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CHEN, LI. "A BIOINSPIRED MICRO-COMPOSITE STRUCTURE." Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1118471877.
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Peditto, Francesca Priola Aldo Gérard Jean-François. "Photopolymerized micro-and nano-composites interface chemistry and its role on interfacial adhesion /." Villeurbanne : Doc'INSA, 2005. http://docinsa.insa-lyon.fr/these/pont.php?id=peditto.
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Peng, Suili. "Nano/micro particle-based functional composites and applications /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?NSNT%202007%20PENG.
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Bailey, Stephen Peter. "Design, fabrication and characterisation of functional cement-composite micro-devices." Thesis, Birkbeck (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401238.
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Zhao, Hang. "Comportement multifonctionnel des composites comportant des nano/micro renforts." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLC020/document.
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En raison de leurs propriétés mécaniques, électriques et thermiques exceptionnelles, les nanotubes de carbone (NTC) ont reçu une importante attention mondiale. Les NTC ont un grand potentiel dans différents domaines d'applications tels que le stockage d'énergie et la microélectronique. Grâce à leur structure unidimensionnelle, leur important facteur d'aspect et leur faible densité, les NTC servent comme charges dans les composites. Par contre, en raison des fortes interactions entre eux, il est difficile de les disperser et de les aligner dans une matrice de polymère.Il est connu qu'une bonne conception d'hybrides, constitués de NTC verticalement lignés sur des substrats, améliore de manière significative la dispersion de ces derniers dans la matrice. Ces hybrides sont préparés par le procédé de dépôt chimique en phase vapeur (CVD). Une fois, ces hybrides sont dispersés dans la matrice du composite cela conduit à une nette amélioration des propriétés multifonctionnelles de ce composite. Les substrats utilisés dans cette thèse sont les nanoplaquettes de graphite (NPG) pour donner des hybrides NPG-NTC que nous appellerons par la suite GCHs. Les GCHs ont l'avantage d'avoir une faible densité et une structure totalement conductrice qui améliore les propriétés diélectriques et électriques des composites.Dans l'état de l'art, les relations entre l'organisation des GCHs et les conditions de synthèse par CVD et entre l'ajout des GCHs dans les composites et les réseaux conducteur interne dans les composites n'ont jamais été étudiées. Pour cela, dans cette thèse, nous allons soigneusement étudier et discuter ces problèmes mentionnés.Dans le premier chapitre, nous présentons une revue générale de la structure, des propriétés, des applications et de la synthèse des NTC et des NPG. Nous présentons aussi les procédures de l'intégration des nanoparticules dans des matrices polymères et les méthodes de fonctionnalisation des NTC. Nous discutons aussi des états électriques et les caractéristiques (di)électriques des composites en fonction de la quantité de la charge conductrice.Le deuxième chapitre présente tout d'abord la synthèse des NTC sur les NPG par CVD. Ensuite, l'influence des paramètres de la CVD, la température, la composition du gaz et le temps de la réaction, ont été étudié. Les résultats qualitatifs et quantitatifs obtenus d'après les caractérisations des ces hybrides peuvent servir comme base de données pour l'intégration et l'influence des ces hybrides dans les composites.Le troisième chapitre présente les composites binaires polyvinylidene fluoride/GCHs et leurs propriétés diélectriques qui sont nettement améliorées par rapport aux composites ternaires composés de polyvinylidene fluoride/NPG/NTC. Les composites obtenus par dispersion des GCHs dans la matrice à l'aide du procédé d'extrusion-injection, présentent un seuil de percolation fortement réduit (5,53 vol%) et une stabilité thermique relativement élevée. Leurs propriétés diélectriques améliorées peuvent être attribuées à des réseaux sous forme de micro-condensateurs et le changement de la cristallinité de la matrice peut être attribué à la bonne conception des hybrides.Le quatrième chapitre étudie les composites GCHs/polydiméthylsiloxane (PDMS) avec la haute performance piézo-résistive dans une large gamme de température. Le composite présente un seuil de percolation ultra-bas et une grande sensibilité piézo-résistive. En particulier, les autres améliorations des propriétés électriques obtenues dans les composites GCHs/PDMS par rapport à celles des composites à base de NTC/PDMS, de NPG/PDMS ou encore de NTC-NPG/PDMS. Les légers mouvements des doigts peuvent être détectés grâce à l'usage de ces films composites en tant que capteurs de mouvementDue to the outstanding mechanical electrical and thermal properties, carbon nanotubes (CNTs) received worldwide attentions and intensive investigations in last decades. CNTs are greatly potential in applications such as energy storage and microelectronics. The one dimensional structure, high aspect ratio and low density, promote CNTs serving as the excellent fillers in composites field. However, due to the strong interactions, CNTs are usually difficult to be dispersed and aligned in a polymer matrix. Designing the CNTs construction reasonably is an effective way to ameliorate the dispersion states of CNTs in matrix. These specific hybrid constructions allowed CNTs arrays synthesized vertically onto the substrates through catalyst chemical vapor deposition method. These CNT arrays effectively overcome the problem of CNTs aggregation and promote the interconnection among CNTs, leading to a considerable improvement of multi-functional properties of composites. Graphite nanoplatelets (GNPs) served as substrate make their synthesizing products-GNP-CNTs hybrids (GCHs) possess distinct merits of all-carbon composition, totally-conductive coupling structure and the low intrinsic density. These GCHs constructions provide a great improvement in the dielectric and electrical properties of composites. However, the relationship between GCHs organization and synthesizing conditions during CVD process and the influence of the addition of GCHs to internal conductive networks have not been reported in detail. These mentioned issues will be investigated and discussed in this thesis, which is divided into four chapters:The first chapter makes a general review of the structure, properties, application and synthesis of CNTs and GNP substrates, and the main procedures of fabricating composites and surface functionalization of CNTs. Moreover, a short introduction of the development of micro-nano hybrids applied to the functional composites is made. Most importantly, the developing electrical states and (di) electrical characteristics of composites with ever-increasing conducting filler loading are reviewed in detail at the last part.The second chapter discusses firstly the synthesis process through the CCVD approach and the relationship between CVD parameters and the corresponding construction of GCHs, where the temperature, gas composition and reaction time were controlled. The constructions CNT arrays are dependent on the synthesis conditions. Furthermore, the results obtained from analysis can provide a structural foundation for the huge application potential of GCHs constructions. The third chapter introduces the poly(vinylidene fluoride)-based nanocomposites containing GCH particles, the dielectric properties of which are improved more greatly than the ternary composites loading equivalent mixture of GNPs and CNTs. The composites achieved by dispersing GCH particles into matrix using the mechanical melt-mixing process, showing a strongly reduced percolation threshold (5.53 vol %) and the relatively high thermal stability. Their improved dielectric properties can be attributed to the formed microcapacitor networks and the change of crystalline formation of matrix, caused by well-designed CNT arrays constructions. The fourth chapter investigates the advanced GCHs/ polydimethylsilicone (PDMS) composites with high piezo-resistive performance at wide temperature range. The synthesized GCHs can be well dispersed in the matrix through the mechanical blending process. The flexible composite shows an ultra-low percolation threshold (0.64 vol%) and high piezo-resistive sensitivity (gauge factor ~103 and pressure sensitivity ~ 0.6 kPa-1). Particularly, the much improvements of electrical properties achieved in GCHs/PDMS composites compared with composites filled with equivalent CNT, GNP or mixture of CNTs/GNPs. Slight motions of finger can be detected and distinguished accurately using the composites film as typical wearable sensor
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Tertrais, Hermine. "Développement d’un outil de simulation pour le chauffage de matériaux composites par micro-ondes." Thesis, Ecole centrale de Nantes, 2018. http://www.theses.fr/2018ECDN0061/document.
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Le travail présenté dans cette thèse s’inscrit dans le contexte du développement de nouveaux procédés pour la mise en forme de matériaux composites pour répondre aux contraintes industrielles de gain de temps et d’énergie. Le procédé de chauffage par micro-onde reposant sur un principe de chauffage volumique permet de garantir ces avantages. L’inconvénient majeur est que le comportement du champ électrique lors de l’interaction entre matériaux composites et micro-ondes est peu connu. L’objectif de cette thèse est donc de proposer des solutions numériques pour approfondir la connaissance du procédé et la physique associée afin de mettre en avant ses capacités quant à un développement industriel. Pour ce faire, le travail réalisé est axé autour de trois verrous. En premier lieu, une nouvelle méthode numérique est proposée afin de résoudre les équations de Maxwell en 3D dans un stratifié composite. Prendre en compte le comportement 3D est essentiel afin de décrire avec précision l’impact des différentes couches du matériau et de leur épaisseur sur la propagation du champ électrique. Dans un second temps, la simulation électromagnétique est couplée à une résolution thermique afin de simuler le procédé de chauffage d’une pièce composite. Différents paramètres du procédé sont étudiés afin de mettre en avant les plus sensibles pour l’utilisation du chauffage micro-onde pour les matériaux composites. Enfin, l’attention du lecteur est portée sur le développement d’une méthode de simulation pour un contrôle en temps réel du procédé en comparaison avec des essais expérimentauxThe context of the present work is the development of new processes for the heating and forming of composite materials in order to provide an answer to the industrials needs for less energy and less time-consuming processes. In that sense, microwave heating is perfect match as it relies on volumetric heating. The major drawback is that the behaviour of the electric field while interacting with composite material is poorly known. Therefore, the main objective of this thesis is to provide numerical solutions to go more deeply in the understanding of such process and put forward its capabilities for an industrial development.To fulfil this objective, the work is oriented over three main axes. First, an innovative simulation tool is presented in order to solve the Maxwell’s equations in a thin multi layered domain. Taking into account the 3D behaviour of the electric field is a major issue in order to describe precisely the impact of the different plies of the laminate on the propagation of the electric field.Then, the electromagnetic simulation is coupled with a thermal simulation in order to simulate the full heating process of a composite part. Parameters of the process are investigated to bring forward the most crucialones. Finally, real-time control of the process is tackled using a model order reduction simulation technique. These results are compared to experimental work on two sets of samples
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Peters, Sarah June. "Fracture Toughness Investigations of Micro and Nano Cellulose Fiber Reinforced Ultra High Performance Concrete." Fogler Library, University of Maine, 2009. http://www.library.umaine.edu/theses/pdf/PetersSJ2009.pdf.
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Graham, Samuel Jr. "Effective thermal condutivity of damaged composites." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/16935.
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Ben, ghzaiel Tayssir. "Synthèse, caractérisation et étude des propriétés magnétiques et diélectriques de nanocomposites Polyaniline/hexaferrite pour l'absorption des micro-ondes." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLN003/document.
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Ces travaux de thèse consistent à élaborer des nanocomposites Polyaniline/hexaferrite pour l’absorption des micro-ondes. L’idée principale est la mise en œuvre de matériaux composites à base de polymères conducteurs intrinsèques telle la Polyaniline que nous avons dopée avec différents types d’acides (HCl, CSA, NSA et TSA…) et l’hexaferrite de baryum de type magnétoplombite (M) stœchiométrique ou substitué. Au niveau de l’hexaferrite de baryum, la substitution du Fe3+ s’est faite par les ions Al3+, Bi3+, Cr3+ et Mn3+.L’hexaferrite de baryum et les hexaferrites substitués par les différents ions cités ci-dessus ont été synthétisés par voie hydrothermale dynamique en faisant varier divers paramètres au cours de la synthèse (pH, température, temps, rapport [OH-]/[NO3-]…).L’élaboration des composites Polyaniline/hexaferrite (pur ou substitués) a été effectuée par polymérisation oxydative en utilisant plusieurs techniques de synthèse : la polymérisation chimique en solution (en tenant compte de la nature de l’acide utilisé) avec ou sans agitation (Aqueous-Based Polymerization with or without stirring) et la polymérisation oxydative par voie solide (Solid-Based Polymerization). L’optimisation de ces différentes techniques de synthèse après caractérisations physicochimiques (DRX, FTIR, ATG, MEB, EDX), diélectriques (ε’, ε’’, σdc) et magnétiques (Mr, Ms, Hc, Tc, µ’, µ’’) des échantillons, a montré que la polymérisation par voie solide se trouve la méthode la plus facile, économique et respectueuse de l’environnement. Elle est aussi adaptée à la production du composite Pani/BaFe12O19 avec de bonnes propriétés structurales, physiques et magnétiques. L’étude de la substitution du Fe3+ dans le BaFe12O19 par Al3+, Bi3+, Cr3+ et Mn3+ a montré une forte dépendance des propriétés structurales et magnétiques avec la distribution de ces ions dans la maille cristalline hexagonale. En effet, les ions Al3+, Cr3+ et Mn3+ ont une tendance à occuper les sites tétraédriques, alors que le Bi3+ occupe les sites octaédriques. Une augmentation de Hc associée à la taille des cristallites a été observée pour les particules substituées avec l'Al et le Cr alors qu’une modification de l'anisotropie magnetocristalline (fort terme d'ordre supérieur) a été mise en évidence pour les substitutions Bi et Mn, dû à leur grand rayon ionique. L’incorporation des hexaferrites substitués dans la Polyaniline pour obtenir des composites Pani/BaMeFe11O19, où Me = Al, Bi, Cr et Mn, révèle une variation des propriétés électromagnétiques dans la gamme de fréquences allant de 1 à 18 GHz. En effet, ces variations sont dues à la formation de dipôles entre l’ion de substitution et les cations O2- dans le ferrite qui sont responsables de la résonance ferromagnétique, de l'anisotropie magnétocristalline et des interactions avec la matrice polymérique. Le composite Pani/BaFe12O19 présente des absorptions dans la bande X qui se déplacent vers la bande Ku avec la substitution du fer confirmantThis thesis deals with the formulation of Polyaniline/hexaferrite nanocomposite for absorbing electromagnetic waves. The main idea is the process of composite materials based on polymers intrinsic conductors such as polyaniline that we doped with different types of acids (HCl, CSA, NSA, and ... TSA) and barium hexaferrite with magnetoplumbite structure with or without substitution according to desired stoichiometries. In the barium hexaferrite, the substitution of Fe 3+ is made by Al3+, Bi3+, Cr3+ and Mn3+ ions.The barium hexaferrite and its substitutions by different ions mentioned above were synthesized dynamic hydrothermal method by varying various parameters during the synthesis (pH, temperature, time, ratio [OH-]/[NO3-] ...).The elaboration of polyaniline/hexaferrite composite (pure or substituted) was carried out by oxidative polymerization using various synthesis techniques: Aqueous-Based Polymerisation with or without agitation (taking into account the nature of the acid used) (ABP) and Solid-Based Polymerization (SBP). The optimization of these various synthesis techniques after physicochemical (XRD, FTIR, TGA, SEM, EDX), dielectric (ε ', ε' ', σdc) and magnetic (Mr, Ms, Hc, Tc, µ', µ'') characterizations of the samples showed that the solid route is the easiest method, economical and environmentally friendly. It is also suitable for the production of composite Pani/BaFe12O19 with good structural, physical and magnetic properties.The study of the substitution of Fe 3+ in the BaFe12O19 by Al3+, Bi3+, Cr3+ and Mn3+ showed a strong dependence of the structural and magnetic properties with the distribution of these ions in the hexagonal crystal lattice. In fact, Al3+, Cr3+ and Mn3+ ions tend to occupy the tetrahedral sites, while the Bi3+ favoured the octahedral sites. An increase in Hc associated with the small crystallite size observed for particles substituted with Al and Cr and the enhancement magnetocristalline anisotropy (strong higher order term) for Bi and Mn due to their high ionic radius.The incorporation of the substituted hexaferrite in the polyaniline to obtain Pani/BaMeFe11O19 composite, where Me = Al, Bi, Cr and Mn, reveals a variation in electromagnetic properties in the frequency range from 1 to 18 GHz. In fact, these variations are due to the formation of dipoles between the substituting ion and surrounding O2- cations in the ferrite which are responsible for the ferromagnetic resonance, the magnetocrystalline anisotropy and the exchange interaction with the polymer. The composite Pani/BaFe12O19 shows absorption bands at the X-band that shift to the Ku-band with the substitution of iron, confirming the potential of these materials for microwave applications
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Naser, Hasan. "Développement de micro-composites architecturés en aciers inoxydables duplex : élaboration, microstructure et propriétés mécaniques." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI024/document.
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L'utilisation de l'acier inoxydable duplex (DSS) pour des applications structurales est considérée comme l'un des progrès les plus notables et qui a le plus grand impact sur le secteur de la construction. Ceci est grâce à ses propriétés mécaniques élevées couplées avec des propriétés fonctionnelles intéressantes telles que la résistance à la corrosion, ou encore la faible conductivité thermique par rapport aux aciers au carbone. En raison de sa microstructure et l'interaction complexe entre les phases, DSS a un fort potentiel pour le développement des propriétés uniques. Une meilleure compréhension est nécessaire pour obtenir des propriétés exceptionnelles et fournir la possibilité de concevoir un DSS sur-mesure et architecturé pour des applications spécifiques. Dans ce travail, nous avons proposé une approche différente de celle utilisée jusqu'à présent pour comprendre le comportement du DSS. La stratégie adoptée dans ce travail était une stratégie dite top-down dans laquelle au moins deux métaux ayant un comportement et des propriétés bien connues sont mécaniquement assemblés par déformation plastique sévère (SPD). Cette stratégie proposée a pour objectifs: i) améliorer les propriétés par raffinement de microstructure jusqu’à une échelle sub-micrométrique ii) l'élaboration d'un matériau modèle permettant de comprendre le comportement DSS obtenu par les méthodes métallurgique conventionnelles. Le premier objectif de ce travail était, par conséquent, la mise en œuvre d'une méthodologie de fabrication en utilisant la technique SPD par co-tréfilage. Cette technique permettra l'obtention d'une microstructure ultrafine des composites 316L / 430LNb. L'un des défis rencontrés au cours de notre étude était l'inter-diffusion significative lors de traitement thermique susceptible de limiter un raffinement supplémentaire de la microstructure en question. Une étude d'optimisation a été effectuée pour tenir compte du rôle de cette inter-diffusion pour un couple 316L / 430LNb. Ainsi, des micro-composites multi-échelles ont été obtenus. Dans ce travail, nous avons montré la limitation de ce processus en termes de raffinement de microstructure. Une rationalisation de ces limites a été donnée par une étude thermocinétiques sur les micro-composites et matériaux brut initialement utilisés. Parallèlement à l'évaluation de la microstructure, le comportement mécanique de ces nouveaux micro-composites a été examiné. Afin de fournir une explication plus approfondie sur le comportement plastique de nos composites, des essais de traction in situ par rayonnement X synchrotron à haute énergie ont été effectuésThe use of duplex stainless steel (DSS) grades for structural applications is considered as one of the most significant advances impacting the construction sector. This is because of their high mechanical properties coupled with interesting functional properties such as corrosion resistance or even the low thermal conductivity compared to carbon steels. Due to their complex microstructure and interaction between the phases, DSS have a significant potential for unique properties. A better understanding is needed to give the possibility to obtain break through properties and to provide the possibility to design tailor-made, architectured DSS for specific applications. In this work we proposed a different approach from that used until now to understand the behavior of DSS. The strategy adopted in this work was a top-down strategy in which at least two bulk metals with well known behavior and properties are mechanically alloyed by Severe Plastic Deformation (SPD). This proposed strategy served two main objectives: i) enhancing the properties by microstructure refining down to sub-micron scale ii) elaborating a material model for understanding the DSS behavior obtained by the conventional metallurgical methods. The first objective of this work was, therefore, the implementation of a methodology of manufacturing using SPD technique by co-drawing. This technique will allow obtaining an ultra-fine microstructure of 316L/430LNb composites. One of the challenges met during our study was the significant inter-diffusion during heat-treatment step necessary during processing preventing by consequence further refining. An optimization investigation was carried out to account the role of this inter-diffusion for 316L/430LNb couple. Multi-scale micro-composites have been then obtained. In this work, we showed the limitation of this process in terms of microstructure refining. A rationalization of these limits was given by studying the thermo-kinetics of both micro-composites and bulk materials. In parallel with the microstructural evaluation, the mechanical behavior of these new micr-composites was examined. In order to provide a more in-depth explanation of the plastic behavior of our composites, in situ tensile test using high energy X-ray synchrotron have been performed
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Struble, John D. "Micro-scale planar and two-dimensional modeling of two phase composites with imperfect bonding between matrix and inclusion." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/17345.
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Njuguna, James A. K. "Micro- and macro-mechanical properties of aerospace composite structures and their dynamic behaviour." Thesis, City University London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440734.
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Patel, Nirajkumar. "Micro scale flow behavior, fiber wetting and void formation in liquid composite molding." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1299253097.
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Lanzarini, Julien. "Elaboration et caractérisation thermo-physique de micro-composants fonctionnels à base de poudres magnétocaloriques." Thesis, Besançon, 2016. http://www.theses.fr/2016BESA2053.
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Les travaux de cette thèse proposent le développement d’un procédé de fabrication de composants micro-structurés à base d’unmatériau magnétocalorique. A plus long terme, ces composants de type lame mince seront intégrés à des dispositifs deréfrigération magnétique. Leur réalisation par les procédés conventionnels tels que l’usinage n’est pas envisageable dansl’optique d’une industrialisation. La solution envisagée est basée sur la mise en forme de composants par réplication d’uncomposite magnétocalorique. Ce micro-composite est défini par le mélange des poudres magnétocaloriques hydrogénées detype La(Fe,Si)13 dans une matrice thermoplastique (PP, LDPE). Cette technique permet de bénéficier des avantages desprocédés de mise en forme des polymères comme l’extrusion ou le moulage par injection. Le développement d’un tel procédéest divisé en deux parties. La première partie concerne l’élaboration et la caractérisation du micro-compositemagnétocalorique. Les tests réalisés en mélangeur ont permis de proposer plusieurs formulations micro-compositesmagnétocaloriques selon différents taux de charge. Cette première partie du développement étudie les différents aspects dumatériau micro-composite comme la rhéologie et les propriétés magnétocaloriques des mélanges. La caractérisationrhéologique basée sur les tests au rhéomètre capillaire est réalisé afin d’évaluer la capacité de mise en forme des mélangesassociée au procédé d’extrusion-conformage. Les propriétés propres aux matériaux magnétocaloriques telles que la variationde température adiabatique (ΔT) et la température de Curie (Tc) sont investiguées. Le contrôle de la Tc par mesure DSC a misen évidence des problématiques de déshydrogénation des poudres liées à la température d’élaboration. L’impact du taux decharge en poudre est étudié par la mesure des ΔT permettant d’estimer les performances finales du micro-composite. Ladeuxième partie traite du développement du procédé de mise en forme par extrusion-conformage. Une ligne d’outillages dédiéeà l’extrusion-conformage des lames micro-structurées a été réalisée et validée à l’échelle du laboratoire. La stabilité de latempérature de Curie a été vérifiée tout au long du processus d’élaboration des composants micro-structurés. Les paramètresd’extrusion tels que la température d’extrusion ont pu être définis afin d’éviter la déshydrogénation des poudresmagnétocaloriques. Les composants extrudés sont caractérisés en termes d’homogénéité du taux de charge en poudre et detolérances géométriques aboutissant à laThis thesis proposes the development of a method of manufacturing micro-structured components made of a magnetocaloricmaterial. In the long term, these blade-type components will be integrated in magnetic refrigeration devices. On an industrialscale, their production by the conventional process, machining, is not possible. The solution proposed is based on shaping thecomponent by a replication process via a magnetocaloric composite material. This micro-composite is defined by the mixtureof hydrogenated magnetocaloric powders of La(Fe,Si)13 in a thermoplastic matrix (PP, LDPE). This technique allowsutilization of the polymer shaping process, extrusion. The development of this process is divided into two parts. The first partconcerns the development and characterization of the magnetocaloric micro-composite. Results from tests performed with themixer allow the proposal of several micro-composite formulations under different loading rates. These formulations are thenstudied for various aspects of micro-composite material. The rheological characterization based on capillary rheometer tests istaken to evaluate the shaping ability of the mixtures associated with the extrusion process. Specific properties ofmagnetocaloric materials such as the adiabatic temperature variation (ΔT) and the Curie temperature (Tc) are also investigated.The control of the Tc by DSC measurement highlighted problematic dehydrogenation of the powders as a result of theelaboration temperature. The impact of loading rate is studied by measuring the ΔT in order to estimate the final performanceof the micro-composite. The second part deals with the development of the shaping process by extrusion. A tooling linededicated to extrusion of the micro-structured blades is carried out and validated at the laboratory scale. The stability of Tc ischecked throughout the elaboration process of the micro-structured components. The extrusion parameters are defined to avoidthe dehydrogenation of magnetocaloric powders. The extruded components are characterized in terms of homogeneity of thepowder loading rate and geometric tolerances resulting in the validation of the developed process. The industrial transfer isnow possible to a large scale production
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Malaspina, Odirlei Arruda. "Avaliação da estabilidade de cor e rugosidade superficial de resinas compostas micro-híbridas, submetidas ao processo de envelhecimento artificial acelerado, em função da fotoativação com lâmpada halógena e LED." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/25/25131/tde-05112009-104015/.
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O estudo avaliou, in vitro, as variáveis relacionadas à alteração de cor e à rugosidade superficial das resinas compostas micro-híbridas: Charisma (Heraeus-Kulzer), Filtek Z-250 (3M - Espe), Herculite XRV (Kerr), Opallis (FGM), TPH Spectrum (Dentsply) e W3D (Wilcos), antes e após o envelhecimento artificial acelerado, tendo como fatores de variação duas fontes de luz, lâmpada halógena e LED, com densidades de potência de 300 mW/cm2 ou 600 mW/cm2. Foram confeccionados 240 corpos-de-prova distribuídos em grupos de 10 unidades para cada condição de estudo totalizando 24 grupos constituídos por 4 protocolos de fotoativação para cada marca de resina composta. Estes corpos-de-prova foram armazenados em água deionizada, ao abrigo de luz e a temperatura de 37oC por 1 semana quando então receberam polimento superficial com discos Diamondpro (FGM). Sequencialmente, os mesmos foram submetidos às análises iniciais de rugosidade superficial (rugosímetro Hommle Tester T1000 basic) e de cor (Espectrofotômetro EasyShade). Decorridas 24 horas, os espécimes foram submetidos ao Sistema de Envelhecimento Acelerado para materiais não metálicos C-UV por 384 horas quando então foram novamente realizadas as leituras de rugosidade e cor. Os valores de rugosidade superficial e alteração de cor das resinas compostas, após o processo de envelhecimento acelerado, demonstraram alterações significativas, sendo os valores de E muito superiores ao considerado clinicamente aceitável (E3,3). De forma geral, o efeito exercido pelos protocolos de fotoativação não permitiu distinguir a influência direta das irradiâncias das fontes de luz no comportamento das diferentes resinas compostas, observando-se uma correlação positiva média entre rugosidade superficial e a alteração de cor.This study aimed to evaluate changes in color and surface roughness, before and after artificial accelerated aging of six micro hybrids composites resins (comparable to Vita shade A2) cured by quartz tungsten halogen (H) or a light emitting diode (L) polymerization unit with 300 mW/cm2 or 600 mW/cm2. Forty disc specimens (7 x 2 mm) were prepared for each composite (Charisma®, Filtek Z-250®, Herculite XRV®, Opallis®, TPH Spectrum®, W3D®), being 10 specimens for each condition (Q 300/600 mW/cm2 or L 300/600 mW/cm2). After cured, each specimen was evaluated by color (Easy Shade® spectrophotometer) according to CIE L*a*b* color scale and by surface roughness (Hommelwerke GmbH ) Ra values before and after submitting to artificial accelerated aging (4 h UV-B/4 h condensing vapor) for 384 hours total. The surface roughness and color change values of composite resins, after the process of accelerated aging, showed significant changes. Also, the values of E after accelerated aging were much higher than the values considered clinically acceptable (E 3.3). In general, the protocols curing effects showed varied influence over different composite resins and a positive correlation between average change in surface roughness and color change after accelerated aging process.
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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.
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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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Zhang, Yan. "Relationship between morphology, crystallization behavior and mechanical properties of polypropylene micro- and nanocomposites /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CENG%202004%20ZHANG.
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Mohd, Zawawi Fazila. "Analyse aéroélastique d'une pale flexible composite : application au microdrone." Thesis, Toulouse, ISAE, 2014. http://www.theses.fr/2014ESAE0027/document.
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The vision driving the work reported herein is to investigate the fluid-structure interac-tion (FSI) effects of the flexible laminated blades for tilt-body micro-air-vehicles (MAV)proprotors in hover and forward flight configurations. This is in order to exploit the po-tential of flexible-bladed proprotor over the rigid-bladed proprotor in the enhancementof proprotor performance during hovering and cruising at a target forward speed. Forthat, the FSI model taking into account the specific problems devoted to MAV-sizedproprotor made of laminate composite was developed. The FSI model combines aerody-namic model adapting Blade Element Momentum (BEM) theory and structural modeladapting Anisotropic Finite Element Beam (AFEM) theory. The aerodynamic model isdeveloped to be capable of adapting in the analysis on low Reynolds number proprotors.In the structural model, the blade is modeled as an elastic beam undergoing deflectionsin flap, lag, and torsion to capture the coupling effects in anisotropic materials, adaptsthe structural analysis on proprotor blades made of laminate composite. The reliabilityof the developed FSI model is verified through a validation on both aerodynamic andstructural models, separately, on several MAV-sized proprotors. As for a direction to theanalysis on passively-adaptive proprotor blades, an optimal design on actively-adaptiveproprotor was carried out. For this, a program for designing the optimum rigid blades atsingle-point (for either isolated cruise-point or isolated hover-point) and multiple-point(combined cruise and hover point) for proprotors have been developed. The proceduresin the optimal design program employs the numerical iterative inverse design method,based upon the minimum thrust induced losses (MIL). Even if the work in this thesiswas directed primarily towards the proprotor, however, the propulsion system from themotor part was not neglected since the propulsion efficiency is a crucial factor to the suc-cess of MAVs. A cheap and time-effective method of proposing the best motor from theselected commercial motors was developed, based on Taguchi’s method. The sensitivityof the total power consumption to the variation of value of each motor design variableswas also studied. The benefit of the use of tip body in the blade and the effect of bendingon the induced twist and on the thrust degradation, respectively, were also analyzed andidentified. Finally, the systematically designed passively-adaptive composite proprotors were evaluated under steady operating conditions. Hovering and cruise propulsive performance, characterized by total power Ptotal, were compared between the rigid-bladed and flexible-bladed proprotors. As a result of the comparison, the flexible-bladed proprotor with fixed system is found to be capable of slightly enhancing the performance through the reduction in Ptotal over its optimal rigid-bladed proprotorL’idée principale du travail rapporté ici est d’étudier les effets de l’intéraction fluide-structure (FSI) de pales laminées flexibles pour les proprotors de micro véhicules aériens(MAV) de type tilt-body dans les configurations de vol stationnaire et en avant. Eneffet, le but est d’exploiter les possibilités offertes par les proprotors à pales flexiblespar rapport aux proprotors à pales rigides pour améliorer leur performance dans cesphases de vol. Le modèle FSI a été développé à cet effet. Ce modèle tient compte desproblèmes spécifiques liés aux proprotors de MAV faits de composite laminé. Il com-bine l’adaptation de modèle aérodynamique par la théorie d’élement de pale (BEM) etl’adaptation de modèle structurel par la théorie des éléments finis de poutre anisotropes(AFEM). Le modèle aérodynamique est développé pour être capable de s’adapter àl’analyse des proprotors à bas nombres de Reynolds. Dans le modèle structural, la paleest modélisée comme une poutre élastique subissant des déviations dans la flexion, latraction et la torsion afin de capturer les effets de couplage de matériaux anisotropes.Il adapte l’analyse structurale des pales du proprotor faites de composite laminé. Lafiabilité du modèle FSI développé est vérifiée à travers une validation par modèles aéro-dynamique et structural, séparément, sur plusieurs proprotors de MAV. Afin de se dirigervers une analyse de pales de proprotors à adaptation passive , une recherche de designoptimal a été effectuée pour des proprotor à adaptation active. Pour cela, un programmepour la conception de pales rigides optimales à un unique point de fonctionnement (soitle vol de croisière soit le vol stationnaire) et à plusieurs points (combinant croisière etvol stationnaire) ont été développés. Les procédures du programme de design optimalemploient les mèthodes de design inverse par itération numérique, sur la base de pertesde poussée induites minimales (MIL). Même si le travail dans cette thèse a été dirigéprincipalement vers le proprotor, la partie moteur du système de propulsion n’a pasété négligée puisque l’efficacité de la propulsion est un facteur crucial pour le succès desMAVs. Une méthode simple et rapide de sélection du meilleur moteur parmi les moteurscommerciaux choisis est élaborée sur la base de la méthode de Taguchi. La sensibilitéde la consommation d’énergie totale à la variation de la valeur de chaque variable deconception du moteur a été étudiée. Le bénéfice de l’utilisation de la charge à la pointe de la pale et l’effet de la flexion sur la torsion induite et sur la dégradation de la poussée respectivement ont aussi été analysés et identifiés. Enfin, les proprotors à pales flexibles conçues systématiquement ont été évalués dans des conditions de fonctionnement stables. Performances en vol stationnaire et performances croisière propulsive, caractérisées par la puissance totale Ptotal ont été comparées entre les proprotors à pales rigides et à pales flexibles. En tant que résultat de la comparaison, les proprotors à pales flexibles s’avère capable d’améliorer légèrement les performances par la réduction de la Ptotal surson optimal proprotors à pales rigides
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Elagroudy, Hossam Aly. "BOND CHARACTERISTICS OF MICRO-COMPOSITE MULTI-STRUCTURAL FORMABLE STEEL USED IN REINFORCED CONCRETE STRUCTURES." NCSU, 2003. http://www.lib.ncsu.edu/theses/available/etd-07252003-213630/.
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The bond performance of a unique type of reinforcing steel rebars, claimed to have high corrosion resistance as well as high tensile strength, with concrete was studied. The objective was to investigate the bond behavior of straight rebars made out of this steel, named MMFX, embedded in concrete flexural members and to examine the applicability of the current expressions for bond force to predict the bond capacity of the MMFX bars embedded in concrete. Two phases of experimental investigation was conducted. In the first phase, four beam end specimens were tested and in the second phase eight splice beams were studied. The bond behavior of the MMFX steel bars was found to be similar to that of carbon steel. The bond strength of the MMFX is significantly reduced as the tensile stresses developed in the bar went beyond the proportional limit. Both the ACI code 318-02 equation for bond force and the current equation proposed by the ACI committee 408 for bond force gave conservative prediction for bond force for low stress levels. However, at high stress levels, the prediction of the two equations went to the unconservative side. The non linear behavior of the MMFX stress-strain curve was the reason behind the unconservative prediction. The above two equations were modified to ensure conservative prediction at high stress levels. A second degree best fitting curve was found to be the best to describe the relationship between the splice length and the bond force capacity for both # 6 and # 8 MMFX bars.
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Abughufa, Hajer. "Micro-hardness and depth of cure of dental bulk-fill composites." University of the Western Cape, 2015. http://hdl.handle.net/11394/5039.
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Magister Scientiae Dentium - MSc(Dent)Resin composite is one of the most commonly used materials in restorative dentistry. However, it has undergone continuous developments like changes in the fillers and initiators. One such improvement is the new bulk-fill composites which are materials intended for bulk placement up to 4mm. However, an optimum polymerization to the full depth of the restoration i.e. complete depth of cure is of utmost importance in order to obtain proper mechanical and physical properties of resin composites. Aim: The aim of this study was to measure the surface hardness of the top and bottom surfaces of the composites and to determine the depth of cure of bulk-fill composites using two different types of light curing units. Material and methods: A total of 160 specimens were used in this study: four bulk-fill composite were used of which two were conventional viscosity bulk-fill composites namely, Tetric N Ceram (Ivoclar Vivadent) and SureFil bulk-fill composite (Densply Caulk) and two were low viscosity flowable bulk-fill composites namely, SDR flowable (Densply Caulk) and Filtek bulk-fill flowable restorative (3M ESPE). Two different curing light were used namely, LED (Elipar Freelight, 3M ESPE) at 1500mW/cm2 and a Quartz Tungsten Halogen (QTH) curing unit (Megalux CS, Megadenta, Germany) at 600 mW/cm2. To evaluate micro-hardness, Vickers hardness at top and bottom of each sample was measured immediately after light curing and after 24 hours post curing using a Zwick micro-hardness machine load 300g/15 seconds. The mean hardness values obtained from the top and the bottom surface of each material were used to compare the micro-hardness of the various materials. The mean values obtained from the bottom surface were compared to the respective values of the top surface of each material (bottom/top ratio) and used to calculate the depth of cure. Results: The micro-hardness test showed a significant difference between the four materials (ANOVA, p<0.05) immediately after curing and after 24 hours post curing. The material with the greatest micro-hardness was SureFil followed by Tetric N Ceram, Filtek bulk-fill flowable and SDR flowable respectively. The material with the greatest depth of cure was Filtek bulk-fill flowable followed by SDR flowable, Tetric N Ceram and SureFil. When the curing lights were compared the Light Emitting Diode Curing Unit (LED) obtained significantly better depth of cure compared to Quartz Tungsten Halogen Light Curing Units. The LED curing light showed greater micro-hardness values than the QTH curing light except for Tetric N Ceram where the QTH curing showed more hardness values than the LED curing light. For all materials, the surface hardness and depth of cure values increased when tested 24hrs after light curing. Conclusion: There was a difference in the micro-hardness values between the four materials where the conventional viscosity materials showed greater surface hardness values than the low viscosity materials but the depth of cure compared to the bulk-fill flowable LED curing lights showed higher hardness values than QTH curing light except for Tetric N Ceram. Depth of cure ratios were found to be lower than 0.80 for all composite types, however the flowable bulk-fill materials showed higher depth of cure than the conventional viscosity bulk-fills. In general LED curing light produced better hardness and depth of cure values than QTH curing light. The low micro-hardness values for the bulk-fill flowable composites and the inadequate polymerization raises a concern regarding placing these materials in bulk. In such cases, the flowable bulk-fills should be protected with a conventional composite "covering or capping" especially in posterior teeth and in deeper cavities. Furthermore, bulk-fill composites should be used in layering incremental technique to ensure sufficient depth of cure.
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Bilgen, Onur. "Macro Fiber Composite Actuated Unmanned Air Vehicles: Design, Development, and Testing." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/33117.
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The design and implementation of a morphing unmanned aircraft using smart materials is presented. Articulated lifting surfaces and articulated wing sections actuated by servos are difficult to instrument and fabricate in a repeatable fashion on thin, composite-wing micro-air-vehicles. Assembly is complex and time consuming. A type of piezoceramic composite actuator commonly known as Macro Fiber Composite (MFC) is used for wing morphing. The actuation capability of this actuator on fiberglass unimorph was modeled by the Rayleigh-Ritz method and quantified by experimentation. Wind tunnel tests were performed to compare conventional trailing edge control surface effectiveness to an MFC actuated wing section. The continuous surface of the MFC actuated composite airfoil produced lower drag and wider actuation bandwidth. The MFC actuators were implemented on a 0.76 m wingspan aircraft. The remotely piloted experimental vehicle was flown using two MFC patches in an elevator/aileron (elevon) configuration. Preliminary testing has proven the stability and control of the design. Flight tests were performed to quantify roll control using the actuators. Force and moment coefficients were measured in a low-speed, open section wind tunnel, and the database of aerodynamic derivatives were used to analyze control response.Master of Science
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Lv, Peng. "Performance aérodynamique et structurelle du rotor flexible pour micro-drones." Thesis, Toulouse, ISAE, 2014. http://www.theses.fr/2014ESAE0058/document.
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Les essais en environnement libre et en soufflerie ont été effectués pour étudier la performance propulsive et la déformation de pales de référence et de pales souples. La poussée et le couple ont été évalués par deux méthodes: une mesure directe par balance et une estimation indirecte par bilan de quantité de mouvement, les deux méthodes ayant leurs avantages et limitations respectifs. La méthode indirecte s’est construite sur l’acquisition de champs de vitesse obtenus par PIV et s’appuie sur une estimation de la pression par mise en œuvre de l’équation de Poisson. En vol stationnaire, les pales flexibles ne peuvent pas aider à l’amélioration du rendement en mode rotor (FM), à chargement faible, puisque la distribution de vrillage est sans doute assez éloignée de l’optimal de vol stationnaire. En vol avancé, le rendement propulsif des pales flexibles est la plupart du temps plus élevé que l’hélice rigide de référence en raison de la torsion bénéfique généré en rotation. Dans le cas des pales flexibles, la vitesse axiale se trouve être inférieure au cas rigide, à même station aval; ceci correspondant à la la déformation de vrillage négatif. Pour les deux pales, la différence de poussée entre celle déduite du champ PIV test 2et celle obtenue avec la balance est plus grande que la différence entre les valeurs déduites du champ PIV test 1 et de la mesure directe. La technique de mesure laser pour les déplacements(LDS) a été utilisée pour mesurer la déformation stationnaire des pales lors de leur rotation. Par analyse du nuage de points mesurés par la LDS, la flexion et la torsion de la lame en rotation ont été identifiées à l’aide des régressions multiplesThe wind tunnel tests were conducted to explore the performance difference caused by the potential twist deformation between baseline blades and flexible blades. The balance was built in SaBre wind tunnel for measuring the thrust and torque of blades. The BEMT predictions of blades with varied twist were also performed in hover and forward flight, respectively. In hover,flexible blades cannot help in improving the FM at light disk loading since the twist generated on flexible blades is probably beyond the ideal hover twist. In forward flight, the propulsive efficiency η of flexible blades is mostly higher than baseline blades due to the beneficial twist generated in rotation. A Particle Image Velocimetry (PIV) approach of loads determination was developed based on control volume method to obtain thrust and torque of small-scale proprotor,especially for off-optimum conditions. The pressure Poisson equation was implemented for the pressure estimation based on the PIV velocity data. The axial velocity of flexible blades is found to be lower than baseline blades on the same station at downstream. This corresponds to the lower inflow ratio distribution along flexible blade, which results from the negative twist deformation. For both baseline blades and flexible blades, the thrust differences between PIV test 2 and balance are larger when compared to the differences between PIV test 1 based on nearfield and balance. The Laser Displacement Sensor (LDS) technique was employed for measuring the stationary deformation of rotating flexible blades. By obtaining the LDS point cloud, the bending and torsion of the rotating blade were identified using the multiple regressions
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Curto, Hugo. "Couplage de la stéréolithographie et du frittage par micro-ondes pour l'élaboration rapide de pièces céramiques en alumine et zircone." Thesis, Valenciennes, Université Polytechnique Hauts-de-France, 2020. http://www.theses.fr/2020UPHF0016.
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Ce travail de thèse porte sur l’élaboration rapide de pièces céramiques de formes complexes. L’alumine, la zircone, et les composites alumine-zircone présentent un vaste champ d’applications allant de la joaillerie au biomédical en passant par des applications thermostructurales. Afin d’élaborer rapidement des pièces, une approche couplant deux techniques est considérée : la stéréolithographie (SLA) pour la mise en forme des pièces par fabrication additive et le frittage par micro-ondes (MO) monomode pour la densification rapide des pièces. Dans cette optique, les massifs élaborés sont caractérisés tant du point de vue mécanique, que du point de vue microstructural. Dans ce contexte, trois études sont menées. La première porte sur l’alumine et met en évidence qu’un mélange de deux nuances de granulométries différentes est indispensable pour mener à bien le couplage des deux techniques. Dans la seconde étude, des pièces de zircone de grandes dimensions mises en forme par SLA sont frittées par MO dans un dispositif original, permettant le frittage de trois objets simultanément. Enfin, des composites mis en forme de manière conventionnelle (pressage) présentent des propriétés mécaniques supérieures lors du frittage par MO par rapport au frittage conventionnel. Ce travail montre que pour l’ensemble des matériaux étudiés : (i) le couplage des techniques mène à des propriétés similaires à celles obtenues après mise en forme et frittage conventionnels ; (ii) le frittage par MO permet un gain de temps allant jusqu’à 94% par rapport au frittage conventionnel ; (iii) les pièces mises en forme par SLA présentent des propriétés équivalentes à celles obtenues par mise en forme conventionnelleThis thesis work focuses on the rapid processing of complex-shaped ceramic parts. Alumina, zirconia, and alumina-zirconia composites have a wide range of applications from jewellery to biomedical and thermostructural applications. In order to process parts quickly, stereolithography (SLA) as a shaping method and single-mode microwave (MW) sintering for the densification of the parts are coupled. To improve the coupling, experimental parameters are set up and optimized after mechanical and microstructural characterizations. Within this framework, three main studies are conducted. The first study deals with alumina and highlights that a mix of two granulometry grades of alumina has to be used to achieve the coupling. In the second study, large-sized zirconia parts are shaped by SLA. An original device is used to realise the MW sintering of three samples simultaneously. Finally, alumina-zirconia composites are conventionally shaped (pressing) and exhibit higher mechanical properties when MW sintered, in comparison with conventional sintering. For all the investigated materials, this work shows that: (i) coupling SLA and MW sintering leads to similar properties than those obtained by conventional shaping and sintering. Moreover, this coupling permits to obtain pieces with complex geometry; (ii) MW sintering allows up to 94% timesaving process in comparison with conventional sintering; (iii) mechanical properties of SLA-shaped parts are close to those obtained after conventional shaping (pressing)
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Hamilton, Bruce Howard. "Study of damage evolutions in composite plates subjected to bending loads using micro-macro analysis." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA288523.
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Paul, Ewart D. "Micro-mechanical predictive modelling as an aid to CAD based analysis of composite sporting equipment." The University of Waikato, 2008. http://hdl.handle.net/10289/2509.
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The sport and leisure industry in New Zealand (NZ) has the potential to become a major user of composite materials. Given the size of NZ industry, design and manufacturing strategies based on virtual engineering should be developed to suit NZ requirements. Virtual methods use computer aided engineering capabilities to find faults, explore alternatives and optimise product performance before detailed design or prototyping. When doing computer aided simulation the required mechanical properties of individual reinforcement and matrix components are well documented. However, the mechanical properties of composite materials are not as simple to obtain. Micro-mechanical modelling could therefore be used to aid the design and development of composite equipment, where mechanical properties are unknown. In this study, solids modelling was used to produce an analog model of a composite, and it was found that it lead to reductions in file size and simulation time. Representing a composite with an analog model implies that the behavioural characteristics are modelled, but not the physical characteristics of the individual components. Three micro-mechanical models were developed to predict the flexural modulus of composite materials, based on perfect, partial and no adhesion. It was found that the partial adhesion model was both practical and consistently accurate. The partial adhesion model accounted for adhesion between components by considering an 'effective shear value' at the interface. Validation of the models was done by flexural testing injection moulded samples of glass, wood and carbon fibre reinforced polyethylene. It was shown that the adhesion coefficient range was 0.1 for carbon fibre, 0.5 for glass fibre and 0.9 for the wood fibre composites. It was concluded that the adhesion coefficient is crucial and it is recommended that further work is done to validate effective shear values by empirical means. The predicted flexural modulus values were used to enable finite element simulation of modelled analog beams as well as commercial kayak paddles. It was determined that accurate simulation is possible for composite equipment using the partial adhesion model.
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RamiÌrez, JimeÌnez Carlos Rafael. "Analysis of micro mechanical events in fiber reinforced composite materials by means of acoustic emissions." Thesis, University of Warwick, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441575.
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Bai, ShuLin. "Caractérisation mécanique d'un composite unidirectionnel fibres de verre-E/matrice époxyde élaboré sous micro-ondes." Châtenay-Malabry, Ecole centrale de Paris, 1993. http://www.theses.fr/1993ECAP0317.
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Le comportement mécanique d'une résine époxyde (DGEBA-3DCM) et d'un composite unidirectionnel fibres de verre-E/matrice époxyde a été étudié. Nous avons comparé l'élaboration sous micro-ondes et l'élaboration thermique de ces matériaux, et nous avons dégagé les résultats suivants: 1) en traction monotone, la résine élaborée sous micro-ondes montre une légère amélioration des propriétés mécaniques. Après le vieillissement dans l'eau, elle garde sa supériorité sur la résine réticulée thermiquement. Cette amélioration des propriétés mécaniques est attribuée à la plus grande homogénéité. La contrainte à rupture et le module augmentent avec la vitesse de sollicitation. 2) la présence de porosité plus importante dans le composite élaboré sous micro-ondes provoque la baisse des propriétés mécaniques globales. Il est apparu nécessaire de diminuer le taux de porosité en modifiant le processus d'élaboration (temps et pression). 3) par l'essai in situ sous MEB en traction transverse et en flexion 4 points sous appuis rapproches, l'interface fibre/matrice du composite élaboré sous micro-ondes apparait plus résistante en traction et en cisaillement. À l'aide d'un modèle développé en se basant sur la mécanique de la rupture, l'énergie surfacique de l'interface fibre/matrice apparait également plus grande pour le composite élaboré sous micro-ondes. 4) l'étude numérique et analytique montre que la fragmentation des fibres aura lieu préférentiellement a l'intérieur du composite en traction longitudinale. Lorsque des fibres sont rompues, le décollement de l'interface fibre/matrice démarre à la surface si la fraction volumique des fibres est élevée. Sinon, le résultat est inverse. La fragmentation des fibres conduit a une baisse du module du composite. Cette baisse est d'autant plus importante que les fibres sont courtes
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Greco, Pier Paolo. "Development of novel polymeric and composite nano-structured micro-porous materials for impact resistance applications." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2517.
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Impact resistant materials (IRMs) are widely used in the automotive and packaging industry. Their main purpose is the protection of the transported occupants or goods. Cellular materials as well as structures combine lightness with large deformation under load. The energy absorption mechanism is provided by limiting the peak load and ensuring the elastic deformation of the IRMs. Polymeric foams are largely used as IRMs due to their cellular structure. Prediction of the foam properties in terms of Young’s Modulus (Elastic Modulus) and the onset of Plateau Region can be related to the foam density and the mechanical properties of the bulk material (Gibson and Ashby model). The structure of the foam is only partly accounted for in the Gibson and Ashby model in terms of material density. However, it is possible to produce cellular materials with the same density but very different internal architectures. This cannot easily be exploited in conventional polymer foams but the processing of High Internal Phase Emulsion (PolyHIPE) and its polymerisation route to produce PolyHIPE Polymers (PHPs) can produce materials with very different structures. Experiments have revealed that the PHPs properties are dictated by their detailed structure. Elastic PHPs with: 1) varying ratio of polymerizable oil phase with respect to aqueous phase and 2) varying mixing time/energy input were produced and tested by mechanical compression at different temperatures and strain rates. The elastic modulus increases with a quadratic law as a function of the polymerizable oil phase content of the HIPE when the mixing time is the same, as predicted by the model. The Specific Absorption Energy (SAE), represented by the area under the stress-strain curve, increases in a similar way. Increasing mixing time on HIPE has the effect of modifying the cellular structure. Smaller pores and narrower distribution of pores are observed. Such features are consistent for any set of PHPs densities and represent a design tool when some specific mechanical characteristics are prescribed. The assessment of process-structure-properties relationships was performed by combining the mechanical response of the various PHPs with the imaging of their structure by Scanning Electron Microscopy. The properties of PHPs were benchmarked with reference to two commercially available products. One material is characterised by a porous structure with a relatively high Young’s Modulus while the other by a non-porous and composite-like solid structure with lower elastic modulus. The properties of the PHPs can be engineered to shift from a foam-like material to a composite-like through the processing parameters which in turn modify the material porous structure. The temperature has very limited effect on the PHPs material unlike for the reference commercial materials. The enhancement of properties (increasing Elastic Modulus and SAE) induced by changing the processing route are remarkable for such a class of porous materials. When plotted on a Modulus-Density chart, the PHPs fill an existing material-chart gap, representing a new class of materials and opening new possibilities as IRMs.
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Calard, Vincent. "APPROCHES STATISTIQUES - PROBABILISTES DU COMPORTEMENT MÉCANIQUE DES COMPOSITES À MATRICE CÉRAMIQUE." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1998. http://tel.archives-ouvertes.fr/tel-00003071.
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Des approches statistiques-probabilites du comportement mécanique des composites à matrice céramique, fondées sur la description des phénomènes stochastiques à l'origine de la fragmentation matricielle et de la rupture ultime, ont été développées. Elles ont été appliquées à des composites unidirectionnels et tissés de type SiC/SiC. Elles ont permis de calculer le comportement mécanique et la rupture en traction et en flexion. L'approche de la fragmentation matricielle repose sur l'analyse des populations de défauts qui provoquent cette fragmentation. Dans le cas des composites unidirectionnels étudiés, une seule population est suffisante pour calculer le comportement. Pour les composites tissés étudiés, trois populations de défauts caractérisent le processus de fissuration. En ce qui concerne la rupture, une classification, fondée sur les effets de volumes et les ruptures successives d'éprouvettes en traction, permet de définir convenablement le choix du critère probabiliste de rupture (Weibull, Ergodique ...). Ainsi le caractère ergodique de la rupture d'un composite tissé SiC/SiC a été mis en évidence et vérifié sur des essais de flexion 3 points et 4 points.
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Mallikarachchi, H. M. Yasitha Chinthaka. "Thin-walled composite deployable booms with tape-spring hinges." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/239395.
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Deployable structures made from ultra-thin composite materials can be folded elastically and are able to self-deploy by releasing the stored strain energy. Their lightness, low cost due to smaller number of components, and friction insensitive behaviour are key attractions for space applications. This dissertation presents a design methodology for lightweight composite booms with multiple tape-spring hinges. The whole process of folding and deployment of the tape-spring hinges under both quasi-static and dynamic loading has been captured in detail through finite element simulations, starting from a micro-mechanical model of the laminate based on the measured geometry and elastic properties of the woven tows. A stress-resultant based six-dimensional failure criterion has been developed for checking if the structure would be damaged. A detailed study of the quasi-static folding and deployment of a tape-spring hinge made from a two-ply plain-weave laminate of carbon-fibre reinforced plastic has been carried out. A particular version of this hinge was constructed and its moment-rotation profile during quasi-static deployment was measured. Folding and deployment simulations of the tape-spring hinge were carried out with the commercial finite element package Abaqus/Explicit, starting from the as-built, unstrained structure. The folding simulation includes the effects of pinching the hinge in the middle to reduce the peak moment required to fold it. The deployment simulation fully captures both the steady-state moment part of the deployment and the final snap back to the deployed configuration. An alternative simulation without pinching the hinge provides an estimate of the maximum moment that could be carried by the hinge during operation. This moment is about double the snap-back moment for the particular hinge design that was considered. The dynamic deployment of a tape-spring hinge boom has been studied both experimentally and by means of detailed finite-element simulations. It has been shown that the deployment of the boom can be divided into three phases: deployment; latching, which may involve buckling of the tape springs and large rotations of the boom; and vibration of the boom in the latched configuration. The second phase is the most critical as the boom can fold backwards and hence interfere with other spacecraft components. A geometric optimisation study was carried out by parameterising the slot geometry in terms of slot length, width and end circle diameter. The stress-resultant based failure criterion was then used to analyse the safety of the structure. The optimisation study was focused on finding a hinge design that can be folded 180 degrees with the shortest possible slot length. Simulations have shown that the strains can be significantly reduced by allowing the end cross-sections to deform freely. Based on the simulations a failure-critical design and a failure-safe design were selected and experimentally verified. The failure-safe optimised design is six times stiffer in torsion, twice stiffer axially and stores two and a half times more strain energy than the previously considered design. Finally, an example of designing a 1 m long self-deployable boom that could be folded around a spacecraft has been presented. The safety of this two-hinge boom has been evaluated during both stowage and dynamic deployment. A safe design that latches without any overshoot was selected and validated by a dynamic deployment experiment.
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SANTOS, THAIS da S. "Micro-nanocompósitos de Al2O3/ NbC/ WC e Al2O3/ NbC/ TaC." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/23599.
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Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Joesbury, Adam Michael. "New approaches to composite metal joining." Thesis, Cranfield University, 2015. http://dspace.lib.cranfield.ac.uk/handle/1826/10009.
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This thesis explores new methods for achieving load-carrying joints between the dissimilar materials of continuous fibre reinforced polymer matrix composites and structural metals. The new composite-to-metal joining methods investigated in this work exploit the metal-to-metal joining techniques of arc micro-welding, resistance spot welding, and metal filler brazing, to form novel micro-architectured metal adherends that can be used for enhanced composite-to-metal joining. Through a combination of equipment instrumentation and metallographic inspection of fabricated prototype joints, understanding is gained of how materials respond when processed by manufacturing techniques that have not previously been exploited for dissimilar material joining. Mechanical testing of prototype joints; both to ultimate loading strength and partial failure states, with subsequent inspection of specimens and comparative performances evaluation enabled joining performance characterisation of the new joining methods. Key results include: the identification of micropin reinforced adhesive joints to exhibit pseudo-ductile failure characteristics, resistance spot weld reinforcement of adhesive joints to boost bonding performance, and the use of a polymer infused metal foam to overcome difficulties of thermoplastic to metal adhesion. Through this work knowledge of how novel micro-architectures reacted under mechanical loading enabled insights to be gained into how perceived manufacturing defects can benefit joining performance. Such examples include, localised material weakness that lead to global pseudo-ductile failure behaviour, and low-strength secondary joining mechanisms boosting primary load transfer systems. By comparison of the diverse joining methods investigated in this work, trends were identified that suggest joining performance between the two dissimilar materials is improved by increasing the direct interaction between the composite reinforcement fibres and the metal structure. It is demonstrated that joining improvements are gained by forming mechanical connections between metals and composite precursory material before the final manufacturing process of the composite.
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Thayer, Patrick Scott. "Strategies for the Fabrication of Cellularized Micro-Fiber/Hydrogel Composites for Ligament Tissue Engineering." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/78209.
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Partial or complete tears of the anterior cruciate ligament (ACL) can greatly afflict quality of life and often require surgical reconstruction with autograft or allograft tissue to restore native knee biomechanical function. However, limitations exist with these treatments that include donor site pain and weakness found with autografts, and longer "ligamentization" and integration times due to the devitalization of allograft tissue. Alternatively, a tissue engineering approach has been proposed for the fabrication of patient-specific grafts that can more rapidly and completely heal after ACL reconstruction. Electrospun micro-fiber networks have been widely utilized as biomaterial scaffolds to support the growth and differentiation of mesenchymal stem cells toward many tissue lineages including ligament. However, these micro-fiber networks do not possess suitable sizes and shapes for a ligament application and cannot support cell infiltration. The objective of this work was to develop techniques to 1) rapidly cellularize micro-fiber networks, 2) assemble micro-fiber networks into cylindrical composites, 3) provide cues to mesenchymal stem cells (MSCs) to guide their differentiation toward a ligament phenotype.
The cellularization of micro-fiber networks was performed utilizing a co-electrospinning/electrospraying technique. Cells deposited within a cell culture medium solution remained where they were deposited and did not proliferate. The inclusion of space-filling hydrogel network such as collagen was necessary to reduce the density of the micro-fiber network to facilitate spreading. However, it became apparent that the incorporation of significant collagen phase was necessary for long-term MSC survival within the micro-fiber network. Next, two approaches were developed to fabricate large cylindrical, composites. The first approach utilized a co-electrospinning/electrospraying technique to generate micro-fiber/collagen composites that were subsequently rolled into cylinders. These cylindrical composites exhibited greater diameters and water weight percentages as collagen content increased. However, the high micro-fiber content of these composites was inhibitory to cell survival. In the second approach, thin layers (~5-10 fibers) of aligned electrospun PEUR fibers were encapsulated within a collagen gel and subsequently rolled the composites into cylinders. These sparse-fiber composites were nearly 98% by weight water and confocal imaging revealed the presence of sparse fiber layers (~5 fibers thick) separated by approximately 200 μm thick collagen layers. We hypothesize that the proliferation and migration of MSCs within these micro-fiber/collagen composites may not be restricted by the presence of a dense, non-manipulatable electrospun fiber network present in traditionally rolled fiber composites.
Simple model platforms were then developed to study the influence of sparse micro-fibers on MSCs differentiation within a collagen hydrogel. MSCs in the presence of the softest (5.6 MPa) micro-fibers elongated and oriented to the underlying network and exhibited greater expression of scleraxis, and α-smooth muscle actin compared to the stiffest (31 MPa) fibers. Additionally, preliminary results revealed that the incorporation of fibroblast growth factor-2 and growth and differentiation factor-5 onto micro-fibers through chemical conjugation enhanced expression of the ligamentous markers collagen I, scleraxis, and tenomodulin.
In conclusion, micro-fiber/collagen composite materials must possess sufficient space to support the infiltration and differentiation of MSCs. The strategies described in this document could be combined to fabricate large, micro-fiber/collagen composites that can support cell infiltration and provide relevant cues to guide the formation of an engineered ligament tissue.Ph. D.
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Imbaby, Mohamed. "Fabrication of 316-L stainless steel and composite micro machine components using softlithography and powder metallurgy process." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/1212/.
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This thesis presents a new approach to fabricate high precision micro machine components from stainless steel and stainless steel ceramic composite materials, using Softlithography and powder metallurgy processes. Three different 316-L stainless steel powders, including 5, 10 and 16 μm in size, and two different ceramics powders, including 400 nm alumina and 320 nm titania, were tested. The PhD research process can be divided into three main stages. In the first stage, high quality SU-8 master moulds and their negative replicas soft moulds are produced using Softlithography technique. The second stage includes preparing the stainless steel slurries, filling the soft micro moulds, obtaining the green micro components, de-binding and sintering. In the third stage, the fabrication process has been developed further to produce stainless steel-ceramic composite micro components. Fabrication process in each stage was investigated in detail and the optimum properties were produced. Dispersant acrylic-based binder is adopted in this research successfully in producing damage-free green micro components. A cold isostatic pressing technique is also adopted to improve the densities and linear shrinkages of the stainless steel green and sintered micro components. A new mixing method is used to improve the homogeneity of the ceramic inclusions in the stainless steel matrix of the composite micro components. Characterization of the sintered stainless steel and composite micro components in terms of shape retention, density, linear shrinkage, internal structure, hardness and surface roughness were investigated in detail. The resultant stainless steel and composite micro components retain the same high geometric quality as the SU-8 master moulds.
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Elbishari, Haitham Idris. "Characterisation of the effect of filler size on handling, mechanical and surface properties of resin composites." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/characterisation-of-the-effect-of-filler-size-on-handling-mechanical-and-surface-properties-of-resin-composites(64a8b96f-1cd0-459c-9865-1c5f35567982).html.
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Resin composites have been in the dental field for over forty years. They are now thought to be the most commonly used restorative material due to their aesthetic and mechanical properties. Although resin composites have high success rates as restorations, they do not offer all properties of an ideal restorative material. The aims of this research were to characterise the effects of variation in resin composite formulation on handling, mechanical; and physical properties. In particular the influence of the size and distribution of the inorganic components was investigated through the study of experimental formulations. Packing stress and viscosity were assessed with pentrometer principle at two different temperatures (23 and 37 ºC). It was found that filler size was strongly correlated with both packing stress and viscosity. Additionally, temperature has a dominant effect on packing stress and viscosity. Micro computed tomography [μCT] was used to investigate percentage of voids [% voids] in 3D dimensions. It was found that smaller filler size incorporated less % voids. In contrast filler size and disruption had a little effect on fracture toughness of resin composites. 3D surface topography was used to investigate the surface roughness before and after tooth brush abrasion. It was found filler size had a significant influence in both gloss retention and surface roughness (smaller filler size exhibited higher surface gloss). Finally, the effect of different storage media (distilled water, Coca Cola and red wine) on colour stability and gloss were investigated. It was found that dietary habits effect discolouration of resin composite restorations with the acidic drinks caused more staining.
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Beguinel, Johanna. "Interfacial adhesion in continuous fiber reinforced thermoplastic composites : from micro-scale to macro-scale." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI051.
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L’intérêt croissant de l’industrie pour les matériaux composites thermoplastiques est motivé par leurs propriétés de thermoformabilité, de recyclabilité ainsi que leurs capacités de cadences de production élevées. Le développement de matériaux pré-imprégnés thermoplastiques, apparus dès les années 1980, s’est imposé comme un moyen efficace de contourner les fortes viscosités des polymères utilisés en réduisant la distance d’écoulement des polymères à l’état « fondu ». Cette étude s’est plus particulièrement intéressée au développement de composites à base de tissus de verre et de carbone pré-imprégnés par un latex acrylique, le TPREG I. En outre, les propriétés mécaniques élevées des matrices acryliques, alliées à un coût relativement faible, en font un matériau intéressant, de nature à permettre un saut technologique dans la conception et la fabrication de composites structuraux à matrice organique. Notre étude s’est concentrée sur la mesure de l’adhésion à l’interface fibre/matrice acrylique car cette région est au cœur du transfert de charge de la matrice vers les fibres et conditionne donc les propriétés mécaniques du composite. Nous avons choisi d’évaluer l’adhésion interfaciale en combinant des analyses de mouilllage avec des tests mécaniques aux échelles microscopique et macroscopique. Le test micromécanique de la microgoutte permet de mettre en évidence le rôle central de l’ensimage des fibres sur la contrainte de cisaillement interfaciale. L’adhésion thermodynamique, déterminé par des mesures d’énergie de surface, est en accord avec la contrainte de cisaillement et souligne l’influence de la polarité de l’ensimage. A l’échelle macroscopique, les essais de traction hors-axe sur composites unidirectionnels permettant de solliciter l’interface en cisaillement quasi-plan ont mis en exergue une corrélation entre les échelles micro et macro. L’étude a également permis de dégager une forte augmentation de l’adhésion grâce à une modification de la matrice acrylique, ainsi qu’une dégradation des propriétés interfaciales à l’échelle micro par vieillissement hydrolytique. Cette étude constitue une première base de données concernant les propriétés interfaciales de composites thermoplastiques acryliques et démontre l’importance d’une étude multi-échelles dans la conception de nouveaux compositesThe present study was initiated by the development of a new processing route, i.e. latex-dip impregnation, for thermoplastic (TP) acrylic semi-finished materials. The composites resulting from thermocompression of TPREG I plies were studied by focusing of interfacial adhesion. Indeed the fiber/matrix interface governs the stress transfer from matrix to fibers. Thus, a multi-scale analysis of acrylic matrix/fiber interfaces was conducted by considering microcomposites, as models for fiber-based composites, and unidirectional (UD)macro-composites. The study displayed various types of sized glass and carbon fibers. On one hand, the correlation between thermodynamic adhesion and practical adhesion, resulting from micromechanical testing, is discussed by highlighting the role of the physico-chemistry of the created interphase. Wetting and thermodynamical adhesion are driven by the polarity of the film former of the sizing. On the other hand, in-plane shear modulus values from off-axis tensile test results on UD composites are consistent with the quantitative analyses of the interfacial shear strength obtained from microcomposites. More specifically, both tests have enabled a differentiation of interface properties based on the fiber sizing nature for glass and carbon fiber-reinforced (micro-)composites. The study of overall mechanical and interface properties of glass and carbon fiber/acrylic composites revealed the need for tailoring interfacial adhesion. Modifications of the matrix led to successful increases of interfacial adhesion in glass fiber/acrylic composites. An additional hygrothermal ageing study evidenced a significant loss of interfacial shear strength at micro-scale which was not observed for UD composites. The results of this study are a first step towards a database of relevant interface properties of structural TP composites. Finally, the analyses of interfaces/phases at different scales demonstrate the importance of a multi-scale approach to tailor the final properties of composite parts
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Ali, Mohamed. "Calcul statique et dynamique par elements finis sur micro-ordinateurs de structures composites et metalliques." Paris 6, 1986. http://www.theses.fr/1986PA066443.
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L'objectif du present travail est d'etudier et de mettre au point un code de calcul de structures par elements finis sur micro-ordinateurs. Ce code est essentiellement constitue de deux programmes : a) un programme de modelisation de plaques composites generales, b) un programme de resolution statique et dynamique. Dans cette etude, la theorie des plaques de mindlin, qui tient compte des effets du cisaillement transverse, est adoptee. L'element quadratique lagrangien isoparametrique tridimensionnel degenere et base sur cette theorie nous servira comme element de base. Notre code permet d'aborder une large variete de plaques (isotropes, stratifiees et sandwiches) dans des cas de chargement tres vastes (membrane ou flexion pure, cas du couplage membrane-flexion). L'assemblage et la resolution reposent sur une methode par blocs avec stockage sur disquettes des grands tableaux et des matrices globales ; car la capacite reduite de la memoire centrale des micro-ordinateurs impose une utilisation permanente des memoires de masse. L'elimination de gauss (dans la resolution statique) et la methode d'iteration sur sous-espace (dans le cas dynamique) ont ete developpees pour traiter des systemes lineaires stockes en memoire de masse par schemas hypermatriciels. A la fin de notre etude, plusieurs tests numeriques sur des plaques isotropes et composites ont ete effectues. Ils concernent la convergence des fleches maximales (pour des plaques en flexion statique) et la convergence des valeurs propres (pour des plaques en vibration libre). Les resultats obtenus sont compares avec des solutions theoriques, numeriques et experimentales existant dans la litterature; nos resultats sont en bonne concordance avec elles
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Ladj, Rachid. "Elaboration de nanoparticule composite à propriétés optiques non-linéaires pour applications biomédicales." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENA032.
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Des marqueurs biologiques exogènes à base de nanoparticules hybrides possédant des propriétés optiques non-linéaires ont été préparés en tant qu'agent de contraste pour l'imagerie de second harmonique et le diagnostic de cellules pathogènes. L'iodate de fer est l'un des matériaux proposés dans ce domaine en raison de ses bonnes propriétés de second harmonique et de sa faible toxicité. Des nanoparticules d'iodate de fer ont été synthétisées par microémulsion inverse et miniémulsion inverse. Un bon contrôle de taille et de morphologie des particules a été obtenu dans les deux cas. En vue d'applications biomédicales, l'encapsulation des particules a été réalisée in situ par polymérisation en miniémulsion inverse. Enfin, l'encapsulation de particules de niobate de potassium par un polymère biocompatible a été étudiée. L'intérêt de ces particules hybrides a été démontré par des études in vitro en imagerie de second harmoniqueExogenous biomarkers based on hybrid nanoparticles with nonlinear optical properties were prepared as a contrast agent for second harmonic imaging and diagnosis of pathogenic cells. Iron iodate is one of the selected materials for this specific field due to its good second harmonic properties and its low toxicity. Iron iodate nanoparticles were synthesized by inverse microemulsion and inverse miniemulsion. In both cases, a good control of size and morphology was achieved. For biomedical applications, nanoparticles encapsulation was carried out in situ by reverse miniemulsion polymerization. Finally, encapsulation of potassium niobate nanoparticles with a biocompatible polymer was conducted. Their interest was demonstrated in vitro by second harmonic imaging studies
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Ulhôa, Michele Paoline de Marins [UNESP]. "Desgaste abrasivo e dureza de seis resinas compostas expostas a diferentes tempos de fotopolimerização com aparelhos de LED e lâmpada incandescente." Universidade Estadual Paulista (UNESP), 2006. http://hdl.handle.net/11449/88482.
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A Humanidade, ao buscar as melhoras nas suas condições de vida, vem desenvolvendo materiais capazes de reparar e melhorar imperfeições naturais e acidentais. Encontra nas resinas compostas, constantemente utilizadas por dentistas, uma maneira de reparar imperfeições e perdas de materiais dentários no ser humano. A escolha de resinas compostas em substituição aos antigos materiais de restauração, como o amálgama, se dá pelo fato de serem fáceis de preparar, apresentarem menor desgaste, serem praticamente imperceptíveis após sua aplicação devido à grande quantidade de cores fornecidas pelos fabricantes. Porém não apresentam desgaste semelhante ao do esmalte dentário, sendo necessária substituição com o passar do tempo, devido ao desgaste abrasivo. Dentre os vários fatores determinantes do processo de desgaste abrasivo, encontram-se, genericamente, as características da própria resina e do preparo cavitário, assim como da restauração confeccionada e das condições das agressões a que ela for submetida. Para fazer a medição da resistência ao desgaste abrasivo, utilizou-se o método do disco retificado aperfeiçoado para Odontologia (COELHO, 1991; BIANCHI et al., 2002). É utilizado um banco de ensaios onde um disco dinâmico revestido com porcelana desgasta um disco estático revetido com a resina polimerizada em um tempo pré-estabelecido...
Humanity, when searching for a better life conditions, is developing materials capable to repair and to improve natural and accidental imperfections. It finds in composite resins, constantly used for dentists, a way to repair imperfections and losses of human dental material. The composed resin choice in substituion to the old restoration materials, as the amalgamates, it is for the fact of being easy to prepare, to present less wear, to be practically invisible after its application due to great amount of colors supplied for the manufacturers. However they do not show similar wear as the dental enamel, being necessary the substitution after a while, due to the abrasive wear. Among some determinative factors of the process of abrasive wear, there are, generically, the characteristics of the resin and the cavitary preparation, as well as the confectioned restoration and the conditions of the aggressions that it is submitted. To make the measurement of the resistance to the abrasive wear, the method of the rectified circular surface improved for odontology was used (COELHO, 1991; BIANCHI et al., 2002). A Test bench is used where a dynamic circular surface covered with porcelain consumes a static circular surface covered with the polymerized resin in a pre-established time... (Complete abstract, click electronic address below)
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Siron, Olivier. "Approche micro-macro du comportement mécanique et de la rupture d'un composite carbone-carbone à architecture fibreuse multidirectionnelle." Bordeaux 1, 1996. http://www.theses.fr/1996BOR10609.
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Les relations entre le comportement mecanique non lineaire, les mecanismes d'endommagement et la texture de renfort, ont ete etudiees pour un composite carbone-carbone 2. 5d. L'endommagement de la matrice a ete suivi lors des essais de traction uniaxiale et de cisaillement (iosipescu) grace a un microscope optique monte sur la machine de traction. Un modele macroscopique du comportement mecanique est propose en fonction des caracteristiques des modes d'endommagement. La rupture est analysee a differentes echelles
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Recman, Lukáš. "Deformační chování nano/mikro vyztuženého PMMA." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2010. http://www.nusl.cz/ntk/nusl-233297.
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Práce sleduje vliv velikosti částic na elastický modul a deformační chování za mezí kluzu. Bylo pozorováno, že jak elastická oblast, tak oblast za mezí kluzu ukazuje silnou závislost chování na velikosti částic. Cílem této práce je korelovat experimentální data a teoretické předpoklady které bylo odvozeny pro deformační chování v elastické oblasti a v oblasti za mezí kluzu pro amorfní polymery a konkrétně pro PMMA. Vše je motivováno propojit zatím oddělené oblasti kontinuální mikromechaniky a diskrétní nanomechaniky. Deformační chovaní PMMA plněného nano a mikro plnivem bylo pozorováno v elastické a plastické oblasti. Byl zkoumán vliv velikosti částic na velikost modulu a deformačního zpevnění. Mechanizmus vyztužení je interpretován s použitím teorie imobilizace řetězců, nanočástice mají silný vliv na molekulární dynamiku a kinetiku zapletenin. Mým příspěvkem k tomuto tématu je ukázat výraznou závislost na mechanizmu vyztužení v závislosti na velikosti částic. A to jak pod teplotou skelného přechodu tak nad teplotou skelného přechodu. Ačkoli pro velikost modulu byla publikována značná množství dat, která byla následně i interpretována, vliv částic na deformační zpevnění je poskrovnu. Během elastické deformace je primární struktura materiálu neměnná, jedná se o elastickou deformaci, za mezí kluzu již toto neplatí a primární struktura je zde nevratně poškozena. Bylo ukázáno, že obsah nano částic vede ke zvýšení meze kluzu a vyššímu deformačnímu zpevnění. Tento nárůst deformačního zpevnění je v korelaci s Guth-Gold rovnicí. Je předpokládáno, že nanočástice slouží jako další fyzikální zapleteniny a vedou k fyzikálně více zapletenému systému. Stejný efekt jako v elastické oblast tj. vliv velikosti částic na modul, byla pozorována i během deformačního zpevnění.
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Tchangoulian, Ardaches. "Utilisation de matériaux composites magnétiques à nanoparticules pour la réalisation de composants passifs non réciproques micro-ondes." Thesis, Saint-Etienne, 2014. http://www.theses.fr/2014STET4016/document.
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Dans les systèmes des télécommunications, beaucoup d’études ont été entreprises pour intégrer des composants passifs non réciproques. Le bon fonctionnement des circulateurs exige souvent des aimants volumineux et lourds qui assurent une orientation uniforme des moments magnétiques du matériau ferrite. Pour tendre vers l’intégration et la miniaturisation des circulateurs, les nanotechnologies peuvent offrir des solutions intéressantes. L’objectif de cette thèse a été de développer un circulateur coplanaire auto-polarisé. L'approche choisie est fondée sur la réalisation de substrats composites à «nano-fil ferrimagnétiques». Elle consiste à faire un dépôt par magnétophorèse ou dip-coating de nanoparticules de ferrite de cobalt dans des membranes d’alumine poreuses et de les orienter sous champ magnétique de manière uniforme. Des substrats composites magnétiques ont été fabriqués à partir de nanoparticules CoFe2O4 dispersées dans une matrice sol-gel de silice en utilisant la technique de Dip-coating avec et sans un champ magnétique appliqué. De nombreuses études ont été faites afin d'étudier le comportement magnétique et diélectrique de ces substrats : VSM, polarimétrie spectrale, MFM et autres. Les cycles d'hystérésis montrent une forte différence des valeurs des champs coercitifs (μ0Hc) et rémanents (Mr/Ms) si, durant la fabrication, un champ magnétique est appliqué ou non, démontrant ainsi l'orientation (ou non) des nanoparticules. Ce nano-composite est un candidat intéressant pour la fabrication de circulateurs même si la concentration et l’orientation des particules sont insuffisantes. Des circulateurs ont été conçus, modélisés et simulés à l'aide du logiciel HFSS. Suite à des résultats de simulation intéressants; un premier prototype a été fabriqué et caractérisé en hautes fréquences. Les résultats de mesure ont montré un phénomène de circulation, qui reste très faible en raison du faible pourcentage de nanoparticules magnétiques dans le composite et de leur orientation imparfaite. Les verrous technologiques ont été clairement identifiés et ne permettent pas, pour l’instant, de réaliser un circulateur opérationnelIn telecommunications systems, many studies have been undertaken to integrate non-reciprocal passive components. The proper functioning of circulators often requires large and heavy magnets that ensure a uniform orientation of the magnetic moments of the ferrite material. To work towards the integration and miniaturization of circulators, nanotechnology can offer interesting solutions. The aim of this thesis was to develop a self-biased coplanar circulator. The approach is based on the production of composite substrates "ferrimagnetic nanowire." It consists in a magnetophoresis or a dip-coating deposition of cobalt ferrite nanoparticles in porous alumina membranes and orienting them in a magnetic field uniformly. Magnetic composite substrates were made from CoFe2O4 nanoparticles dispersed in a matrix of silica sol-gel using the dip-coating technique with and without an applied magnetic field. Many studies have been made to study the magnetic and dielectric behavior of these substrates: VSM, spectral polarimetry, MFM and others. The hysteresis loops show a strong difference in the values of coercive fields (μ0Hc) and persistent (Mr / Ms) if, during the fabrication, a magnetic field is applied or not, therefore showing the orientation (or not) of nanoparticles. This nano-composite is an interesting candidate for the fabrication of circulators even if the concentration and the particle orientation are insufficient. Circulators were designed, modeled and simulated using the HFSS software. Following the interesting results of simulation; a first prototype was fabricated and characterized at high frequencies. The measurement results showed a circulation phenomenon, which is very low due to the small percentage of magnetic nanoparticles in the composite and their imperfect orientation. Technological barriers have been clearly identified and do not allow for the time to achieve an operational circulator
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Ha, Hung M. "Micro- and Nano-Scale Corrosion in Iron-Based Bulk Metallic Glass Sam 1651 and Silver-cored MP35N Lt Composite." Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1260391940.
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Jordan, Jeff. "Composites at micro- and nano-scale and a new approach to the problem of a concentrated force on a half-plane." Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/16431.
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Pinelli, Marília de Morais. "Evaluation of changes in surface roughness and chemical composition of the composite and bovine enamel submitted different surface treatments." Universidade de Taubaté, 2009. http://www.bdtd.unitau.br/tedesimplificado/tde_busca/arquivo.php?codArquivo=444.
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Objectives: To evaluate qualitatively and quantitatively changes in the surface and chemical composition of bovine enamel and composite, using hydrogen peroxide 38% when submitted to different surface treatments. Method: It was used 120 fragments from the tooth surface of bovine incisors, and in one half was prepared and a standard cavity restored with composite. Subsequently, the specimens were submitted to thirty hundreds brushing cycles, immersion in two different drinks: orange juice (Del Valle ), Whiskey (Johnnie Walker ), and last session of bleaching with hydrogen peroxide 38%. The surface changes and mineral composition of enamel and composite was determined using a superficial roughness and by Micro-Fluorensce X-ray Dispersion Energy before and after treatments. Dada were statiscally tabulated and analyzed. Calcium and Fhosphorum relative amounts and Zirconium and Silica were measured on enamel and resin composite, respectively. Results: The results showed significant difference when compared to the control group and treatment group. Conclusion: It was concluded that all bleaching alone does not cause surface changes and loss of chemical components in both the enamel and composite resin; brushing significantly increased surface roughness of the composite and enamel, comparing the initial and final time, the Association of brushing with whitening enhances the effects of surface changes and chemical composition in both the enamel and the resin.Objetivos: Avaliar qualitativamente e quantitativamente as alterações na superfície e composição química do esmalte dental bovino e compósito nanoparticulado, utilizando peróxido de hidrogênio 38% quando submetidos a diferentes tratamentos superficiais. Método: Foram utilizados 120 fragmentos da superfície dental de incisivos bovinos, sendo que em uma das metades foi preparado uma cavidade padronizada e restaurada com compósito. Posteriormente, os espécimes foram submetidos a trinta mil ciclos de escovação, imersão em duas diferentes bebidas: Suco de laranja (Del Valle), Uísque (Johnnie Walker) e finalmente, sessão de clareamento com peróxido de hidrogênio 38%. As alterações superficiais e a composição mineral do esmalte e compósito foram determinadas com a utilização do rugosímetro e por meio de Micro-fluorescência de raios-x por energia dispersiva antes e após os tratamentos. Os dados obtidos foram tabulados e submetidos a análise estatística. Foram avaliados os teores de Cálcio e Fósforo no esmalte e de Zircônia e Sílica no compósito. Resultados: Os resultados mostraram diferença significativa quando comparado grupo controle e grupo tratamento. Conclusão: Concluiu-se que, o clareamento dental isoladamente não causa alterações superficiais e perda de componentes químicos tanto no esmalte quanto na resina composta; a escovação aumenta significativamente a rugosidade superficial do compósito e do esmalte, comparando-se tempos iniciais e finais; a associação da escovação com clareamento potencializa os efeitos de alterações superficiais e composição química tanto no esmalte quanto na resina; o uso de bebidas com baixo pH causa alterações superficiais e na composição do esmalte e do compósito.
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Laisney, Jérôme. "Influence de l’environnement sur la commutation et la bistabilité thermique de micro- et de nanoparticules à transition de spin." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112002.
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Les composés à transition de spin forment une classe spécifique de matériaux pour lesquels la commutation de l’état de spin du centre métallique peut être pilotée par divers stimuli (T, P, irradiation lumineuse, …) et s’accompagne de changements remarquables des propriétés physiques (magnétiques, optiques, structurales ou encore vibrationnelles). Ils se distinguent des autres matériaux commutables par l’observation, pour un certain nombre d’entre eux, de processus coopératifs à l’état solide, donnant lieu à l’ouverture d’une hystérèse thermique (bistabilité) particulièrement intéressante pour le stockage de l’information. Un des challenges technologiques actuels est de réduire la taille des matériaux susceptibles d’application et de les mettre en forme au sein de dispositifs sans altérer pour autant leurs propriétés. Les objectifs de la thèse ont été d’élaborer des micro- et nanoparticules à conversion de spin à partir de composés moléculaires présentant une transition de spin du premier ordre à l’état massif, puis d’étudier et analyser l’influence de la taille et de la matrice dispersante sur les processus de transition de spin. Après un premier chapitre introductif portant sur les matériaux à transition de spin, les méthodes de nanochimie et de mise en forme, le deuxième chapitre décrit l’élaboration de particules des composés FeII(phen)2(NCX)2 (X = S, Se) et [FeIII(3-OMeSalRen)2]PF6 (R = Me, Et). Comme la technique de précipitation rapide convient pour des composés ioniques, son application à FeII(phen)2(NCX)2 composé neutre, a nécessité la mise au point d’une synthèse indirecte de particules, basée sur l’extraction de ligand de précurseurs solubles, et le contrôle via des paramètres expérimentaux, des étapes de nucléation-croissance. De nouvelles particules de composés ioniques de Fe(III) [FeIII(3-OMeSalRen)2]PF6 (R = Me, Et) et des films minces contenant ces particules dispersées dans un polymère (PVP) ont été préparées. Les études magnétique et optique de ces films montrent que la matrice et la mise en forme modifient toujours les caractéristiques de la transition de spin des particules.La deuxième partie des travaux a été consacrée à l’étude des effets d’environnement. L’interaction entre des microparticules de Fe(phen)2(NCS)2 et des matrices vitreuses (Tg > T1/2; T1/2, étant la température de transition) peut conduire à l’ouverture d’un large cycle d’hystérésis, déplacé vers les plus basses températures. Cette zone de bistabilité a été examinée à l’aide de la méthode FORC (First-Order Reversal Curves). L’analyse a permis d’établir l’existence de composantes réversibles attribuées aux interactions élastiques à l’interface matrice/particule et au changement de volume de la particule à transition de spin.L’étude des effets de matrice et de taille a été poursuivie avec des micro- et nanocristaux de [FeIII(3-OMeSalEen2]PF6 dispersés dans des polymères ou des liquides moléculaires formant des verres à basse température. L’encapsulation dans des verres rigides de particules haut-spin (T1/2 < Tg) ou bas-spin (T1/2 > Tg) donnent lieu à des conversions de spin déplacées respectivement vers les plus basses ou plus hautes températures, éventuellement des processus coopératifs avec hystérésis. Le renforcement de la coopérativité et la bistabilité observées dans le second cas ont été interprétés comme résultant des contraintes mécaniques vis-à-vis du changement de volume BS-HS de la particule. Enfin, le changement d’état de la matrice induit par des étapes de trempe (ou recuit) en-dessous (au-dessus) de la température de transition vitreuse, a été exploité pour moduler ces effets. Dans la perspective d’une application, de nouvelles études de composites ont été engagées avec des complexes présentant une transition de spin proche de la température ambiante. Le choix de la matrice dispersante selon certains critères (nature chimique, température de transition vitreuse) a permis de retrouver certains effetsSpin-transition compounds are a class of materials for which the spin-state switching of the metal center can be controlled by various stimuli (T, P, light irradiation,...) and produces dramatic changes of physical properties (magnetic, optical, structural or vibrational). With respect to the set of switchable materials, a number of spin-transition compounds exhibit at solid-state cooperative processes and thermal hysteresis loops (bistability), particularly suitable for information storage. One of the current technological challenges is to integrate in devices such potentially interesting materials without altering their properties. The goal of the research, recently developed by several teams, is to determine the smaller size of object in which an information can be stored, and thus to understand the effect of downsizing on cooperativity and bistability. Therefore, the objectives of the Ph-D thesis were (i) to synthesize spin-crossover nano- and microparticles from molecular materials that in the form of bulk undergo a first-order phase transition; (ii), to investigate the importance of particles size and matrix effects on the spin-transition process.After a first chapter in which the spin crossover materials are introduced, the second chapter describes the synthesis of particles of FeII(phen)2(NCX)2 (X = S, Se) and [FeIII(3-OMeSalRen)2]PF6 (R = Me, E) compounds. As the fast precipitation technique essentially suits for ionic compounds, its application to neutral ones like FeII(phen)2(NCX)2, has been made possible by an indirect syntheses based on the ligand extraction from soluble precursors and the control of nucleation and growth processes of neutral products via experimental parameters. New particles of [FeIII(3-OMeSalEen)2]PF6 and thin films containing them after their dispersion in a polymeric matrix (PVP) have been prepared. The study of these films with UV-vis and magnetic measurements has raised the issue of the impact of the polymeric matrix and processing on the spin transition properties of these particles.The second part of the manuscript focuses on the interaction between the spin-crossover particles and the dispersing medium. This interaction between microparticles of Fe(phen)2(NCS)2 and glassy matrices (Tg > T1/2, T1/2, being the transition temperature) may result in the observation of large hysteresis loops shifted towards lower temperatures. This bistability has been examined with the FORC (First-Order Reversal Curves) method, magnetic measurements and a theoretical model. This analysis has shown the existence of reversible components associated to the particles/matrix interactions and the change of volume of spin-crossover particles.In a third part, the study of matrix and size effect has been pursued with micro- and nanocrystals of [FeIII(3-OMeSalEen2]PF6 encapsulated in polymeric or molecular liquids which form glasses at sufficiently low temperature. The encapsulation in rigid glasses of high spin (T1/2 < Tg) or low spin (T1/2 > Tg) particles give rise to transitions shifted towards lower or higher temperature respectively, possibly with cooperativity and hysteresis. The reinforcement of cooperativity and the bistability observed in the second case have been accounted for by the effect of the mechanical stress exerted by the glassy matrix on the particle volume. In addition, it has been shown that a thermal treatment of matrices (quenching or annealing steps below or above the glass transition) results in the modulation of the matrix effects. Finally, in the last chapter, a few composites including compounds undergoing a spin transition close to room temperature have been shortly investigated in presence of dispersing matrices. The choice of the matrices characteristics (chemical nature, glass transition temperature) has allowed some of these effects to be observed
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Dau, Anh Tuan. "Elaboration d’un outil numérique reliant les échelles micro/méso d’un composite thermoplastique sensible à l’humidité et à la température en quasi-statique." Thesis, Ecole centrale de Nantes, 2019. http://www.theses.fr/2019ECDN0004/document.
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Les travaux de cette thèse se sont intéressés à l’obtention du comportement d’un composite sergé 2x2 verre/PA66 via un outil numérique basé sur une double homogénéisation : la première concerne les torons et la seconde le volume élémentaire représentatif du composite. A partir d’une campagne de caractérisation expérimentale sur le PA66, nous avons dans un premier temps identifié l’influence à la fois de l’hygrométrie et de la température sur le comportement de la matrice en quasi-statique. Ensuite, nous avons élaboré, implémenté et validé une loi de comportement isotrope élasto-plastique endommageable. Cette loi a servi à identifier par homogénéisation le comportement des torons en supposant un collage parfait des fibres et de la matrice ainsi qu’une homogénéité de l’eau dans le toron. Grâce à ces comportements identifiés et à l’élaboration d’une loi de comportement anisotrope élasto-plastique endommageable, nous avons pu déterminer les caractéristiques élastiques dans un premier temps et les comportements longitudinaux et en cisaillement dans un second temps. Les comparaisons aux résultats expérimentaux menés sur le composite offrent des résultats satisfaisants et permettent de penser que l’outil numérique développé, permettrait, à termes, d’aider à une conception rapide incluant ce genre de matériau en diminuant le nombre d’essais expérimentaux à faire. Des perspectives enfin sont proposées notamment pour l’extension aux comportements en dynamique (crash)The objective of this PhD thesis is to create a methodology to simulate the behavior of a 2x2 glass/PA66 twill composite using homogenization. To achieve this goal, we use two steps: first one is dedicated to represent the yarn behavior and the second one to represent the behavior of the composite RVE. An experimental characterization campaign about the PA66 has been done in order to quantify the influence of both hygrometry and temperature on the behavior of the matrix in quasi-static. Then, we formulated, implemented and validated an isotropic elasto-plastic damageable constitutive law. It was used to identify by homogenization the behavior of the yarns by assuming a perfect bonding of the fibers and the matrix as well as a water homogeneity inside the yarn. Thanks to the identified behavior of the yarns and by formulating a compatible constitutive law (anisotropic elasto-plastic damageable), we have determined for the woven composite on one hand the elastic properties and in the other hand the longitudinal/transversal and shear nonlinear behaviors. The comparisons of the numerical and experimental results offer satisfactory results. It provides good outlook in short-term in regard of structures design which include this type of woven composite materials. The main advantage of the methodology is to decrease the number of required experimental tests. Some outlook dedicated to crash studies are finally suggested
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Gopinath, Gautam. "Progressive damage and failure of unidirectional fiber reinforced laminates under impact loading with composite properties derived from a micro-mechanics approach." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/37534.
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Micromechanics theories have been used to develop macro-level constitutive relations for infinitesimal elastoplastic deformations of unidirectional fiber reinforced laminates. The matrix is assumed to be isotropic and deform elasto-plastically and the fibers transversely isotropic and linear elastically. We have analyzed damage initiation, damage progression, and failure of 16-ply unidirectional fiber reinforced laminates impacted at normal incidence by a rigid sphere. The damage is assumed to initiate when at least one of Hashinâ s failure criteria is satisfied with the evolving damage modeled by an exponential relation. Transient three dimensional impact problems have solved using the finite element method (FEM) by implementing the material damage model as a user defined subroutine in the FE software ABAQUS. From strains supplied by ABAQUS the subroutine uses the free shear traction technique and values of material parameters of the constituents to find average stresses in a FE, and checks for Hashinâ s failure criteria. If the damage has initiated, the subroutine evaluates the damage developed, computes resulting stresses, and provides them to ABAQUS. The irreversibility of the damage is satisfied by requiring that the damage evolved does not decrease during unloading. The delamination failure mode is simulated by using the cohesive zone model and the degradation of material properties already available in ABAQUS. The computed time histories of the axial load acting on the impactor are found to agree well with the experimental ones available in the literature. The effect of stacking sequence in the laminate upon the impact load has been ascertained.Ph. D.
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Ehrenhofer, Adrian, and Thomas Wallmersperger. "Active hydrogel composite membranes for the analysis of cell size distributions." SPIE, 2019. https://tud.qucosa.de/id/qucosa%3A74237.
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Active membranes with switchable pores that are based on hydrogels can be used to measure the cell size distribution in blood samples. The system investigated in the present research is based on a polyethylene terephthalate (PET) membrane that is surface polymerized with poly (N-isopropyl acrylamide) (PNiPAAm) to form active pores of arbitrary geometry. The PET membrane provides the functionality of a backbone for mechanical rigidity, while the soft PNiPAAm hydrogel forms the active pores. Modeling and simulation of the active hydrogel behavior proved to adequately predict the opening and closing of the pores under application of an activating stimulus, e.g. temperature. The applied model is called Temperature-Expansion-Model and uses the analogy of thermal expansion to model the volume swelling of hydrogels. The Normalized Extended Temperature-Expansion-Model can englobe arbitrary hydrogels and large geometric displacements. Studies of pore opening - performed by using commercial finite element tools - show good agreement of the experimentally measured shape change of active pores. Based on these studies, the particulate fluid flow through the switchable pores is analyzed. Through application of a membrane process, i.e. a given variation of applied pressure and switching stimulus for the hydrogel, the size profile of the blocking particles can be measured directly using the flux difference under constant pressure. This allows the measurement of the cell size distribution in blood samples, e.g. to detect circulating tumor cells or anomalies in the distribution that hint to anemia.
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Lopez-Pamies, Oscar. "Sur le comportement effective, l'évolution de microstructure et la stabilité macroscopique des composite élastomères." Phd thesis, Ecole Polytechnique X, 2006. http://pastel.archives-ouvertes.fr/pastel-00002978.
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Les composites élastomères sont actuellement utilisés dans de nombreuses applications commerciales et ont montré de grandes promesses pour l'utilisation dans les nouvelles technologies. Cela soulève la pratique, ainsi que théorique nécessaire pour comprendre le lien entre la microstructure sous-jacente de composites en élastomère et de leurs propriétés mécaniques et physiques, et comment celui-ci peut être améliorée avec des changements dans l'ancienne. Dans ce contexte, l'objectif principal de cette thèse est le développement d'une analyse, le cadre homogénéisation non linéaire pour déterminer la réponse globale des composites élastomères soumis à des déformations finies. Les comptes-cadre pour l'évolution de la microstructure sous-jacente, ce qui entraîne des changements dans la géométrie finie induite par la charge appliquée. Ce point est essentiel que l'évolution de la microstructure peut avoir un assouplissement significatif géométrique (ou raidissage) effet sur la réponse globale du matériau, qui, à son tour, peut conduire à l'élaboration éventuelle d'instabilités macroscopiques. Le concept principal derrière la méthode d'homogénéisation non linéaire proposé est la construction de principes variationnels appropriés en utilisant l'idée d'un "portail composite linéaire», qui a finalement permettre la conversion des estimations disponibles homogénéisation linéaire dans les estimations analytiques pour la grande déformation de réponse global de l' non linéaire des composites en élastomère. Cette thèse comprend des applications de la théorie proposée pour les différentes classes des élastomères renforcés et poreux aléatoire et des microstructures périodiques. Une analyse complète du comportement efficace, l'évolution de la microstructure et le développement d'instabilités macroscopiques est prévu pour toutes ces applications.