Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-08-22T14:23:35Z No. of bitstreams: 1 KÊNIA ARAÚJO DE LIMA SCARIOT - DISSERTAÇÃO (PPGECA) 2018.pdf: 3614373 bytes, checksum: debef6a639457f042d11c7f1a33519ea (MD5) / Made available in DSpace on 2018-08-22T14:23:35Z (GMT). No. of bitstreams: 1 KÊNIA ARAÚJO DE LIMA SCARIOT - DISSERTAÇÃO (PPGECA) 2018.pdf: 3614373 bytes, checksum: debef6a639457f042d11c7f1a33519ea (MD5) Previous issue date: 2018-06-08 / Capes / Os movimentos de massa de solo em morros, taludes e encostas têm se intensificado nas últimas décadas. A região Nordeste lidera no Brasil o ranking de maior número de desabrigados afetados por problemas de instabilidade, uma vez que a ruptura de um maciço ocasiona danos materiais e perdas sociais e econômicas. Para mitigar os efeitos da instabilidade dos taludes são aplicadas técnicas de consolidação, melhoramento e reforços no intuito de gerar uma redistribuição global das tensões e deformações. Entre elas pode-se citar as técnicas como estabilização química e contenção com geossintéticos. A presente pesquisa teve por objetivo realizar um estudo paramétrico da resistência ao cisalhamento de um solo de baixa capacidade de suporte, no seu estado natural e após o emprego de técnica de estabilização química e da inserção de materiais de reforço (geotêxtil não-tecido e geogrelha). A pesquisa foi dividida em três etapas para atingir os fins propostos: caracterização do solo, estabilização química do solo e avaliação do comportamento mecânico do solo. Na primeira etapa foram realizados ensaios de caracterização física, química e mineralógica do solo. Na segunda fase foram realizados ensaios de compressão simples com o propósito de determinar um teor ótimo para a estabilização química do solo. Posteriormente submeteu-se amostras de solo natural, solo estabilizado e solos reforçados a ensaios de compressão triaxial não adensado e não drenado (UU), a fim de analisar os parâmetros geotécnicos de cada modelo e os ganhos de resistência e de rigidez dos solos melhorados em comparação ao solo natural. Em geral, os resultados indicaram que as inserções do geotêxtil não-tecido e da geogrelha contribuem para o aumento da resistência ao cisalhamento. A técnica de estabilização química do solo, comparada as técnicas de reforço com geossintéticos proporcionou melhor comportamento resistente, visto que a inserção do cimento ao solo promoveu resultados superiores de resistência ao cisalhamento do solo pesquisado. Entretanto, a presente pesquisa não considerou as vantagens técnicas, econômicas e ambientais de cada tecnologia, visto que estes aspectos podem inviabilizar as construções com solo melhorado. / Soil mass movements in hills, slopes and slopes have intensified in recent decades. The Northeast Region is the leader in Brazil of the highest number of homeless people affected by instability problems, since the rupture of a massif causes material damages and social and economic losses. To mitigate the effects of slope instability are applied consolidation techniques, improvement and reinforcement in order to generate a global redistribution of stresses and deformations. Among these may be mentioned the techniques as chemical stabilization and containment with geosynthetics. The objective of this research was to perform a parametric study of the shear strength of a soil with low support capacity, in its natural state and after the use of chemical stabilization technique and the insertion of reinforcement materials (non-woven geotextile and geogrid). The research was divided in three stages to reach the proposed ends: soil characterization, soil chemical stabilization and evaluation of soil mechanical behavior. In the first stage, physical, chemical and mineralogical characterization of the soil were performed. In the second phase, simple compression tests were carried out with the purpose of determining an optimum content for soil chemical stabilization. Subsequently, samples of natural soil, stabilized soil and reinforced soils were submitted to non-densified and non-drained triaxial (UU) compression tests in order to analyze the geotechnical parameters of each model and the strength and stiffness gains of the improved soils in compared to natural soil. In general, the results indicated that the insertions of the non-woven geotextile and the geogrid contribute to the increase in shear strength. The soil chemical stabilization technique, compared to the geosynthetic reinforcement techniques provided better resistant behavior, since the cement insertion in the soil promoted superior results of shear strength of the studied soil. However, the present research did not consider the technical, economic and environmental advantages of each technology, since these aspects can make feasible the constructions with improved soil.

Made available in DSpace on 2014-12-17T14:58:15Z (GMT). No. of bitstreams: 1 JoseHBL_DISSERT_PARCIAL.pdf: 2505963 bytes, checksum: 1b82ec8a8147b2b7e13d0af6880855f0 (MD5) Previous issue date: 2012-05-02 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Materials denominated technical textiles can be defined as structures designed and developed with function to fulfill specific functional requirements of various industrial sectors as are the cases of the automotive and aerospace industries. In this aspect the technical textiles are distinguished from conventional textile materials, in which the aesthetic and of comfort needs are of primordial importance. Based on these considerations, the subject of this dissertation was established having as its main focus the study of development of textile structures from aramid and glass fibers and acting in order to develop the manufacture of composite materials that combine properties of two different structures, manufactured in an identical operation, where each structure contributes to improving the properties of the resulting composite material. Therefore were created in laboratory scale, textile structures with low weight and different composition: aramid (100%), glass (100%) and aramid /glass (65/35%), in order to use them as a reinforcing element in composite materials with polyester matrix. These composites were tested in tension and its fracture surface, evaluated by MEV. Based on the analysis of mechanical properties of the developed composites, the efficiency of the structures prepared as reinforcing element were testified by reason of that the resistance values of the composites are far superior to the polyester matrix. It was also observed that hybridization in tissue structure was efficient, since the best results obtained were for hybrid composites, where strength to the rupture was similar to the steel 1020, reaching values on the order of 340 MPa / Os materiais denominados t?xteis t?cnicos podem ser definidos como estruturas projetadas e desenvolvidas com a fun??o de atender a requisitos funcionais espec?ficos de diversos setores da ind?stria, caso da ind?stria automotiva e aeroespacial. Nesse aspecto, distinguem-se dos materiais t?xteis convencionais, nos quais as necessidades est?ticas e de conforto t?m import?ncia primordial. Com base nessas considera??es, o tema dessa disserta??o foi estabelecido tendo como enfoque principal o estudo do desenvolvimento de estruturas t?xteis a partir de fibras de aramida e de vidro, atuando no sentido de elaborar a fabrica??o de materiais comp?sitos que combinem propriedades de duas estruturas diferentes, fabricadas em uma mesma opera??o, onde cada estrutura contribui para melhoria das propriedades do material comp?sito resultante. Para tanto foram desenvolvidas em escala laboratorial estruturas t?xteis de baixa gramatura e composi??o diferenciada de aramida (100%), vidro (100%) e aramida/vidro (65/35%) para utiliza??o como elemento refor?ante em comp?sitos com matriz de poli?ster. Os comp?sitos produzidos foram ensaiados em tra??o e sua superf?cie de fratura avaliada por MEV. Com base nas analises das propriedades mec?nicas dos comp?sitos desenvolvidos, observou-se a efici?ncia das estruturas ou elaboradas como elemento refor?ante tendo em vista que os valores de resist?ncia dos comp?sitos foram muito superiores ? matriz de poli?ster. Tamb?m foi observado que a hibridiza??o na estrutura dos tecidos foi eficiente, uma vez que os melhores resultados obtidos foram para os comp?sitos h?bridos, onde a resist?ncia na ruptura foi semelhante ? do a?o 1020, atingindo valores na ordem de 340 MPa

Made available in DSpace on 2014-12-17T14:58:20Z (GMT). No. of bitstreams: 1 AnaCMCB_DISSERT.pdf: 5204946 bytes, checksum: 70bedde30acbc8578034105c8c4fc24e (MD5) Previous issue date: 2013-07-25 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The utilization of synthetic fibers for plastic reinforcement is more and more frequent and this growing interest requires that their mechanic behavior under the most variable conditions of structural applications be known. The use of such materials in the open and exposed to the elements is one of them. In this case, it becomes extremely necessary to study their mechanical properties (strength, stiffness) and the mechanism of fracture by which the environment aging them out. In order to do that, the material must be submitted to hot steam and ultraviolet radiation exposure cycles, according to periods of time determined by the norms. This study proposal deals with the investigation of accelerated environmental aging in two laminated polymeric composites reinforced by hybrid woven made up of synthetic fibers. The configurations of the laminated composites are defined as: one laminate reinforced with hybrid woven of glass fibers/E and Kevlar fibers/49 (LHVK) and the other laminate is reinforced with hybrid tissue of glass fibers/E and of carbon fibers AS4 (LHVC). The woven are plane and bidirectional. Both laminates are impregnated with a thermofix resin called Derakane 470-300 Epoxy Vinyl-Ester and they form a total of four layers. The laminates were industrially manufactured and were made through the process of hand-lay-up. Comparative analyses were carried out between their mechanical properties by submitting specimen to uniaxial loading tractions and three-point flexion. The specimen were tested both from their original state, that is, without being environmentally aging out, and after environmental aging. This last state was reached by using the environmental aging chamber / O interesse na utiliza??o dos pl?sticos refor?ados por fibras sint?ticas ? cada vez mais crescente e esse grande interesse na utiliza??o dos mesmos faz com que seja necess?rio o conhecimento do comportamento mec?nico desses materiais sob as mais variadas condi??es de aplica??o estrutural. Dentre estas pode ser destacada a aplica??o desses materiais em situa??es em o elemento encontra-se exposto ? intemp?rie, e nesse caso os estudos das propriedades mec?nicas (resist?ncia, rigidez) al?m do mecanismo fratura frente ao envelhecimento ambiental s?o de extrema necessidade. Para tanto, submeter o material ? per?odos c?clicos de exposi??o ao vapor aquecido e ? de radia??o ultravioleta, por tempo definido em norma, se faz necess?rio. A presente proposta de trabalho de investiga??o consiste no estudo do envelhecimento ambiental acelerado em dois laminados comp?sitos polim?ricos refor?ados por tecidos h?bridos ? base de fibras sint?ticas. As configura??es dos laminados comp?sitos s?o definidas como: um laminado refor?ado com tecido h?brido de fibras de vidro/E e de fibras kevlar/49 (LHVK) e outro laminado refor?ado com tecido h?brido de fibras de vidro/E e de fibras de carbono AS4 (LHVC). Os tecidos s?o dos tipos planos e bidirecionais. Ambos os laminados foram impregnados a base de resina termofixa Derakane 470-300 Ep?xi Vinil-Ester e constitu?dos com quatro camadas no total. Os laminados t?m fabrica??o industrial e foram obtidos atrav?s do processo de lamina??o manual (Hand-lay-up). Foram realizados estudos comparativos entre as propriedades mec?nicas sob a a??o dos carregamentos de tra??o uniaxial e flex?o em tr?s pontos, nas condi??es dos corpos de prova sem o efeito do envelhecimento ambiental (estado original) e sob o efeito desse envelhecimento (estado envelhecido). O envelhecimento ambiental foi acelerado atrav?s do uso da c?mara de envelhecimento

The epoxy resin has a widespread use in the manufacture of polymer composites to obtain various elements of structural engineering. The overall objective of this research is to evaluate the effect of reinforcing fabric architecture fiber-based Kevlar 49 and glass S on the mechanical performance of composites with epoxy matrix. It was observed that the mechanical performance of the epoxy resin and the composite, after natural aging and in seawater at a temperature of 70 ° C. Three architectures are designed for the production of tissue related to the structural reinforcement of the composite element: only aramid (Kevlar 49), and hybrid Kevlar 49 and glass S; varying the type of yarn and intertwining of the composition (fiber content in percentage) in each frame. The composite plates were made by hand casting process with epoxy matrix reinforced with woven fabrics of Kevlar fiber and Kevlar hybrid/glass, according to an innovative architecture. The mechanical properties of the composites were determined by tensile, bending and impact carried out in parallel and perpendicular to the warp direction. We used scanning electron microscopy to observe the reinforcement and matrix fractures after the mechanical tests. The composites with hybrid structure of Kevlar/glass on reinforcing fabric showed the best results with respect to the specific strength and impact energy. / A resina epóxi possui uma ampla utilização na fabricação de compósitos poliméricos, para obtenção de diversos elementos da engenharia estrutural. O objetivo geral desta Tese é avaliar o efeito da configuração do tecido de reforço à base de fibras de Kevlar 49 e vidro S no desempenho mecânico de compósitos com matriz epoxídica. Observou-se o desempenho mecânico da resina epóxi e do compósito, após envelhecimento natural ao ar livre e na água do mar sob temperatura de 70 ºC. Foram concebidas três configurações para produção do tecido referentes ao elemento de reforço estrutural do compósito: apenas em aramida (Kevlar 49), e híbrido de Kevlar 49 e fibra de vidro S; variando-se o tipo de entrelaçamento dos fios e composição (teor de fibra em percentual) em cada estrutura. Foram fabricadas placas do compósito pelo processo de moldagem manual com matriz epoxídica, reforçadas por tecidos planos em fibra de Kevlar, e híbrido Kevlar/vidro, de acordo com uma configuração inovadora. As propriedades mecânicas dos compósitos foram determinadas por ensaios de tração, flexão e impacto, realizados nas direções paralela e perpendicular ao urdume. Utilizou-se a microscopia eletrônica de varredura para observar as fraturas do reforço e matriz após os ensaios mecânicos. Os compósitos com estrutura híbrida de Kevlar/vidro no tecido de reforço apresentaram os melhores resultados com relação à resistência mecânica específica, bem como energia de impacto.

L'allègement des véhicules est un enjeu majeur de l'industrie automobile pour participer, avec l'évolution des motorisations, à la maîtrise des consommations énergétiques et la réduction des émissions de gaz à effet de serre. Dans ce travail, nous nous intéressons à l'introduction des matériaux composites dans les pièces de structure et particulièrement dans le périmètre de la liaison au sol composé d'organes de sécurité active, sujets au phénomène de fatigue multi axiale à grand nombre de cycles.Les matériaux composites présentent une solution séduisante en raison de leurs propriétés mécaniques intéressantes combinées à une faible densité. Toutefois, la fatigue des matériaux composites reste un sujet complexe relativement peu abordé. C'est dans ce cadre que s'inscrit cette thèse qui vise à mettre en place une méthodologie de dimensionnement des composants automobiles de structure, à partir d'un composite tissé verre/époxy. Cette méthodologie s'attache à être facile d'utilisation et adaptable au calcul de structure pour être applicable en Bureau d'Études. La première étape de cette étude est la caractérisation de la tenue en service du matériau sous chargements monotones et cycliques et l'identification des cinétiques d'endommagement. Au vu des résultats expérimentaux obtenus et à partir des approches de dimensionnement existantes, un critère de fatigue multi axiale est proposé. Ensuite, une optimisation du protocole d'identification des paramètres est effectuée afin de réduire au minimum le volume des campagnes d'essais. Enfin, le critère mis en place pour évaluer la durée de vie en fatigue du matériau composite tissé est validé sur des éprouvettes trouées et sur le train avant à lame composite. / The reduction of fuel consumption and greenhouse gas emissions is one of the most important challenges facing the automotive industry. An efficient strategy to meet these targets is by reducing the weight of vehicle. In this work, we are interested in introducing composite materials in automotive structural parts and especially in suspensions which are subjected in service to high-cycle fatigue loadings. Therefore, a good prediction of fatigue life is required. As continuous fibre-reinforced composites provide good mechanical properties combined with a low density, they have been increasingly used in many lightweight structures. However, the fatigue behaviour of composites has not been widely investigated. This work aims at developing an approach to predict the lifetime in service of structural automotive components, made with woven glass / epoxy composite. This approach has to be easy to use by design engineers at the scale of the structure. The first step is the characterization of the material. Then, the processes involved in degradation of the composite subjected to both monotonic and cyclic loadings were identified.Given the experimental results and the existing approaches, a multiaxial fatigue criterion is proposed. An optimization of the identification protocol is also performed to reduce the quantity of needed experimental data. Finally, the fatigue life prediction model criterion is validated by tests on notched coupons and on composite vehicle's suspension.

Die Entwicklung von Geweben mit gestreckten Fadenlagen ist Gegenstand aktueller Forschungen, die vielfach Sondermaschinen für ganz spezielle Anwendungen hervorbringen. Eine systematische Analyse und Optimierung der unter Berücksichtigung der Verbundeigenschaften existiert nach bekanntem Stand des Wissens nicht. Ziel der Dissertation ist es, diese Lücke zu schließen und einen Beitrag zur Etablierung von Geweben mit gestreckten Fadenlagen in Faserverbundwerkstoffen zu leisten. Die Arbeit basiert zum Teil auf den Ergebnissen, die in der Zeit von 2006 – 2012 am Institut für Textilmaschinen und textile Hochleistungswerkstofftechnik der Technischen Universität Dresden im Rahmen verschiedener AiF und DFG Vorhaben entstanden sind. Weiterführende Überlegungen wurden 2015 – 2017 im Rahmen eines Promotionsstudiums an der Professur für Textile Technologien der Technischen Universität Chemnitz angefertigt. Wie anhand konkreter Ausführungsbeispiele gezeigt wird, stößt das Weben insbesondere für Anwendungen im Faserverbundleichtbau an technologisch bedingte Grenzen. Es erfolgt zunächst eine Gegenüberstellung konventioneller Flächenbildungsverfahren und der Anforderungen seitens der Endanwender, insbesondere aus dem Bereich der Verbundwerkstoffindustrie, gleichermaßen. Daraus wird ein Anforderungsprofil für ein anforderungsgerechtes Flächenbildungsverfahren abgeleitet und konstruktive Lösungsvorschläge zu dessen Umsetzung aufgezeigt. / The development of non-crimped-fabrics (NCF) is subject of current research activities. These often led to special machines for very special applications. There is no systematic analysis and optimization of the properties of composites based on the state of the art. The aim of this dissertation is to close this gap and to contribute to the establishment of woven NCF in fiber-reinforced composites. The work is based partially on the results obtained at the Institut für Textilmaschinen und textile Hochleistungswerkstofftechnik der Technischen Universität Dresden from 2006 to 2012 within the framework of various AiF and DFG projects. Further reflections were made between 2015 and 2017 as part of a doctoral study at the Chair of Textile Technologien der Technischen Universität Chemnitz. As shown from examples of the design, weaving is reaching technological limits, especially for applications in composite construction. First of all, conventional surface formation methods are compared with the requirements of end users, especially from the composites industry. From this, a requirement profile is derived for a requirements-based surface formation process and constructive proposals for solutions for its implementation are identified.

In recent times, composite materials have gained mainstay acceptance as a structural material of choice due to their tailorability and improved thermal, specific strength/stiffness and durability performance. Carbon-Carbon (C/C) composites are used for high temperature applications such as exit nozzles for rockets, leading edges for missiles, nose cones, brake pads etc. Mechanical property estimation of C/C composites is challenging due to their highly heterogeneous microstructure. Computed Tomography (CT) images (volumetric imaging) coupled with Scanning Electron Microscopy (SEM) reveal a highly heterogeneous microstructure comprised of woven C-fibers, amorphous C-matrix, irregularly shaped voids, cracks and other inclusions. The images also disclose structural hierarchy of the C/C composite at different length scales. Predicting the mechanical behavior of such complex hierarchical materials like C/C composites forms the motivation for the present work. A systematic study to predict the effective mechanical properties of C/C Composite using numerical homogenization has been undertaken in this work. The Micro-Meso-Macro (MMM) principle of ensemble averages for estimating the effective properties of the composite has been adopted. The hierarchical length scales in C/C composites has been identified as micro (single fiber with matrix), meso (fabric) and macro (laminate). Numerical homogenization along with periodic boundary conditions (PBCs) have been used to estimate the effective engineering properties of the material at different length scales. Concurrently, mechanical testing has also been carried out at macro (compression tests) and micro scale (using nano-indentation studies) to characterize the mechanical behavior of C/C composites.

La simulation des procédés de production des composites à renforts tissés est un enjeu majeur pour les industries de pointe, où leur utilisation s’intensifie. La maitrise des procédés d’obtention des composites à matrice et fibres en céramique, notamment les étapes de mise en forme et de pyrolyse, s’avère primordiale. La connaissance et la simulation du comportement mécanique aux différentes étapes est nécessaire pour optimiser les performances des pièces finales. Deux approches de modélisation macroscopique des renforts tissés épais de composite sont détaillées : une approche continue classique et une approche semi-discrète. Pour cela, une loi de comportement hyperélastique initialement orthotrope est développée. Cette loi est basée sur l’observation phénoménologique des modes de déformation privilégiés, à partir desquels sont proposés des invariants physiques de la transformation. L’identification des paramètres matériaux nécessaires est décrite. Une version modifiée de cette loi, sans contribution en tension, est implémentée dans un élément semi-discret, où le travail en tension est alors pris en compte par des barres discrétisant le tissage réel. Les importantes différences de rigidités entre sollicitations en tension et en cisaillements font des renforts tissés épais des matériaux fortement anisotropes. Leur modélisation numérique met en évidence des phénomènes parasites ou des limitations liés à cette spécificité. Le phénomène de verrouillage en tension est tout d’abord mis en évidence. Une solution basée sur une formulation éléments finis enhanced assumed strain est proposée pour des éléments continus classiques ou semi-discrets. Puis des problèmes liés aux simulations numériques dominées par la flexion sont soulevés : l’hourglassing transverse et l’absence de résistance locale à la courbure. Dans le cas de l’hourglassing transverse, deux méthodes de rigidification de ces modes de déplacement sont proposées : par moyennage des dilatations dans l’élément ou par ajout d’une rigidité matérielle tangente supplémentaire. Pour l’introduction d’une résistance à la courbure, une méthode basée sur l’utilisation purement numérique de plaques rotation free est proposée. Celles-ci permettent le calcul de la courbure induisant, par l’intermédiaire d’un moment de flexion, des efforts internes supplémentaires. Finalement, la modélisation du retour élastique après pyrolyse de la matrice organique à précurseurs céramique est réalisée. Le comportement de la matrice pyrolysée est identifié expérimentalement à l’aide d’une loi hyperélastique isotrope transverse. L’addition de cette loi, qui prend comme référence la préforme déformée, à la loi de comportement initiale du renfort tissé permet de visualiser les déformations obtenues en fin de pyrolyse. Cette modélisation est comparée à des résultats expérimentaux. / Manufacture processes modeling of woven fabrics composites is a major stake for state-of-the-art industrial parts, where their usage is intensifying. Control of all the manufacturing stages of ceramic matrix composites, particularly the forming and pyrolysis steps, is essential. Understanding and simulation of the mechanical behavior at each stage is required to optimize the final product performances. Two macroscopic modeling approaches of thick woven fabric reinforcements are detailed: a continuous classical one and a semi-discrete one. An initially orthotropic hyperelastic constitutive law is thus established. This law is based on a phenomenological observation of the main fabric deformation modes, from where physical invariants of the deformation are suggested. The required material parameters identification is explained. A modified version of this law, without any tensile energetic contribution, is implemented in a semi-discrete element where the tensile work is taken into account by bars that discretize the real weaving. Thick woven reinforcements are highly anisotropic materials due to the large ratio between the tensile rigidity and the others. Their numerical modeling highlights spurious phenomena and limitations related to this specificity. The tension locking is firstly tackled. A remedy based on an enhanced assumed strain finite element formulation is suggested for classical continuum and semi-discrete elements. Problems linked to bending-dominated numerical simulations are brought to attention : transverse hourglassing and lack of local bending stiffness. For the transverse hourglassing situation, two stiffening technics are proposed : averaging the dilatation through the whole element or adding a supplementary tangent material rigidity in a specific direction. The local bending stiffness problem is solved by calculating the curvature inside the element by using rotation free plates. The induced bending moment leads to supplementary internal loads. Finally, the elastic springback following the pyrolysis of the polymer matrix with ceramic precursors is modeled. The constitutive behavior is experimentally identified with a transverse isotropic hyperelastic law. Added to the initial reinforcements’ hyperelastic law, with the preformed fabric as reference configuration, the pyrolysis induced deformations can be visualized. This final model is compared with experimental results.

L’introduction des composites dans des pièces structurelles critiques pour les aéronefs représente une réelle rupture technologique et nécessite des études spécifiques afin de maîtriser leur comportement et leur durabilité. Ce travail a pour objectifs de caractériser et de comprendre les mécanismes de vieillissement de composites interlock 3D à fibres de carbone et à matrice polymère lorsqu’ils sont soumis à des cycles thermiques.Dans ce but, un essai de cyclage thermique (-55°C/120°C), dont l’environnement thermique et gazeux est totalement maitrisé, a été mis en place pour le vieillissement d’échantillons composites représentatifs du motif interlock élémentaire. L’analyse des mécanismes de dégradation induits a été réalisée grâce i/ à la mise au point d’une méthode de caractérisation quantitative 3D de l’évolution des microfissures au cours du cyclage, basée sur des observations par microtomographie RX et sur le développement d’une procédure de traitement d’images spécifique, ii/ au développement d’un essai de cyclage thermique in situ synchrotron couplé à une technique de corrélation d’images volumiques 3D, et iii/ à des simulations par éléments finis prenant en compte l’architecture réelle des échantillons à l’échelle mésoscopique et le comportement thermo-viscoélastique de la matrice.Les résultats obtenus mettent en évidence des couplages thermo-chimio-mécaniques complexes,qui s’expriment à travers quatre paramètres influents : le temps (et le nombre de cycles),l’architecture de l’interlock, la ténacité de la matrice et sa sensibilité à la thermo-oxydation. / The introduction of composite materials in critical structural parts for aircrafts represents a real technological breakthrough and requires specific studies to understand their behavior and durability. This work aims to characterize and understand the ageing mechanisms incarbon/epoxy 3D interlock composites when they are submitted to thermal cycling.For this purpose, a thermal cycle test (-55°C/120°C), whose heat and gaseous environment istotally mastered, was set up for the ageing of composite samples of elemental interlock pattern dimensions. Analysis of induced degradation mechanisms was achieved by i/ the development ofa 3D quantitative characterization method of the evolution of microcracks during cycling, basedon observations by microtomography RX and the development of a specific image processing procedure, ii/ the development of an in situ thermal cycle test under synchrotron light, coupled to a digital volume correlation technique, and iii/finite elements simulations taking into account the actual mesoscopic architecture of the samples and the thermo-viscoelastic behavior of thematrix.The results reveal complex thermo-chemo-mechanical couplings that are linked to four important parameters: time (and the number of cycles), the interlock architecture, the matrix toughness andits sensitivity to thermo-oxidation.

La démarche expérimentale menée dans cette thèse a eu comme objectif l'étude des facteurs qui influent l'efficacité de collecte des médias non-tissés chargés par décharge couronne, utilisés pour la filtration de l'air. Les recherches se sont focalisées sur les techniques faisant appel à la décharge couronne en configuration fil-plan et en configuration triode (électrode duale + grille + plan de masse). L'étude s'est déroulée en trois phases : (1) mise au point de dispositifs expérimentaux pour générer la décharge couronne et mesurer le potentiel électrique à la surface des échantillons chargés ; (2) caractérisation de l'état de charge des médias ; (3) évaluation de l'efficacité de collecte, en corrélation avec les résultats des mesures de charge. La distribution de charges a été plus homogène en configuration triode et le niveau de charge a été meilleur en polarité positive. Le déplacement de l'échantillon dans la zone de décharge électrique permet de mieux uniformiser la distribution de la charge. L'augmentation du courant de décharge et du potentiel de grille permet d'amplifier le niveau de charge des médias, suite à l'intensification du champ électrique moyen entre l'électrode active et le plan de masse (en configuration fil – plan), ou entre la grille et le plan de masse (en configuration triode). L'efficacité de la collecte est meilleure si la charge est uniformément déposée, sous l'action d'un champ électrique plus intense. Elle est plus élevée pour les configurations dites « multicouches » où la captation des particules est améliorée par l'association de plusieurs mécanismes physiques, mettant en jeux des forces électriques et mécaniques. / The experimental approach undertaken in this thesis was aimed at the study of the factors affecting the collection efficiency of nonwoven media charged by corona discharge, used for air filtration. Research was focused on techniques using the corona discharge generated by wire-plane and triode configurations (dual electrode + grid + ground plane). The study was conducted in three phases: (1) development of experimental devices to generate corona discharge and measure the electrical potential on the surface of charged samples; (2) characterization of the electrostatic charge state of the media; (3) evaluation of the collection efficiency, correlated with the results of charge measurements. The charge distribution was more homogeneous in triode configuration and the charge level was higher in positive polarity. The sample movement in the electric discharge zone allowed for more uniform distribution of the charge. The increase of the discharge current and gate voltage amplifies the charge level of the media, due to the intensification of the average electric field between the active electrode and the ground plane (configuration wire - plane) or between the gate and the ground plane (in triode configuration). The collection efficiency is better when the charge is uniformly deposited, under the action of a strong electric field. It is higher for the so-called "multi-layer" configurations where the capture of the particles is improved by the combination of several physical mechanisms, involving electrical and mechanical forces.