To see the other types of publications on this topic, follow the link: Matrix interfaces.
Dissertations / Theses on the topic 'Matrix interfaces'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Matrix interfaces.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Shyr, Tien-Wei. "Studies of fibre-matrix interfaces." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329201.
Full text
2
Gregory, Jeremy R. (Jeremy Ryan) 1976. "The role of precipitates on fiber/matrix interfaces in metal matrix composites." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/89301.
Full text
3
Blaese, Diego. "Processing and characterization of monoclinic-zirconia fibre-matrix interfaces in dense matrix alumina-alumina composites." reponame:Repositório Institucional da UFSC, 2013. https://repositorio.ufsc.br/handle/123456789/107283.
Full textAbstract:
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2013.Made available in DSpace on 2013-12-05T23:42:12Z (GMT). No. of bitstreams: 1 318449.pdf: 2754019 bytes, checksum: d73daae4512a7cb151813f0d7e905cae (MD5) Previous issue date: 2013
Interfaces fibra-matriz tem um papel muito importante no desempenho de compósitos de matriz cerâmica. Sendo a interação entre fibra e matriz for muito forte, o compósito se comportará como uma cerâmica monolítica, e sendo muito fraca, o compósito perderá sua integridade estrutural e suas propriedades interlaminares. Zircônia monoclínica (não-estabilizada) tem mostrado ser uma boa alternativa na produção de interfaces fibra-matriz para compósitos cerâmicos à base de alumina devido à sua baixa interação química durante a sinterização e também devido ao fenômeno de microtrincamento causado pela transformação tetragonal-monoclínica durante o resfriamento. Interfaces porosas à base de zircônia monoclínica, as quais apresentam baixa tenacidade devido à sua porosidade e microtrincamento, haviam sido usadas no passado para criar interfaces com baixa interação entre fibras de safira e matrizes de alumina. Neste sistema, as interfaces se mostraram quimicamente estáveis mesmo acima de 1300 °C. Compósitos tenazes à base de alumina haviam sido fabricados com zircônia monoclínica como interface. Entretanto, a porosidade da matriz era ? 13%, o que dificulta a interpretação dos resultados, pois as propriedades mecânicas do compósito não podem ser claramente atribuídas às propriedades da zircônia monoclínica. Neste trabalho, compósitos-modelo com matriz densa e fibras individuais de alumina foram produzidos. A interface fibra-matriz foi produzida através de recobrimento por dip-coating das fibras em suspensões cerâmicas de zircônia monoclínica. Diferentes tamanhos de partícula foram utilizados no processo de dip-coating com o objetivo de variar a porosidade e assim, as propriedades das interfaces. A tensão de cisalhamento interfacial foi determinada através do teste de pushin nas fibras. O fenômeno de deflexão de trincas foi avaliado através de trincas criadas por indentação Vickers e o fenômeno de pullout das fibras através de observações nas superfícies de fratura. Propriedades como tenacidade à fratura, dureza e módulo de elasticidade da matriz e interface foram avaliadas para determinar os parâmetros de deflexão de trincas propostos por He e Hutchinson.
Abstract : Fibre-matrix interface properties play an important role on the performance of ceramic matrix composites. Being the fibre-matrix interaction too strong, the composite will behave such as a monolithic ceramic and being too weak, the composite will lose its structural integrity and its interlaminar properties. Monoclinic (unstabilized) zirconia has shown to be a suitable alternative for the production of fibre-matrix interfaces for alumina ceramic matrix composites due to its low chemical interaction during sintering and due to the microcracking phenomenon caused by the tetragonal-monoclinic transformation during cooling. Porous oxide coatings of monoclinic zirconia, which have low toughness because of their porosity and microcracking, have been used in the past to achieve debonding between sapphire fibres and alumina matrices and were to be chemically stable with sapphire above 1300 °C. Tough alumina matrix composites have been fabricated using monoclinic zirconia as fibres coating. However the matrix porosity was = 13%, which makes it difficult to interpret the results, because the toughness cannot be unambiguously attributed to the properties of the unstabilized zirconia interfaces. In this work, model composites with dense alumina matrix and single alumina fibres were fabricated. The fibre-matrix interface was produced via dip-coating single fibres in monoclinic zirconia suspensions. Different particle sizes were used for the dip-coating in order to vary the coating porosity. The interfacial sliding stress was determined via a modified fibre pushin test. The crack deflection behaviour was analysed from cracks created via Vickers indentations and the fibre pullout via surface fracture observations. Properties such as fracture toughness, hardness and elastic modulus for the interface and matrix were also evaluated in order to determine the crack deflection parameters established by He and Hutchinson.
4
Robinette, Eric Jason Palmese Giuseppe R. "Toughening vinyl ester matrix composites by tailoring nanoscale and mesoscale interfaces /." Philadelphia, Pa. : Drexel University, 2005. http://hdl.handle.net/1860/1125.
Full text
5
Zeiger, Adam Scott. "Chemomechanics at cell-cell and cell-matrix interfaces critical to angiogenesis." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/88378.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, February 2014.Cataloged from PDF version of thesis. "February 2014."
Includes bibliographical references.
The ability to characterize and control cellular responses in vitro has far reaching implications for basic science and applied medical research. For well over 125 years, researchers have studied the behavior of biological cells under in vitro conditions where rigid glass or plastic Petri dishes and defined media in the laboratory replace the compliant solids and crowded fluids of the human body in vivo. While these tools have enabled several important advances in understanding cell functions and pathological mechanisms, the behavior of tissue cells in vitro can differ remarkably from those observed in in vivo tissue microenvironments. It is becoming increasingly appreciated that there is a close coupling between the chemical and mechanical microenvironments of the cell (i.e., the chemomechanical niche). Therefore, the biochemical reactions and conditions responsible for generating mechanical stresses and attendant cell behaviors may not be well represented in typical in vitro assays. In several key respects, particularly in terms of cell proliferation, adhesion, migration and phenotypic metabolism, in vitro assays often misrepresent the major characteristics of these behaviors in vivo. Most physiological processes are defined in part by mechanical force, mechanical microenvironment, and chemical stimuli (e.g., in angiogenesis or regulation of stern cell differentation), and therefore require an updated methodology to studying cellular mechanics and behavior. This thesis aims to address the molecular- to cellular-level chemical and mechanical environments that modulate cell function in vivo at the cell-cell and cell-matrix interfaces, while aiming to more accurately reproduce these cell responses in vitro. The experiments and analyses described in this work investigate two key questions at the heart of angiogenesis. First, how does the protein dense nature of tissue nicroenvironments affect extracellular matrix organization and, in turn, direct cell-matrix guided functions and cytoskeletal organization? This will be addressed by the addition of inert crowders which artificially enhance the effective concentration of relevant macromolecules and proteins in vitro. Second, how do the mechanically couplings and biochemical signals between adjacent, dissimilar cell types in the microvasculature coordinate and guide angiogenesis? Multiple types of deformable substrata will be used to investigate the mechanical strain and soluble growth factors generated by perivascular cells and the response of microvascular endothelial cells to those cues. This includes the development of a novel uniaxial strain-generating device and tissue culture surfaces for endothelial cells. Atomic force microscopy enabled imaging and nanoindentation, mechanically and chemically defined substrata, immunocyto-chemistry, and novel quanitification and analysis techniques are used concomitantly to answer these questions. Ultimately, this thesis aims to close the gap between in vitro cell culture and in vivo cell physiology, especially in directing and characterizing chemomechanical cues implicated in angiogenesis, and to inform the design of future experiments and microenvironments with non-dilute culture media and deformable substrata.
by Adam Scott Zeiger.
Ph. D.
6
Benethuilière, Thibaut. "Phénomènes physico-chimiques aux interfaces fibre/matrice dans des composites SMC structuraux : Du mouillage à l'adhésion." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI151.
Full text
7
Shu, Shu. "Engineering the performance of mixed matrix membranes for gas separations." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/26626.
Full textAbstract:
Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2008.Committee Chair: Koros William; Committee Member: Hess Dennis; Committee Member: Jones Christopher; Committee Member: Meredith Carson; Committee Member: Wong CP. Part of the SMARTech Electronic Thesis and Dissertation Collection.
8
Di, Ciò Stefania. "How cells sense the matrix geometry : a novel nanopatterning approach." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/31789.
Full textAbstract:
Tissue engineering and regenerative medicine aim to develop materials that mimic some of the characteristics of the tissue they are replacing and control the growth and proliferation of cells. Despite exceptional advances in the range and quality of materials used, much remains to discover about the processes regulating interfaces between cells and their surroundings, or at cell-material interfaces. In order to study and control such interactions, scientists have produced engineered matrices aiming to mimic some of the feature of natural extra-cellular matrix (biochemistry, geometry/topography and mechanical properties). In order to pattern 2D-nanofibers on relatively large areas and throughput, allowing comprehensive biological studies, we developed a nano-fabrication technique based on the deposition of sparse mats of electrospun fibres with different diameters. These mats are used as masks to grow cell resistant polymer brushes from exposed areas. After removal of the fibres, the remaining brushes define a quasi-2D fibrous pattern onto which ECM molecules such as fibronectin can be adsorbed. Chapter 2 includes details of the techniques used to produce and characterize the fibrous nanopattern. Chapter 3 is focused on cell phenotype observed on the different nanofibres sizes. Adhesion assays showed that cell spreading, shape and polarity are regulated by the size of fibres but also the density of the nanofibres, similarly to previous observations made on circular nanopatterns. We then focused on the study of focal adhesion formation and maturations on these nanofibres and the role of key proteins involved in the regulation of the adhesion plaque: integrins and vinculin. Cells expressing different integrins were found to sense the nanoscale geometry differently. Vinculin sensing is the topic of Chapter 4. Although vinculin recruitment dynamics was affected by the nanofibrous patterns and focal adhesions arrange differently on the nanofibres, this protein does not seem to mediate nanoscale sensing. In Chapter 5, we finally focused on the role of the actin cytoskeleton as a direct sensor of nanoscale geometry. A gradual decrease in stress fibre formation was observed as the nanofibres dimensions decrease. Live imaging also demonstrated that the geometry of the extracellular environment strongly affects cytoskeleton rearrangement, stress fibres formation and disassembly. We identify the role of cytoskeleton contractility as an important sensor of the nanoscale geometry. Our study provides a deeper insight in understanding cell adhesion to the extracellular environment and the role of the matrix geometry and topography on such phenomena, but also raises questions regarding the more detailed molecular sensory elements enabling the direct sensing of nanoscale geometry through the actin cytoskeleton.
9
Duarte, Carlos. "Design and Evaluation of Adaptative Multimodal Systems." Doctoral thesis, Department of Informatics, University of Lisbon, 2008. http://hdl.handle.net/10451/14293.
Full textAbstract:
This thesis focuses on the design and evaluation of adaptive multimodal systems. The design of such systems is approached from an integrated perspective, with the goal of obtaining a solution where aspects related to both adaptive and multimodal systems are considered. The result is FAME, a model based framework for the design and development of adaptive multimodal systems, where adaptive capabilities impact directly over the process of multimodal fusion and fission operations. FAME overviews the design of systems capable of adapting to a diversified context, including variations in users, execution platform, and environment. FAME represents an evolution from previous frameworks by incorporating aspects specific to multimodal interfaces directly in the development of an adaptive platform. One of FAME's components is the Behavioral Matrix, a multipurpose instrument, used during the design phase to represent the adaptation rules. In addition, the Behavioral Matrix is also the component responsible for bridging the gap between design and evaluation stages. Departing from an analogy between transition networks for representing interaction with a system, and behavioral spaces, the Behavioral Matrix makes possible the application of behavioral complexity metrics to general adaptive systems. Moreover, this evaluation is possible during the design stages, which translates into a reduction of the resources required for evaluation of adaptive systems. The Behavioral Matrix allows a designer to emulate the behavior of a non-adaptive version of the adaptive system, allowing for comparison of the versions, one of the most used approaches to adaptive systems evaluation. In addition, the designer may also emulate the behavior of different user profiles and compare their complexity measures. The feasibility of FAME was demonstrated with the development of an adaptive multimodal Digital Book Player. The process was successful, as demonstrated by usability evaluations. Besides these evaluations, behavioral complexity metrics, computed in accordance with the proposed methodology, were able to discern between adaptive and non-adaptive versions of the player. When applied to user profiles of different perceived complexity, the metrics were also able to detect the different interaction complexity
10
Barros, Fábio Monteiro de. "Species composition, ecological functions and ecosystem services by birds across forest-matrix interfaces in tropical disturbed landscapes /." Rio Claro, 2017. http://hdl.handle.net/11449/152541.
Full textAbstract:
Orientador: Milton Cezar RibeiroBanca: Danilo Boscolo
Banca: Victor Satoru Saito
Banca: Karl Stephan Mokross
Banca: Erica Hasui
Resumo: A perda e fragmentação dos habitats tem levado a crescentes perdas de biodiversidade e serviços ecossistêmicos em todo mundo. Em paisagens antropogênicas, diversos fatores são conhecidos por moldarem essa biodiversidade e serviços ecológicos, entre elas a quantidade de cobertura florestal e o tipo e composição da matriz antrópicas. Usando aves como objeto de estudo, nesta tese nós basicamente buscamos quantificar a composição, função e serviços ecossistêmicos de espécies de aves que ocorrem em dois tipos de interfaces de habitat mais comum ao longo da Mata Atlântica brasileira (floresta-pasto e floresta-eucalipto), e tentamos entender melhor como as características da paisagem ajudam a moldar os padrões encontrados. No capítulo 1, nossos dados sugeriram que pastagens são capazes de prover maior potencial de prover serviços de dispersão de sementes, controle de pragas e polinização por aves do que plantações de eucalipto, no entanto algumas particularidade e limitações de interpretação desses resultados são apontadas e discutidas. No mesmo capítulo também elucidamos a importância das espécies generalistas na provisão de serviços de dispersão de sementes, assim como a presença das áreas habitadas por pessoas dentro de propriedades rurais como potencial facilitador desse serviço pelas aves em paisagens alteradas. No segundo capítulo, verificamos que o tipo de matriz adjacente (pasto ou eucalipto) interfere na composição taxonômica e funcional das comunidades de aves que habitam ... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Habitat loss and fragmentation have led to increasing biodiversity and ecosystem loss worldwide. In anthropogenic landscapes, several factors are kn own to modulate biodiversity and ecosystem services, mainly the amount of forest cover and matrix type and composition. Using birds as study object, in this thesis we basically aimed to quantif y composition, function and ecosystem services by birds occurri ng in two types of most common habitat interfaces across Atlantic forest in Brazil (forest - pastures and forest - eucalyptus), and tried to better understand how landscapes attributes help to drive the patterns found. In the chapter 1, we demonstrated that pa stures stands are able to provide higher potential provision of seed dispersal, pest control and pollination services by birds, however some limitation and particularities on these results are pointed and discussed. In the same chapter, we also highlighted the importance of habitat generalist birds as potential providers of ecosystem services as well as the presence of rural homesteads as likely seed dispersal facilitator in highly disturbed landscapes. In the second chapter, we verified that type of adjace nt matrix alters taxonomic and functional composition of bird communities inhabiting forest edges, and that an increase of forest cover may lead to a decrease in functional dissimilarities between bird communities within the both types of habitat interface s (forest - pasture and forest - eucalyptus). Lastly, in the f... (Complete abstract click electronic access below)
Doutor
11
Barros, Fábio Monteiro de [UNESP]. "Species composition, ecological functions and ecosystem services by birds across forest-matrix interfaces in tropical disturbed landscapes." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152541.
Full textAbstract:
Submitted by FÁBIO MONTEIRO DE BARROS null (barros.fmon@gmail.com) on 2018-01-18T16:36:40Z
No. of bitstreams: 1
tese_fabio.pdf: 4417866 bytes, checksum: 351d3f2b0c3e1ff647e634b4e693f898 (MD5)Approved for entry into archive by Adriana Aparecida Puerta null (dripuerta@rc.unesp.br) on 2018-01-19T12:45:50Z (GMT) No. of bitstreams: 1 barros_fm_dr_rcla.pdf: 4417866 bytes, checksum: 351d3f2b0c3e1ff647e634b4e693f898 (MD5)
Made available in DSpace on 2018-01-19T12:45:51Z (GMT). No. of bitstreams: 1 barros_fm_dr_rcla.pdf: 4417866 bytes, checksum: 351d3f2b0c3e1ff647e634b4e693f898 (MD5) Previous issue date: 2017-11-24
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
A perda e fragmentação dos habitats tem levado a crescentes perdas de biodiversidade e serviços ecossistêmicos em todo mundo. Em paisagens antropogênicas, diversos fatores são conhecidos por moldarem essa biodiversidade e serviços ecológicos, entre elas a quantidade de cobertura florestal e o tipo e composição da matriz antrópicas. Usando aves como objeto de estudo, nesta tese nós basicamente buscamos quantificar a composição, função e serviços ecossistêmicos de espécies de aves que ocorrem em dois tipos de interfaces de habitat mais comum ao longo da Mata Atlântica brasileira (floresta-pasto e floresta-eucalipto), e tentamos entender melhor como as características da paisagem ajudam a moldar os padrões encontrados. No capítulo 1, nossos dados sugeriram que pastagens são capazes de prover maior potencial de prover serviços de dispersão de sementes, controle de pragas e polinização por aves do que plantações de eucalipto, no entanto algumas particularidade e limitações de interpretação desses resultados são apontadas e discutidas. No mesmo capítulo também elucidamos a importância das espécies generalistas na provisão de serviços de dispersão de sementes, assim como a presença das áreas habitadas por pessoas dentro de propriedades rurais como potencial facilitador desse serviço pelas aves em paisagens alteradas. No segundo capítulo, verificamos que o tipo de matriz adjacente (pasto ou eucalipto) interfere na composição taxonômica e funcional das comunidades de aves que habitam bordas de floresta e também que o aumento da cobertura florestal é capaz de aproximar funcionalmente as comunidades de aves adjacente dentro de interfaces de floresta-matriz. Por fim, no terceiro e último capítulo, através de modelos que simulam cenários, nós tentamos predizer como as características funcionais das aves em borda de floresta tendem a se distribuir em função do tipo de matriz adjacente, cobertura florestal e heterogeneidade da paisagem.
Habitat loss and fragmentation have led to increasing biodiversity and ecosystem loss worldwide. In anthropogenic landscapes, several factors are kn own to modulate biodiversity and ecosystem services, mainly the amount of forest cover and matrix type and composition. Using birds as study object, in this thesis we basically aimed to quantif y composition, function and ecosystem services by birds occurri ng in two types of most common habitat interfaces across Atlantic forest in Brazil (forest - pastures and forest - eucalyptus), and tried to better understand how landscapes attributes help to drive the patterns found. In the chapter 1, we demonstrated that pa stures stands are able to provide higher potential provision of seed dispersal, pest control and pollination services by birds, however some limitation and particularities on these results are pointed and discussed. In the same chapter, we also highlighted the importance of habitat generalist birds as potential providers of ecosystem services as well as the presence of rural homesteads as likely seed dispersal facilitator in highly disturbed landscapes. In the second chapter, we verified that type of adjace nt matrix alters taxonomic and functional composition of bird communities inhabiting forest edges, and that an increase of forest cover may lead to a decrease in functional dissimilarities between bird communities within the both types of habitat interface s (forest - pasture and forest - eucalyptus). Lastly, in the final chapter, using simulation scenarios we tried to predict how some bird functional traits at forest edges tend to be distributed according to adjacent matrix type, forest cover and land use heter ogeneity.
FAPESP 2013/19732-1.
FAPESP 2016/15376-4.
12
Krause, Stefan, Pedro F. Aramendia, Daniela Täuber, and Borczyskowski Christian von. "Freezing single molecule dynamics on interfaces and in polymers." Universitätsbibliothek Chemnitz, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-122254.
Full textAbstract:
Heterogeneous line broadening and spectral diffusion of the fluorescence emission spectra of perylene diimide molecules have been investigated by means of time dependent single molecule spectroscopy. The influence of temperature and environment has been studied and reveals strong correlation to spectral diffusion processes. We followed the freezing of the molecular mobility of quasi free molecules on the surface upon temperature lowering and by embedding into a poly(methyl methacrylate) (PMMA) polymer. Thereby changes of optical transition energies as a result of both intramolecular changes of conformation and external induced dynamics by the surrounding polymer matrix could be observed. Simulations of spectral fluctuations within a two-level system (TLS) model showed good agreement with the experimental findings.
13
Bertram, Brian D. "Effects of interfaces and preferred orientation on the electrical response of composites of alumina and silicon carbide whiskers." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42895.
Full textAbstract:
Ceramic-matrix composites of alumina and silicon carbide whiskers have recently found novel commercial application as electromagnetic absorbers. However, a detailed understanding of how materials issues influence the composite electrical response, which underpins this application, has been absent until now. In this project, such composites were electrically measured over a wide range of conditions and modeled in terms of various aspects of the microstructure in order to understand how they work. For this purpose, three types of composites were made by different methods from the same set of ceramic powder blends loaded with different volume fractions of whiskers. In doing so, the interfaces between whiskers, the preferred orientations of whiskers, and the structure of electrically-connected whisker clusters were varied; the whisker aspect-ratio distributions were the same for all methods.
At the electrode interfaces, Schottky barriers at the junctions of the electrically-percolating wide-bandgap semiconductor whiskers on the surface were responsible for a significant portion of the total measured impedance. The associated electrical response was studied on the microscopic and macroscopic level, and the gap between these different scales was bridged. Also, a modeling approach was developed for the non-linear behavior of the composite which results from these barriers.
In regards to the whiskers within the composite bulk, the effects of various factors on the wide-band frequency dependence of the dielectric response and dc conductivity were explained and contextualized for the electromagnetic absorber application. Such factors include whisker preferred orientation, electrical percolation and cluster structure, the interfaces between electrically-connected SiC whiskers, and porosity. A quantitative correlation between the anisotropy of the microstructure and that of the conductivity was found, and was understood in terms of the interfacial SiC-Al2O3-SiC conduction mechanism. This behavior was shown to differ from the behavior commonly observed for other disordered mixtures of relatively conductive particles dispersed inside insulating polymer hosts. A description of this new mechanism was developed based on an observed correlation between the temperature dependencies of the static and radio-frequency electrical responses. Also, the aforementioned non-linear response model was expanded upon to describe conduction through and across electrically-percolated clusters. The model demonstrates how loading and interface behavior influence the topology and the strength of the non-linear response of the clusters.
14
Fellah, Clémentine. "Influence de la nature des interfaces carbonées au sein des composites SiC/SiC à renfort Hi-Nicalon S et Tyranno SA3 sur leur comportement mécanique." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEM078.
Full textAbstract:
Les composites SiC/SiC à interphase pyrocarbone (PyC) sont des candidats prometteurs en tant que matériau de gainage du combustible et de structure des réacteurs à neutrons rapides, constituant une alternative aux alliages métalliques. Leur comportement sous irradiation neutronique et leur caractère réfractaire sont de sérieux atouts en milieu irradiant. Néanmoins, les fibres et la matrice en carbure de silicium (SiC) sont, individuellement, des céramiques fragiles. L’intégrité des structures ne peut donc être assurée que si le composite acquiert une tolérance aux déformations. Cette tolérance n’est possible que grâce à la présence d’une interphase de pyrocarbone, entre la matrice et les fibres, assurant le rôle de déviateur de fissures. La capacité des composites SiC/SiC à résister à l’endommagement est dictée par le couplage fibre/matrice (F/M). L’intensité de ce couplage peut être influencée par de nombreux paramètres, tels que la rugosité et la physicochimie de surface du renfort. Les travaux faisant l’objet de cette thèse ont mis en évidence une couche de carbone en surface des fibres par microscopie électronique en transmission à haute résolution (METHR) et via des analyses physicochimiques de surface. Les caractéristiques de cette couche de carbone varient avec le procédé de fabrication des fibres. Son impact sur le couplage F/M a été appréhendé par l’observation des mécanismes locaux d’endommagement. La décohésion fibre/matrice a été étudiée en analysant par METHR les régions interfaciales des composites SiC/SiC ayant subi un essai mécanique. La compréhension de l’origine de cette couche de surface de fibres a permis de mieux connaitre les mécanismes locaux d’interaction. Ces mécanismes dépendent de la structure du carbone de surface des fibres dont découle le mode d’adhésion entre ce carbone de surface et l’interphase de pyrocarbone. Un traitement de surface sur un type de fibres a alors été développé, suggérant une légère amélioration du comportement mécanique des composites SiC/SiC élaborés à partir de ces renforts fibreuxSiC/SiC composites including the third generation SiC fibers with pyrocarbon interphase (PyC) are promising candidates to improve the safety of nuclear reactors, especially for core materials such as cladding and to replace metallic alloys for these applications. Their intrinsic refractory properties, their neutron transparency and their microstructural stability when irradiated or exposed to high temperatures make them attractive for nuclear applications. However SiC fibers and SiC matrix are brittle ceramics. The integrity of the structures can be fulfilled only if the composite is damage tolerant and can acquire a pseudo-ductile mechanical behavior. An interphase is deposited between the fibers and the matrix to provide this damage tolerance of SiC/SiC composites.The ability of SiC/SiC composites to sustain damage is dictated by the fiber/matrix (F/M) coupling mode. The intensity of this coupling can be related to many parameters such as the roughness and the chemistry of the surface of the reinforcement. A carbon layer on the fiberssurface was highlighted by High Resolution Transmission Electronic Microscopy (HRTEM) and by physico-chemical analyses. The characteristics of this carbon layer vary with the fabrication process of the fibers. The impact of this carbon layer on the F/M coupling was investigated by the observation of the local damage mechanisms. To elucidate the local bonding modes governing the damage mechanisms at the F/M interface of these SiC/SiC composites, macroscopic mechanical tests have been coupled with observations of structural modifications occurring in the interface region after loading. Understanding the origin of this carbon layer allowed elucidating the local interaction mechanisms according to these studied materials. These mechanisms depend on the carbon structure of the SiC fibers surface which in turn governs the adhesion between this carbon and the PyC interphase. Thanks to this study, a surface treatment on fibers was developed to optimize the mechanical behavior of SiC/SiC composites, whatever the fibrous reinforcement chosen
15
Krause, Stefan, Pedro F. Aramendia, Daniela Täuber, and Borczyskowski Christian von. "Freezing single molecule dynamics on interfaces and in polymers." Physical Chemistry Chemical Physics. - 2011,13, S. 1754-1761, 2011. https://monarch.qucosa.de/id/qucosa%3A19944.
Full textAbstract:
Heterogeneous line broadening and spectral diffusion of the fluorescence emission spectra of perylene diimide molecules have been investigated by means of time dependent single molecule spectroscopy. The influence of temperature and environment has been studied and reveals strong correlation to spectral diffusion processes. We followed the freezing of the molecular mobility of quasi free molecules on the surface upon temperature lowering and by embedding into a poly(methyl methacrylate) (PMMA) polymer. Thereby changes of optical transition energies as a result of both intramolecular changes of conformation and external induced dynamics by the surrounding polymer matrix could be observed. Simulations of spectral fluctuations within a two-level system (TLS) model showed good agreement with the experimental findings.
16
Shi, Yang. "Economie circulaire pour les composites à fibres de carbone : du déchet aéronautique vers les composites carbone+ thermoplastiques recyclés." Electronic Thesis or Diss., Bordeaux, 2022. http://www.theses.fr/2022BORD0153.
Full textAbstract:
Depuis leur industrialisation, la production de composites en fibres de carbone augmente de façon continue. Lors du recyclage des composites à fibres de carbone, seules les fibres seront recyclées. La « suppression » de la matrice est réalisée par pyrolyse, solvolyse ou vapo-thermolyse, procédés qui n’entraînent que peu de dégradation des fibres. Afin de susciter une demande pour les fibres de carbone recyclées, il faut donner de la valeur ajoutée aux fibres recyclées en démontrant la faisabilité de fabriquer des pièces composites (fibre recyclée+matrice) de haute qualité.Les architectures de fibres recyclées semi longues avec un très bon alignement ont été produites par la technologie de réalignement brevetée du laboratoire qui permet d’assurer une exploitation optimale des propriétés des fibres de carbone recyclées. Dans le but de maîtriser et d’optimiser les propriétés du nouveau composite (à fibres discontinues), les mécanismes de transfert de charge entre fibres ont été étudiés, et les propriétés utiles de la matrice ont été identifiées. Une attention particulière a été portée au calcul de la longueur de transfert de charge entre deux fibres discontinues en fonction des propriétés de l'interface fibre recyclée / matrice thermoplastique. En effet, notre objectif est non seulement de rechercher des solutions optimales en termes de résistance mais aussi des solutions qui permettent de limiter l’impact environnemental, d’où notre choix des matrices thermoplastiques (y compris recyclées) pour cette étude.Tous les résultats des simulations numériques ont été validés par comparaison avec des résultats expérimentaux. De plus des composites fibres de carbone recyclées/matrice thermoplastique (PA6 et PC) ont été mis en œuvre et testés. Ces matériaux présentent des taux de fibres supérieurs à 50% et offrent de meilleures propriétés mécaniques que les mêmes matériaux avec matrice epoxy.Une analyse environnementale a été propsée sur l’exemple d’une pale d’éolienne portative en comparant les impacts de la matière première, de la fabrication et de la fin de vie d’une pièce réalisée avec différents matériaux (alliage léger, composite fibres de verre, composites à fibres recyclées). Cela démontre l’intérêt des fibres de carbone recyclées associées à une matrice thermoplastique recyclée, pour minimiser l’impact environnemental tout en maximisant les performances mécaniquesSince their industrialization, the production of carbon fiber composites is continuously increasing. When recycling carbon fiber composites, only the fibers are recycled. The matrix is "removed" by pyrolysis, solvolysis or vapour-thermolysis, processes that cause little degradation of the fibres. In order to create a demand for recycled carbon fibers, it is necessary to add value to recycled fibers by demonstrating the feasibility of manufacturing high quality composite parts (recycled fiber + matrix).Semi-long recycled fiber architectures with very good alignment were produced by the laboratory's patented realignment technology that ensures optimal exploitation of recycled carbon fiber properties. In order to control and optimize the properties of the new composite (staple fiber), the mechanisms of load transfer between fibers were studied, and the useful properties of the matrix were identified. Particular attention has been paid to the calculation of the load transfer length between two staple fibers as a function of the properties of the recycled fiber/thermoplastic matrix interface. Indeed, our objective is not only to find optimal solutions in terms of strength but also solutions that allow to limit the environmental impact, hence our choice of thermoplastic matrices (including recycled) for this study.All the results of the numerical simulations were validated by comparison with experimental results. In addition, recycled carbon fiber/thermoplastic matrix composites (PA6 and PC) were implemented and tested. These materials have fiber contents higher than 50% and offer better mechanical properties than the same materials with epoxy matrix.An environmental analysis was performed on the example of a portable wind turbine blade by comparing the impacts of the raw material, manufacturing and end of life of a part made with different materials (light alloy, glass fiber composite, recycled fiber composites). This demonstrates the interest of recycled carbon fibers associated with a recycled thermoplastic matrix, to minimize the environmental impact while maximizing mechanical performance
17
Charlier, Quentin. "Adhesion phenomena in thermoplastic composites based on acrylic matrices obtained by free radical polymerization." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI140.
Full textAbstract:
Ce mémoire de thèse s’intéresse aux phénomènes d’adhésion dans des composites à matrice thermoplastique obtenus par polymérisation radicalaire de mélanges réactifs. Après une courte introduction bibliographique sur les thématiques d’adhésion et d’adhérence, les propriétés générales des principaux éléments constitutifs des assemblages finaux sont étudiées séparément pour discuter de leur pertinence en vue d’une application composite. Une attention particulière est portée sur les systèmes réactifs acryliques à l’état liquide. L’étude se concentre ensuite sur les mécanismes réactionnels et l’évolution des propriétés des systèmes réactifs lors de la polymérisation. Ces problématiques sont de première importance pour anticiper les mécanismes gouvernant l’adhésion dans les composites obtenus mais aussi pour appréhender les potentielles problématiques à venir lors des étapes de mise en forme. Enfin, une étude est spécifiquement dédiée au cas de l’adhésion entre matrice acrylique et fibres de verre dans des composites à fibres de renfort continues. Les propriétés à l’interface verre/acrylique ont été évaluées à l’échelle microscopique dans des systèmes modèles et à l’échelle macroscopique dans des composites unidirectionnels, c'est à dire pouvant les défauts d’adhésion générés lors de la mise en forme. L’ensemble de ces résultats permet de se positionner quant à l’utilisation de solutions acryliques thermoplastiques pour des applications composites structurauxThese PhD research works focus on adhesion phenomena involved in thermoplastic composites based on acrylic matrices obtained by free radical polymerization. After a short bibliographic section introducing some basics on adhesion phenomena and practical adhesion measurements, properties of elementary constituents are assessed to discuss their relevancy for composite applications. Special attention is paid to acrylic reactive systems and properties of acrylic resins at liquid state. Then, the reaction mechanisms involved in free radical polymerization are detailed. The changes in acrylic system properties during polymerization are investigated to anticipate further processing-related issues. At last, a study is dedicated to the assessment of interfacial adhesion between glass fiber and acrylic matrices in fiber reinforced composites. Interfacial properties are characterized at microscale in model systems and at macroscale in real-sized composites, i.e. integrating process-induced defects. From overall results, the relevancy of acrylic thermoplastic solutions for structural composite applications is discussed
18
Beker, Karine Kyomi. "Apoio matricial e institucional: investigando interfaces com a Residência Multiprofissional em Saúde da Família e Comunidade." Universidade Federal de São Carlos, 2014. https://repositorio.ufscar.br/handle/ufscar/6921.
Full textAbstract:
Made available in DSpace on 2016-06-02T20:45:41Z (GMT). No. of bitstreams: 1
5985.pdf: 2116461 bytes, checksum: 1e77261f8536c46cd37684186d9b6518 (MD5)
Previous issue date: 2014-03-21The Family Health Strategy (FHS) is focused on family and community, acting through strategies of promotion, prevention, recovery and rehabilitation. Complementing the actions of family health teams, matrix support consists in an organizational arrangement that offers specialized care as much rear of technical and pedagogical support teams and institutional support is intended to facilitate the spaces of co-management and joint teams, enabling the expansion of capacity and facilitating analysis of the process of reflection on the difficulties of everyday life. The need for training of professionals capable of these changes in health services has encouraged the creation and development of Multiprofessional Residences in Health. The Federal University of São Carlos (UFSCar) and the Municipal Health Secretariat of the municipality proposed the insertion of the Multiprofessional Residence in Health Family and Community (RMSFC) in municipal health network, in which residents work in the logic of FHS. The study aimed to understand the interfaces between activities as supporters and the process experienced in training RMSFC UFSCar. This is a qualitative study and by applying via online, a questionnaire with open and closed to graduates of the period 2007-2012 residency program questions, 21 answers to the questionnaire were obtained. Empirical data were examined using thematic analysis and divided into two themes: support and network school. For each theme, two categories were compiled: matrix support as an activity that focuses on care, the organization of the work process as the focus of institutional support, practical learning scenarios theoretical and practical training and theoretical spaces. The matrix support actions related to health care were assigned, while institutional support refers to the organization of the work process, according to the same. The scenario of practical and theoretical learning as well as the use of tools of lifelong education favor the formation of capable workers to collective actions, presenting augmenting elements for both supports, in particular the matrix. It appears, therefore, that the political pedagogical project (PPP) and the organizational arrangement of the residency program were developed and established in order to promote the full learning on the matrix support. The same is not true with respect to institutional support, for which some gaps should be analyzed. However, if the PPP does not endorse this type of support, the management powers of the work contained in assignments and assessments of residents, includes unique elements of the institutional support. In light of the theoretical framework, discusses the importance of integration between the educational institution and the municipal health system, providing residents an apprenticeship in which practice and theory complement each other. Thus it is apparent that, with this approach, fosters the formation of workers to adequate Unified Health System can affirm that there is an interface between the training process experienced in the residence and the practice of both supports listing, Top basement of the matrix support.
A Estratégia de Saúde da Família (ESF) tem como foco a família e a comunidade, atuando mediante estratégias de promoção, prevenção, recuperação e reabilitação. Complementando as ações das equipes de saúde da família, o apoio matricial compõe-se em um arranjo organizacional que oferece retaguarda especializada tanto assistencial quanto de suporte técnico-pedagógico às equipes e o apoio institucional tem o intuito de favorecer os espaços de cogestão e de articulação das equipes, possibilitando a ampliação da capacidade de análise destas e facilitando o processo de reflexão acerca das dificuldades do cotidiano. A necessidade de formação dos profissionais aptos a estas mudanças nos serviços de saúde incentivou a criação e desenvolvimento das Residências Multiprofissionais em Saúde. A Universidade Federal de São Carlos (UFSCar) e a Secretaria Municipal de Saúde do município propuseram a inserção da Residência Multiprofissional em Saúde da Família e Comunidade (RMSFC) na rede municipal de saúde, na qual os residentes atuam na lógica da ESF. O estudo objetivou compreender as interfaces entre a atuação como apoiadores e o processo de formação vivenciado na RMSFC da UFSCar. Trata-se de um estudo qualitativo e por meio da aplicação, via online, de um questionário com perguntas abertas e fechadas aos egressos do programa de residência do período de 2007 a 2012, foram obtidas 21 respostas ao questionário. Os dados empíricos foram examinados utilizando-se a análise temática e divididos em dois temas: apoio e rede escola. Para cada tema foram elaboradas duas categorias: apoio matricial como atividade que privilegia o cuidado, a organização do processo de trabalho como enfoque do apoio institucional, cenários de aprendizagem prática e espaços formativo teóricos e teórico práticos. Ao apoio matricial foram atribuídas ações relacionadas ao cuidado em saúde, enquanto que o apoio institucional refere-se à organização do processo de trabalho, segundo os mesmos. Os cenário de aprendizagem prática e teórica, bem como a utilização de ferramentas da educação permanente favorecem a formação de trabalhadores aptos às ações coletivas, apresentando elementos potencializadores para ambos os apoios, em especial o matricial. Constata-se, portanto, que o projeto político pedagógico (PPP) e o arranjo organizacional do programa de residência foram elaborados e estabelecidos de forma a favorecer o completo aprendizado sobre o apoio matricial. O mesmo não ocorre com relação ao apoio institucional, para o qual algumas lacunas devem ser analisadas. Porém, se o PPP não respalda esta modalidade de apoio, a competência de gestão do trabalho, contida nas atribuições e avaliações dos residentes, apresenta elementos próprios do apoio institucional. À luz do referencial teórico, discute-se a importância da aproximação entre a instituição formadora e a rede municipal de saúde, proporcionando aos residentes um aprendizado no qual a prática e a teoria se complementam. Desta maneira é perceptível que, com essa aproximação, fomenta-se a formação de trabalhadores com o perfil adequado ao Sistema Único de Saúde. Pode-se afirmar que há interface entre o processo de formação vivenciado na residência e a prática de ambos os apoios, com melhor embasamento do apoio matricial.
19
Barbière, Romain. "Comportement en fatigue et optimisation de l’interface d’un composite tissé chanvre/époxy : effet de l’humidité Influence of moisture and drying on fatigue damage mechanisms in a woven hemp/epoxy composite : acoustic emission and micro-CT analysis." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0016.
Full textAbstract:
Les composites à renfort d’origine végétale constituent une alternative écologique aux matériaux composites traditionnels tels que les composites à fibres de verre. Cependant, les renforts d’origine végétale sont fortement hydrophiles par rapport à la matrice polymère. Il est donc nécessaire d’étudier l’influence de l’eau sur le comportement mécanique de ces éco-matériaux.Dans ce travail, trois conditionnements ont été mis en place. Le conditionnement Ambiant correspond à l’étude du composite en environnement ambiant : stockage et essais à l’ambiante. Le conditionnement Eau permet d’étudier les échantillons dans des conditions extrêmes d’humidité : les éprouvettes sont saturées en eau puis testées dans une enceinte saturée en humidité. Le conditionnement Séché a pour objectif d’étudier le rôle de la désorption sur les propriétés mécaniques du composite. Des éprouvettes de composite tissé chanvre/époxy de deux orientations, [(0/90)]7 et [(±45)]7, ont été testées en traction et en fatigue suivant les trois conditionnements. Des analyses in situ par émission acoustique et post-mortem par MEB et microtomographie ont été réalisées.Les essais de fatigue ont permis d’établir les courbes de Wöhler pour les deux orientations et les trois conditionnements. Un modèle phénoménologique a été utilisé pour modéliser la durée de vie du composite dans toutes les configurations. Les comparaisons montrent que le conditionnement Eau a une sensibilité à la fatigue plus faible que les conditionnements Ambiant et Séché. La classification des évènements acoustiques a permis d’identifier trois classes correspondant chacune à un type d’endommagement (endommagement matriciel, endommagement interfacial et rupture de fibres). Pour les deux orientations, les résultats ont montré que la proportion en nombre et la cinétique d’apparition de chaque type d’endommagement dépendent du niveau de contrainte maximale appliquée et du type de conditionnement, les endommagements matriciels et interfaciaux étant toujours largement majoritaires. L’analyse microtomographique a montré que les endommagements sont différents selon l’orientation. Cependant, pour chaque orientation, on retrouve le même type d’endommagement pour les trois conditionnements, à différents stades de développement : plus avancé pour le conditionnement Eau, intermédiaire pour le Séché et le moins développé pour l’Ambiant.Pour analyser l’adhésion à l’interface fil/matrice, des tests de fragmentation ont été réalisés sur des éprouvettes monofilamentaires chanvre/époxy. Un moule spécifique a été conçu et développé pour réaliser ces éprouvettes par coulée. Un suivi par émission acoustique couplé à des observations en lumière polarisée a permis de mieux comprendre le phénomène de fragmentation dans ce type d’éprouvettes. Les valeurs de la contrainte maximale de cisaillement à l’interface fil/matrice (IFSS) ont été calculées et les longueurs de décohésion interfaciale ont été mesurées. Les résultats montrent que l’interface fil/matrice est affaiblie après séchage, avec une diminution de l’IFSS de 33%. Pour améliorer l’adhésion à l’interface, un traitement au peroxyde d’hydrogène et un traitement par plasma froid ont été appliqués au renfort de chanvre. Les tests de fragmentation montrent que l’IFSS est presque deux fois plus élevée avec le traitement au peroxyde et trois fois plus avec le plasma, par rapport aux éprouvettes non traitées. Un changement d’échelle a ensuite été effectué en appliquant le traitement au peroxyde d’hydrogène sur le tissu de chanvre. Le comportement en traction et en fatigue des composites chanvre/époxy élaborés avec ce tissu traité a été étudié. Les résultats obtenus à cette échelle ne sont pas satisfaisants. Le traitement par plasma reste donc la voie la plus prometteuse, mais appliquer cette technique à l’échelle d’un tissu est complexe et nécessite de mettre au point un nouveau réacteurPlant fibre composites are an environmentally friendly alternative to traditional composite materials such as fibreglass composites. However, plant fibres are highly hydrophilic in comparison with the polymer matrix. It is therefore necessary to study the influence of moisture on the mechanical behaviour of these eco-materials.In this work, three conditionings were applied. “Ambient” samples were stored and tested in ambient environment. “Wet” samples were immersed in water until saturation and tested in a climatic chamber at RH97. The objective of the “Wet/Dry” conditioning was to study the role of desorption on the mechanical properties of the composite. Woven hemp/epoxy composite samples with two orientations, [(0/90)]7 and [(± 45)]7, were tested in tension and fatigue according to the three conditionings. In situ analyses by acoustic emission and post-mortem analyses by SEM and micro-CT were carried out.Fatigue tests allowed to determine the Wöhler curves for the two orientations and the three conditionings. A phenomenological model was used to simulate the fatigue life of the composite in all configurations. The comparisons showed that the Wet samples exhibit a lower tensile strength than the Ambient specimens and a lower fatigue sensitivity, while the behaviour of the Wet/dry samples is similar to the Wet conditioning one concerning the tensile strength and similar to the Ambient one concerning the fatigue sensitivity. The classification of acoustic events allowed the identification of three clusters, each cluster corresponding to a type of damage (matrix damage, interfacial damage and fibre breakage). For the two orientations, the results showed that the proportion in number and the kinetics of development of each type of damage depend on the level of the maximum applied stress and on the conditioning. Matrix and interfacial damages are largely the most numerous acoustic events for all the configurations. Micro-CT analysis showed that the damage is different depending on the orientation. However, for each orientation, the same type of damage is observed for the three conditionings, at different stages of development: more advanced for the Wet conditioning, intermediate for the Wet/Dry one and the least developed for the Ambient one.The analysis of the yarn/matrix interface adhesion was performed through fragmentation tests realised on monofilament hemp/epoxy specimens. A specific mould was designed and developed to produce these specimens by casting. Acoustic emission monitoring and observations in polarized light allowed a better understanding of the fragmentation phenomenon in this type of material. The Interfacial Shear Strength (IFSS) values were calculated and the interfacial debonding lengths were measured. The results show that the yarn/matrix interface is weakened after drying, with a decrease in IFSS of 33%. To improve adhesion at the interface, treatments with hydrogen peroxide and non-thermal plasma were applied to the hemp yarns. Fragmentation tests showed that IFSS is almost twice as high with the peroxide treatment and three times higher with plasma, compared to untreated specimens. An upscale was made by applying the hydrogen peroxide treatment to the hemp fabric. The tensile and fatigue behaviour of hemp/epoxy composites produced with this treated fabric was studied. The results obtained at this scale are disappointing. Therefore, the non-thermal plasma treatment remains the most promising solution, but applying this technique at the fabric scale is complex and requires the development of a new reactor
20
Taddei, Fabio. "Spin-polarized transport in superconducting and ferromagnetic nanostructures." Thesis, Lancaster University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369499.
Full text
21
Nouvian, Laurine. "Élaboration et caractérisation d'une nouvelle matrice céramique pour CMC par réaction solide-gaz activée et expansive." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0187.
Full textAbstract:
Parmi les différents procédés d’élaboration d’un composite à matrice céramique (CMC), peu d’entre eux permettent d’obtenir un matériau dont la densité dépasse 90%, hormis la Melt Infiltration (MI). Le but de cette thèse est donc d’élaborer une nouvelle matrice céramique pour obtenir un CMC avec une porosité résiduelle inférieure à 10%. En se basant sur le procédé présenté par Peter Greil en 1992, cette matrice est élaborée selon un procédé hybride combinant d’une part la voie liquide et d’autre part la voie solide. Ainsi, une charge réactive pulvérulente, composée d’un mélange de TiSi2 et de Ni, a été associée à une résine précéramique. Lors de sa nitruration, la poudre s’expanse et compense le retrait volumique de la résine. Par pyrolyse de la résine et nitruration de la poudre, sous diazote, une matrice type nitrure est formée. L’additif métallique ajouté, Ni, favorise la nitruration de la poudre qui, sans son ajout, demeure partiellement nitrurée : Du Si libre subsiste dans la matrice, et détériore les propriétés du matériau. Un certain nombre de paramètres influe sur cette réaction : la granulométrie de la poudre, la méthode de broyage, la teneur en nickel, les impuretés, la mise en forme ou encore la durée et la température du traitement thermique. L’ensemble de ces paramètres a été étudié afin d’élaborer la matrice souhaitée. Cette nouvelle matrice a ensuite été caractérisée afin d’étudier l’évolution de sa porosité, ainsi que son comportement physico-chimique tel que sa résistance à l’oxydation ou sa stabilité thermique. Enfin, la faisabilité d’un composite a été étudiée pour conclure ces travaux de rechercheAmong the various processes for producing a ceramic matrix composite (CMC), few of them make it possible to obtain a material whose density exceeds 90%, except for Melt Infiltration (MI). The aim of this thesis is to develop a new ceramic matrix to develop a CMC with a residual porosity of less than 10%. Based on the process presented by Peter Greil in 1992, this matrix is developed using a hybrid process combining both the liquid and the solid paths. Thus, a powdered reactive filler composed of a mixture of TiSi2 and Ni has been associated with a preceramic resin. During its nitridation, the powder expands and compensates for the volume shrinkage of the resin. By pyrolysis of the resin and nitridation of the powder, under nitrogen, a nitride type matrix is formed. The metal additive, Ni, promotes the nitridation of the powder which, without its addition, remains partially nitride: Free Si remains in the matrix, and deteriorates the properties of the material. Several parameters influence this reaction: the particle size of the powder, the grinding method, the nickel content, the impurities, the shaping or the duration and the temperature of the heat treatment. All these parameters have been studied in order to elaborate the desired matrix. This new matrix was then characterized in order to study the evolution of its porosity, as well as its physicochemical properties such as its resistance to oxidation or its thermal stability. Finally, the feasibility of a composite was studied to complete this work
22
Shi, Jingyi [Verfasser], Winfried [Akademischer Betreuer] Petry, Winfried [Gutachter] Petry, and Peter [Gutachter] Böni. "Qualification of U-Mo fuel for research reactors: Characterisation of the interfaces between U-Mo kernel, diffusion barrier and Al matrix under heavy ion irradiation / Jingyi Shi ; Gutachter: Winfried Petry, Peter Böni ; Betreuer: Winfried Petry." München : Universitätsbibliothek der TU München, 2021. http://d-nb.info/1240384238/34.
Full text
23
Scaffa, Polliana Mendes Candia 1983. "Estudo do perfil proteolítico da matriz dentinária e interface adesiva = comportamento mecânico, bioquímico e efeito da clorexidina." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/289853.
Full textAbstract:
Orientador: Marcela Rocha de Oliveira Carrilho, Mario Fernando de GóesTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
Made available in DSpace on 2018-08-22T04:19:13Z (GMT). No. of bitstreams: 1 Scaffa_PollianaMendesCandia_D.pdf: 3692601 bytes, checksum: 6b5331b03a6d5fcfc0192039b767ea01 (MD5) Previous issue date: 2012
Resumo: Para o entendimento do processo de adesão à dentina é fundamental conhecer a estrutura bioquímica e biomecânica deste substrato em condições normais ou quando submetido às diferentes etapas do procedimento restaurador adesivo. Evidências indicam que a reportada degradação da camada híbrida pode ocorrer pela ação de enzimas proteolíticas, pertencentes à família das metaloproteinases da matriz (MMPs) e das cisteíno-catepsinas (CTs). No entanto, é ainda necessário elucidar as funções biológicas dessas enzimas nesse processo, bem como, definir uma estratégia para prolongar a durabilidade das restaurações adesivas. O presente estudo teve como objetivo caracterizar o perfil proteolítico da dentina humana frente a sua exposição a diferentes concentrações de digluconato de clorexidina (CHX), um potente inibidor da atividade de MMPs. O efeito da CHX sobre a atividade proteolítica intrínseca da dentina foi avaliado a partir da análise do comportamento mecânico e bioquímico da matriz dentinária e da durabilidade de restaurações adesivas. No primeiro estudo, foi analisada a capacidade da CHX em inibir a atividade das CTs (B, K e L) por hidrólise de substratos fluorogênicos específicos, verificando a afinidade de ligação entre a CHX e as enzimas. No segundo estudo, o tratamento da matriz de dentina com diferentes concentrações de CHX foi avaliado pela análise do módulo de elasticidade e do grau de hidrólise do colágeno (liberação de hidroxiprolina) após armazenagem das amostras em solução fisiológica por 1 dia, 7 ou 30 dias. Finalmente, a função terapêutica da CHX como agente inibitório da atividade proteolítica da dentina foi investigada a partir de sua capacidade em preservar a integridade mecânica (resistência de união) e morfológica de interfaces adesivas tratadas com diferentes concentrações de CHX (0,2; 2,2 e 22 mM) e armazenadas por 6 a 18 meses. No terceiro estudo, a presença das CT-B e CT-K na dentina humana foram avaliadas por imunomarcação em MEV e MET. A atividade enzimática das MMPs e CTs na dentina e uma possível interação entre as duas famílias de enzimas foram verificadas por zimografia in situ e por espectrofluorimetria. Os resultados mostraram, de forma até então inédita, que a CHX é um potente inibidor das CTs presentes no complexo dentino-pulpar. No entanto, a CHX não foi capaz de preservar integralmente o módulo de elasticidade (E) da matriz dentinária após o período mais longo de armazenagem. De modo similar, maior grau de hidrólise do colágeno ocorreu após 30 dias de armazenamento para as amostras que não foram tratadas com CHX ou que foram tratadas com baixa concentração da mesma (0,2 mM) (p<0,05). Notavelmente, o grau de hidrólise do colágeno foi mínimo ou insignificante quando a matriz dentinária foi tratada com concentração mais elevada de CHX (22 mM) (p>0,05). A CHX não afetou a resistência de união imediata da interface adesiva e preservou a resistência da união dentina/resina mesmo após 6 ou 18 meses de armazenamento. Similarmente, menor grau de nanoinfiltração com prata, significando maior integridade morfológica, foi observado para os espécimes tratados com CHX e envelhecidos por 6 ou 18 meses em comparação com as amostras do grupo controle. As imagens de imuno-histoquímica mostraram que as proteases CT-B e CT-K estão presentes na dentina humana, e não apenas na região de pré-dentina e interior dos túbulos dentinários como anteriormente antecipado. A zimografia in situ sugere que a atividade gelatinolítica das MMPs na dentina parece ser preponderante em relação à atividade das CTs, embora a espectrofluorimetria sugira que a atividade proteolítica de ambas as famílias de enzimas esteja presente no tecido dentinário. Dessa forma, concluiu-se que MMPs e CTs podem atuar sinergicamente na degradação da matriz orgânica dentinária, mas que parte dessa atividade proteolítica pode ser controlada pela presença de CHX, sobretudo, se essa estiver confinada no interior da camada híbrida
Abstract: To better understand the process of adhesion to dentin is essential to understand the biochemical and biomechanical structures of this substrate under normal conditions or when subjected to the different steps of the adhesive restorative procedure. Evidences indicate that the hybrid layer degradation can result from the activity of proteolytic enzymes, belonging to the family of matrix metalloproteinases (MMPs) and cysteine-cathepsins (CTs). However, it is still necessary to comprehend the role of these enzymes in this degrading process as well as to determine the best way to extend the durability of adhesive restorations. The general purpose of the present study was to characterize the human dentin proteolytic profile when exposed to different concentration of chlorhexidine digluconate (CHX), a potent inhibitor of MMPs activity. The effect of CHX on the dentin endogenous proteolytic activity was evaluated by the analysis of dentin matrix mechanical and biochemical properties and adhesive restorations durability. The first study evaluated the CHX ability to inhibit CTs (B, K and L) activity by the hydrolysis of fluorogenic substrates, verifying the binding affinity between CHX and enzymes. The dentin matrix treatment with different CHX concentrations was evaluated in the second study by the elastic modulus (E) and degree of collagen hydrolysis (hydroxyproline release) after storage for 1, 7 or 30 days in saline solution. Finally, the CHX therapeutic action as an inhibitor of dentin proteolytic activity was investigated by its ability to maintain the mechanical (bond strength) and morphological (nanoleakage) properties of adhesive interfaces treated with different CHX concentrations (0.2, 2.2 and 22 mM) after aging for 6 to 18 months. The third study evaluated the presence of CT-B and CT-K in human dentin using immunolabeling in SEM and TEM. MMPs and CTs proteolytic activities and a possible interaction between these two families were verified by in situ zymography and by spectrofluorimetry. Results showed, for the first time, that the CHX is a potent inhibitor of CTs in the pulp-dentin complex. However, CHX was not able to preserve the integrity of the dentin matrix E after the longest storage period. Likewise, higher collagen hydrolysis occurred after 30 days of storage when the samples were not treated or treated with low CHX concentration (0.2 mM) (p<0.05). It was noticeable that the collagen hydrolysis was minimum or insignificant when the dentin matrix was treated with the highest CHX concentration (22 mM) (p>0.05). CHX did not affect the immediate bond strength of adhesive interfaces and preserved the resin/dentin bond strength even after 6 or 18 months of storage. Similarly, less nanoleakage with silver particles, which means better morphological integrity, was observed for specimens treated with CHX and aged for 6 or 18 months in comparison with control samples. Immunohistochemistry images showed that the proteases CT-B and CT-K are present in human dentin matrix, not only in pre-dentin region and inside the dentin tubules as previous suggested. In situ zymography suggests that the MMPs gelatinolytic activity in dentin seems to be predominant when compared to CTs activities, although the spectrofluorimetry suggests that the proteolytic activity of both families of enzymes are present in dentin. In this way, it was concluded that MMPs and CTs may synergistically act in the dentin organic matrix degradation, but part of this proteolytic activity can be controlled by the presence of CHX, especially when it is restrained inside the hybrid layer
Doutorado
Materiais Dentarios
Doutora em Materiais Dentários
24
Di, Stasio Luca. "Effet de la microstructure sur le décollement à l'interface fibre/matrice dans les stratifiés à matrice polymère avec renfort en fibre soumis à traction." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0229.
Full textAbstract:
L'objectif principal de cette thèse est d'étudier l'effet de la microstructure sur l'amorçage et propagation de décollements entre fibre et matrice. Dans ce but, des modèles de Volume Elémentaire Représentatif (VER) des composites unidirectionnels et des stratifiés croisés sont développés, caractérisés par différentes configurations des fibres et degré d'endommagement. L'amorçage du décollement est analysé par rapport à la distribution des contraintes à l'interface entre fibre et matrice. En revanche, la propagation du décollement est étudiée avec l'approche de la Mécanique Linéaire Elastique de la Rupture (MLER), et plus spécifiquement avec l'évaluation du taux de restitution d'énergie en Mode I et Mode II. Les champs de déplacement et contrainte sont calculés avec la Méthode des éléments finis (MEF) dans le logiciel Abaqus. La détermination des composants du taux de restitution d'énergie est effectuée avec la technique de fermeture virtuelle de fissure implémentée par l'auteur en langage Python. La solution élastique du problème de décollement entre fibre et matrice est caractérisée par la présence de deux régimes : celui de fissure ouverte et celui de fissure fermée. Dans le premier cas, il n'existe aucun contact entre les lèvres du décollement et les champs des déplacements et contraintes présentent une singularité oscillatoire. Un 'étude de convergence de la technique de fermeture virtuelle de fissure est donc requis et constitue le premier élément du travail de cette thèse. Ensuite, la propagation de décollement est étudiée dans Volume Elémentaire Représentative de : composites unidirectionnels avec épaisseur variable, mesuré par le nombre des rangées des fibres ; stratifié croisé avec un pli central à 90° d'épaisseur variable, mesuré par le nombre des rangées des fibres ; composites unidirectionnels épais, modélisés comme infinis à travers l'épaisseur. Configurations multiples de l'endommagement sont aussi examinées, qui correspondent à différentes étapes du processus d'amorçage des fissures transverses : décollements isolés ; décollements interagissant distribués dans la direction d'application de la charge mécanique ; décollements localisés sur fibres consécutives à travers l'épaisseur. Enfin, la taille du décollement juste après l'amorçage et la taille ultime du décollement sont estimées à partir de l'analyse de la distribution des contraintes à l'interface entre fibre et matrice (pour l'amorçage) et sur la base du critère de Griffith de la MLERThe main objective of the present work is to investigate the influence of the microstructure on debond growth along the fiber arc direction. To this end, models of 2-dimensional Representative Volume Elements (RVEs) of Uni-Directional (UD) composites and cross-ply laminates are developed. The Representative Volume Elements are characterized by different configurations of fibers and different damage states. Debond initiation is studied through the analysis of the distribution of stresses at the fiber/matrix interface in the absence of damage. Debond growth on the other hand is characterized using the approach of Linear Elastic Fracture Mechanics (LEFM), specifically through the evaluation of the Mode I, Mode II and total Energy Release Rate (ERR). Displacement and stress fields are evaluated by means of the Finite Element Method (FEM) using the commercial solver Abaqus. The components of the Energy Release Rate are then evaluated using the Virtual Crack Closure Technique (VCCT), implemented in a custom Python routine. The elastic solution of the debonding problem presents two different regimes: the open crack and the closed crack behavior. In the latter, debond faces are in contact in a region of finite size at the debond tip and it is known that stress and displacement fields at the debond tip present an oscillating singularity. A convergence analysis of the VCCT in the context of the FEM solution is thus required to guarantee the validity of results and represents the first step of the work presented in this thesis. Debond growth under remote tensile loading is then studied in Representative Volume Elements of: UD composites of varying thickness, measured in terms of number of rows of fibers; cross-ply laminates with a central 90° ply of varying thickness, measured as well in terms of number of rows of fibers; thick UD composites (modelled as infinite along the through-the-thickness direction). Different damage configurations are also considered, corresponding to different stages of transverse crack onset: non-interacting isolated debonds; interacting debonds distributed along the loading direction; debonds on consecutive fibers along the through-the-thickness direction. Finally, an estimation of debond size at initiation and of debond maximum size is proposed based on arguments from stress analysis (for initiation) and on Griffith's criterion from LEFM (for propagation)
25
Elouaer, Abdelmonem. "Contribution à la compréhension et à la modélisation du comportement mécanique de matériaux composites à renfort en fibres végétales." Thesis, Reims, 2011. http://www.theses.fr/2011REIMS003/document.
Full textAbstract:
L’industrie des matériaux composites ne cesse d’évoluer et de croître en mettant en place de nouveaux matériaux et de nouvelles technologies. En substitution des matériaux d’origine fossile que les matériaux d’origine naturelles (et surtout végétales) commencent à voir le jour. C’est dans ce contexte que notre travail de recherche est proposé. Il s’intéresse à la caractérisation du comportement mécanique d’un composite à matrice Polypropylène, renforcé avec des fibres de Chanvre et du bois de Chanvre (Chènevotte). Les différents moyens et techniques de caractérisation, utilisés par la présente étude, ont montré que ces nouveaux matériaux sont dotés de propriétés, en particulier mécaniques, de haut niveau, qui viennent rivaliser avec celles des autres composites classiques à base de fibres de verre et de carbone.Les essais expérimentaux en statique et de fatigue, ont révélé beaucoup de détails en comparaison avec d’autres matériaux composites. Ces informations ont permis de créer une sorte de base de données qui pourra servir de référence pour d’autres composites de la même famille à base de fibres végétales. Ainsi, des mécanismes d’endommagement ont été mis en évidence grâce aux essais mécaniques (traction monotone, charge-décharge, …) associés à des observations microscopiques (Microscope Electronique à Balayage), et à des outils de détection du dommage basés sur l’émission acoustique. Par le biais de cette technique, nous avons pu apprécier la qualité et l’importance de l’interface fibre/matrice qui est un paramètre fondamental pour la présente étude et pour la détermination de la loi de comportement du composite.La modélisation micromécanique a été intégrée dans ce travail de thèse, grâce au modèle de Mori-Tanaka. Le comportement des matériaux à l’endommagement n’a pas été pris en considération ; seule l’élasticité a été étudiée. A l’aide de ce modèle, nous avons pu remonter aux propriétés intrinsèques des constituants (le module d’élasticité longitudinale des renforts: Chanvre et Chènevotte)The composites industry continues to evolve and grow by developing new materials and new technologies. Replacing fossil materials by materials with natural origin (especially vegetable) seems to be one of the most promising. In this context our research is proposed. It is interested to characterize the mechanical behavior of a polypropylene matrix composite reinforced with fibers of Hemp and Wood of Hemp (Chenevotte). The various means and characterization techniques used in this study showed that these new materials have interesting mechanical properties, coming rival those of other conventional composites based on carbon and glass fibers.The experimental static and fatigue tests have revealed many details in comparison with other composite materials. The information help creates a database that can serve as reference for other composites of the same family and vegetable fibers. Mechanisms of damage have been highlighted through mechanical tests (tensile monotonous charge-discharge …) associated with microscopic observations (Scanning Electron Microscope), and tools for damage detection based on emission acoustics. Thanks to this technique, we could improve the quality of the interface fiber / matrix which is a basic parameter for this study and for determining the behavior of composite.Micromechanical modeling has been integrated in this thesis, through the Mori-Tanaka model. The behavior of materials during damage has not been taken into account: only the elasticity has been studied. Using this model, we were able to trace the intrinsic properties of the constituents (the longitudinal modulus of elasticity of the reinforcements: Hemp and Chenevotte)
26
Escobar-Mejia, Andres. "Indirect Matrix Converter as Standard Power Electronic Interface." Thesis, University of Arkansas, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3667722.
Full textAbstract:
The increase in the penetration levels of distributed generation in the modern power grid and its importance in future energy systems have accelerated the interest of developing new power electronic interfaces for the energy conversion process. The feasibility of applying the indirect matrix converter as the standard power electronic interface for applications with power ratings from several kW to few MW is addressed in this dissertation. Special attention is given to those applications where space dominates the power electronic requirements. The main motivation for using the indirect matrix converter is that eliminates the energy storage component in the way of a dc-link capacitor for the energy conversion process. This contributes to reduce size and weight, and potentially, increase reliability of the power electronic interface. Two main new contributions are presented. First, a new power electronic interface that allows the connection of two ac power grids through a medium- or high-voltage dc system is proposed. The new topology contemplates the use of two high-voltage dc-link converters based on the modular multilevel converter, two indirect matrix converters and two medium-frequency transformers. Second, a new sensorless control technique working in the d – q reference is developed. The controller is used to interface a distributed generation unit to the power grid when the indirect matrix converter is used as the power electronic interface. The design and performance of the proposed power electronic interface is validated through time-domain simulations and a laboratory prototype is built to experimentally validate the sensorless controller.
27
Smith, Joel Edmund. "Development of improved metal matrix composite via the control of interface and matrix microstructure." Thesis, University of Bath, 1995. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296330.
Full text
28
Zhuang, Linqi. "Fiber/matrix interface crack propagation in polymeric unidirectional composite." Licentiate thesis, Luleå tekniska universitet, Materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17391.
Full textAbstract:
Fiber/matrix interface cracking plays an important role in determining the final failure of unidirectional composites. In the present study, energy release rate (ERR) for fiber/matrix interface debond growth originated from fiber break in unidirectional composite is calculated using 5-cylinders axisymmetric and 3-D FEM models with hexagonal fiber arrangement. In the model the debonded fiber is central in the hexagonal unit which is surrounded by effective composite. The effect of neighboring fibers focusing on local fiber clustering on the ERR is analyzed by varying the distance between fibers in the unit. Two different scenarios are considered, one is the steady-state debond where debond are long and thus there is no interaction between debond tip and fiber break; the other case is when debond are relatively short when debond tip interacts with fiber break. The steady-state ERR is calculated from potential energy difference between a unit in the bonded region far away from the debond front and a unit in the debonded region far behind the debond front. The ERR for different modes of crack propagation is obtained from a FEM model containing a long debond by analyzing the stress at the debond front. For very short debonds, the ERR was calculated by both the J integral and the Virtual crack closure technique (VCCT).For steady-state debond growth, results show that in mechanical axial tensile loading fracture Mode II is dominating, it has strong angular dependence (effect of closest fibers) but the average ERR is not sensitive to the local fiber clustering. In thermal loading the Mode III is dominating and the average ERR is highly dependent on the distance to neighboring fibers. For short debod growth, results show that the debond growth is Mode II dominated and that the ERR strongly depends on the angular coordinate. The local fiber clustering has larger effect on the angular variation for shorter debonds and the effect increases with larger local fiber volume fraction. Finally, the ERR values from 5-cylinder axisymmetric model could be considered as upper bound for the 3-D hexagonal model.Godkänd; 2016; 20160415 (linzhu); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Linqi Zhuang Ämne: Polymera konstruktionsmaterial/Polymeric Composite Material Uppsats: Fiber/Matrix Interface Crack Propagation in Polymeric Unidirectional Composite Examinator: Professor Janis Varna, Avdelningen för materialvetenskap, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet, Luleå. Diskutant: PhD, R&D Manager Anders Holmberg, ABB AB Composites, Piteå. Tid: Fredag 27 maj, 2016 kl 15.00 Plats: F531, Luleå tekniska universitet
29
Miller, Sandi G. "Effects of Nanoparticle and Matrix Interface on Nanocomposite Properties." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1216947385.
Full text
30
Limaiem, Sarra. "Étude et développement d’une interface fibre-matrice spécifique dans les composites à matrice thermoplastique renforcés en fibres de verre continues." Thesis, Mulhouse, 2016. http://www.theses.fr/2016MULH8553.
Full textAbstract:
Au cours de cette étude, il a été question de développer une méthodologie d’élaboration et d’évaluation de la qualité de l’interface fibre-matrice au sein d’un composite à matrice polyamide 12 renforcé par du verre. Un modèle macroscopique a été élaboré dans un premier temps sous forme d’un assemblage lame de verre/film polyamide 12, et plusieurs promoteurs d’adhésion, principalement des organosilanes, de fonctionnalités différentes et compatibles avec la matrice polyamide ont été testés. La qualité du greffage a pu être caractérisée grâce à des techniques d’analyses physico-chimiques adaptées (AFM, PM-IRRAS, mouillabilité,…), et la performance adhésive des assemblages a pu être évaluée par des tests mécaniques spécifiques (pelage, clivage). Dans une seconde étape, le protocole de dépôt décrit à l’échelle macroscopique a été adapté à l’échelle des fibres de verre, plus particulièrement à l’échelle mésoscopique des fibres optiques. Des essais mécaniques spécifiques à l’échelle microscopique (fragmentation) ont été réalisés afin d’évaluer la performance adhésive de l’interface dans les assemblages concernés. Une étude focalisée sur la compréhension des mécanismes interfaciaux a également été réalisée afin de clarifier la nature des interactions établies à l’interface fibre-matrice. Grâce aux différentes techniques de caractérisation physico-chimiques il a été possible de mettre en évidence l’influence de différents paramètres expérimentaux, tels que la durée du greffage, la densité de greffage et la chimie des surfaces traitées, sur la cristallisation de la matrice à l’interface. La dernière partie de ce travail de thèse concerne le passage à l’échelle du semi-produit sous forme de rubans. Des analyses des propriétés de l’interface ainsi que des caractéristiques mécaniques ont été réaliséesDuring this study, the aim was to develop a methodology to elaborate and evaluate the quality of the fiber-matrix interface in a glass fiber reinforced polyamide 12 composite.At first, a macroscopic model was developed using a glass slide/polyamide 12 film assembly. Several organosilane adhesion promoters with different features and compatible with the polyamide matrix were tested. The grafting quality was characterized through appropriate physico-chemical analytical techniques (AFM, PM-IRRAS, Wetting…), and the adhesive performance of the assemblies was evaluated by specific mechanical tests (Peel test, Wedge test). In a second step, the deposition procedure described in macroscopic scale has been adapted to the glass fibers’ scale, more particularly to optical fibers. Specific mechanical tests were performed (fragmentation test) to assess the adhesive performance at the interface of the concerned assemblies.A study focused on the understanding of the interfacial mechanisms was also conducted to clarify the nature of the interactions established at the fiber-matrix interface. Thanks to the different physico-chemical characterization techniques, it has been possible to demonstrate the influence of various experimental parameters such as the surface treatment time, the grafting density and the chemistry on the treated surfaces on the crystallization of the matrix at the interface. The last part of this work concerns the transition to the semi-scale form of ribbons. The analysis of the interface’s properties and the mechanical characteristics has been investigated
31
Azina, Clio. "Optimisation de multi-matériaux à base de diamant pour la gestion thermique." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0767/document.
Full textAbstract:
De nos jours, l'industrie microélectronique utilise des fréquences de fonctionnement plus élevées dans les composants commercialisés. Ces fréquences entraînent des températures de fonctionnement plus élevées et limitent donc l'intégrité et la durée de vie des composants électroniques. Cependant, les besoins actuels nécessitent des dispositifs miniaturisés et de haute densité de puissance. De ce fait, la dissipation thermique dans les composants microélectroniques s’avère capitale. Ainsi, des drains thermiques sont utilisés pour évacuer la chaleur produite par le fonctionnement du composant. Les drains thermiques actuels sont composés de métaux, tels que le cuivre et l’aluminium, présentant des conductivités et des coefficients de dilatation thermiques élevés. Néanmoins, les coefficients de dilatation thermique des différents matériaux présents dans un circuit peuvent induire des contraintes thermo-mécaniques aux interfaces et engendrer une défaillance des composants après plusieurs cycles de fonctionnement. Dans ce contexte, nous proposons de remplacer ces drains métalliques par un système composite à matrice cuivre renforcée par du carbone, sur lequel est déposé un diffuseur thermique sous forme de diamant. Ces composites Cu/C présentent des propriétés thermo-mécaniques adaptatives pouvant palier aux contraintes induites durant l’utilisation des composants. Le transfert optimal des propriétés dans les MMC est souvent compromis par l'absence de liaison chimique interfaciale, en particulier dans les systèmes non réactifs telsque Cu/C. Cependant, pour un assemblage thermiquement efficace, l'interface devrait permettre un bon transfert de charges thermo-mécaniques entre les matériaux. L'objectif de cette étude est de combiner les propriétés exceptionnelles du diamant et les propriétés thermo-mécaniques adaptatives des MMC. Les composites à matrice de cuivre renforcés au carbone sont synthétisés à l'aide d'un processus dit semi-liquide pour obtenir des gradients de composition et des propriétés optimisées d'interface matrice - renfort. Par conséquent, des éléments d'alliage sont insérés dans le matériau pour former des interphases de carbure à l'interface Cu/C. Le film mince de diamant est obtenu par dépôt chimique en phase vapeur assisté par laser. Cette méthode de dépôt permet d’agir sur la qualité du film ainsi que sur l’adhésion avec le substrat composite. Finalement, une importance particulière est portée à l’influence des interfaces sur les propriétés thermiques tant au sein du matériau composite (interface matrice – renfort), qu’au sein de l’assemblage film diamant – MMC.Ces travaux ont été menés dans le cadre d’un accord franco-américain de cotutelle de thèse entre l’Institut de Chimie de la Matière Condensée de l’Université de Bordeaux, en France, et le département d’Ingénierie Electrique de l’Université du Nebraska-Lincoln, aux Etats-Unis. Ils ont été financés, en France, par la Direction Générale de l’Armement (DGA), et par l’équivalent Américain aux Etats-UnisToday, the microelectronics industry uses higher functioning frequencies in commercialized components. These frequencies result in higher functioning temperatures and, therefore, limit a component’s integrity and lifetime. Until now, heat-sink materials were composed of metals which exhibit high thermal conductivities (TC). However, these metals often induce large coefficient of thermal expansion (CTE) mismatches between the heat sink and the nonmetallic components of the device. Such differences in CTEs cause thermomechanical stresses at the interfaces and result in component failure after several on/off cycles.To overcome this issue, we suggest replacing the metallic heat sink materials with a heat-spreader (diamond film) deposited on metal matrix composites (MMCs), specifically, carbon-reinforced copper matrices (Cu/C) which exhibit optimized thermomechanical properties. However, proper transfer of properties in MMCs is often compromised by the absence of effective interfaces, especially in nonreactive systems such as Cu/C. Therefore, the creation of a chemical bond is ever more relevant. The goal of this research was to combine the exceptional properties of diamond by means of a thin film and the adaptive thermomechanical properties of MMCs. Carbon-reinforced copper matrix composites were synthesized using an innovative solid-liquid coexistent phase process to achieve designed composition gradients and optimized matrix/reinforcement interface properties. In addition, the lack of chemical affinitybetween Cu and C results in poor thermal efficiency of the composites. Therefore, alloying elements were inserted into the material to form carbide interphases at the Cu/C interface. Their addition enabled the composite’s integrity to be optimized in order to obtain thermally efficient assemblies. The diamond, in the form of a thin layer, was obtained by laser-assisted chemical vapor deposition. This process allowed action on the film’s phase purity and adhesion to the substrate material. Of particular importance was the influence of the interfaces on thermal properties both within the composite material (matrix-reinforcement interface) and within the diamond film-MMC assembly. This work was carried out within the framework of a Franco-American agreement between the Institute of Condensed Matter Chemistry of the University of Bordeaux in France and the Department of Electrical Engineering at the University of Nebraska-Lincoln, in the United States. Funding, in France, was provided by the Direction Générale de l’Armement (DGA), and by the American equivalent in the United States
32
Kieschke, Robert Richard. "The interface region in titanium reinforced with silicon carbide monofilaments." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335165.
Full text
33
Yhuel, Grégory. "Contribution à l’étude de polyesters aliphatiques renforcés par des fibres naturelles." Thesis, Reims, 2011. http://www.theses.fr/2011REIMS019/document.
Full textAbstract:
De par ses propriétés thermomécaniques proches des polyoléfines, le poly(butylene succinate)est l’un des polymères biosourcés les plus attractifs pour la substitution de matériaux pétro-sourcés pour des applications automobiles. L’incorporation de fibres de chanvre, via une étape d’extrusion,renforce la matrice et permet de tendre vers les propriétés cibles exigées par les cahiers des charges automobiles pour les applications visées dans cette étude. Afin d’améliorer les propriétés thermomécaniques de ce matériau, trois sujets ont été développés dans cette étude :1- Qualification de l’interface PBS / fibres de chanvre : via une nouvelle méthodologie basée sur l’analyse de la contribution effective des fibres sur la contrainte (CFC) durant une sollicitation mécanique, il est montré que les liaisons hydrogène formées entre le PBSet la fibre influent fortement sur les mécanismes de transfert de charge. Couplée au modèle de Bowyer et Bader, cette approche permet d’identifier les mécanismes d’endommagement de l’interface et de quantifier la contrainte interfaciale (τchanvre/PBS=25,2MPa).2 - Signification du ratio L/D d’une fibre naturelle : au cours des procédés de mises en oeuvre (extrusion et injection), la morphologie d’une fibre végétale évolue et apparait complexe due à la structure branchée engendrée par la fibrillation. A partir d’une nouvelleméthodologie d’analyse d’images spécifiquement développée, il est montré que la fibrillation contribue au renforcement de la matrice au même titre que le défibrage.3 -Synthèse de PBS-co-amides : afin de couvrir les contraintes thermomécaniques exigées,l’introduction de groupements amide dans le PBS est étudiée pour augmenter le point de fusion du polymère. Afin de contourner notamment la réaction parasite de cyclisation entre l’acide succinique et les amines, une stratégie de synthèses multi-étapes de monomères et de poly(ester-amide) est étudiée permettant d’obtenir un PEA de faible masse molaire dont le point de fusion atteint 172°CWith its thermomechanical properties closed to polyolefins, poly(butylene succinate) is one ofthe most interesting bio-based polymers for substitution of oil-based polymers for automotive applications. Addition of hemp fibers, through an extrusion process step, reinforces matrix and enables to fit with the targeted technical profile required by automotive specifications. In order to improve thermomechanical properties, three main topics have been investigated in this study:1 - PBS / hemp fibers interface qualification: through a new methodology based on the analysis of the effective fiber contribution on stress during mechanical solicitation, it was shown that hydrogen bonds between PBS and fibers play a major role in load transfer.Combined with the Bowyer and Bader model, this approach enables to highlight interface damages and to determine the interfacial shear strength (τhemp/PBS=25,2 MPa)2 - Meaning of natural fiber L/D ratio: during processes (extrusion and injection), vegetal fiber morphology changes and becomes complex due to the fibrillated structure. With anew developed image analysis tool, it was shown that fibrillation contributes to matrix einforcement as well as defibering.3 - Synthesis of PBS-co-amide: to reach the targeted thermomechanical performances,introduction of amide groups into PBS was studied to increase the melting point. In order to avoid the cyclic imide formation between succinic acid and amines, synthesis of monomers and poly(ester amide) were studied through a multistep strategy, enabling to get low molecular weight PEA with melting temperature around 172°C
34
Beguinel, Johanna. "Interfacial adhesion in continuous fiber reinforced thermoplastic composites : from micro-scale to macro-scale." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI051.
Full textAbstract:
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
35
Levchuk, Svetlana. "Interface development for a EUROFER steel matrix composite with SiC-fibre reinforcement." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=97895694X.
Full text
36
Karevan, Mehdi. "Understanding effects of nano-reinforcement-matrix interphase on the elastic response of polymer nanocomposites." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52916.
Full textAbstract:
Current technology of polymer nanocomposites (PNC) emphasizes the need for fundamental understanding of the links between manufacturing method and macro-scale properties in order to engineer processing and performance of PNCs. The manufacturing method is one key variable that dramatically defines interfacial interactions on the nano-scale and thus the properties of polymer near the interface of nanomaterial/polymer or interphase, level of dispersion and the crystallization behavior of semi-crystalline PNCs. These factors in particular govern reinforcing mechanisms at the interface and consequently impart important properties to PNCs. The current approach to manufacturing PNCs involves trial and error with elaborate, costly and time consuming experimental characterization of PNCs. Therefore, a deep insight into the links among manufacturing method, interfacial interactions and bulk properties is essential in order to design and fabricate PNCs with engineered performance.
The main goal of this study was to provide a better understanding of the effect of manufacturing methods on the macro-scale properties of PNCs, with a focus on the role of interfacial interactions, that can lead to fabrication of PNCs with multifunctional performance. The objectives of this research were to: i) determine the detail correlations among manufacturing method, nano- and microstructure and macro-scale properties of multifunctional exfoliated graphite nanoplatelets/polyamide 12 polymer nanocomposites with enhanced mechanical and electrical performance through systematic manufacturing and experimental methodologies, ii) understand correlations among nano-scale interfacial interactions, physical and structural properties of the polymer at the interface and macro-scale behavior of PNCs, and iii) evaluate effect of manufacturing method on electrical behavior of PNCs with directionally dependent performance.
This study demonstrated key correlations among manufacturing techniques, interfacial interactions and macro-scale properties of PNCs. A methodology was introduced to understand and determine the characteristics of a complex constrained region produced at the interface of nanomaterials and polymer in semi-crystalline PNCs. Finally, the study illustrated superior electrical and morphological properties of selective laser sintering (SLS) processed parts over injection molded PNCs and thus confirmed the capability of SLS in the development of electrically conductive PNCs that exhibit multifunctional performance. In conclusion, the study provided an insight into the links among process, nano-scale interfacial interactions and microstructure to better understand effects of manufacturing technique on macro-scale properties of PNCs, which enables fabrication of conductive PNCs with multifunctional performance.
37
Filho, Antônio de Pádua Lima. "Interface filamento-matriz e propriedades associadas em compósitos metal-metal." Instituto Tecnológico de Aeronáutica, 1991. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=1780.
Full textAbstract:
É apresentado um estudo experimental das ligas de alumínio com 4,5% de cobre, vazadas a 950C, numa lingoteira pré-aquecida a 800C e a 150C, com arranjos de arames de Nikrothal-20 de O, 55mm de diâmetro, alinhados e dispostos numa direção perpendicular ao fluxo de extração de calor. As amostras do compósito assim obtidas, foram analizadas por microscopia ótica e eletrônica, para caracterizar as variações metalúrgicas na interface matriz-reforço. Além disso, ensaios de tração na direção longitudinal e transversal aos reforços, seguida de análise fratográfica, foram realizados no compósito fundido e envelhecido artificialmente, para avaliar o comportamento mecânico do material (grau de aderência matriz/reforço). Análises pontoadas (micro-análises), efetuadas nas amostras dos compósitos resultantes, para acompanhar os perfis de difusidades dos elementos (AI, Cu, Fe, Cr, Ni, Si e Ti), na interface matriz/reforço, revelaram que o não molhamento, é devido à formação de uma camada espessa de óxido em torno dos reforços, principalmente na parte superior da lingoteira. Por outro lado, em outras regiões ao longo da placa do compósito fundido, o molhamento é efetivado. Através das curvas tensão-deformação do compósito obtido, observa-se que um acréscimo nos produtos de reação interfacial, provoca um aumento no módulo de elasticidade do material.
38
Prangnell, Philip B. "The development of matrix and interface microstructures and their effect on the mechanical behaviour of SiC particulate reinforced Al matrix composites." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239188.
Full text
39
Funn, John V. "Creep behavior of the interface region in continuous fiber reinforced metal-matrix composites." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1997. http://handle.dtic.mil/100.2/ADA341255.
Full textAbstract:
Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, September 1997."September 1997." Thesis advisor(s): Indranath Dutta. Includes bibliographical references (p. 91-93). Also available online.
40
Chambers, Brent Victor. "The synthesis and characterization of model interface couples for inorganic matrix composite applications." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/32135.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994.Includes bibliographical references (leaves 157-164).
by Brent Victor Chambers.
Ph.D.
41
Lafabrier, Aurore. "Etude de l'adhérence de revêtements poudre appliqués sur substrats composites à matrice polymère." Thesis, Toulon, 2014. http://www.theses.fr/2014TOUL0017.
Full textAbstract:
Sur de nombreuses pièces et structures, la peinture garantit une protection de surface et assure l'esthétique du produit final. Cependant, l'arrivée de nouvelles directives visant à réduire les sources de rejets majoritaires de Composés Organiques Volatiles (COV) incite les industriels à s'orienter vers des technologies alternatives aux peintures solvantées classiques, telles que les revêtements poudres. Dans le cas d'un substrat non-conducteur thermosensible, cette substitution implique de développer de nouvelles méthodes de mise en œuvre et d'en optimiser les paramètres.Ce travail de thèse vise à maîtriser l'adhérence et à comprendre les phénomènes d'adhésion de peintures poudre sur substrats composites à matrice organique, d'un point de vue physico-chimique. Notre travail s'est articulé autour d'une peinture poudre et de deux substrats composites dont l'un possède une matrice thermodurcissable (époxy) et l'autre une matrice thermoplastique (PEEK).Dans un premier temps, nous avons analysé l'influence des conditions de mise en œuvre sur l'interface substrat époxy/revêtement, afin de déterminer quel procédé favorise le plus l'adhérence entre la méthode "fond de moule" et l'application directe. Nous nous sommes, ensuite, intéressés à la durabilité de ces systèmes revêtus lors d'un vieillissement hygrothermique. Enfin, nous avons étudié l'effet des traitements plasmas atmosphérique et basse pression sur l'adhérence entre le revêtement poudre et le substrat à matrice PEEKOn many products and structures, the painting ensures surface protection and provides aesthetic of final product. However, the new guidelines to reduce the main release's sources of Volatile Organic Compounds (VOCs) incite the industrials to use alternative to usual solvent-based paints such as powder coatings. In the case of non-conductive and heat-sensitive substrate, this substitution involves the development of new processes and the optimization of their parameters.This thesis is about controlling adhesion and understanding the adhesion of powder coatings on organic matrix composites substrates, on a physico-chemical point of view. Our work focus on a powder coating and two substrates, one containing thermosetting resin (epoxy) and the other a thermoplastic resin (PEEK) .As a first step, we analyzed the influence of the characteristic of the process on the epoxy substrate/coating interface to determine which one promotes the best adhesion between the "in mold-coating" and direct application. Then we studied the durability of these coated systems in a hydrothermal aging. Finally, we studied the effect of atmospheric plasma treatment and low pressure plasma treatment on the adhesion between powder coating and PEEK matrix substrate
42
Zhong, Yunlong [Verfasser]. "Interface Structure, Interface Properties and Tensile Properties of Single Crystalline Al2O3 Fiber Reinforced NiAl and IP75 Matrix Composites / Yunlong Zhong." Aachen : Shaker, 2008. http://d-nb.info/1164341332/34.
Full text
43
Decataldo, Francesco <1992>. "Semiconducting Polymers for Electronic Biosensors and Biological Interfaces." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amsdottorato.unibo.it/9344/1/PhD_Thesis_Complete_Decataldo.pdf.
Full textAbstract:
Bioeletronics aims at the direct coupling of biomolecular function units with standard electronic devices. The main limitations of this field are the material needed to interface soft living entities with hard inorganic devices. Conducting polymers enabled the bridging between these two separate worlds, owing to their biocompatibility, soft nature and the ability to be tailored according to the required application. In particular, the intrinsically conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is one of the most promising polymers, having an excellent chemical and thermal stability, reversible doping state and high conductivity.
This thesis relies on the use of PEDOT:PSS as semiconducting material for biological interfaces and biosensors.
In detail, OECTs were demonstrated to be able to real-time monitor growth and detachment of both strong-barrier and no-barrier cells, according to the patterning of the device active area and the selected geometry. Thus, these devices were employed to assess silver nanoparticles (AgNPs) toxicity effects on cell lines, allowing further insights on citrate-coated AgNPs uptake by the cells and their toxic action, while demonstrating no cytotoxic activity of EG6OH-coated AgNPs.
Moreover, PEDOT:PSS OECTs were proved to be capable of detecting oxygen dissolved in KCl or even cell culture medium, in the oxygen partial pressure range of 0-5%.
Furthermore, PEDOT:PSS OECTs were biofunctionalized to impart specificity on the device sensing capabilities, through a biochemical functionalization strategy, electrically characterized. The resulting devices showed a proof of concept detection of a fundamental cytokine for cells undergoing osteogenic differentiation.
Finally, PEDOT:PSS thickness-controlled films were employed as biocompatible, low-impedance and soft interfaces between the animal nerve and a gold electrode. The introduction of the plasticizer polyethylene glycol (PEG) enhanced the elasticity of the polymer, while keeping good conductivity and low-impedance properties. An in-vivo, chronic recording of the renal sympathetic nerve activity in rats demonstrated the efficiency of the device.
44
Shin, Hyunho. "Interface reactions and their influence on properties of SiC fiber-reinforced ceramic matrix composites." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/19122.
Full text
45
Pubellier, Pierre. "Influence de charges micrométriques sur le vieillissement de composites à matrice polymère." Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1177/document.
Full textAbstract:
La compréhension des phénomènes de vieillissement dans les élastomères réticulés chargés par des particules inorganiques est primordiale pour proposer un critère de fin de vie aux câbles électriques en usage au sein des centrales nucléaires. En effet, la gaine isolante de ces câbles met en jeu une matrice élastomère formulée par différents adjuvants et charges. Une quantité importante de particules inorganiques, du tri-hydrate d’aluminium (ATH), est usuellement introduite au sein de la matrice afin de lui conférer des propriétés anti-feu satisfaisantes. Les particules utilisées sont de taille micrométrique et du fait de la faible surface de contact polymère / charge intrinsèque aux microcomposites, l’ajout d’ATH est supposé n’impliquer aucune modification des mécanismes de vieillissement de la matrice. Or, des travaux récents ont mis en évidence un comportement au vieillissement thermique différent entre une matrice d’EPDM (élastomère à base d’unités éthylène, propylène et diène) chargée par des particules d’ATH micrométriques et la même matrice, sans ATH.L’objectif de cette thèse est de renseigner plus en détail l’effet du vieillissement thermo- et radio-oxydatif sur une matrice d’EPDM chargée par des particules d’ATH et de mieux comprendre les modifications observées. L’influence de paramètres physico-chimiques importants (taux de charges, fonctionnalisation de la surface des charges) sur le comportement en vieillissement sera en particulier abordée. Nous nous sommes, plus précisément, attachés à décrire l’évolution du réseau à l’échelle macromoléculaire, en déterminant les différentes populations du réseau (chaînes élastiquement actives, chaînes pendantes et extractibles) ainsi que la distribution de la densité de réticulation. Ces données ont été obtenues par le biais de la RMN (Résonance Magnétique Nucléaire) du solide.Les résultats de ces expériences montrent une diminution importante de la période d’induction au vieillissement thermo-oxydatif des matrices d’EPDM lors de l’ajout de particules d’ATH dans le réseau. Cet effet dépend fortement de la quantité de charges ATH introduites et de la fonctionnalisation ou non de leur surface. Lors du vieillissement radio-oxydatif, en revanche, aucune modification des cinétiques de vieillissement n’est observée. La confrontation des données issues des deux types de vieillissement suggère une modification des mécanismes d’amorçage de l’oxydation, dans les réseaux d’EPDM, lorsque ces derniers sont chargés par des particules d’ATH. Le rôle des interfaces charge / matrice semble donc déterminant dans ces modificationsA deep understanding of the ageing behaviour within cross-linked elastomers filled by inorganic particles is a key feature to propose a criterion for the end of life of electric cables in nuclear power plants. Indeed, materials used for wire insulation are usually composed of rubbers designed with several adjuvants and fillers. A significant amount of inorganic particles, such as aluminium trihydrate (ATH), is usually incorporated with the polymer matrix in order to achieve satisfactory fire-retardant properties. The ATH particles used are characterized by a micrometric-size and due to the weak polymer / filler contact area involved in such composites, the ageing mechanisms of the polymer matrix are expected to be essentially unchanged compared to the ones involved in the unfilled matrix. However, recent studies pointed out some differences in the thermal-ageing mechanisms between a cross-linked EPDM rubber (elastomer based on ethylene, propylene and diene units) filled by micrometric ATH (aluminium trihydrate) particles and the corresponding unfilled cross-linked EPDM.In that respect, this work aims at investigating the extent of generality of the above-mentioned filler effect on both thermo- and radio-oxidative ageing behaviour of an EPDM matrix filled by ATH particles. In particular, the influence of both filler content and filler surface functionalization is investigated. A special attention was paid to the evolution of the network at the macromolecular scale by determining the fraction of the various network components (elastically active chains, dangling chains and extractibles) as well as the cross-link density distribution. Such information have been derived using solid-state NMR (Nuclear Magnetic Resonance).The results obtained evidence a significant decrease of the thermal-ageing induction period for the EPDM network filled by ATH particles. This effect display a strong dependence with the amount and the surface functionalization of the ATH particles. However, no modifications of the oxidation kinetics may be observed under radio-chemical ageing. The comparison between the results suggests a possible modification of the oxidation initiation mechanisms within EPDM networks filled by ATH particles. Therefore, interfacial areas should play a great role in the observed modifications
46
Wern, Chien Wei. "Fiber and fiber-matrix interface effects on the orthogonal cutting of fiber reinforced plastics /." Thesis, Connect to this title online; UW restricted, 1995. http://hdl.handle.net/1773/7133.
Full text
47
Bouzouita, Sofien. "Optimisation des interfaces fibre-matrice de composites à renfort naturel." Phd thesis, Ecole Centrale de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00769959.
Full textAbstract:
Les fibres naturelles ont réussi à acquérir un grand intérêt à l'échelle académique et industrielle. Ces fibres sont résistantes, possèdent des densités relativement basses, ont de faibles coûts et proviennent de ressources renouvelables abondantes. Les mêmes techniques classiques peuvent être utilisées pour la mise en œuvre des composites à base de fibres naturelles. Tous ces avantages ont fait que des constructeurs automobiles, par exemple, s'intéressent massivement à intégrer des pièces en ce type de composite dans plusieurs modèles de leurs véhicules. Cependant, les problèmes de compatibilité entre les fibres lignocellulosiques et les thermoplastiques limitent le transfert de charge entre fibre et matrice et ainsi les propriétés mécaniques des composites. La durabilité de ces matériaux en présence d'eau ou d'humidité est aussi problématique à cause de la haute hydrophilie des fibres naturelles. Le but de ce travail est de mieux comprendre les phénomènes relatifs à la mise en œuvre et à la l'utilisation de matériaux composites à base de polypropylène renforcé par des fibres de chanvre. L'influence d'un séchage préalable des fibres et d'une nouvelle technique de pré-imprégnation à sec, appelée Fibroline, ont été particulièrement étudiées. Cette dernière consiste à soumettre une poudre et un substrat fibreux à imprégner à un champ électrique de haute tension. Celui-ci provoque l'accélération des grains et crée une parfaite répartition de la résine dans le support fibreux. Au cours de ce traitement, des modifications chimiques et physiques peuvent se produire et entraîner l'amélioration de l'adhésion fibre/matrice. L'influence des techniques de préparation et de mise en œuvre sur les propriétés morphologiques, chimiques et mécaniques des fibres a été analysée. Des observations MEB ont permis de mettre en évidence des modifications de la surface par apparition de micro-craquelures après séchage, application du champ électrique et surtout après double traitement (séchage et Fibroline). Des analyses chimiques par XPS (spectroscopie photo-électronique aux rayons X) des fibres ont montré aussi des modifications de la chimie des surfaces. Principalement des phénomènes d'oxydation sont apparus. D'autre part, la caractérisation mécanique par traction sur mono-filaments dans différents états, a montré une dégradation des propriétés des fibres lors de leur préparation et lors de la phase d'imprégnation en utilisant la technique Fibroline, comparé au cas brut de réception. Les propriétés interfaciales ont été analysées en utilisant trois techniques. D'une part mécaniquement en utilisant le test de fragmentation et le test de déchaussement de micro-goutte, et d'autre part, par suivit de cristallisation isotherme à l'aide de platine chauffante et microscopie optique en lumière polarisée. Les essais mécaniques ont montré l'amélioration de la résistance interfaciale des fibres pré-séchées et celles traitées par la technique Fibroline. Celles doublement traitées ont vu leurs propriétés interfaciales chuter. L'analyse sous conditions isothermes des phénomènes de cristallisation ont permis d'observer l'apparition de zones transcristallines uniformes dans les deux cas ayant été imprégnés par la technique Fibroline. Ceci peut être expliqué par les modifications apportées par cette technique au niveau des surfaces des fibres. [...]
48
Montagner, Anelise Fernandes. "Influência do pré-tratamento dentinário na estabilidade da interface adesiva." Universidade Federal de Pelotas, 2013. http://repositorio.ufpel.edu.br/handle/ri/2251.
Full textAbstract:
Made available in DSpace on 2014-08-20T14:30:10Z (GMT). No. of bitstreams: 1
tese_anelise_fernandes_montagner.pdf: 2069040 bytes, checksum: f8827dc228fd6085f72280a7c6d30b98 (MD5)
Previous issue date: 2013-08-29The aim of this study was to evaluate the influence of chlorhexidine digluconate and sodium hypoclorite application on dentin after acid ecthing on the performance of adhesive restorations subjected to aging of the adhesive interface. For this, three studies were performed (in vitro, in situ and a systematic review). The in vitro study aimed to evaluate the effect of chlorhexidine digluconate (CHX) and sodium hypochlorite (NaOCl) on the microtensile bond strength values (μTBS) in dentin after cariogenic challenge and aging. Thirty sound human molars were selected and randomly assigned into 3 dentin pre-treatments (control, 2% chlorhexidine and 10% NaOCl) and 4 different types of aging (control -C-, biofilm without cariogenic challenge -NCC-, biofilm with cariogenic challenge -CC- and 18-month water storage -WS-). The same etch-and-rinse adhesive system (Adper Single Bond 2, 3M ESPE) and composite resin (Z250, 3M ESPE) were used for all the groups (n=30). For NCC and CC groups, dental biofilm in microcosm derived from saliva of a healthy donor was added on the samples. The biofilm grew up in a defined medium enriched with mucin (DMM), with or without 10% sucrose, according to the group. After the experimental period, all the samples were cleaned up and microtensile test was carried out. The data, in MPa, were subjected to ANOVA and a post-hoc Tukey Test (p < 0.05). The pre-treatment did not influence the μTBS, for all the aging conditions (p = 0.188); however the type of aging statistically affected the bond strength (p = 0.000). The bond strength values showed the following trend: C = NCC < CC = WS. Cariogenic challenge and water storage aging affected the bond strength stability and the former seems to be a suitable short-term methodology to assess the degradation of the resin-dentin. The in vivo study aimed to evaluate the effect of chlorhexidine (CHX) application in etched dentin on the 6-month retention of restorations of noncarious cervical lesions (NCCLs). A randomized controlled splitmouth and blind trial was carried out. Patients (n = 42) with at least two noncarious cervical lesions were included. NCCLs were randomly assigned according to the type of tooth into two groups: control (application of a placebo solution) or experimental group (application of 2% CHX for 60s after acid etching). Class V restorations (n = 169) were performed with an etch-and-rinse adhesive system (Adper Single Bond 2) and a composite resin (Filtek Z350) according to the manufacturer instructions, by 10 previously trained operators. The restorations were evaluated by a calibrated examiner at 1 week (baseline) and 6-month using the FDI criteria. The outcome was retention of the restoration. The analysis of factors associated to the failure of restoration was carried out through Fisher s Exact Test (α = 0.05). After 6 months of follow-up, 3.4% (CI 95% 1.3 - 7.3) of the Class V restorations failed. There was no significant difference between control and CHX (p = 0.920). Regarding the cavity s variables, deeper (p = 0.024) and wider cavities (p = 0.004) showed more failures, and wedge-shaped cavities failed more than saucer-shaped ones (p = 0.033). Regarding the patient s variables, restorations in patients with lower salivation 8 showed a higher percentage of failure (p = 0.034). Both treatments provided acceptable clinical performance of the restorations. The use of CHX as a coadjuvant in dentin adhesion did not influence the retention of Class V restorations after 6 months of follow-up. The systematic review aimed to systematically review the literature for in vitro and ex vivo studies that evaluated the resin-dentin bond strength immediately and longitudinal with the use of MMP inhibitor on the adhesive procedure. The systematic review was conducted sourcing the following databases (Pubmed, TRIP, LILACS, Scielo, Cochrane and ISI web Science) with no publication year or language limit. From 1.336 potentially eligible studies, 48 were selected for full text analysis and 30 were included for review. Two independently reviewers selected the studies, abstracted information and assessed the risk of bias on standardize scales. The results showed high heterogeneity in some comparisons and showed no difference for CHX 2% and control at baseline, however after 6-month of aging the CHX 2% and 0.2% presented a trend showing higher bond strength values than control groups (p < 0.05). The literature review was possible to observe the trend towards the decreased of the bond strength through time most for the control groups than for the experimental one. From of the 30 studies included, only 5 studies (16.6%) presented medium risk of bias while 25 (83.4%) showed high risk of bias and none showed low risk of bias. The use of MMPs inhibitor did not negatively affect the immediate bond strength, and it influenced the bond strength values long-time regarding the dentin adhesion stability.
O objetivo deste estudo foi avaliar a influência da aplicação do digluconato de clorexidina (CRX) e hipoclorito de sódio (NaOCl) em dentina, após o condicionamento ácido, na performance da interface adesiva submetida a envelhecimento da interface adesiva. Para isto, foram realizados 3 estudos (in vitro, in vivo e revisão sistemática). O estudo in vitro objetivou avaliar o efeito do prétratamento da dentina nos valores de resistência de união (RU) após diferentes tipos de envelhecimentos da interface adesiva. A dentina de todos os espécimes foi submetida ao condicionamento com ácido fosfórico por 15s e em seguida a 3 tipos de pré-tratamento: água destilada (controle - soluçao placebo - 60s), digluconato de clorexidina 2% - 60s, ou hipoclorito de sódio 10% - 60s. O sistema desivo (Single Bond 2 3M/ESPE) foi aplicado na superfície dentinária conforme indicação do fabricante. Palitos resina-dentina foram obtidos e submetidos a 4 níveis de envelhecimento: controle (CO), biofilme sem desafio cariogênico (BSD), biofilme com desafio cariogênico (BCD) e armazenamento em água por 18 meses (AGU). Nos grupos com biofilme, modelo de microcosmo foi utilizado e o biofilme foi crescido em meio definido enriquecido com mucina, com (BCD) ou sem (BSD) sacarose por 14 dias. Após o período experimental os espécimes foram limpos e preparados para o teste de microtração e o padrão de fratura foi analisado. Os valores de RU, em MPa, foram submetidos a ANOVA e teste post hoc Tukey (p < 0,05). O pré-tratamento não influenciou nos valores de RU, para todos os envelhecimentos avaliados (p = 0,188), entretanto o tipo de envelhecimento estatisticamente influenciou os valores de RU (p = 0,000). O envelhecimento CO foi similar ao BSD, com valores RU maiores que o BCD e AGU. A interface adesiva foi negativamente afetada pelo desafio cariogênico e pela degradação em água. No estudo in vivo, com objetivo de avaliar a retenção de restaurações classe V em dentina tratada ou não com CRX, um ensaio clínico controlado randomizado, boca dividida e triplo-cego foi conduzido. Pacientes (n = 42) com no mínimo 2 lesões cervicais não cariosas (LCNC) foram selecionados. As LCNC foram randomizadas em 2 grupos: tratamento controle e tratamento experimental (CRX 2% - 60s). Restaurações (n = 169) foram realizadas com Single Bond 2 (3M EPSE) e Filtek Z350 por 10 operadores previamente treinados. As restaurações foram avaliadas por um examinador calibrado em 1 semana e 6 meses após, usando os critérios da FDI. A análise dos fatores associados às falhas nas restaurações foi conduzida através do teste exato de Fisher (α = 0,05). Após 6 meses de acompanhamento, 3,4% (IC95% 1,3 - 7,3) das restaurações falharam devido a retenção. Não houve diferença significante entre os tratamentos controle e CRX para retenção (p = 0,920) e para manchamento marginal (p = 0,734). Em relação às variáveis relativas à cavidade, cavidades com maior profundidade (p = 0,024) e com maior altura (p = 0,004) 6 apresentaram maior ocorrência de falhas. Ainda, cavidades em formato de V apresentaram mais falhas que aquelas em formato de U (p = 0,033). Quanto as variáveis relativas aos pacientes, restaurações em pacientes que apresentavam boca seca falharam em maior porcentagem (p = 0,034). O uso de clorexidina como um coadjuvante na adesão a dentina não influenciou na retenção das restaurações após 6 meses de acompanhamento. E a revisão sistemática teve o objetivo de revisar a literatura acerca de estudos in vitro que avaliaram a RU resina-dentina imediata e após envelhecimento com o uso de inibidores de MMPs no procedimento adesivo. A revisão sistemática foi conduzida em 6 databases (Pubmed, TRIP, LILACS, Scielo, Cochrane and ISI web Science) sem limite de ano ou língua. De 1.336 estudos potencialmente elegíveis, 48 foram selecionados para análise de todo texto e 30 estudos foram incluiídos na revisāo. Dois revisores selecionaram os estudos, extraíram as informações e dados e verificaram o risco de viés em escalas padronizadas. Os resultados demostraram uma grande heterogeneidade em algumas comparações e nāo mostraram diferenças entre clorexidina 2% e o grupo controle sem envelhecimento, porém após 6 meses de envelhecimento observou-se uma tendência a favor dos grupos controle (p < 0,05). Todavia, foi possível observar na revisāo de literatura descritiva a tendência da diminuiçāo dos valores de RU (porcentagem) ao longo do tempo, mais para o grupo controle do que para o grupo experimental. De 30 estudos incluídos, apenas 5 estudos (16,6%) apresentaram médio risco de viés, enquanto 25 estudos (83,4%) mostraram alto risco de vieés e nenhum mostrou baixo risco. Os inibidores de MMPs nāo afetaram negativamente a RU da resina a dentina sem envelhecimento, e nāo influenciaram os valores de RU após envelheciemento.
49
Nguyen, Duy Cuong. "Caractérisation de l'interface fibre/matrice : application aux composites polypropylène/chanvre." Thesis, Troyes, 2016. http://www.theses.fr/2016TROY0009/document.
Full textAbstract:
Les agro-composites font l'objet de nombreuses études et applications industrielles en raison des multiples propriétés mécaniques qu'ils présentent. Ces propriétés présentent de grandes perspectives comparées à celles des composites traditionnels. Cependant les connaissances sur le comportement mécanique de l'interface fibre/matrice restent limitées. De plus, la différence de propriété entre la fibre hydrophile et la matrice hydrophobe peut causer des défauts au niveau de l’interface. Il est donc important de caractériser finement la décohésion à l'interface au cours d'une sollicitation. Plusieurs méthodes ont été proposées dans la littérature, elles sont généralement très complexes à mettre en œuvre et sont coûteuses. Dans cette étude, nous avons développé une méthode de caractérisation en se basant sur l'essai de « pull-out ». La géométrie de la fibre a été prise en compte dans le calcul des propriétés mécaniques de l'interface par la mise à profit d'une approche inspirée de la tomographie. L'influence de la température d'élaboration sur les propriétés mécaniques de l'interface a été étudiée de manière à définir la température optimale. L'évolution des propriétés interfaciales a été suivie au cours d'un vieillissement en humidité relative. Après quatre semaines, la résistance au cisaillement et la rigidité au cisaillement de l'interface sont diminuées fortement alors que la déformation à la rupture est augmentéeAgro-composites are increasingly studied and applied to various industries over recent years due to good mechanical properties compared to conventional composites especially in terms of specific values. However, since low adhesion between the hydrophilic fiber and hydrophobic matrix, which occurs one of the main breaks modes in this kind of material, the characterization of the interface becomes a key problem. For investigation of this issue, existing methods show limitation for reasons of complexity (in preparation, in principle) and of cost. In this study, we developed a « pull-out ». In particular, the real fiber geometry of the plant fiber was taken into the calculation of mechanical properties of interface using a tomography inspired method. By checking the effective temperature of the molding then varying it, we studied the effect of this processing parameter to mechanical properties of fibre/matrix interface and determined the optimal conditions. The developed experimental protocol is applied to aged interfaces in order to clarifying the evolution of interfacial properties during the aging time to relative humidity. After four weeks, the interfacial shear strength and the shear modulus of the interface were greatly reduced while the shear deformation at the rupture was greatly increased
50
Tran, Manh Tien. "Caractérisation expérimentale et modélisation numérique du comportement thermomécanique à haute température des matériaux composites renforcés par des fibres." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1111/document.
Full textAbstract:
Les matériaux composites TRC (Textile Reinforced Concrete), consistant d'une matrice cimentaire et d'un renforcement par des textile ou fibres (en carbone, en verre ou en autre matière, …) sont souvent utilisés pour réparer ou/et renforcer les éléments structurels porteurs (dalle, poutre, colonne) d'anciens ouvrages de génie civil. Ils peuvent être également utilisés comme des éléments porteurs dans les structures neuves (éléments de préfabrications). Afin de développer des composites TRC avec de bonnes caractéristiques à température élevée, on a fait une combinaison entre les textiles de carbone qui possède une bonne capacité mécanique et une matrice réfractaire qui assurent une transmission de charge entre le textile de renforcement et les protège thermiquement contre l'action de température élevée. Le comportement thermomécanique des composites TRC de carbone est expérimentalement et numériquement étudié à l'échelle mésoscopique dans cette thèse. L'avancement scientifique sur ce sujet de thèse permettrait d'améliorer la stabilité au feu des structures qui sont renforcées par des matériaux composites TRC. Ce sujet contribuerait aux intérêts sociaux et économiques significatifs pour le génie civil dans le monde entier en général et au Vietnam en particulier. La thèse concerne la caractérisation expérimentale et modélisation numérique du comportement thermomécanique à température élevée des matériaux composites TRC à l'échelle mésoscopique. Dans une première partie expérimentale, les textiles de carbone (des produits commerciaux sur le marché), la matrice du béton réfractaire et l'interface textile/matrice ont été testés au régime thermomécanique à température constante (allant de 25 °C à 700 °C). Les résultats obtenus montrent un effet du traitement du textile sur le comportement et mode de rupture des textiles de carbone et de l'interface textile/matrice. Un modèle analytique a été également utilisé pour déterminer l'évolution des propriétés thermomécaniques des textiles de carbone en fonction de la température. Le transfert thermique dans l'éprouvette cylindrique du béton réfractaire a été réalisé pour valider les propriétés thermiques du béton réfractaire. Tous les résultats obtenus dans cette partie sont utilisés comme données pour le modèle numérique dans la partie de modélisation. La deuxième partie expérimentale explore le comportement thermomécanique des TRCs sous deux régimes : thermomécanique à température constante et thermomécanique à force constante. Deux textiles de carbone, qui ont donné les meilleures performances à température élevée, ont été choisis pour une fabrication des TRCs. Les résultats expérimentaux montrent un comportement thermomécanique avec l'écrouissage (trois ou deux phases) à température modérée et un comportement fragile à température supérieure de 500 °C. Au régime thermomécanique à force constante, deux composites TRCs peuvent résister plus long que les textiles de carbone seuls grâce à bonne isolation thermique de la matrice cimentaire. En comparant les deux résultats sur les éprouvettes de TRC, l'effet du renforcement de textile (le taux de renfort, le produit de traitement, la géométrie du textile) sur le comportement thermomécanique a été analysé. Tous les résultats expérimentaux de cette partie ont été utilisés pour valider et comparer avec ceux obtenus à partir du modèle numérique. La partie de modélisation numérique a deux buts : prédire le comportement thermomécanique global du composite TRC à partir des propriétés thermomécaniques des matériaux constitutifs ; valider le transfert thermique dans le composite en cas d'augmentation de la température pour prédire la température de rupture ou la durée d'exposition du composite [etc...]TRC materials, consisting of a cement matrix and a reinforcement by textiles or fibers (carbon, glass or other fibre, etc) are often used to repair or/and strengthen the loading structural elements (slab, beam, column) of old civil engineering works. They can also be used as loading elements in new structures (prefabrication element). In order to develop TRC composites with good characteristics at high temperature, a combination has been made between the carbon textiles which have a good mechanical capacity and a refractory matrix which provides a load transfer between the reinforcement textiles and thermally protects them against the action of high temperature. The thermomechanical behavior of carbon TRC composites is experimentally and numerically studied at the mesoscale in this thesis. Scientific advancement on this thesis topic would improve the fire stability of structures that are reinforced by TRC composite materials. This topic would contribute to significant social and economic interests for civil engineering worldwide in general and Vietnam in particular. My thesis work concerns the experimental characterization and numerical modeling of the high temperature thermomechanical behavior of composite materials TRC at the mesoscale. In a first experimental part, the carbon textiles (commercial products on the market), the refractory concrete matrix and the textile/matrix interface were tested at constant temperature thermomechanical regime (ranging from 25 °C to 700 °C). The results obtained showed an effect of the textile treatment on the mechanical behavior and failure mode of the carbon textiles and the textile/matrix interface. An analytical model was also used to identify the evolution of thermomechanical properties of carbon textiles as a function of temperature. The thermal transfer in the cylindrical specimen was carried out to validate the thermal properties of refractory concrete. All results obtained in this part are used as input data for the numerical model in the modeling part. The second experimental part explores the thermomechanical behavior of TRCs under two regimes: thermomechanical at constant temperature and thermomechanical at constant force. Two carbon textiles, which gave the best performance at high temperature, were chosen for the manufacture of TRCs. The experimental results showed a hardening behavior with three or two phases at moderate temperature and a brittle behavior at higher temperature of 500 °C. In thermomechanical regime at constant force, two TRC composites can resist longer than carbon textiles alone thanks to good thermal insulation of refractory matrix. By comparing the two results on the TRC specimens, the effect of textile reinforcement (reinforcement ratio, treatment product and textile geometry) on the thermomechanical behavior was analyzed. All the experimental results of this part were used to validate and compare with those obtained from the numerical model. The purpose of the numerical modeling part is to predict the global thermomechanical