Carbon nanotubes are known as one of the strongest materials in nature and since their discovery; they have triggered the scientific interest for fabricating multi-functional polymer composites. However, a well-known problem associated to the incorporation of nanoparticulate materials in polymer matrices is their tendency to agglomerate in order to reduce their surface energy, and the extreme increase of the polymer viscosities (i.e melts, solutions, etc), which makes it very difficult to process them. Polymers can be efficiently reinforced by fibers for applications where high strength and stiffness are required. Micro-scale short fiber reinforced polymer composites have been an alternative way to obtain fiber reinforced composites since the long fiber incorporation is a painful job and not always feasible and easy to produce composites in big scale. Therefore, use of long glass fibers as the support for depositing CNTs as well as CNTs+other kind of nanoparticles was made, and the resulting interfaces were investigated in detail by single fiber model composites. This approach can bring the CNT functionality, fiber strength and toughness to the final composite, and simultaneously alleviate the manufacturing process from increase of the polymer high viscosities. Finally, very logically the question of whether to improve or destroy the interface integrity comes before implementing the hybrid hierarchical reinforcements in bigger scales, and an output out of this work will be given. Furthermore, several information and functionalities arising from the CNTs at the interphase region will be elucidated like cure monitoring of the epoxy resin matrix, UV-sensing ability, and thermoelectric energy harvesting, giving rise to multi-functional structural composites. CNT-modified natural fibers also have been utillised to fabricate short fiber reinforced composites, and have shown a promising reinforcement effect due to the CNT nanostructured interfaces. The ‘interface’ in fiber reinforced polymer composites (FRPCs) is known as a very crucial parameter that has to be considered in the design of a composite with desired properties. Interfaces are often considered as surfaces however, they are in fact zones or areas with compositional, structural, and property gradients, typically varying from that of the fiber and the matrix material. Characterization of the mechanical properties of interfaces is necessary for understanding the mechanical behavior of scaled-up composites. In fact, the mechanical characteristics of a fiber/resin composite depend mainly on i) the mechanical properties of the component materials, ii) the surface of the fiber, and iii) the nature of the fiber/resin bonding as well as the mode of stress transfer at the interface. Among the many factors that govern the characteristics of composites involving a glass, carbon, natural or ceramic fiber, and a macromolecular matrix, the adhesion between fiber and matrix plays a predominant role. In specific, the stress transfer at the interface requires an efficient coupling between fiber and matrix. Therefore, it is important to optimize the interfacial bonding since a direct linkage between fiber and matrix gives rise to a rigid, low impact resistance composite material.

La modélisation numérique des structures composites à renfort fibreux de géométrie complexe constitue un axe de recherche majeur afin de prédire correctement leur comportement mécanique. Dans ce contexte, l’étude menée dans ce travail de thèse porte sur le développement de nouveaux éléments finis basés sur une approche numérique multi-échelle, appelée Approche de la Fibre Projetée (AFP). Cette approche a l’avantage de tenir compte de la présence des fibres au sein d’un espace matrice sans les discrétiser, ce qui limite considérablement la taille du système à résoudre. Pour analyser le comportement des structures composites, plusieurs éléments finis 2D et 3D ont été développés et implémentés dans le code ABAQUS via la routine UEL. Plusieurs cas tests de validation sont considérés pour tester la précision et l’efficacité des éléments finis proposés et les résultats obtenus sont globalement en bon accord avec les solutions de référence. De plus, l’intérêt de la nouvelle approche (AFP) est particulièrement mis en exergue en étudiant des structures composites complexe à renfort 3D : une plaque sandwich cousue et une plaque sandwich à âme creuse renforcée par des fibres en forme de « 8 ». / Numerical modeling of composite materials and structures with complex geometry of fiber reinforcement, such as stitched composites, constitutes a major research axis in order to correctly predict their mechanical behavior. Within this context, this study focuses on the development of new linear and nonlinear specific finite elements based on a multiscale numerical approach, called the Projected Fiber Approach (PFA). This numerical approach has the advantage of taking into account the presence of fi bers, long or short and distributed randomly or specifically, within a matrix space without discretizing them. Consequently, the obtained system of equations size is equivalent to that without reinforcement (matrix), which considerably reduces the computational cost. To analyze the linear and geometrically nonlinear behaviors of composite structures, two membrane finite elements, named PFT3 and PFQ4, and a 3D solid finite element, named PFH8, were developed and implemented into the commercial finite element code ABAQUS via the user element subroutine (UEL). Several numerical linear and nonlinear tests are considered to assess the accuracy and efficiency of the proposed composite finite elements, and the obtained results are globally in good agreement with the reference solutions. Moreover, the major interest of the PFA approach is particularly emphasized by studying two 3D complex reinforced composite structures: a stitched sandwich plate and a hollow core sandwich plate reinforced by "8" shape fibers.

Le développement d’agents interfaciaux pour des matériaux composites renforcés de fibres est nécessaire afin d’obtenir des matériaux performants notamment pour l’industrie automobile. Le projet se concentre sur la synthèse d’oligomères à séquences contrôlées préparés par synthèse en phase solide par réaction d’amidification et de cycloaddition assistée par le cuivre entre un azoture et un alcyne pour introduire précisément des unités de phénylalanine et des groupes aliphatiques. Ces oligomères ont été testés comme agents interfaciaux pour des matériaux composites à base de polypropylène renforcés de fibres de Kevlar. Leur capacité à s’adsorber sur les fibres a été étudiée de façon qualitative par microscopie électronique à balayage et quantitative par analyse gravimétrique. Des expériences préliminaires sur des fibres de Kevlar traitées avec des oligomères synthétisés dans une matrice de polypropylène ont été réalisées pour estimer leur potentielle utilisation dans des matériaux composites. / The development of interfacial agents for fibre-reinforced composite materials is needed to obtain performant materials especially for the automotive industry. The project focused on the synthesis of sequence-controlled oligomers prepared by solid phase synthesis using amidation and copper-assisted alkyne-azide cycloaddition reactions to introduce precisely phenylalanine and aliphatic building blocks. These oligomers were evaluated as potential interfacial agents for Kevlar fibre-reinforced polypropylene composite materials. Their ability to adsorb on the fibres was investigated qualitatively by scanning electron microscopy and quantitatively by gravimetric analysis. Some preliminary experiments on the Kevlar fibres treated with some of the synthesised oligomers in a polypropylene matrix were conducted to estimate their potential use in composite materials.

Carbon nanotubes are known as one of the strongest materials in nature and since their discovery; they have triggered the scientific interest for fabricating multi-functional polymer composites. However, a well-known problem associated to the incorporation of nanoparticulate materials in polymer matrices is their tendency to agglomerate in order to reduce their surface energy, and the extreme increase of the polymer viscosities (i.e melts, solutions, etc), which makes it very difficult to process them. Polymers can be efficiently reinforced by fibers for applications where high strength and stiffness are required. Micro-scale short fiber reinforced polymer composites have been an alternative way to obtain fiber reinforced composites since the long fiber incorporation is a painful job and not always feasible and easy to produce composites in big scale. Therefore, use of long glass fibers as the support for depositing CNTs as well as CNTs+other kind of nanoparticles was made, and the resulting interfaces were investigated in detail by single fiber model composites. This approach can bring the CNT functionality, fiber strength and toughness to the final composite, and simultaneously alleviate the manufacturing process from increase of the polymer high viscosities. Finally, very logically the question of whether to improve or destroy the interface integrity comes before implementing the hybrid hierarchical reinforcements in bigger scales, and an output out of this work will be given. Furthermore, several information and functionalities arising from the CNTs at the interphase region will be elucidated like cure monitoring of the epoxy resin matrix, UV-sensing ability, and thermoelectric energy harvesting, giving rise to multi-functional structural composites. CNT-modified natural fibers also have been utillised to fabricate short fiber reinforced composites, and have shown a promising reinforcement effect due to the CNT nanostructured interfaces. The ‘interface’ in fiber reinforced polymer composites (FRPCs) is known as a very crucial parameter that has to be considered in the design of a composite with desired properties. Interfaces are often considered as surfaces however, they are in fact zones or areas with compositional, structural, and property gradients, typically varying from that of the fiber and the matrix material. Characterization of the mechanical properties of interfaces is necessary for understanding the mechanical behavior of scaled-up composites. In fact, the mechanical characteristics of a fiber/resin composite depend mainly on i) the mechanical properties of the component materials, ii) the surface of the fiber, and iii) the nature of the fiber/resin bonding as well as the mode of stress transfer at the interface. Among the many factors that govern the characteristics of composites involving a glass, carbon, natural or ceramic fiber, and a macromolecular matrix, the adhesion between fiber and matrix plays a predominant role. In specific, the stress transfer at the interface requires an efficient coupling between fiber and matrix. Therefore, it is important to optimize the interfacial bonding since a direct linkage between fiber and matrix gives rise to a rigid, low impact resistance composite material.

In den letzten Jahren gewinnt der Leichtbau im Bauwesen im Zuge der Ressourceneinsparung wieder stärker an Bedeutung, denn ohne eine deutliche Steigerung der Effizienz ist zukunfts-fähiges Bauen und Wohnen nur schwer zu bewerkstelligen. Optimiertes Bauen, im Sinne der Errichtung und Unterhaltung von Bauwerken mit geringem Einsatz an Material, Energie und Fläche über den gesamten Lebenszyklus eines Gebäudes hinweg, bedarf des Leichtbaus in punkto Material, Struktur und Technologie. In der vorliegenden Arbeit wird ein wissenschaftlicher Überblick zum aktuellen Stand der eigenen Forschungen in Bezug auf funktionsintegrativen Leichtbau im Bauwesen gegeben sowie erweiterte Methoden und Ansätze abgeleitet, die eine Konzeption, Bemessung und Erprobung von neuartigen Hochleistungs-Tragstrukturen in Leichtbauweise gestatten. Dabei steht die Entwicklung leistungs-starker und zugleich multifunktionaler Werkstoffkombinatio-nen und belastungsgerecht dimensionierter Strukturkomponenten unter dem Aspekt der Gewichtsminimalität in Material und Konstruktion im Fokus. Ein breit gefächertes Eigen-schaftsprofil für \"maßgeschneiderte\" Leichtbauanwendungen besitzen textilverstärkte Ver-bundbauteile, denn sowohl die Fadenarchitektur als auch die Matrix können in weiten Berei-chen variiert und an die im Bauwesen vorliegenden komplexen Anforderungen angepasst werden. In der vorliegenden Arbeit werden hierzu vor allem Methoden und Lösungen anhand von Beispielen zu: multifunktionalen Faser-Kunststoff-Verbunden (FKV), funktionsintegrier-ten faserverstärkten mineralischen Tragelemente und Verbundstrukturen in textilbewehrter Beton-GFK-Hybridbauweise betrachtet. Von zentraler Bedeutung ist dabei die Schaffung von materialtechnischen, konstruktiven und technologischen Grundlagen entlang der gesamten Wertschöpfungskette – von der Leichtbauidee über Demonstrator und Referenzobjekt bis hin zur technologischen Umsetzung zur Überführung der Forschungsergebnisse in die Praxis. / In the last few years, lightweight construction in the building sector has gained more and more importance in the course of resource saving. Without a significant increase in efficiency, future-oriented construction and resource-conserving living is difficult to achieve. Optimized building, in the sense of the erection and maintenance of buildings with little use of material, energy and surface over the entire life time cycle of a building, requires lightweight design in terms of material, structure and technology. In this thesis, a scientific overview of the current state of research on function-integrative light-weight construction in architecture is presented. Furthermore, advanced methods and research approaches were developed and applied, that allows the design, dimensioning and testing of novel high-performance supporting structures in lightweight design. The focus is on the development of high-performance, multi-functional material combinations and load-adapted structural elements, under the aspect of weight minimization in material and construction. Textile-reinforced composites have a broad range of material properties for optimized \"tailor-made\" lightweight design applications, since the thread architecture as well as the matrix can be varied within wide ranges and can adapted to the complex requirements in the building industry. Within the scope of this thesis, methods and solutions are examined in the field of: multifunc-tional fiber-reinforced plastics (FRP), function-integrated fiber-reinforced composites with mineral matrix (TRC) and textile-reinforced hybrid composites (BetoTexG: combination of TRC and FRP). In this connection the creation of material, structural and technological foundations along the entire value chain is of central importance: From the lightweight design idea to the demonstrator and reference object, to the technological implementation for the transfer of the research results into practice.

In den letzten Jahren gewinnt der Leichtbau im Bauwesen im Zuge der Ressourceneinsparung wieder stärker an Bedeutung, denn ohne eine deutliche Steigerung der Effizienz ist zukunfts-fähiges Bauen und Wohnen nur schwer zu bewerkstelligen. Optimiertes Bauen, im Sinne der Errichtung und Unterhaltung von Bauwerken mit geringem Einsatz an Material, Energie und Fläche über den gesamten Lebenszyklus eines Gebäudes hinweg, bedarf des Leichtbaus in punkto Material, Struktur und Technologie. In der vorliegenden Arbeit wird ein wissenschaftlicher Überblick zum aktuellen Stand der eigenen Forschungen in Bezug auf funktionsintegrativen Leichtbau im Bauwesen gegeben sowie erweiterte Methoden und Ansätze abgeleitet, die eine Konzeption, Bemessung und Erprobung von neuartigen Hochleistungs-Tragstrukturen in Leichtbauweise gestatten. Dabei steht die Entwicklung leistungs-starker und zugleich multifunktionaler Werkstoffkombinatio-nen und belastungsgerecht dimensionierter Strukturkomponenten unter dem Aspekt der Gewichtsminimalität in Material und Konstruktion im Fokus. Ein breit gefächertes Eigen-schaftsprofil für \"maßgeschneiderte\" Leichtbauanwendungen besitzen textilverstärkte Ver-bundbauteile, denn sowohl die Fadenarchitektur als auch die Matrix können in weiten Berei-chen variiert und an die im Bauwesen vorliegenden komplexen Anforderungen angepasst werden. In der vorliegenden Arbeit werden hierzu vor allem Methoden und Lösungen anhand von Beispielen zu: multifunktionalen Faser-Kunststoff-Verbunden (FKV), funktionsintegrier-ten faserverstärkten mineralischen Tragelemente und Verbundstrukturen in textilbewehrter Beton-GFK-Hybridbauweise betrachtet. Von zentraler Bedeutung ist dabei die Schaffung von materialtechnischen, konstruktiven und technologischen Grundlagen entlang der gesamten Wertschöpfungskette – von der Leichtbauidee über Demonstrator und Referenzobjekt bis hin zur technologischen Umsetzung zur Überführung der Forschungsergebnisse in die Praxis. / In the last few years, lightweight construction in the building sector has gained more and more importance in the course of resource saving. Without a significant increase in efficiency, future-oriented construction and resource-conserving living is difficult to achieve. Optimized building, in the sense of the erection and maintenance of buildings with little use of material, energy and surface over the entire life time cycle of a building, requires lightweight design in terms of material, structure and technology. In this thesis, a scientific overview of the current state of research on function-integrative light-weight construction in architecture is presented. Furthermore, advanced methods and research approaches were developed and applied, that allows the design, dimensioning and testing of novel high-performance supporting structures in lightweight design. The focus is on the development of high-performance, multi-functional material combinations and load-adapted structural elements, under the aspect of weight minimization in material and construction. Textile-reinforced composites have a broad range of material properties for optimized \"tailor-made\" lightweight design applications, since the thread architecture as well as the matrix can be varied within wide ranges and can adapted to the complex requirements in the building industry. Within the scope of this thesis, methods and solutions are examined in the field of: multifunc-tional fiber-reinforced plastics (FRP), function-integrated fiber-reinforced composites with mineral matrix (TRC) and textile-reinforced hybrid composites (BetoTexG: combination of TRC and FRP). In this connection the creation of material, structural and technological foundations along the entire value chain is of central importance: From the lightweight design idea to the demonstrator and reference object, to the technological implementation for the transfer of the research results into practice.