Thèses sur le sujet « Composites material »
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1
Sinclair, Chad. « Co-deformation of a two-phase FCC/BCC material / ». *McMaster only, 2001.
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Siritanaratkul, Bhavin. « Enzyme-material composites for solar-driven reactions ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:55df8993-254b-4960-8ef4-fd9624206f3b.
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Using sunlight to drive chemical reactions has long been one of the goals in developing sustainable processes. Previous research has focused on solar fuel production in the form of H2, but this thesis demonstrates that solar-to-chemicals processes can be constructed to produce more complex compounds, using hybrid systems composed of enzymes and inorganic materials. Tetrachloroethene reductive dehalogenase (PceA), an enzyme that catalyzes the conversion of tetrachloroethene (PCE) to trichloroethene (TCE) and subsequently to cis-dichloroethene (cDCE), was shown to accept electrons from both graphite and TiO2 electrodes. Irradiation by UV light onto PceA-adsorbed TiO2 particles led to the selective production of TCE and cDCE, which was not possible without PceA as a catalyst. Ferredoxin-NADP+ reductase (FNR) is a key enzyme in photosynthesis, as it receives energetic electrons from Photosystem I and produces NADPH as an energy carrier for downstream 'Dark' reactions involving CO2 assimilation. This thesis presents the discovery of FNR activity on indium tin oxide (ITO) electrodes which led to direct electrochemical investigation of the properties of FNR, both in the absence and presence of its substrate, NADP+. The FNR-adsorbed electrode, termed 'the electrochemical leaf', rapidly interconverts NADP+/NADPH, and this was coupled to a downstream NADPH-dependent enzyme, thus demonstrating a new approach to cofactor regeneration for enzyme-catalyzed organic synthesis. The NADP+ reduction by FNR was also driven by light using a photoanode made of visible-light responsive semiconductors.
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Guodong, Xu. « Fibre-cement hybrid composites ». Thesis, University of Surrey, 1994. http://epubs.surrey.ac.uk/844012/.
Texte intégralRésumé :
The theoretical stress-strain behaviour of individual fibre reinforced cement composites is reviewed. Based on the multiple cracking concept of the existing theory, analytical expressions are developed to describe the tensile stress-strain behaviour of a fibre-cement hybrid composite consisting of three components, i.e. two reinforcing fibres with different moduli, strengths and strains to failure and a common cement binder. The model predicts that the tensile stress-strain curve of the hybrid composites consists of five stages, instead of three stages of the existing models for individual fibre cements, and relates the tensile behaviour of each stage to the component properties of the components and the test system parameters. A description is given of the physical and mechanical properties of four types of reinforcing fibres used in the study. These were fibrillated polypropylene film, alkali-resistant glass, polyvinyl alcohol fibres and carbon fibres. A small number of direct tensile tests on continuous glass, carbon and polyvinyl alcohol were performed. The tensile stress-strain behaviour of four types of fibre-cement hybrid composites was studied with particular emphasis on that of the glass- polypropylene hybrids for which the flexural load-deflection behaviour was also examined. It is shown that the fibre-cement hybrid composites yield superior engineering properties over their parent composites and the improvements are sensitive to volume fractions of each of the two fibres. The measured tensile stress-strain curves of the hybrids were compared with the theoretical predictions and satisfactory agreement in general is obtained. Implications from the present work for the design of fibre-cement hybrid composites are assessed.
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Sacks, Serena. « Effects of thermal aging on the mechanical behavior of K3B matrix material and its relationship to composite behavior ». Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/18865.
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Teh, Kuen Tat. « Impact damage resistance and tolerance of advanced composite material systems ». Diss., This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06062008-170512/.
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Marklund, Erik. « Micromechanism based material models for natural fiber composites / ». Luleå : Luleå University of Technology, 2005. http://epubl.luth.se/1402-1757/2005/84.
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Kruch, Serge. « Comportement global des materiaux composites viscoelastiques ». Paris 6, 1988. http://www.theses.fr/1988PA06A006.
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Apres un rappel de la theorie d'homogeneisation en elasticite, on developpe l'etude des lois de comportement viscoelastiques homogeneisees. Analyse du module complexe homogeneise. Application a l'etude du composite sic/sic
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Jack, David Abram. « Advanced analysis of short-fiber polymer composite material behavior ». Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4363.
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Thesis (Ph. D.) University of Missouri-Columbia, 2006.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 2, 2007) Includes bibliographical references.
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Foston, Marcus Bernard. « Cyclic, tethered and nanoparticulate silicones for material modification ». Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24762.
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Thesis (Ph.D.)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2009.Committee Chair: Dr. Haskell W. Beckham; Committee Member: Dr. Anselm Griffin; Committee Member: Dr. Johannes Leisen; Committee Member: Dr. Sankar Nair; Committee Member: Dr. Uwe Bunz.
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Yar, Mazher Ahmed. « Development of Nanostructured Tungsten Based Composites for Energy Applications ». Doctoral thesis, KTH, Funktionella material, FNM, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-101319.
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Tungsten (W) based materials can be used in fusion reactors due to several advantages. Different fabrication routes can be applied to develop tungsten materials with intended microstructure and properties for specific application including nanostructured grades. Therein, innovative chemical routes are unique in their approach owing numerous benefits. This thesis summarizes the development of W-based composites dispersed-strengthened by rare earth (RE) oxides and their evaluation for potential application as plasma facing armour material to be used in fusion reactor. Final material development was carried out in two steps; a) fabrication of nanostructured metallic tungsten powder dispersed with RE-oxides and b) powder sintering into bulk oxide-dispersed strengthened (ODS) composite by spark plasma process. With the help of advanced characterization tools applied at intermediate and final stages of the material development, powder fabrication and sintering conditions were optimized. The aim was to achieve a final material with a homogenous fine microstructure and improved properties, which can withstand under extreme conditions of high temperature plasma. Two groups of starting materials, synthesized via novel chemical methods, having different compositions were investigated. In the first group, APT-based powders doped with La or Y elements in similar ways, had identical particles’ morphology (up to 70 μm). The powders were processed into nanostructured composite powders under different reducing conditions and were characterized to investigate the effects on powder morphology and composition. The properties of sintered tungsten materials were improved with dispersion of La2O3 and Y2O3 in the respective order. The oxide dispersion was less homogeneous due to the fact that La or Y was not doped into APT particles. The second group, Ydoped tungstic acid-based powders synthesized through entirely different chemistry, contained nanocrystalline particles and highly uniform morphology. Hydrogen reduction of doped-tungstic acid compounds is complex, affecting the morphology and composition of the final powder. Hence, processing conditions are presented here which enable the separation of Y2O3 phase from Y-doped tungstic acid. Nevertheless, the oxide dispersion reduces the sinterability of tungsten powders, the fabricated nanostructured W-Y2O3 powders were sinterable into ultrafine ODS composites at temperatures as low as 1100 °C with highly homogeneous nano-oxide dispersion at W grain boundaries as well as inside the grain. The SPS parameters were investigated to achieve higher density with optimum finer microstructure and higher hardness. The elastic and fracture properties of the developed ODS-W have been investigated by micro-mechanical testing to estimate the materials’ mechanical response with respect to varying density and grain size. In contrast from some literature results, coarse grained ODS-W material demonstrated better properties. The developed ODS material with 1.2 Y2O3 dispersion were finally subjected to high heat flux tests in the electron beam facility “JUDITH-1”. The samples were loaded under ELM-like thermal-shocks at varying base temperatures up to an absorbed power density of 1.13 GW/m2, for armour material evaluation. Post mortem characterizations and comparison with other reference W grades, suggest lowering the oxide contents below 0.3 wt. % Y2O3. As an overview of the study conducted, it can be concluded that innovative chemical routes can be potential replacement to produce tungsten based materials of various composition and microstructure, for fusion reactor applications. The methods being cheap and reproducible, are also easy to handle for large production at industrial scale.QC 20120827
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Karmarkar, Makarand Anand. « Smart material composites for magnetic field and force sensors ». Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/34686.
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Piezoelectric material based sensors are widely used in applications such as automobiles, aircraft, and industrial systems. In past decade, attention has been focused on synthesizing composites that can provide multifunctional properties, i.e., same material exhibits two or more properties. In this group of composites, magnetoelectric materials are particularly interesting as they provide the opportunity of coupling magnetic and electric field. Another class of composite materials that are being actively pursued is piezoresistive materials. Piezoresistivity refers to change in resistance with applied stress and these materials are promising for enhancing the sensitivity of current generation pressure sensors based on silicon.
In this study, we focus on two composites systems: ferrite / Terfenol-D / nickel â lead zirconate titanate (magnetoelectric); and lanthanum strontium manganate (LSMO) â carbon nanotube (CNT) â silicon carbonitride (SiCN) (piezoresistive). Recently, Islam et al. have reported a magnetic field sensor based on a piezoelectric transformer with a ring- dot electrode pattern. In this thesis, this design was further investigated by synthesizing Terfenol-D / PZT laminate. The fabricated sensor design consists of a ring-dot piezoelectric transformer laminated to a magnetostrictive disc and its working principle is as follows: When a constant voltage is applied to the ring section of the piezoelectric layer at resonance, a stress is induced in the dot section. Then, if an external magnetic object is introduced in the vicinity of the dot section, the effective elastic stiffness is increased, altering the resonance frequency (fr). The variation of resonance frequency and magnitude of output voltage with applied magnetic field was characterized and analyzed to determine the sensitivity. The sensor showed a shift of ~1.36Hz/Oe over the frequency range of 137.4
Lastly, the thesis investigates the piezoresistive properties of LSMO â CNT â SiCN composites that were synthesized by the conventional ceramic sintering technique. Recent investigations have shown that CNTs and SiCN have high piezoresistive coefficient. DSC/TGA results showed that pure CNTs decompose at temperatures of ~600oC, however, SiCN was found to sustain the sintering temperature of 1300oC. Thus, LSMO â SiCN composites were used for the final analysis. A fractional resistivity change of 4% was found for LSMO â 12.5 vol% SiCN composites which is much higher compared to that of unmodified LSMO.
Master of Science
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Mohammed, Reza Dave. « Material properties and fracture mechanisms of epoxy nano-composites ». Thesis, Imperial College London, 2007. http://hdl.handle.net/10044/1/11296.
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Herlocker, Jon Alan. « Dynamic response and material processing of photorefractive polymer composites ». Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284284.
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This dissertation describes advances in the photorefractive dynamic response, and in the understanding of response limitations. In a PVK/ECZ based composite using a tolane chromophore and TNFDM sensitization, a photorefractive response time constant of 4 ms was observed at an applied field (Eₐ) of 95 V/μm with a writing fluence of 0.5 W/cm², while the birefringence response time was under a millisecond. This showed that the chromophore orientational response does not limit speed, and suggests further investigation of photogeneration and transport processes to improve dynamic response. Another segment of research investigated performance changes by exposure under working conditions. Photorefractive properties for composites using chromophores of varied ionization potential (I(p)) were characterized as a function of exposure at Eₐ = 80 V/um, up to 10⁴ J/cm² total optical field exposure. The response time and photoconductivity were found to fatigue for all samples, but a higher chromophore I(p) was correlated to greater stability. The four-wave mixing dependence upon E a showed a variation in trap density with exposure which verifies the role of the C₆₀ anion, the ionized sensitizer, as a photorefractive trap. The third segment of research was the proof-of-principle of a photorefractive injection molding process. Photorefractive properties of molded materials were verified by four-wave mixing and two-beam coupling measurements. At Eₐ = 95 V/μm a diffraction efficiency of 25-30% and a gain coefficient near 50 cm⁻¹ was observed. This shows industrial processing potential of these materials and provides a path from hand crafted devices to mass-production techniques, promoting commercial acceptance.
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David, Claire. « Modélisation de coques composites multicouches ». Cachan, Ecole normale supérieure, 1996. http://www.theses.fr/1996DENS0027.
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La mise en place d'un modèle théorique de coque composite multicouche est proposée. Parmi les objectifs du modèle, on retiendra: " la satisfaction exacte des conditions de continuité aux interfaces pour les déplacements et les contraintes, ainsi que des conditions aux limites ; " le raffinement des termes de membrane, de cisaillement transverse ; " l'amélioration du calcul des contraintes de cisaillement transverse, sans recours a des facteurs de correction. L'approche retenue est de type cinématique. Les raffinements des termes de membrane et de cisaillement sont pris en compte par l'intermédiaire de fonctions trigonométriques suivant la variable d'épaisseur, la continuité du champ de déplacement étant automatiquement assurée par l'introduction, dans le champ de cinématique, de la fonction de Heaviside. Les équations du mouvement et conditions aux limites sont déduites du principe de Hamilton. On ne conserve que cinq déplacements généralisés indépendants. La validité du modèle est testée sur des problèmes pour lesquels une solution tridimensionnelle exacte existe. La sensibilité aux effets de bord est également examinée. La comparaison avec des calculs éléments finis est effectuée. Enfin, l'application directe à des problèmes de dynamique est envisagée
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Nestler, Daisy Julia. « Beitrag zum Thema VERBUNDWERKSTOFFE - WERKSTOFFVERBUNDE ». Doctoral thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-134459.
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Vielschichtige Eigenschaftsprofile benötigen zunehmend moderne Verbundwerkstoffe und Werkstoffverbunde einschließlich der raschen Entfaltung neuer Fertigungstechnologien, da der monolithische Werkstoff bzw. ein einziger Werkstoff den heutigen komplexen Anforderungen nicht mehr genügen kann. Zukünftige Werkstoffsysteme haben wirtschaftlich eine Schlüsselposition und sind auf den Wachstumsmärkten von grundlegender Bedeutung. Gefragt sind maßgeschneiderte Leichtbauwerkstoffe (tailor-made composites) mit einem adaptierten Design. Dazu müssen Konzepte entwickelt werden, um die Kombination der Komponenten optimal zu gestalten. Das erfordert werkstoffspezifisches Wissen und Korrelationsvermögen sowie die Gestaltung komplexer Technologien, auch unter dem Aspekt der kontinuierlichen Massen- und Großserienfertigung (in-line, in-situ) und damit der Kostenreduzierung bislang teurer Verbundwerkstoffe und Werkstoffverbunde. In der vorliegenden Arbeit wird in vergleichbarer und vergleichender Art und Weise sowie abstrahierter Form ein Bogen über das Gesamtgebiet der Verbundwerkstoffe und Werkstoffverbunde gespannt. Eine zusammenfassende Publikation über dieses noch sehr junge, aber bereits breit aufgestellte Wissenschaftsgebiet fehlt bislang. Das ist der Separierung der einzelnen, fest aufgeteilten Gruppierungen der Verbundwerkstoffe geschuldet. Querverbindungen werden selten hergestellt. Dieses Defizit in einem gewissen Maße auszugleichen, ist Ziel der Arbeit. Besondere Berücksichtigung finden Begriffsbestimmungen und Klassifikationen, Herstellungsverfahren und Eigenschaften der Werkstoffe. Es werden klare Strukturierungen und Übersichten herausgearbeitet. Zuordnungen von etablierten und neuen Technologien sollen zur Begriffsstabilität der Terminologien „Mischbauweise“ und „Hybrider Verbund“ beitragen. Zudem wird die Problematik „Recycling und Recyclingtechnologien“ diskutiert. Zusammenfassend werden Handlungsfelder zukünftiger Forschungs- und Entwicklungsprojekte spezifiziert. Aus dem Blickwinkel der verschiedenen Herstellungsrouten insbesondere für Halbzeuge und Bauteile und der dabei gewonnenen Erkenntnisse werden verallgemeinerte Konzepte für tailor-made Verbundwerkstoffe und Werkstoffverbunde vorgeschlagen („Stellschraubenschema“). Diese allgemeinen Werkstoffkonzepte werden auf eigene aktuelle Forschungsprojekte der Schwerpunktthemen Metallmatrix- und Polymermatrix-Verbundwerkstoffe sowie der hybriden Werkstoffverbunde appliziert. Forschungsfelder für zukünftige Projekte werden abgeleitet. Besonderes Augenmerk gilt den hybriden Verbunden als tragende Säule zukünftiger Entwicklungen im Leichtbau. Hier spielen in-line- und in-situ-Prozesse eine entscheidende Rolle für eine großseriennahe, kosteneffiziente und ressourcenschonende ProduktionComplex property profiles require increasingly advanced composite materials and material compounds, including the rapid deployment of new production technologies, because the monolithic material or a single material can no longer satisfy today's complex requirements. Future material systems are fundamentally important to growth markets, in which they have an economically key position. Tailor-made lightweight materials (tailor-made composites) with an adapted design are needed. These concepts have to be developed to design the optimum combination of components. This requires material-specific knowledge and the ability to make correlations, as well as the design of complex technologies. Continuous large-scale and mass production (in-line, in-situ), thus reducing the costs of previously expensive composite materials and material compounds, is also necessary. The present work spans the entire field of composite materials and material compounds in a comparable and comparative manner and abstract form. A summarizing publication on this still very new, but already broad-based scientific field is not yet available. The separation of the individual, firmly divided groups of the composite materials is the reason for this. Cross-connections are rarely made. The objective of this work is to compensate to some extent for this deficiency. Special consideration is given to definitions and classifications, manufacturing processes and the properties of the materials. Clear structures and overviews are presented. Mapping established and new technologies will contribute to the stability of the terms "mixed material compounds" and "hybrid material compounds". In addition, the problem of recycling and recycling technologies is discussed. In summary, areas for future research and development projects will be specified. Generalized concepts for tailor-made composite materials and material compounds are proposed ("adjusting screw scheme") with an eye toward various production routes, especially for semi-finished products and components, and the associated findings. These general material concepts are applied to own current research projects pertaining to metal-matrix and polymer-matrix composites and hybrid material compounds. Research fields for future projects are extrapolated. Particular attention is paid to hybrid material compounds as the mainstay of future developments in lightweight construction. In-line and in-situ processes play a key role for large-scale, cost- and resource-efficient production
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Swanprateeb, Jintamai. « Creep behaviour of hydroxyapatite reinforced polythylene composites ». Thesis, Queen Mary, University of London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307513.
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Nazhat, Showan Najdat. « Dynamic mechanical characterisation of hydroxyapatite reinforced biomedical composites ». Thesis, Queen Mary, University of London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267610.
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Kato, Junji. « Material optimization for fiber reinforced composites applying a damage formulation ». Stuttgart Inst. für Baustatik und Baudynamik, 2010. http://d-nb.info/1001076508/34.
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O'Neal, Justin Earl. « Thermal protection of high temperature polymer-material-carbon fiber composites ». Texas A&M University, 2005. http://hdl.handle.net/1969.1/3189.
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Two evaporative-cooling materials were studied which are (i) salt hydrates and (ii)
polyacrylic acid for the purpose showing proof of concept of being able to put
evaporative-cooling materials into a composite with the Air Force polyimide AFR-PEPAN.
The salt hydrates were observed to absorb water and then evaporate water, but due to
having a collapsible lattice, made them incapable of reabsorbing water. Polyacrylic acid
was mixed into an epoxy sheet at polacrylic acid weight percentages of 5, 10, 12.5. For
each weight percentage there was a hydrated epoxy specimen and a dry epoxy specimen.
All specimens were individually shot with a hot air stream (temperature approximately
1300C). Temperature readings were taken for each sheet. The hydrated specimen
exhibited greater evaporative cooling over its dry counterpart. 12.5 wt% was shown to
have the best evaporative cooling mechanism. Experiments were repeated to show that
the polyacrylic could reabsorb water. This study illustrates proof of concept utilizing
polyacrylic acid as an evaporative cooling material.
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Jiba, Zetu. « Coating processes towards selective laser sintering of energetic material composites ». Diss., University of Pretoria, 2019. http://hdl.handle.net/2263/79246.
Texte intégralRésumé :
This research aims to contribute to the safe methodology for additive manufacturing (AM) of
energetic materials. Coating formulation processes were investigated to find a suitable method
that may enable selective laser sintering (SLS) as the safe method for fabrication of high
explosive (HE) compositions. For safety and convenience reasons, the concept demonstration
was conducted using inert explosive simulants with properties quasi-similar to the real HE.
Coating processes for simulant RDX-based microparticles by means of PCL and 3,4,5-
trimethoxybenzaldehyde (as TNT simulant) are reported. These processes were evaluated for
uniformity of coating the HE inert simulant particles with binder materials to facilitate the SLS
as the adequate binding and fabrication method. The critical constraints being the coating
effectiveness required, spherical particle morphology, micron size range (>20 μm) and a good
powder deposition and flow, and performance under SLS to make the method applicable for
HEs.
Of the coating processes investigated, suspension system and single emulsion methods gave
required particle near spherical morphology, size and uniform coating. The suspension process
appears to be suitable for the SLS of HE mocks and potential formulation methods for active
HE composites. The density was estimated to be comparable with the current HE compositions
and plastic bonded explosives (PBXs) such as C4 and PE4, produced from traditional methods. The formulation method developed and the understanding of the science behind the processes
paves the way toward safe SLS of the active HE compositions and may open avenues for further
research and development of munitions of the future.Dissertation (MSc)--University of Pretoria, 2019.
Chemical Technology
MSc
Unrestricted
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Phillips, Lakin N. « Evaluation of Ohio Coal as Filler Material for Thermoplastic Composites ». Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1512564409202248.
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Howarth, Jack. « Material characterisation and interface optimisation of recycled carbon fibre composites ». Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/4042/.
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Composites manufactured from a novel non-woven veil of recycled carbon fibre were tested in longitudinal tension, 3-point bend and short beam shear to assess their mechanical properties with respect to other commonly available materials. It was found that their mechanical properties were intermediate between ‘high-end’ unidirectional pre-preg and ‘low-end’ chopped strand mat, and similar to that of other short-fibre reinforced plastics. A range of oxygen plasma treatments were carried out on the fibres to improve interfacial performance of the composites. It was found that treatment at an intermediate plasma power of 20 W resulted in the greatest improvement in tensile strength of a 10⁰ off-axis composite. Samples were manufactured from either 2 individual veils (IV) or from 2, 10-layer ‘pre-forms’ (PF). Both exhibited similar improvements in 10⁰ off-axis strength. Thus shadowing of the fibre within the plasma did not appear to be significant. Overtreatment at higher plasma powers (35 and 50 W for IV and 50 W for PF) resulted in a significant reduction in tensile strength and failure strain. X-ray Photoelectron Spectroscopy (XPS) showed that plasma treatment at 20 W resulted in the highest level of oxygen functionality on the fibre surface, correlating with the best interfacial performance. Plasma treatment at 10 and 35 W resulted in slightly elevated surface oxygen content, however the off-axis tensile properties of 10 W treated samples were not significantly improved compared to the untreated control. The poor mechanical performance of the over-treated samples can be attributed to either an overly strong interface resulting from increased adhesion or damage to the fibres as a result of the treatment process. There were large variations in fibre wettability across treatments, such that no discernible pattern was present between wettability and interfacial performance. XPS and ToF-SIMS analysis showed that there was almost complete coverage of the veil by the binder in the veil-making process, and that silicon contamination on the fibre itself is likely silica based, and that silicon present in the binder is PDMS.
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Ribes, Hervé. « Microstructure de composites aluminium-carbure de silicium après traitements thermomécaniques ». Grenoble INPG, 1989. http://www.theses.fr/1989INPG0084.
Texte intégralRésumé :
Ce travail porte sur l'etude de composites a matrices aluminium (al-mg-si) renforcees par des particules de carbure de silicium qui ont ete utilisees soit brut de reception soit prealablement oxydees. Une investigation microstructurale detaillee (realisee en partie par microscopie electronique en transmission) a permis de preciser la nature de l'interface al/sic dans ces composites ainsi que l'evolution de la precipitation apres traitements thermiques. Nous avons montre que l'interface est souvent composee par differentes interphases dont la composition et le mode de formation sont presentes. Nous montrons alors que la nature de l'interface modifie les proprietes mecaniques et en particulier l'allongement a rupture. A partir de l'etude de la precipitation et d'essais de durete, nous montrons qu'il est necessaire d'optimiser les conditions de traitements thermiques dans les composites. Ainsi en modifiant les interfaces, en optimisant la composition de la matrice et les traitements thermiques dans les composites. Ainsi en modifiant les interfaces, en optimisant la composition de la matrice et les traitements thermiques il doit etre possible d'obtenir une nouvelle generation de composites
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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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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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Jelf, Peter Myles. « Compressive failure of aligned fibre composites ». Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281932.
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Wang, Aiguo. « Abrasive wear of metal matrix composites ». Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305516.
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CHEN, Yiqing. « POLISHING OF POLYCRYSTALLINE DIAMOND COMPOSITES ». Thesis, The University of Sydney, 2007. http://hdl.handle.net/2123/3682.
Texte intégralRésumé :
This thesis aims to establish a sound scientific methodology for the effective and efficient polishing of thermally stable PCD composites (consisting of diamond and SiC) for cutting tools applications. The surface roughness of industrial PCD cutting tools, 0.06 μm Ra is currently achieved by mechanical polishing which is time consuming and costly because it takes about three hours to polish a 12.7 mm diameter PCD surface. An alternative technique, dynamic friction polishing (DFP) which utilizes the thermo-chemical reactions between the PCD surfaces and a catalytic metal disk rotating at high peripheral speed has been comprehensively investigated for highly efficient abrasive-free polishing of PCD composites. A special polishing machine was designed and manufactured in-house to carry out the DFP of PCD composites efficiently and in a controllable manner according to the requirements of DFP. The PCD polishing process and material removal mechanism were comprehensively investigated by using a combination of the various characterization techniques: optical microscopy, SEM and EDX, AFM, XRD, Raman spectroscopy, TEM, STEM and EELS, etc. A theoretical model was developed to predict temperature rise at the interface of the polishing disk and PCD asperities. On-line temperature measurements were carried out to determine subsurface temperatures for a range of polishing conditions. A method was also developed to extrapolate these measured temperatures to the PCD surface, which were compared with the theoretical results. The material removal mechanism was further explored by theoretical study of the interface reactions under these polishing conditions, with particular emphasis on temperature, contact with catalytic metals and polishing environment. Based on the experimental results and theoretical analyses, the material removal mechanism of dynamic friction polishing can be described as follows: conversion of diamond into non-diamond carbon takes place due to the frictional heating and the interaction of diamond with catalyst metal disk; then a part of the transformed material is detached from the PCD surface as it is weakly bonded; another part of the non-diamond carbon oxidizes and escapes as CO or CO2 gas and the rest diffuses into the metal disk. Meanwhile, another component of PCD, SiC also chemically reacted and transformed to amorphous silicon oxide/carbide, which is then mechanically or chemically removed. Finally an attempt was made to optimise the polishing process by investigating the effect of polishing parameters on material removal rate, surface characteristics and cracking /fracture of PCD to achieve the surface roughness requirement. It was found that combining dynamic friction polishing and mechanical abrasive polishing, a very high polishing rate and good quality surface could be obtained. The final surface roughness could be reduced to 50 nm Ra for two types of PCD specimens considered from pre-polishing value of 0.7 or 1.5 μm Ra. The polishing time required was 18 minutes, a ten fold reduction compared with the mechanical abrasive polishing currently used in industry.
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CHEN, Yiqing. « POLISHING OF POLYCRYSTALLINE DIAMOND COMPOSITES ». University of Sydney, 2007. http://hdl.handle.net/2123/3682.
Texte intégralRésumé :
Doctor of Philosophy (PhD)This thesis aims to establish a sound scientific methodology for the effective and efficient polishing of thermally stable PCD composites (consisting of diamond and SiC) for cutting tools applications. The surface roughness of industrial PCD cutting tools, 0.06 μm Ra is currently achieved by mechanical polishing which is time consuming and costly because it takes about three hours to polish a 12.7 mm diameter PCD surface. An alternative technique, dynamic friction polishing (DFP) which utilizes the thermo-chemical reactions between the PCD surfaces and a catalytic metal disk rotating at high peripheral speed has been comprehensively investigated for highly efficient abrasive-free polishing of PCD composites. A special polishing machine was designed and manufactured in-house to carry out the DFP of PCD composites efficiently and in a controllable manner according to the requirements of DFP. The PCD polishing process and material removal mechanism were comprehensively investigated by using a combination of the various characterization techniques: optical microscopy, SEM and EDX, AFM, XRD, Raman spectroscopy, TEM, STEM and EELS, etc. A theoretical model was developed to predict temperature rise at the interface of the polishing disk and PCD asperities. On-line temperature measurements were carried out to determine subsurface temperatures for a range of polishing conditions. A method was also developed to extrapolate these measured temperatures to the PCD surface, which were compared with the theoretical results. The material removal mechanism was further explored by theoretical study of the interface reactions under these polishing conditions, with particular emphasis on temperature, contact with catalytic metals and polishing environment. Based on the experimental results and theoretical analyses, the material removal mechanism of dynamic friction polishing can be described as follows: conversion of diamond into non-diamond carbon takes place due to the frictional heating and the interaction of diamond with catalyst metal disk; then a part of the transformed material is detached from the PCD surface as it is weakly bonded; another part of the non-diamond carbon oxidizes and escapes as CO or CO2 gas and the rest diffuses into the metal disk. Meanwhile, another component of PCD, SiC also chemically reacted and transformed to amorphous silicon oxide/carbide, which is then mechanically or chemically removed. Finally an attempt was made to optimise the polishing process by investigating the effect of polishing parameters on material removal rate, surface characteristics and cracking /fracture of PCD to achieve the surface roughness requirement. It was found that combining dynamic friction polishing and mechanical abrasive polishing, a very high polishing rate and good quality surface could be obtained. The final surface roughness could be reduced to 50 nm Ra for two types of PCD specimens considered from pre-polishing value of 0.7 or 1.5 μm Ra. The polishing time required was 18 minutes, a ten fold reduction compared with the mechanical abrasive polishing currently used in industry.
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Mokhtari, Morgane. « FeCr composites : from metal/metal to metal/polymer via micro/nano metallic foam, exploitation of liquid metal dealloying process ». Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI088/document.
Texte intégralRésumé :
Les métaux micro ou nanoporeux sont très attrayants notamment pour leur grande surface spécifique. Le désalliage dans un bain de métal liquide permet une dissolution sélective d'une espèce chimique (l'élément soluble) à partir d'un alliage d'origine (le précurseur) composé de l'élément soluble et d'un élément cible (qui deviendra nano/micro poreux) non soluble dans le bain de métal liquide. Quand le précurseur est plongé dans le bain de métal liquide, à son contact, l'élément soluble va se dissoudre dans le bain tandis que l'élément cible va en parallèle se réorganiser spontanément afin de former une structure poreuse. Quand l'échantillon est retiré du bain, il est sous la forme d'une structure bi-continue composée de deux phases : l'une étant la structure poreuse composée de l'élément cible et l'autre est une phase dans laquelle est présente l'élément du bain avec l'élément sacrificiel en solution solide. Cette phase peut être dissoute par une attaque chimique afin d’obtenir le métal nano/micro poreux. Les objectifs principaux de cette thèse sont l'élaboration et la caractérisation microstructurale et mécanique de 3 différents types de matériaux par désalliage dans un bain de métal liquide : des composites métal-métal (FeCr-Mg), des métaux poreux (FeCr) et des composites métal-polymère (FeCr-matrice époxy). Le dernier objectif est l'évaluation des possibilités d'utiliser la technique de désalliage dans un bain de métal liquide dans un contexte industriel. L'étude de la microstructure est basée sur des observations 3D faites par tomographie aux rayons X et des analyses 2D réalisées en microscopie électronique (SEM, EDX, EBSD). Pour mieux comprendre le désalliage, le procédé a été suivi in situ en tomographie aux rayons X et diffraction. Enfin, les propriétés mécaniques ont été évaluées par nanoindentation et compressionNanoporous metals have attracted considerable attention for their excellent functional properties. The first developed technique used to prepare such nanoporous noble metals is dealloying in aqueous solution. Porous structures with less noble metals such as Ti or Fe are highly desired for various applications including energy-harvesting devices. The less noble metals, unstable in aqueous solution, are oxidized immediately when they contact water at a given potential so aqueous dealloying is only possible for noble metals. To overcome this limitation, a new dealloying method using a metallic melt instead of aqueous solution was developed. Liquid metal dealloying is a selective dissolution phenomenon of a mono-phase alloy solid precursor: one component (referred as soluble component) being soluble in the metallic melt while the other (referred as targeted component) is not. When the solid precursor contacts the metallic melt, only atoms of the soluble component dissolve into the melt inducing a spontaneously organized bi-continuous structure (targeted+sacrificial phases), at a microstructure level. This sacrificial phase can finally be removed by chemical etching to obtain the final nanoporous materials. Because this is a water-free process, it has enabled the preparation of nanoporous structures in less noble metals such as Ti, Si, Fe, Nb, Co and Cr. The objectives of this study are the fabrication and the microstructure and mechanical characterization of 3 different types of materials by dealloying process : (i) metal/metal composites (FeCr-Mg), (ii) porous metal (FeCr) (iii) metal/polymer composites (FeCr-epoxy resin). The last objective is the evaluation of the possibilities to apply liquid metal dealloying in an industrial context. The microstructure study was based on 3D observation by X-ray tomography and 2D analysis with electron microscopy (SEM, SEM-EDX, SEM-EBSD). To have a better understanding of the dealloying, the process was followed in situ by X-ray tomography and X-ray diffraction. Finally the mechanical properties were evaluated by nanoindentation and compression
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Nestler, Daisy Julia. « Beitrag zum Thema VERBUNDWERKSTOFFE - WERKSTOFFVERBUNDE : Status quo und Forschungsansätze ». Doctoral thesis, Universitätsverlag Chemnitz, 2012. https://monarch.qucosa.de/id/qucosa%3A20009.
Texte intégralRésumé :
Vielschichtige Eigenschaftsprofile benötigen zunehmend moderne Verbundwerkstoffe und Werkstoffverbunde einschließlich der raschen Entfaltung neuer Fertigungstechnologien, da der monolithische Werkstoff bzw. ein einziger Werkstoff den heutigen komplexen Anforderungen nicht mehr genügen kann. Zukünftige Werkstoffsysteme haben wirtschaftlich eine Schlüsselposition und sind auf den Wachstumsmärkten von grundlegender Bedeutung. Gefragt sind maßgeschneiderte Leichtbauwerkstoffe (tailor-made composites) mit einem adaptierten Design. Dazu müssen Konzepte entwickelt werden, um die Kombination der Komponenten optimal zu gestalten. Das erfordert werkstoffspezifisches Wissen und Korrelationsvermögen sowie die Gestaltung komplexer Technologien, auch unter dem Aspekt der kontinuierlichen Massen- und Großserienfertigung (in-line, in-situ) und damit der Kostenreduzierung bislang teurer Verbundwerkstoffe und Werkstoffverbunde.
In der vorliegenden Arbeit wird in vergleichbarer und vergleichender Art und Weise sowie abstrahierter Form ein Bogen über das Gesamtgebiet der Verbundwerkstoffe und Werkstoffverbunde gespannt. Eine zusammenfassende Publikation über dieses noch sehr junge, aber bereits breit aufgestellte Wissenschaftsgebiet fehlt bislang. Das ist der Separierung der einzelnen, fest aufgeteilten Gruppierungen der Verbundwerkstoffe geschuldet. Querverbindungen werden selten hergestellt. Dieses Defizit in einem gewissen Maße auszugleichen, ist Ziel der Arbeit. Besondere Berücksichtigung finden Begriffsbestimmungen und Klassifikationen, Herstellungsverfahren und Eigenschaften der Werkstoffe. Es werden klare Strukturierungen und Übersichten herausgearbeitet. Zuordnungen von etablierten und neuen Technologien sollen zur Begriffsstabilität der Terminologien „Mischbauweise“ und „Hybrider Verbund“ beitragen. Zudem wird die Problematik „Recycling und Recyclingtechnologien“ diskutiert. Zusammenfassend werden Handlungsfelder zukünftiger Forschungs- und Entwicklungsprojekte spezifiziert. Aus dem Blickwinkel der verschiedenen Herstellungsrouten insbesondere für Halbzeuge und Bauteile und der dabei gewonnenen Erkenntnisse werden verallgemeinerte Konzepte für tailor-made Verbundwerkstoffe und Werkstoffverbunde vorgeschlagen („Stellschraubenschema“). Diese allgemeinen Werkstoffkonzepte werden auf eigene aktuelle Forschungsprojekte der Schwerpunktthemen Metallmatrix- und Polymermatrix-Verbundwerkstoffe sowie der hybriden Werkstoffverbunde appliziert. Forschungsfelder für zukünftige Projekte werden abgeleitet. Besonderes Augenmerk gilt den hybriden Verbunden als tragende Säule zukünftiger Entwicklungen im Leichtbau. Hier spielen in-line- und in-situ-Prozesse eine entscheidende Rolle für eine großseriennahe, kosteneffiziente und ressourcenschonende Produktion.Complex property profiles require increasingly advanced composite materials and material compounds, including the rapid deployment of new production technologies, because the monolithic material or a single material can no longer satisfy today's complex requirements. Future material systems are fundamentally important to growth markets, in which they have an economically key position. Tailor-made lightweight materials (tailor-made composites) with an adapted design are needed. These concepts have to be developed to design the optimum combination of components. This requires material-specific knowledge and the ability to make correlations, as well as the design of complex technologies. Continuous large-scale and mass production (in-line, in-situ), thus reducing the costs of previously expensive composite materials and material compounds, is also necessary. The present work spans the entire field of composite materials and material compounds in a comparable and comparative manner and abstract form. A summarizing publication on this still very new, but already broad-based scientific field is not yet available. The separation of the individual, firmly divided groups of the composite materials is the reason for this. Cross-connections are rarely made. The objective of this work is to compensate to some extent for this deficiency. Special consideration is given to definitions and classifications, manufacturing processes and the properties of the materials. Clear structures and overviews are presented. Mapping established and new technologies will contribute to the stability of the terms "mixed material compounds" and "hybrid material compounds". In addition, the problem of recycling and recycling technologies is discussed. In summary, areas for future research and development projects will be specified. Generalized concepts for tailor-made composite materials and material compounds are proposed ("adjusting screw scheme") with an eye toward various production routes, especially for semi-finished products and components, and the associated findings. These general material concepts are applied to own current research projects pertaining to metal-matrix and polymer-matrix composites and hybrid material compounds. Research fields for future projects are extrapolated. Particular attention is paid to hybrid material compounds as the mainstay of future developments in lightweight construction. In-line and in-situ processes play a key role for large-scale, cost- and resource-efficient production.
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Schclar, Noemi Alejandra. « Application of the Boundary Element Method to the structural analysis of three dimensional anisotropic material ». Thesis, University of Portsmouth, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334408.
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Lacour, Olivier. « Influence de la piézoélectricité sur l'absorption du son dans les milieux composites ». Grenoble 1, 1989. http://www.theses.fr/1989GRE10058.
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Kovacs, Christopher Joseph. « Influence of Material Properties and Processing on Stability and Protectability in Superconducting Cables and Composites ». The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1574650528575944.
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Gupta, Gaurav. « Computational material science of carboncarbon : composites based on carbonaceous mesophase matrices ». Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=83865.
Texte intégralRésumé :
Carbon/Carbon composites belong to the generic class of fiber reinforced composites and are widely used because of their high strength as well as chemical and thermal stability. Like other fiber reinforced composites they consist of the fibers which act as reinforcements and matrix which acts as a glue that binds the fibers. c/c composites from pitch based precursor are unique since the matrix in this case is a liquid crystal or mesophase. This makes them remarkable in the sense that unlike c/c composites from other precursors such as PAN, rayon etc. they have extremely high degree of molecular orientation and exhibit texture. An important characteristic of their textures is the presence of topological defects. It is hence of great interest to understand and elucidate the principles that govern the formation of textures so as to optimize their properties. In this work we present a computational study of structure formation in carbon-carbon composites that describes the emergence of topological defects due to the distortions in the oriented matrix created by the presence of fiber matrix interaction. Dynamical and structural features of texture formation were characterized using gradient elasticity and defect physics.
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Kwak, Museok. « Microwave curing of carbon-epoxy composites : process development and material evaluation ». Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/39284.
Texte intégralRésumé :
Conventional heating methods offer limited opportunities in cycle time reduction due to the low thermal conductivity of polymer matrices. Microwaves can offer advantages in this sense, however past limitations in hardware, software and lack of suitable operating procedures led to inconsistent results and conclusions. In the present study 2.4 mm, 4.8 mm and 60 mm thick out-of-autoclave unidirectional carbon-epoxy composites were cured using a homogeneous microwave system at 2.45 GHz. A methodology to measure the microwave penetration depth, and to cure carbon fibre reinforced polymer composites without arcing (thus producing reliable and consistent results) were proposed. The results of the curing methodology adopted was demonstrated by measuring the degree of crosslink, axial and transverse tension, axial compression, in-plane shear, indentation, mode I interlaminar fracture and fibre push-out testing. With a suitable microwave cure cycle, the axial tensile performance was similar to those cured using a conventional process. The transverse tensile and in-plane shear strength of microwave-cured samples were lower than those produced using conventional means. In axial compression tests, the microwavecured samples exhibited a significant increase in strength. In interlaminar fracture testing, conventional oven-cured samples showed lower fracture toughness values with little variation with crack propagation, whereas the microwave-cured samples showed an increasing trend with crack propagation, and a greater average toughness value. The fibre-matrix interfacial shear strength was also greater in the microwave-cured samples. The increase in fibre-matrix interfacial shear strength was proportional to the increase in the interlaminar fracture toughness. The changes in properties were due to a change at the microscopic level of the matrix, where the preferential microwave heating of the carbon fibres produced a microstructure where the epoxy closest to the fibres reached a higher degree of cure compared with the rest of the matrix, as well as an increased fibre-matrix interfacial bond. Away from the fibre the matrix was more rubbery, thus producing a multi-phase brittle-ductile region. The contribution to knowledge in the thesis was the conclusion of pragmatic studies, which now permits the manufacture of unidirectional composites cured using microwaves without the damage and inconsistencies that occurred using previous methodologies.
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Carey, Tian. « Two-dimensional material inks and composites for printed electronics and energy ». Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275609.
Texte intégralRésumé :
This thesis explores the application of two-dimensional (2D) materials such as graphene and single layer hexagonal boron nitride (h-BN) which are produced by liquid phase exfoliation for use in printed electronics and energy composite applications. In Chapter 2 I give a broad overview of the electrical, mechanical and optical properties of 2D materials among other nanomaterials that were used in the thesis such as carbon nanotubes and conductive polymers. Additionally I review the techniques and theory behind the exfoliation and dispersion of functional layered materials. In Chapter 3 I present the coating and printing techniques which were used in this thesis along with the experimental techniques and methods which I use to characterise my inks, films and devices. Chapter 4 is the first experimental chapter of the thesis and demonstrates the printing of 2D material heterostructures to create fully printed dieletrically gated field effect transistors with 2D materials on textile and polymer substrates. In this chapter I also demonstrate reprogrammable volatile memory, p and n type inverters, complementary inverters, and logic gates which pave the way to fully printed integrated circuits, operational at room temperature and pressure with 2D materials processed in liquid. In Chapter 5, I review spray coating (a highly industrial scalable printing technique), in terms of the optimisation of its parameters to achieve thin films of nanomaterials on three-dimensional (3D) surfaces. I then demonstrate that it is possible to create large area (∼750 cm2) transparent conducting films around curved surfaces with spray coating enabling a semi-transparent (around 360°) spherical touch sensor for interactive devices. Chapter 6 explores printed photonics for applications in terahertz (THz) frequencies. Here I demonstrate the feasibility of liquid phase exfoliated graphene to create THz saturable absorbers (SAs) which could enable many applications in THz frequencies such as tomography or time-resolved spectroscopy that require mode-locked (i.e. enabling a train of short pulses to be derived from continuous-wave operation) THz pulses. I also demonstrate that these SAs can be inkjet printed on demand providing unprecedented compactness in a quantum cascade laser system. Finally in Chapter 7, I look at the application of graphene in microbial fuel cells (MFC). I demonstrate that enhanced MFC output arises from the interplay of the improved surface area, enhanced conductivity, and catalytic surface groups of a graphene based electrode. As a final step graphene based anodes and cathodes which were entirely platinum free were combined to create an environmentally sustainable energy source.
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Gao, Xiaodong. « Effect of Negative Thermal Expansion Material Cubic ZrW2O8 on Polycarbonate Composites ». University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1420473965.
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Brosious, Derek A. « Nonlinear material behavior and fatigue-accumulated damage of wood plastic composites ». Pullman, Wash. : Washington State University, 2008. http://www.dissertations.wsu.edu/Thesis/Fall2008/D_Brosious_120408.pdf.
Texte intégralRésumé :
Thesis (M.S. in civil engineering)--Washington State University, December 2008.Title from PDF title page (viewed on June 19, 2009). "Department of Civil and Environmental Engineering." Includes bibliographical references.
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Kleczewska, Joanna. « Material aspects of exploitation of dental composites based on dimethacrylate resins ». Thesis, Tours, 2011. http://www.theses.fr/2011TOUR4023/document.
Texte intégralRésumé :
L’objectif de cette étude est de comprendre comment la morphologie des composites dentaires basés sur la résine diméthacrylate peut influer sur les propriétés des prosthèses dentaires. Les expériences ont été menées selon deux directions I ) Analyse des échantillons commerciaux 2) préparation des composites avec des nouveaux renforcements. La morphologie, le comportement tribologique et les propriétés mécaniques des couches superficielles ont été déterminés. Certains composites montrent une résistance à l’abrasion accrue pendant la première heure des mesures tribologiques. Ceci indique l’existence d’une couche superficielle de nature différente que le corps. Ce morphologie bimodale conduit à un meilleur arrangement des particules renforçant, résultant en une résistance à l’usure important et une ténacité élevée.Wollastonité est une alternative intéressante comme renforçant. L’ajout des agents bactéricide est efficace contre S. mutans, mais les propriétés mécaniques de ce composites doivent être améliorésThe aim of this study was an attempt to clarify, how the morphology of dimethacrylate-based dental composite affects the properties of dental fillings. The experiments were carried out bidirectionally: I). The analysis of commercial samples; 2). Preparation ofhome made composites with using of new fillers.Morphology, tribological behavior. mechanical properties of surface layer and bactericidal action of composites were characterized. Some composites exhibit an increased resistance to abrasion during the first hour of tribological measurements. It proves the existence of the “surface layer” of a different nature than the bulk of material.The ‘bimodal’ morphology favors the best packing of filler particles in the matrix, resulting in higher wear resistance and fracture toughness of composites. Wollastonite is an interesting alternative to the commonly used fillers. Addition of bactericidal agents is effective against S. mutans, however, mechanical characteristics of these composites require fine-tuning
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Santandrea, Mattia <1988>. « Bond behavior between fiber reinforced composites and quasi-brittle material interfaces ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amsdottorato.unibo.it/8645/1/Santandrea_Mattia_Tesi.pdf.
Texte intégralRésumé :
The present dissertation presents an investigation of the bond behavior of newly developed fiber reinforced composite systems applied to quasi-brittle material interfaces. Direct shear tests were performed on steel reinforced polymer (SRP) and steel reinforced grout (SRG) composite strips applied to both concrete and masonry substrates. Different types of cementitious matrices and different densities of steel fiber sheets were employed. Tests were performed investigating several parameters, i.e. bonded width, bonded length, loading rate, and face to which the composite strip was applied. Failure modes and load responses were presented and discussed. It was observed that the fracture energy GF of SRP-concrete joints is independent of the composite density but varies as the composite is bonded to different faces of the concrete prism. The width effect was considered in the evaluation of the load-carrying capacity of SRP-concrete joints, while the loading rate influenced the peak load of both SRP and SRG specimens. The behavior of SRP-concrete joints was also investigated through a numerical analysis, using lattice discrete particle model (LDPM), obtaining an excellent match with the experimental results. Some concrete prisms were reinforced and tested using a geopolymer matrix that showed interesting results. Some masonry specimens were subjected to artificially weathering cycles to investigate the durability performances of SRG strips with respect to salt attack. Furthermore, monotonic compressive tests were performed on concrete columns confined with both SRP and SRG composites. Several parameters were investigated, i.e. the density of steel fiber sheets, the concrete corner condition, the overlapping length, the number of confinement layers, the scale effect, and the shape effect. Failure modes and load responses were presented and discussed. Finally, several applications of basalt-fiber reinforced cementitious matrix (B-FRCM) composites bonded to masonry substrates were showed, including full scale tests on existing masonry arches.
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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.
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Kraus, Zachary. « Computational tools for preliminary material design of metals and polymer-ceramic nano composites ». Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51795.
Texte intégralRésumé :
In this dissertation, algorithms for creating estimated potentials for metals and modeling of nano composites are developed. The efficacy of the algorithms for estimated potentials were examined. The algorithm was found to allow molecular dynamic and Monte Carlo modeling to be included in the potential building process. Additionally, the spline based equations caused issues with the elastic constants and Young’s modulus due to extra local minima. Two algorithms were developed for improved modeling of nano composites: one was a random number generation algorithm for initializing polymer, second was a bonding algorithm for controlling bonds between polymer and nano particle. Both algorithms were effective in their tasks. Additionally, the algorithms for improved nano composite modeling were used for preliminary material design of PMMA metal oxide nano composite systems. The results from the molecular dynamic simulations show the bonding between polymer matrix and nanoparticle has a large effect on the Young’s modulus and if this bonding could be controlled, the tensile properties of PMMA-metal oxide nano composites could be tailored to the applications’ requirements. The simulations also showed bonding had caused changes in the density of the material which than effected the energy on the polymer chain and the Young’s modulus. A model was than developed showing the relationship between density and the chain energy, and density and the Young’s modulus. This model can be used for a better understanding and further improvement of PMMA-metal oxide nano composites.
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Lee, Sang Jin. « Active, polymer-based composite material implementing simple shear ». [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2349.
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Tremaine, Kellie Michelle. « MODAL ANALYSIS OF COMPOSITE STRUCTURES WITH DAMPING MATERIAL ». DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/823.
Texte intégralRésumé :
The purpose of this study is to develop an analytical solution for modal analysis of actively damped orthotropic composite plates in bending and to verify it with experimental analysis.
The analytical modal analysis solution for composite plate dynamics is derived using Euler theory. This analysis applies to structures with orthotropic lamina of uniform material properties at any lamination angle. The bending-extensional coupling can be neglected for plates that are symmetric or approximately symmetric, which allows an exact solution for natural frequency and mode shape to be obtained. An exact solution can be found for natural vibration and in general.
The active control is modeled analytically by combining the Lagrange equation with the Ritz Assumed Mode method. This analysis produces a generalized coordinate vector that correlates the assumed mode to the particular amplitude of a particular case. The kinetic energy dissipated by the piezoelectric actuator from the system over one oscillation can be calculated from the generalized coordinate vector and the assumed mode. The equivalent damping ratio of the active control system is calculated as the ratio between the kinetic energy absorbed by the piezoelectric actuator from the system in one oscillation and the maximum strain energy of the system during that oscillation.
A point mass on the plate, such as an accelerometer mass, can also be modeled as a single layer of uniform mass, that is an isotropic layer, by equating the potential energy of the point mass with the potential energy of the uniform mass layer. It is important to note that the mass of the isotropic layer is frequency dependent, and it has no effect on the plate stiffness.
The analytical model is validated by comparison to experimental work. The samples studied were aluminum and composite plates of various lengths. The active control predictions were also validated using previous experimental work completed at California Polytechnic State University in San Luis Obispo. These cases included active control of an aluminum beam with a patch of piezoelectric material and an aluminum sailplane with a patch of piezoelectric material.
Results indicate that while the analytical mode solutions are in good agreement with the experimental results, they are also systematically higher than the experimental results. The analytical active control solutions match previous work when the piezoelectric effects are linear. The main result of adding an active control system is approximately a 5-10% increase in modal frequencies and a 200-800% increase of damping ratio.
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Seraj, Salek Muhammad. « Reinforced and prestressed concrete members designed in accordance to the compressive-force path concept and fundamental material properties ». Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/7685.
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Houskamp, Joshua Robert Kalidindi Surya. « Microstructure sensitive design : a tool for exploiting material anisotropy in mechanical design / ». Philadelphia, Pa. : Drexel University, 2005. http://dspace.library.drexel.edu/handle/1860/724.
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Zhu, Honggang. « Development of epoxy-organoclay nanocomposite as high performance coating and as matrix material of durable GFRP composite for civil engineering applications / ». View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202009%20ZHU.
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Mora, D. F. (Diego Fernando). « Multifield-based modeling of material failure in high performance reinforced cementitious composites ». Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/117529.
Texte intégralRésumé :
Cementitious materials such as mortar or concrete are brittle and have an inherent weakness in resisting tensile stresses. The addition of discontinuous fibers to such matrices leads to a dramatic improvement in their toughness and remedies their deficiencies. It is generally agreed that the fibers contribute primarily to the post-cracking response of the composite by bridging the cracks and providing resistance to crack opening.
On the other hand, the multifield theory is a mathematical tool able to describe materials which contain a complex substructure. This substructure is endowed with its own properties and it interacts with the macrostructure and influences drastically its behavior. Under this mathematical framework, materials such as cement composites can be seen as a continuum with a microstructure. Therefore, the whole continuum damage mechanics theory, incorporating a new microstructure, is still applicable.
A formulation, initially based on the theory of continua with microstructure Capriz, has been developed to model the mechanical behavior of the high perfor-mance fiber cement composites with arbitrarily oriented fibers. This formulation approaches a continuum with microstructure, in which the microstructure takes into account the fiber-matrix interface bond/slip processes, which have been recognized for several authors as the principal mechanism increasing the ductility of the quasi-brittle cement response. In fact, the interfaces between the fiber and the matrix become a limiting factor in improving mechanical properties such as the tensile strength. Particularly, in short fiber composites is desired to have a strong interface to transfer effectively load from the matrix to the fiber. However, a strong interface will make difficult to relieve fiber stress concentration in front of the approaching crack. According to Naaman, in order to develop a better mechanical bond between the fiber and the matrix, the fiber should be modified along its length by roughening its surface or by inducing mechanical defor-mations. Thus, the premise of the model is to take into account this process considering a micro field that represents the slipping fiber-cement displacement. The conjugate generalized stress to the gradient of this micro-field verifies a balance equation and has a physical meaning.
This contribution includes the computational modeling aspects of the high fiber rein-forced cement composites (HFRCC) model. To simulate the composite material, a finite element discretization is used to solve the set of equations given by the multifield approach for this particular case. A two field discretization: the standard macroscopic and the micro-scopic displacements, is proposed through a mixed finite element methodology. Furthermore, a splitting procedure for uncoupling both fields is proposed, which provides a more convenient numerical treatment of the discrete equation system.
The initiation of failure in HPFRCC at the constitutive level identified as the onset of strain localization depends on the mechanical properties of the all compounds and not only on the matrix ones. As localization criteria is considered the bifurcation analysis in combination with the localized strain injection technique presented by Oliver et al. It consists of injecting a specific localization mode during the localization stage, via mixed finite element formulations, to the path of elements that are going to capture the cracks, and, in this way, the spurious mesh orientation dependence is removed.
Model validation was performed using a selected set of experiments that proves the via-bility of this approach. The numerical examples of the proposed formulation illustrated two relevant aspects, namely: 1) the role of the bonding mechanism in the strain hardening be-havior after cracking in the HPFRCC and 2) the role that plays the finite element formulation in capturing the displacement localization in the localization stage.
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Pan, Qing. « Multi-scale modelling and material characterisation of textile composites for aerospace applications ». Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33396/.
Texte intégralRésumé :
Textile composites offer an excellent alternative to metallic alloys in the aerospace engineering due to their high specific stiffness and strength, superb fatigue strength, excellent corrosion resistance and dimensional stability. In order to successfully apply these materials to engineering problems, a methodology to characterise and predict the constitutive response of these materials is essential. The lack of the modelling tools for modern textile composites that would facilitate systematic analysis and characterisation of these materials hinders the wide adoption of such material systems in engineering applications. This defines the focus of the project as represented in this thesis. A multi-scale modelling methodology has been established for the material characterisation and representing the constitutive response of the material at a macroscale. For material characterisation at micro- and mesoscales, an automated material characterisation toolbox, UnitCells©, has been employed and substantially developed in both the scope and complexity through this project. When applying this toolbox, the user selects the required type of a textile or unidirectional reinforcements and provides a parametric input, based on which a finite element model of a unit cell for the composites is generated automatically. The effective properties that can be predicted using this toolbox include stiffness, thermal expansion coefficient, thermal and electric conductivities, static strength and dynamic strength (associated with deformation localisation as the limit of the applicability of unit cells but a conservative estimate of the material strength). There are seven types of microscale models and eleven types of mesoscale models available in the toolbox at present. To represent a constitutive relationship for textile composites at a macroscale, the artificial neural network (ANN) algorithm has been adapted and developed into a useful modelling tool, referred to as the ANN system. A criterion defining an ultimate failure of the material has been proposed. The outcome has made it possible for a user defined material subroutine to be established which can be employed in the analysis of structures made of such textile composites by providing the effective constitutive behaviour of them in a most efficient manner. As a validation, ANN system was used to predict the critical velocities of three types of layer-to-layer interlock 3D woven composite panel subject to ballistic loading. The predicted results matched well with the testing results. Furthermore, as an illustration of potential capability, the ANN system has been used to simulate impact of a textile composite fan blade containment casing in an idealised fan blade off scenario. Through the project, the capability of predicting the impact behaviour of textile composites has been established. This involves unit cell modelling at micro-/mesoscales for material characterisation, strength prediction with due consideration of strain rate sensitivity of the constituent materials, and ANN system to deliver the characterised constitutive relationship in terms of a user defined material subroutine for practical applications at macroscale, such as structural impact analysis.