Les composites à matrice céramique (CMC) sont des matériaux constitués d’une matrice céramique renforcée par des fibres céramiques continues (généralement à base de SiC ou de C). Le travail de thèse présenté, réalisé en collaboration avec Snecma Propulsion solide et l’Agence De l’Environnement et de la Maîtrise de l’Energie, a pour objectif d’introduire des matériaux CMC au sein de pièces de moteurs d’avions civils, concurrençant ainsi les alliages métalliques actuellement utilisés. Pour ce faire, les matériaux CMC devront répondre aux exigences propres à l’aéronautique civil, à savoir qu’ils devront présenter une longue durée de vie en atmosphère oxydante dans une gamme de basse température (400-600°C) et avoir un coût compétitif. Dans ce contexte, des matériaux CMC constitués de fibres SiC de première génération, de coût moins élevé, sont étudiés, mais leur inconvénient majeur est leur plus grande sensibilité à l’oxydation. Des matrices auto-cicatrisantes multicouches à base de Si, B, et C ont été développées ces dernières années afin d’assurer une tenue à l’oxydation des fibres, mais elles ne sont pas opérantes dans la gamme de température imposée. Compte tenu d’études précédemment réalisées et des exigences requises pour l’application visée, l’objectif du travail présenté dans ce mémoire est de proposer des solutions pour améliorer la tenue à l’oxydation de renforts fibreux à base de fibres de SiC de première génération, dans la gamme de température 400-600°C, en évitant un surcoût de production trop important. / Continuous fiber-reinforced ceramic matrix composites (CFCCs) are an important class of materials for structural applications at elevated temperatures because of their improved flaw tolerance, large fracture resistance, improved toughness by crack deflection and crack bridging mechanism, low density and noncatastrophic mode of failure comparing with metallic materials. Fibers play a critical role in both the processing and performance of CFCCs. SiC-based fibers are considered leading candidate materials in the aerospace application, such as engine turbines. However, the major shortcoming of SiC-based fibers is their oxidative embrittlement and degradation, which is caused by the oxygen ingression from the micro cracks and interstitials in the composites, is the dominant life-limiting phenomenon of non-oxide composites. This study carried out with the financial supply of both Snecma Propulsion Solide and Agence De l’Environnement et de la Maîtrise de l’Energie has for objective to integrate SiC-based as reinforcement in CFCCs for civil aircraft engine application. In order to reach this objective, it is imperative to find a novel approach to diminish the oxygen ingression by developing protective fiber coatings.

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The appeal of hybrid composites is the ability to create materials with properties which normally do not coexist such as high specific strength, stiffness, and toughness. One possible application for hybrid composites is as backplate materials in layered armor. Fiber reinforced composites have been used as backplate materials due to their potential to absorb more energy than monolithic materials at similar to lower weights through microfragmentation of the fiber, matrix, and fiber-matrix interface. Composite backplates are traditionally constructed from graphite or glass fiber reinforced epoxy composites. However, continuous alumina fiber-reinforced aluminum metal matrix composites (MMCs) have superior specific transverse and specific shear properties than epoxy composites. Unlike the epoxy composites, MMCs have the ability to absorb additional energy through plastic deformation of the metal matrix. Although, these enhanced properties may make continuous alumina reinforced MMCs advantageous for use as backplate materials, they still exhibit a low failure strain and therefore have low toughness. One possible solution to improve their energy absorption capabilities while maintaining the high specific stiffness and strength properties of continuous reinforced MMCs is through hybridization. To increase the strain to failure and energy absorption capability of a continuous alumina reinforced Nextel" MMC, it is laminated with a high failure strain Saffil® discontinuous alumina fiber layer. Uniaxial tensile testing of hybrid composites with varying Nextel" to Saffil® reinforcement ratios resulted in composites with non-catastrophic tensile failures and an increased strain to failure than the single reinforcement Nextel" MMC. The tensile behavior of six hybrid continuous and discontinuous alumina fiber reinforced MMCs are reported, as well as a description of the mechanics behind their unique behavior. Additionally, a study on the effects of fiber damage induced during processing is performed to obtain accurate as-processed fiber properties and improve single reinforced laminate strength predictions. A stochastic damage evolution model is used to predict failure of the continuous Nextel" fabric composite which is then applied to a finite element model to predict the progressive failure of two of the hybrid laminates. / Ph. D.

The diploma thesis is focused on 3D printing of composites parts. Thesis deals with methods of additive manufacturing and describes principle of selected 3D printing technologies. In addition to additive technologies, the theoretical part presents an overview of composite materials and methods of composite production. Then there are four concepts that lead to 3D printing of continuous fiber reinforced composites components. The final concept is selected according to multi-criteria analysis and then designed. Designed extruder allows 3D printing of composite materials. The principle of the function consists of fiber impregnation by matrix inside the heat chamber and then deposition of composite on printing platform. The extruder also consist of fiber cutting mechanism. The extruder's ability is verified by the experiment.

Thermoplastic prepregs that are also known as organo sheets are processed in presses and formed to half shells. Larger components can be produced by joining the half shells, which results in hollow bodies. However, current manufacturing technologies allow only cap profile shaped joints, which cause fiber deflections in the joint plane. This presentation shows that overlapping infrared welds in organo sheets enable weld strengths close to the interlaminar shear strengths of the unwelded materials and thus a fiber utilization across the joint plane. By using high welding pressures, a matrix depletion and a change of the fiber alignment in the weld plane may occur which causes low weld strengths. Therefore possibilbites to optimize the weld strengths are shown and one possible process variants for the manufacturing of hollow bodies by infrared welding is introduced.

Thermoplastic prepregs that are also known as organo sheets are processed in presses and formed to half shells. Larger components can be produced by joining the half shells, which results in hollow bodies. However, current manufacturing technologies allow only cap profile shaped joints, which cause fiber deflections in the joint plane. This paper shows that overlapping infrared welds in organo sheets enable weld strengths close to the interlaminar shear strengths of the unwelded materials and thus a fiber utilization across the joint plane. By using high welding pressures, a matrix depletion and a change of the fiber alignment in the weld plane may occur which causes low weld strengths. Therefore, criteria for the successful welding were defined and various possibilities to optimize the weld strengths were investigated.

Advanced composites are extremely strong, rigid, and light, even when compared with advanced metals. Advanced composites are replacing high-tech metals as the material of choice for aerospace engineering. However, the processes used to manufacture advanced composites generally lose some of the properties of the materials by their process limitations. One process that keeps the theoretically awesome qualities of the composite materials in tact is filament winding. Filament wound parts are used as rocket shells, bicycle frame tubes, drive shafts, pressure vessels, etc. Filament winding is an automated process and makes reliable parts to close tolerances. If a straight tube were to be made by all the existing composites manufacturing processes, filament wound tubes would be significantly better than any other. However, filament winding is generally limited to making straight tubes. A new process based on filament winding is proposed; one that can wind complex shapes of the same high quality as conventional filament winding. This process has achieved this by winding continuous, uncut, and aligned fibers. This process is called Lotus Filament Winding.

Innerhalb dieser Arbeit wird ein Fertigungsverfahren entwickelt und erprobt, das den additiven Aufbau von großvolumigen faserverstärkten Kunststoffbauteilen in Skelettbauweise erlaubt. Dafür wird ein modifizierter Extruder zusammen mit einer speziellen Kinematik genutzt. Der Fokus liegt auf der Analyse des Einflusses der Steuergrößen auf geometrische und mechanische Eigenschaften, sowie Haftung im Bauteil. Hinsichtlich der geometrischen Eigenschaften wird ein Prozessmodell entwickelt, das die Abhängigkeit der Strangbreite und -höhe von den Steuergrößen darstellt. Durch experimentelle Untersuchungen werden die Prozessgrenzen und an diesen auftretende Effekte ermittelt. Das Verfahren weist hier große Freiräume auf. So können z.B. mit einer 1 mm Düse Strangbreiten von 1,2 bis 3,2mm erzielt werden. Die mechanischen Eigenschaften in Strangrichtung erreichen im 3D-Druck annähernd die Steifigkeit und Festigkeit der Spritzgießreferenz. Prozessbedingt ist eine Porosität im Material nicht ganz vermeidbar, allerdings sind die Fasern stark ausgerichtet und die Faserlänge im Granulat bleibt im Prozess weitestgehend erhalten. Mittels direktem 3D-Drucken auf endlosfaserverstärktes Tape kann mit Vorheizen des Tapes ein guter Haftverbund generiert werden. Ergänzend wurden zwei Komponenten entwickelt, die für eine Industrialisierung des Prozesses entscheidend sind: Zum einen wurde ein neues Düsenkonzept vorgestellt, das eine schnelle Anpassung des Massestroms während des 3D-Druckens ermöglicht. Zum anderen wurde eine Temperierdüse vorgestellt, mit der mittels Konvektion der abgelegte Strang gekühlt bzw. erhitzt werden kann.:1 Einleitung 2 Zielstellung 3 Literaturübersicht 4 Konzeption eines neuartigen 3D-Druck-Verfahrens 5 Analyse der kinematischen Eigenschaften 6 Betrachtung der Haftungsmechanismen 7 Untersuchung der mechanischen Eigenschaften 8 Weiterentwicklung von Anlagenkomponenten 9 Zusammenfassung und Ausblick / In this thesis, a manufacturing process is presented which enables the additive manufacturing of largevolume fibre-reinforced plastic components in skeleton construction by using an extruder together with special kinematics. The focus is on the analysis of the influence of the control variables on geometric and mechanical properties, as well as adhesion in the component. With regard to the geometric properties, a process model is being developed that shows the dependence of the strand width and height on the control variables. Experimental investigations are used to determine the process limits and the effects occurring at these limits. The procedure knows here large free spaces, so e.g. with a 1 mm nozzle strand widths of 1,2 bis 3,2mm can be obtained. The mechanical properties in the strand direction in 3D printing approximate the stiffness and strength of the injection molding reference. Due to the process, porosity in the material cannot be completely avoided, however, the fibers are strongly oriented and the fiber length in the granulate is largely retained in the process. Direct 3D printing on continuous fiber-reinforced tape can be used to generate a good adhesive bond by preheating the tape. In addition, two components were developed that are decisive for industrializing the process: On the one hand, a new nozzle concept was introduced that enables rapid adjustment of the mass flow during 3D printing. On the other hand, a nozzle was presented with which the deposited strand can be cooled or heated by convection.:1 Einleitung 2 Zielstellung 3 Literaturübersicht 4 Konzeption eines neuartigen 3D-Druck-Verfahrens 5 Analyse der kinematischen Eigenschaften 6 Betrachtung der Haftungsmechanismen 7 Untersuchung der mechanischen Eigenschaften 8 Weiterentwicklung von Anlagenkomponenten 9 Zusammenfassung und Ausblick

The challenges faced in today’s industry require materials capable of working in chemically aggressive environments at elevated temperature, which has fueled the development of oxidation resistant materials. All-Oxide Ceramic Matrix Composites (OCMC) are a promising material family due to their inherent chemical stability, moderate mechanical properties, and low weight. However, limited information exists regarding their behavior when in contact with other high-temperature materials such as superalloys. In this work three sets of tribological tests were performed: two at room temperature and one at elevated temperature (650 °C). The tests were performed in a pin-on-disk configuration testing Inconel 718 (IN-718) pins against disks made with an aluminosilicate geopolymeric matrix composite reinforced with alumina fibers (N610/GP). Two different loads were tested (85 and 425 kPa) to characterize the damage on both materials. Results showed that the pins experienced ~ 100 % wear increase when high temperature was involved, while their microstructure was not noticeably affected near the contact surface. After high temperature testing the OCMC exhibited mass losses two orders of magnitude higher than the pins and a sintering effect under its wear track, that led to brittle behavior. The debris generated consists of alumina and suggests a possible crystallization of the originally amorphous matrix which may destabilize the system. The data suggests that while the composite’s matrix is stable, wear will not develop uncontrollably. However, as soon as a critical load/temperature combination is attained the matrix is the first component to fail exposing the reinforcement to damage which drastically deteriorates the integrity of the component.