K 25mm fibre length DCFP option can achieve a specific stiffness 52% higher than the glass/carbon baseline design, but for 1.33 times higher material cost. Alternatively, the specific stiffness of a 24K 50mm fibre length DCFP is marginally lower than the first option, but still out-performs the baseline for just 67% of the material cost. The structural optimisation method demonstrates that discontinuous fibre composites can compete against continuous fibre counterparts for semi-structural applications.