Rozprawy doktorskie na temat „Thermoplastic Matrix Materials”

La sensibilisation accrue aux questions environnementales concerne aujourd'hui les structures aéronautiques en termes d'impact environnemental et traitements de fin de vie. Dans cette optique,la possibilité de remplacer, dans les composites à matrice organique (CMO) utilisés pour des applications aéronautiques, leur matrice thermodurcissable non recyclable par une matrice thermoplastique recyclable est étudiée. En outre, les polymères thermoplastiques, tels que le PEKK, ont la possibilité d'être utilisés dans des structures plus chaudes (par exemple le pylône d'un avion), faisant l'objet de sollicitations de longue durée (fluage). Les températures de service de ces structures plus élevées que celles de la température de transition vitreuse du PEKK : il en découle, dans le matériau, une perte de propriétés due au changement d'état de solide à caoutchoutique, et éventuellement l'activation de phénomènes de cristallisation etde dégradation, qui pourraient également interagir. Ce travail vise à identifier et à modéliser ces mécanismes caractérisant le comportement du PEKK, dans ces conditions extrêmes particulières.Ceci est réalisé à partir de l'analyse des résultats des essais thermomécaniques, physico-chimiques et thermomécaniques couplés avec l’oxydation. Le modèle analytique 1-D du comportement duPEKK qui résulte de l’analyse des essais est étendu en 3-D et implémenté dans une méthode d'homogénéisation/localisation semi-analytique multi-échelle pour simuler le comportement dans mêmes conditions de composites stratifiés à matrice PEKK, en faisant varier l'orientation des plis et la séquence d'empilement
The nowadays increased awareness towards environmental issues concerns aircraft structures in terms of environmental impact and end-of-life disposal. In this optics, the possibility of replacing in the organic matrix composites (CMO) employed for aircraft applications the non-recyclable thermosetting matrix with a recyclable thermoplastic one is investigated. Moreover, thermoplastic polymers, such PEKK, have the possibility of being employed in warmer structures (e.g. the aircraft pylon), undergoing long duration solicitations (creep).The service temperatures for those structures are higher than the PEKK glass transition temperature, provoking, in the material, a loss of properties deriving from a change of state from solid to rubber, and possibly the activation of crystallization and degradation phenomena, which could also interact. This work aims to identify and model the mechanisms characterizing PEKK behavior, under the structure operative service conditions. This is achieved from the analysis of the results of thermomechanical, physical-chemical and coupled thermomechanical/oxidation tests. The resulting 1-D analytical model of the PEKK behavior, is extended in 3-D and implemented in a multi-scale semi-analytical homogenization / localization method to simulate PEKK based composites under the same conditions, varying the plies orientation and stacking sequence

Les technologies de placement de plis ou d’enroulement filamentaire de composite à matrice thermoplastique avec consolidation en continu ont fait l’objet de nombreux travaux ces dernières années. Ces études ont porté principalement sur des composites à base de matrice thermoplastique semi-cristalline comme le poly(éther éther cétone) (PEEK) renforcée de fibres de carbone. L’objectif de la thèse est de déterminer les lois de comportement du composite fibres de carbone/matrice thermoplastique lors de la mise en œuvre afin de déduire quelle étape gouverne le processus de soudage et quels sont les paramètres procédés et matériaux influençant sa durée. Dans ce but, les principales propriétés de la matrice utiles à l’étude ont, dans un premier temps, été déterminées. Une attention particulière a été portée sur la dégradation thermique. Les analyses en thermogravimétrie ont ainsi permis d’évaluer sa cinétique de dégradation. Dans un deuxième temps, les mécanismes de contact intime et d’autohésion, responsables du soudage, ont été étudiés à partir de modèles. Pour cela, les mesures de rugosité de surface et de viscosité ont été intégrées au modèle de contact intime. Le temps de diffusion de la matrice a été déterminé par rhéologie puis intégré au modèle d’autohésion. Enfin, l’influence des paramètres procédé (temps, température et pression) et matériau (masses molaires et rugosité) sur les mécanismes de formation de l’interface et ses performances mécaniques a été évaluée expérimentalement par des tests d’adhérence (clivage et pelage) et comparée aux modèles
The automated tow placement or filament winding processes of thermoplastic-based composites have been intensively studied in recent years. These studies concerned mainly composites with thermoplastic semi-crystalline matrices as carbon fiber reinforced poly(ether ether ketone) (PEEK). The thesis objective is to understand the physical mechanisms taking place in a thermoplastic-based composite during the welding in order to deduce which step governs the welding process and what are the parameters influencing its duration. First, the main properties of matrix of interest for this study were determined, in particular its thermal degradation. The thermal gravimetric analysis thus allowed to evaluate the kinetics of degradation. Secondly, the mechanisms of intimate contact and self-adhesion responsible for welding were studied using models. For this, surface roughness and viscosity measurements were included in the model of intimate contact. The diffusion time of matrix was determined by rheology and integrated into the self-adhesion model. Eventually, the influence of process (time, temperature and pressure) and material (molecular weight and roughness) parameters on the mechanisms of interface formation and its mechanical performance was evaluated experimentally by adhesion tests (wedge test and peeling ) and compared with models

Os compósitos termoplásticos de alto desempenho vêm despertando grande interesse dos fabricantes aeronáuticos por apresentarem algumas vantagens importantes em relação aos tradicionais compósitos termorrígidos, como por exemplo: melhor resistência ao impacto; maior tolerância ao dano; baixa flamabilidade; possibilidades de reprocessamento; não necessitam da utilização de auto-claves para o seu processamento e acondicionamento térmico em baixas temperaturas do pré-impregnado (-18C), pois são armazenados a temperatura ambiente e possuem vida indeterminada de armazenamento (shelf-life). O custo de desenvolvimento de técnicas de processamento e, principalmente, de certificação dos compósitos termoplásticos para uso em estruturas de responsabilidade estrutural primária, tem inibido no presente momento a maior aplicação destes materiais na indústria aeroespacial. O aprimoramento das técnicas atuais e aplicação de novas técnicas de processamento desenvolverão um papel fundamental para ultrapassagem destas barreiras atualmente impostas aos materiais termoplásticos de alto desempenho. Neste contexto, o objetivo do presente trabalho é estudar o processamento por moldagem por compressão a quente de um compósito termoplástico baseado em pré-impregnado de PEEK / fibra de carbono e sua caracterização pelas técnicas: calorimetria exploratória diferencial (DSC), análise termogravimétrica (TGA), análise térmica dinâmico-mecânica (DMTA), microscopia óptica de luz polarizada (MOLP) e resistência ao cisalhamento interlaminar (ILSS). Baseado nos resultados obtidos com as técnicas de DSC, TGA e MOLP foi determinado que a faixa de temperatura mais adequada para o processamento do PEEK encontra-se entre 380C e 440C, a partir do tecido préimpregnado TowFlex CPEEK-101. Por DMTA foi obtida a temperatura máxima de 115C para uso destes compósitos submetidos a cargas estruturais intermitentes. Para o mesmo processo de fabricação e tecido pré-impregnado, utilizando-se pressão de moldagem de 10 MPa, com 16 camadas de tecido, resultou em laminados com valores médios de ILSS de 19,4 MPa, enquanto que usando pressão de moldagem de 5MPa, com 12 camadas de tecido, os valores médios obtidos de ILSS foram de 14,7MPa.
The high performance thermoplastic composites have attracted great interest from aerospace manufacturers for presenting some important advantages over traditional thermoset composites, for example, better impact resistance, greater damage tolerance, low flammability, possibilities reprocessing do not require the use of autoclaves for processing and packing heat at low temperatures of the prepreg (-18 C) as they are stored at room temperature and indefinite storage life (shelf life). The cost of developing processing techniques and especially the certification of thermoplastic composite structures for use in primary structural responsibility, has inhibited at present the largest application of these materials in the aerospace industry. The improvement of current techniques and novel processing techniques to develop a fundamental role exceeded those barriers currently imposed on highperformance thermoplastic materials, requiring greater efforts in research of these solutions. In this context, the objective of this study is the processing by hot compression molding of a thermoplastic-based composite prepreg of PEEK / carbon fiber and its characterization by techniques: differential scanning calorimetry (DSC), thermogravimetric analysis (TGA ), dynamic mechanical thermal analysis (DMTA), polarized light microscopy (MOLP), heat shock (in progress) and shear strength (ILSS). Based on the results obtained with the techniques of DSC, TGA and MOLP was determined that the temperature range suitable for processing of PEEK is between 380 C and 440 C, from the fabric prepreg TowFlex CPEEK-101. By DMTA was obtained by the maximum temperature of 115 degrees to use these composites subjected to intermittent structural loads. For the same manufacturing process and fabric prepreg using molding pressure of 10 MPa, with 16 layers of fabric, resulting in laminates with average values of ILSS of 19.4 MPa, while using pressure molding 5MPa with 12 layers of tissue, average values of ILSS of 14.7 MPa.

In the effort to improve oil production riser performance, new materials are being studied. In the present case, a Polymer Matrix Composite (PMC) is being considered as a replacement for carbon steel in flexible risers manufactured by Wellstream Inc., Panama City, Florida. The Materials Response Group (MRG) at Virginia Tech had the primary responsibility to develop the models for long-term behavior, especially remaining strength and life. The MRG is also responsible for the characterization of the material system with a focus on the effects of time, temperature, and environmental exposure. The present work is part of this effort. The motivation to use a composite material in a non-bonded flexible riser for use in the offshore oil industry is put forth. The requirements for such a material are detailed. Strength analysis and modeling methods are presented with experimental data. The effect of matrix crystallinity on composite mechanical properties is shown. A new method for investigating matrix behavior at elevated temperatures developed. A remaining strength life prediction methodology is recalled and applied to the case of combined fatigue and rupture loading.
Master of Science

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 composites
The 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

Cette thèse présente une étude expérimentale pour améliorer le moulage par compression et transfert de résine thermoplastique (CRTM), axée sur l'efficacité industrielle, la durabilité et la recyclabilité, conformément aux objectifs de développement durable pour l’industrie, l’innovation et l’action climatique. En abordant la complexité de l'écoulement de la résine à plusieurs échelles dans le CRTM, cette recherche étudie l'écoulement transversal (à travers l’épaisseur) et la porosité induite par le processus à l'échelle méso des faisceaux de fibres de verre afin d'améliorer l'uniformité de l'imprégnation et le contrôle du compactage, en faisant le lien entre les cadres théoriques et les applications évolutives. L’étude est conduite sur une préforme, constituées de 6 couches de fibres de verre UD ([0/90]3) et d’une matrice thermoplastique en polypropylene (PP) mise en forme par un procédé CRTM . Un procédé « CRTM simplifié » permettant de contrôler la direction du front de matière est développé sur une presse industrielle, pilotée en déplacement. Trois configurations de procédé sont analysées : Configuration 1 (Référence) : configuration de type « film stacking » comme base de comparaison de la distribution de la résine et de la structure des fibres. Configuration 2 (CRTM simplifié) : Compression contrôlée par déplacement, les films de polymères formant initialement une couche unique en surface de la préforme. Configuration 3 (CRTM simplifié avec scellement des bords) : Compression améliorée avec un dispositif d’étanchéité limitant les fuites de résine en périphérie de la préforme et assurant un écoulement transversal. Un protocole d’analyse d'imagerie 2D est proposé, incluant l’analyse en lumière polarisée, la microscopie à fluorescence et la microscopie électronique à balayage pour caractériser qualitativement et quantitativement les taux de porosités au niveau des mèches et des plis de tissus. Un processus original de polissage en deux étapes permet de préserver l'intégrité de la surface. L'étude est complétée par une évaluation fine des mécanismes d'imprégnation à l'aide de la technique d'inspection hélicoïdale en microtomographie à rayon-X (micro-CT). Les résultats démontrent que les paramètres de compaction influencent directement le niveau d'imprégnation, atteignant une limite d'imprégnation. Cette thèse établit une démarche d’analyse du procédé CRTM pour des composites thermoplastiques haute performance, en vue d’une maitrise et d’une optimisation du procédé. Elle offre des perspectives sur des protocoles d’analyse précis basés sur l’étude à différentes échelles, améliorant la compréhension de l'interaction entre l'imprégnation et la perméabilité. Ces résultats répondent aux exigences de précision dans des secteurs tels que l'automobile et l'aérospatiale, où les composites CRTM sont essentiels pour les applications structurelles
This thesis presents an experimental study to advance thermoplastic Compression Resin Transfer Molding (CRTM), focusing on industrial efficiency, sustainability, and recyclability goals aligned with the Sustainable Development Goals for Industry, Innovation, and Climate Action. By addressing multi-scale resin flow complexity in CRTM, this research investigates transverse flow and process-induced porosity at the meso scale of glass fiber bundles to improve impregnation uniformity and compaction control, bridging theoretical frameworks with scalable applications. The study focuses on a thermoplastic polypropylene matrix reinforced with six layers of bidirectional UD woven glass fibers ([0/90]3) consolidated on a CRTM setup. The “Simplified CRTM” method is developed on an industrial press, using displacement-controlled compaction ratios. This method omits active resin injection, relying on a uniformly distributed viscous polymer pool beneath the unsaturated preform to drive resin flow uniformly with a unidirectional flow path. Controlled displacement and pressure optimize resin paths, manage fiber volume fraction, and reduce porosity. Three multi-step compaction configurations are evaluated: Configuration 1 (Reference): Uses force compaction as a baseline for comparing resin distribution and fiber structure. Configuration 2 (simplified CRTM): Displacement-controlled compaction enhances resin infiltration but faces challenges like edge race-tracking and fiber volume fraction (Vf) variability, affecting impregnation. Configuration 3 (simplified CRTM with Edge Sealing): Introduces high-temperature sealant tape at mold edges, limiting resin escape, maintaining transverse flow, and reducing porosity and race-tracking. Configuration 3 edge-sealing technique establishes a reproducible process for high quality CRTM composites. An advanced 2D multi-modal imaging protocol, tailored for partially impregnated samples produced via simplified CRTM with unfilled spaces and fragile microstructures, includes polarized light microscopy, fluorescence microscopy, and scanning electron microscopy for qualitative and quantitative characterization. An original two-step polishing process preserves surface integrity, and image post-processing workflows quantify impregnation quality and void distribution. The study is completed with a fine evaluation of the impregnation mechanisms using X-ray micro computed tomography technique (micro-CT) relying on helicoidal inspection method. Results demonstrate that compaction parameters directly impact impregnation level, reaching an impregnation limit. This thesis establishes a scalable, data-driven CRTM framework bridging laboratory experimentation with industrial requirements for high-performance thermoplastic composites. It offers insights into streamlined protocols and microstructure-based analysis, enhancing understanding of the interplay between impregnation and permeability in CRTM. These findings align with precision demands in sectors like automotive and aerospace, where CRTM composites are crucial for structural applications

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 augmentée
Agro-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

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
A utilização de materiais compósitos continua crescendo na indústria, porém, problemas relacionados a sua reciclabilidade, principalmente quando utilizadas fibras cerâmicas contínuas ainda não foram adequadamente solucionados. A utilização de fibras curtas associadas a fibras contínuas consiste em uma alternativa não só para a redução dos custos mas também para auxiliar na reciclagem de tais materiais. Desta forma, este trabalho apresenta como principal objetivo e inovação o processamento e caracterização de compósitos termoplásticos reforçados simultaneamente com fibras contínuas e curtas, visando dar aplicabilidade estrutural a fibras de carbono recicladas. Neste trabalho foram processadas placas de um compósito termoplástico utilizando PPS como matriz e fibras contínuas e descontínuas de carbono, mantendo uma relação matriz/reforço em 1/1 em volume e a relação entre fibras contínuas e descontínuas também em 1/1 em volume. Desta forma, como fibra contínua foi utilizado um tecido plain weave e como fibras curtas, cabos de 2 e 6 cm de comprimento. Estes compósitos foram processados a partir de moldagem por compressão a quente e caracterizados por ensaios de excitação por impulso, tração, cisalhamento (IOSIPESCU e ILSS), e compressão (CLC). Com o intuito de avaliar a influência da adição das fibras curtas nestes compósitos, após ensaiados, foi realizada uma análise fractográfica. Após a caracterização do material, foi utilizado o método dos elementos finitos. A partir dos resultados encontrados conclui-se que é possível a obtenção de um compósito envolvendo fibras contínuas e descontínuas com qualidade, e desempenho mecânico intermediário aqueles constituídos apenas de fibras contínuas ou descontínuas. Ainda, a partir deste trabalho, foi observado que os modos de falhas para o compósito avaliado neste trabalho são similares àqueles encontrados para compósitos constituídos apenas de reforços contínuos e que os modelos utilizados durante as simulações apresentaram resultados similares aos resultados encontrados experimentalmente
The use of composite materials continues to grow in the industry, however, problems related to their recyclability, especially when using continuous ceramic fibers have not been adequately solved. The use of chopped fibers alongside continuous fibers is an alternative not only to reducing costs but also to assist in the recycling of such materials. This way, this work presents as main objective and innovation the processing and characterization of thermoplastic laminates reinforced with short and continuous carbon fibers, in order to give structural application for recycling carbon fibers.In this work, plates of a thermoplastic composite were processed using PPS as a matrix and continuous and discontinuous carbon fibers, maintaining a matrix/reinforcement volume ratio of 1/1 and a volume ratio of continuous and discontinuous fibers also of 1/1. Thus, as continuous fiber it was used a plain weave fabric and short fibers of length of 2 to 6 cm. At this moment, an evaluation of the laminates processed by impulse excitation, tensile, shear (IOSIPESCU), compression (CLC) tests is being performed and an evaluation of the fractures will be made by fractographic analysis and the finite element method has been used. From the results found, it is possible to obtain a composite involving continuous and discontinuous fibers with quality, and intermediate mechanical performance those composed only of continuous or discontinuous fibers. Furthermore, from this work, it was observed that the failure modes for the composite evaluated in this work are similar to those found for composites processed only with continuous reinforcements and that the models used during the simulations presented results similar to the results found experimentally
CAPES: 1626401

Les matériaux composites sont largement employés dans le domaine aérospatial grâce à leurs excellentes propriétés mécaniques, leur résistance aux chocs et à la fatigue, tout en restant plus légers que les matériaux conventionnels. Au cours des dernières années, l'industrie automobile a montré un intérêt croissant pour les procédés de fabrication et de transformation de matériaux composites à matrice thermoplastiques. Cela favorisé par le développement et l'optimisation des procèdes de mise en forme tels que le thermostampage, en vue de la réduction de temps de cycle. La modélisation et la simulation de ce procédé sont des étapes importantes pour la prédiction des propriétés mécaniques et de la faisabilité technique des pièces à géométrie complexe. Elles permettent d'optimiser les paramètres de fabrication et du procédé lui-même. À cette fin, ce travail propose une approche pour la simulation de la mise en forme des matériaux composites préimprégnés thermoplastiques. Un modèle viscohyperélastique avec une dépendance à la température a été proposé dans l'objectif de décrire le comportement du composite thermoplastique à l'état fondu. Et permets de faire des simulations de mise en forme à différentes températures. Au cours cette simulation, des calculs thermiques et mécaniques sont effectués de manière séquentielle afin d'actualiser les propriétés mécaniques avec l'évolution du champ température. L'identification des propriétés thermiques sont obtenues par homogénéisation à partir des analyses au niveau mésoscopique du matériau. La comparaison de la simulation avec le thermoformage expérimental d'une pièce représentative de l'industrie automobile analyse la pertinence de l'approche proposée
Pre-impregnated thermoplastic composites are widely used in the aerospace industry for their excellent mechanical properties, impact resistance and fatigue strength all at lower density than other common materials. In recent years, the automotive industry has shown increasing interest in the manufacturing processes of thermoplastic-matrix composites materials, especially in thermoforming techniques for their rapid cycle times and the possible use of pre-existing equipment. An important step in the prediction of the mechanical properties and technical feasibility of parts with complex geometry is the use of modelling and numerical simulations of these forming processes which can also be capitalized to optimize manufacturing practices.This work offers an approach to the simulation of thermoplastic prepreg composites forming. The proposed model is based on convolution integrals defined under the principles of irreversible thermodynamics and within a hyperelastic framework. The simulation of thermoplastic prepreg forming is achieved by alternate thermal and mechanical analyses. The thermal properties are obtained from a mesoscopic analysis and a homogenization procedure. The comparison of the simulation with an experimental thermoforming of a part representative of automotive applications shows the efficiency of the approach

L’utilisation croissante des matériaux composites à matrice thermoplastique dans l’industrie aéronautique passe par une meilleure compréhension de leur comportement mécanique lors d’une exposition à un flux rayonnant (conséquence d’un incendie). Cette étude, portant sur le comportement thermo-mécanique de stratifiés tissés quasi-isotropes composés d’une matrice PPS renforcée par des fibres de carbone, se divise en 3 parties. Tout d’abord, la décomposition thermique du matériau et l’évolution de ses propriétés mécaniques avec la température sont étudiées. Ces données permettent ensuite d’appréhender le comportement de ces matériaux soumis à des chargements combinés (flux rayonnant et chargement mécanique en traction ou en compression, de type monotone à rupture et en fluage). La dernière partie vise à identifier les paramètres matériau nécessaires pour la simulation thermo-mécanique aux échelles macroscopique et mésoscopique
The increasing use of thermoplastic-based composite materials in the aeronautical industry requires a better understanding of their mechanical behavior when exposed to radiant heat flux (consequence of a fire exposure). This study, which examines the thermo-mechanical behavior of quasi-isotropic woven laminates composed of PPS reinforced with carbon fibers, is divided into 3 parts. First, the thermal decomposition of the material and the evolution of its mechanical properties with temperature is studied. These data help to understand the behavior of these materials subjected to combined loads (radiant heat flux and tensile or compressive loadings). The last part aims to identify the material parameters necessary for thermo-mechanical simulation at macroscopic and mesoscopic scales

Ces travaux exposent et analysent les performances d’un composite à matrice thermoplastique semi-cristallin au passage et au-delà de la transition vitreuse. Il est nécessaire de donner des éléments objectifs afin d’évaluer et discuter dans quelles mesures ce matériau peut être utilisé de manière innovante. L’objectif visé est de donner des perspectives en termes de plage de températures d’utilisation des matériaux composites à matrice thermoplastique et plus spécifiquement pour des applications à hautes températures. Le composite à fibres continues de carbone et matrice polyétheréthercétone PEEK a ainsi été étudié sur une large gamme de température, avant et après sa température de transition vitreuse (Tg = 143°C).La phase de caractérisation quasi-statique a mis en évidence l’importance du renfort et le bon transfert de charge de la matrice au-delà de la Tg pour les différentes sollicitations. En particulier, la résistance à la rupture en compression s’est avérée intéressante dans l’optique d’une application structurelle. De plus, les observations fractographiques ont mis en évidence des comportements radicalement différents au passage de la transition vitreuse. Le caractère plus ductile de la matrice permet de limiter la propagation de fissures au travers des plis par dissipation de l’énergie : la plastification de la matrice augmente la capacité du composite à dissiper de l’énergie en limitant ainsi la fissuration. Cependant pour des chargements où la matrice pilote la réponse mécanique du composite tels que des efforts de cisaillement, les comportements non linéaires sont fortement accentués. Des mécanismes de déformations dépendant du temps ont été observés à travers des essais de charge-décharge et de fluage au-delà de la Tg : le caractère visqueux de la matrice joue un rôle prépondérant.Ces mécanismes non linéaires étant identifiables sur des temps longs, il était intéressant de proposer des méthodes de modélisation pour prédire le comportement du composite. C’est pourquoi des modèles à l’échelle du pli ont été adaptés en fonction de la température et de la prépondérance des caractères viscoélastique et viscoplastique. Différents essais de fluage-recouvrance en torsion rectangulaire menés sur un rhéomètre ont permis d’évaluer les composantes viscoélastiques et viscoplastiques de la déformation à des températures inférieures et supérieures à la Tg
The present study shows and analyses the specifications of a semi-crystalline thermoplastic composite as function of temperature, below and above the glass transition. In order to assess and discuss about what extent this material could be innovately use, objective facts must be necessary exposed: the main target is to give the outlooks about the temperature range, in particular the high temperatures. The studied material is a continuous carbon fibre composite with a polyetheretherketone (PEEK) matrix. Its glass transition temperature is around 143°C. It has been characterized throughout a wide temperature range.For several kinds of quasi-static loadings, the load transfer from the matrix to the fibre reinforcement is good even above the glass transition temperature. The compression strength is indeed very interesting for an aeronautical application. In addition, the fracture surface analysis have significantly revealed a different behaviour above the glass transition temperature: the matrix is more ductile and thus the crack propagation is limited thanks to the energy dissipation. However when the mechanical response is driven by the matrix behaviour such as shear loadings, the nonlinear mechanical behaviour of the composite are highly increased. Therefore the time-dependent behaviours have been characterized by using creep experiments and loading-unloading tensile tests as function of the temperature.In order to predict those non-linear behaviours, meso-models have been developed as function of the temperature. Thus viscoelasticity and viscoplasticity have been taken into account to model the nonlinear mechanical behaviour of the composite material, thanks to creep-recovery tests which have been carried out with a torsion rheometer

Lo sviluppo di elettroliti polimerici di nuova generazione è un requisito essenziale per la diffusione su grande scala delle celle a combustibile a membrana polimerica. Tali conduttori protonici devono esibire stabilità morfologica, idrolitica, meccanica ed adeguate proprietà di conducibilità (σ~ 0.01 Scm-1) a temperature superiori a 100 °C per bassi valori d’umidità relativa. Nel presente lavoro sono esplorate diverse strategie per la sintesi di polimeri conduttori ibridi organici-inorganici nanocompositi a partire da polimeri termoplastici aromatici. L'impiego di materiali ibridi permette di sfruttare l'effetto sinergico dovuto alla contemporanea presenza di una componente organica, nel caso specifico polimerica, e di una inorganica, nel caso specifico a base di silicio. Tale effetto sinergico si esplica nella possibilità di modulare e controllare la separazione tra la fase idrolifila ed idrofobica da cui fortemente dipendono le prestazioni dell'elettrolita polimerico. Membrane ibride di classe I a base di polietereterchetone solfonato (S-PEEK) sono così state sintetizzate insieme a numerosi esempi di membrane ibride di classe II a base di S-PEEK e polifenilsolfone solfonato (S-PPSU), contenenti come porzione inorganica atomi di silicio diversamente funzionalizzati. La caratterizzazione dei materiali ha riguardato l’analisi della struttura, le proprietà chimico fisiche ed il comportamento elettrochimico. Risultati molto positivi sono stati ottenuti principalmente con due dei sistemi investigati: una miscela polimerica a base di S-PEEK e S-PPSU sililato ed un polimero interconnesso tramite ponti -SO2- (SOPEEK) e sililato (SOSiPEEK).
The development of new generation polymer electrolytes is an essential prerequisite for grand scale commercialisation on of polymer electrolyte membrane fuel cells. These proton conductors must show good morphological, hydrolytic and mechanical stability and an appropriate conductivity (σ ~ 0.01 Scm-1) at a temperature above 100°C at low relative humidity. In this work, diverse strategies for synthesis of hybrid organic-inorganic proton conducting polymer nanocomposites were explored, based on aromatic thermoplastic polymers. The use of hybrid materials permits exploitation of the synergy between the simultaneously present organic polymeric component and an inorganic silicon-based part. These effects can be explained by the possibility to modulate and to control the separation between hydrophilic and hydrophobic parts, which strongly modify the properties of the electrolytic polymer. Hybrid materials of class I based on sulfonated poly-ether-ether-ketone (S-PEEK) were synthesized as well as several examples of hybrid materials of class II based on SPEEK and poly-phenyl-sulfone sulfonated (S-PPSU) and containing as inorganic part diverse functionalized silicon atoms. These materials were characterized from the point of view of structure, physical and chemical properties and electrochemical behaviour. Very positive results were obtained mainly for two investigated systems: a mixture of S-PEEK and S-PPSU silylated polymer and a cross-linked polymer, through -SO2- bridges (SOPEEK) and silylated (SOSiPEEK).

Pour étendre l'utilisation des composites dans des applications plus variées (applications intelligentes et multifonctionnelles), l'une des barrières est leur faible conductivité électrique et thermique. Dans le cas de composites renforcés par des fibres de carbone, la matrice organique est responsable des propriétés isolantes du composite résultant. L'une des solutions pour améliorer les conductivités des matériaux est l'utilisation des nanocharges conductrices. L'amélioration des propriétés électriques et thermiques des polymères nanochargés est une problématique récurrente dans la littérature. Cependant, étudier les propriétés des composites à fibre de carbone continue et nanochargés est moins abordée. Ce travail porte sur la fabrication et la caractérisation des composites nanochargés par du noir de carbone et des nanotubes de carbone. Tout d'abord, un intérêt particulier a été accordé à la phase délicate de la fabrication. Comme mentionné ci-dessus, la mise en œuvre des composites à renfort continu et matrice nanochargée implique des problèmes liés à l'agglomération et à la dispersion inhomogène des nanocharges dans le composite final. Pour résoudre ces problèmes, le choix de la matrice thermoplastique (Polyamide 6) était judicieux. En fait, la dispersion des nanocharges a été faite par extrusion bi-vis qui est connue comme l'une des voies les plus efficaces de séparation d'agglomérats. De plus, la méthode de fabrication à base de films de Polyamide 6, appelée film stacking, assure une partition homogène dès le début du processus. Des observations MEB ont été effectuées pour localiser les nanoparticules. Ceux-là ont montré que les particules pénétraient dans la zone des fibres. En effet, en atteignant le cœur des torons, les nano-charges ont créé un réseau de connectivité entre les fibres pour le passage de courant. Ceci explique l'amélioration constatée de la conductivité électrique des composites en présence de noir de carbone et des nanotubes de carbone. Ces essais ont été réalisés avec la méthode à 4 points. La conductivité électrique du composite à matrice « pure » est passée de 20S / cm à 80S / cm en ajoutant 8% en poids de noir de carbone et à 15S / cm en ajoutant 18% en poids de la même charge nanométrique. Pour les nanotubes de carbone, avec 2,5% en poids, la conductivité était d'environ 150S / cm. Pour les propriétés thermiques, des tests basés sur l'effet Joule ont été réalisés. L'augmentation de la température a été enregistrée en utilisant une caméra IR. Les résultats obtenus sont en accord avec ceux de la conductivité électrique, montrant une amélioration du comportement thermique en présence de nanocharges. Grâce à ces résultats, l'utilisation de ces composites comme outil de suivi d’endommagement était possible. Par ailleurs, la méthode de variation de la résistance électrique a été effectuée. Les matériaux nanochargés ont montré une meilleure sensibilité aux endommagements. Les résultats ont été comparés aux outils classiques de suivi d’endommagement. A la fin, plusieurs applications « intelligentes » ont été testées telles que : le composite à gradients de propriétés et des matériaux nanochargés cousus
To extend the use of composites in more varied application (smart applications, multifunctional issues), one of the actual barrier is their poor electrical and thermal conductivities. In the case of carbon fiber reinforced composites, organic matrix are in charge of the insulating properties of the resulting composite. One of the solutions to enhance conductivities of materials is the use of conductive nanofillers. Improving the electrical and thermal properties of nanofilled polymers has been investigated in several studies. However, studiing the properties of continuous carbon fiber nano-filled composites is less approached. This work tends to fabricate and characterize carbon black and carbon nanotubes nano-filled composites. First of all, special interest was given to the delicate phase of manufacturing. As mentioned before, processing continuous fiber reinforced nanofilled polymers implies issues related to nanofillers agglomeration and inhomogeneous dispersion in the final composite. To resolve these problems, the choice of the thermoplastic (Polyamide6) matrix seemed preferable. In fact, the dispersion of nanofillers was made by twin screw extrusion which is known as one of the most effective agglomeration separation ways. Adding to this, the fabrication method based on Polyamide 6 shects called film stacking, ensure a homogeneous partition at the beginning of the process. SEM observations were performed to localize the nano-particles. It showed that particles penetrated on the fiber zone. In fact, by reaching the fiber zone, the nano-fillers created network connectivity between fibers which means an easy pathway for the current. It explains the noticed improvement of the electrical conductivity of the composites by adding carbon black and carbon nanotube. This test was performed with the 4 points electrical circuit. It shows that electrical conductivity of 'neat' matrix composite passed from 20S/cm to 80S/cm by adding 8wt% of carbon black and to 15S/cm by adding 18wt% of the same nano-filler. For carbon nanotubes, with '2.5wt% the conductivity was around 150S/cm. For the thermal properties, tests based on Joule's effect were performed. The rise of temperature was recorded using IR camera. Results obtained are in agreement with the electrical conductivity ones, showing enhancement of the thermal behavior in presence of nanofillers. Thanks to these results, the use of these composites as a damage-monitoring tool was possible. By the way, the electrical resistance change method was performed. Nanofilled materials showed better sensitivity to damage. Results were compared with classical damage monitoring tools. At the end, several 'smart' applications were tested such as graded functionalities composite and stitched nanofilled materials

Microstructure et proprietesmecaniques de composites unidirectionnelles polyetherethercetone/ fibres carbone, sulfure de polyphenylene/fibres de carbone et polyetherimide/fibre de carbone. Influence de temps rapide, refroidissement lent etc. Essais mecaniques. Cohesion interne. Mise en evidence d'une phase "transcristalline". Modelisation du comportement viscolastique

The inherent high strength, thermal conductivity, and electrical conductivity make nanotubes attractive reinforcements for polymer matrix composites. However, the structure that makes them desirable also causes highly anisotropic properties and limited reactivity with other materials. This thesis isolates these problems in two separate studies aimed at improving mechanical properties with single wall nanotube (SWNT) reinforced thermoplastic polymer composites. The two studies demonstrate the effect of solid freeform fabrication (SFF) and chemical functionalization on anisotropy and limited reactivity, respectively. Both studies showed mechanical property improvements. The alignment study demonstrates a maximum increase of 93% in tensile modulus with single wall nanotubes (SWNTs). The chemical functionalization study shows a larger increase in storage modulus for functionalized SWNTs as compared to purified SVWNTs with respective increases of 9% and 44% in storage modulus. Improved interfacial properties are also observed as a decrease in mechanical damping. Maximum property increases in composites are obtained when nanotubes are aligned, requiring additional processing consideration to the anisotropic structure. Melt spinning and extrusion processing effectively align nanotubes, but the end product of these techniques, composite fibers, requires further processing to be incorporated into finished parts. Extrusion-based SFF is a novel technique for processing nanotube reinforced composites because it allows for the direct fabrication of finished parts containing aligned nanotubes. SFF processing produces parts containing preferentially oriented nanotubes with improved mechanical properties when compared to isotropic composites. Functionalization of the nanotube surface disrupts the rope structure to obtain smaller ropes and promote further interfacial bonding. The chemically inert nature of nanotubes resulting from a structure containing few defects and the formation of larger, ordered ropes of SWNTs limits the amount of interfacial bonding and load transfer that occurs between nanotubes and a polymer matrix. Improved dispersion, interfacial properties, and mechanical properties are achieved through chemical functionalization. Subsequent partial removal of the functional groups created a direct bond between the nanotubes and the polymer matrix. The alignment and functionalization studies in this thesis further the knowledge of the use of nanotubes as reinforcements in polymer composites through understanding the sensitivity of the nanotubes' anisotropic properties and the nanotube/polymer interface.

The major theme of this dissertation is structure/property relationships in fiber-reinforced thermoplastic-matrix composites. Effort has been focused on the interface: interfacial crystallization and fiber/matrix adhesion. Included are investigations on interfacial nucleation and morphology, measurement of fiber/matrix adhesion, effects of interfacial adsorption and crystallization on fiber/matrix adhesion, and composites reinforced with thermotropic liquid crystal copolyester fibers. Crystallization of a copolyester and poly(butylene terephthalate) with glass, carbon, or aramid fibers has been studied with regard to interfacial mophology. Techniques employed included hot-stage optical microscopy and differential scanning calorimetry. Nucleation by the fibers was found to be a general phenomenon. Morphology could be varied by changing the cooling rate. In order to better monitor fiber/matrix adhesion, a buckled plate test has been developed. The test measures transverse toughness as the parameter characterizing interfacial adhesion in unidirectional, continuous-fiber composites. The test is simple to perform yet has advantages over other interfacial evaluation techniques. The buckled plate test was found to be a sensitive measure of fiber/matrix adhesion. The buckled plate test has been used along with the transverse tensile test to examine how interfacial adsorption and crystallization affect fiber/matrix adhesion in polycarbonate/carbon fiber composites. Adsorption was found to be of primary importance in developing adhesion, while crystallization is a secondary effect. The toughness data have been fit successfully for annealing time and temperature dependence. The dependence of adsorption and transverse toughness on matrix molecular weight was found to be large, with higher molecular weights adsorbing more effectively. Studies of the fiber/matrix interface have been extended to composites reinforced with thermotropic liquid crystal copolyester fibers. Composites made with these fibers had poor transverse properties, regardless of matrix. Surface treatment such as ozonation increased transverse properties, but values were still low. Scanning electron micrographs of fracture surfaces indicated that fiber splitting occurs, especially for surface treated fibers. Poor fiber transverse properties rather than fiber/matrix adhesion thus appear to limit composite transverse properties.

Tese de Doutoramento em Ciência e Engenharia de Polímeros e Compósitos
Due to the material’s intrinsic benefits, the volume of continuous fibre reinforced thermoplastic composites (TPCs) is growing and leading to a rise of industrial waste, though a high-quality recycling route is not yet available. TPC recycling enables reclaiming the high economic value, reducing the environmental impact and to be in-line with environmental directives. In this study a new TPC recycling route was developed and successfully validated allowing to achieve, maximum cost effectiveness and minimum environmental impact. The trade-off between mechanical performance and processability or degree of mixing for long and short fibres respectively, is optimised by developing a micromechanical model. The model was used to predict stiffness and strength and includes distributions for fibre length and the degree of mixing, by local fibre volume variation and fibres per bundle. An appropriate recycling route consisting of shredding, low-shear mixing and compression moulding, was established to experimentally validate the mechanical performance of recycled TPCs. G/PP and C/PPS at various fibre orientations, contents and length distributions and waste material consolidation stages were processed both without mixing and by different levels of low-shear mixing. Characterisation was performed by flexural, impact and cross-sectional microscopy testing. The experimental properties of the recycled material were found to be in-line with theoretical predictions and increase with degree of mixing. Three demonstrator products were designed, produced and tested to prove their technical and application feasibility; a bracket, a safety shoe nose cap and an aerospace access panel. While made of recycled material with inferior material properties, the panel was even lighter than the current solution and gave enough confidence to be flight tested. Life cycle analysis and cost assessment were used to compare the recycled material and demonstrators to currently used alternatives. A significant reduction in cost and environmental impact was found for both the panel and nose cap. The panel made from recycled material offered reductions of over 80% in greenhouse gases (GHG) and 60% in cost, when compared to the virgin C/epoxy benchmark. The work carried out demonstrates that recycling is feasible and enables applications currently made by using virgin materials at a significant reduction in costs and environmental impact and already led to the world’s first flying fully recycled thermoplastic composite application in aerospace*.
Face às suas vantagens intrínsecas, a aplicação de termoplásticos reforçados com fibras contínuas (TPCs) tem aumentado e contribuído para o crescimento do lixo industrial, dada a inexistência duma solução eficaz para a sua reciclagem. A reciclagem dos TPCs deve recuperar o alto valor económico do material, reduzir o impacto ambiental e estar em linha com as diretivas ambientais existentes. Este estudo desenvolveu e validou com sucesso um novo método de reciclagem de TPCs com máximo custobenefício e mínimo impacto ambiental. Desenvolveu-se um modelo micromecânico para otimizar o equilíbrio entre desempenho mecânico e processabilidade ou grau de mistura para, respetivamente, fibras longas e curtas. Sendo usado para prever da rigidez e a resistência mecânica, o modelo incorpora a influência que a variação da fração volúmica localizada de fibras e o seu número nas mechas têm na distribuição dos comprimentos de fibras e grau de mistura obtidos. Definiu-se uma reciclagem adequada envolvendo trituração, mistura com baixa taxa de corte e fabrico por compressão para validar o desempenho mecânico de TPCs reciclados. Fabricaram-se compósitos G/PP e C/PPS reciclados com diferentes teores, orientações, comprimentos e distribuição de comprimentos de fibras, estágios de consolidação de resíduos, sem mistura ou com diferentes níveis de mistura a baixa taxa de corte para caracterização por ensaios de flexão, impacto e microscopia da sua seção transversal. Os TPCs reciclados apresentaram propriedades em linha com as previsões teóricas e que aumentavam com o grau de mistura. Projetaram-se, fabricaram-se e testaram-se três produtos demonstradores para comprovar a sua viabilidade técnica e aplicação: um suporte, uma biqueira de sapato de segurança e um painel de acesso para a indústria aeroespacial. Embora usando material reciclado de propriedades inferiores, o painel mostrou ser ainda mais leve que a solução atualmente existente e ofereceu suficiente confiança para ter já sido testado em voo. A análise de ciclo de vida e a avaliação de custos foram usadas para comparar demonstradores com as suas alternativas atuais. Tanto o painel como a biqueira permitiram reduzir significativamente o custo e impacto ambiental. O painel reciclado, comparado à solução em material virgem, diminuiu as emissões de gases de estufa e o custo em mais de 80% e 60%, respetivamente. Este trabalho comprova que a reciclagem é viável e que a substituição de materiais virgem em muitas aplicações atuais pode reduzir significativamente custos e o impacto ambiental e já contribuiu para a realização do primeiro voo mundial integrando um produto destinado à indústria aeroespacial totalmente fabricado em TPC reciclado*.