Knitting is a class of techniques for production of textile fabrics by inter-looping yarns withthe use of hooked needles. The new loops are created when the yarns drawn through thepreviously formed loops. An apparatus for two needles with adjustable geometry resemblingthe knitting process in weft knitting machines has been constructed and mounted in anordinary tensile testing machine in order to study stress build-up, fibre damage, needle wearetc. The merits of the knittability test-rig set-up are the possibilities to test the performance ofthe yarns with the geometry of the machine and to simulate and identify some of the problemsthat can occur between needles and yarn in the knitting process. Well-defined mechanicalconditions with the static pre-load weight and the possibilities to identify the location of theevents of damage on the fibres during the testing of the specimens and to do furtherexamination before knitting are some obvious merits. The knittability of some extreme yarns,PET-monofilaments, carbon fibre roving and aramid yarn has been studied with respect tofriction and bending stiffness. Friction and bending characteristics exhibit viscoellasticfeatures. The needles have diameters of the same order of magnitude as the diameters ofmonofilaments for example for use in knitted spacer fabrics and the results of this workillustrate strong influence of the fibre diameter on the knittability. / <p>Program: Magisterutbildning i textilteknologi</p><p>Uppsatsnivå: D</p>

Ο κύριος σκοπός της διπλωματικής εργασίας αυτής είναι η εξοικείωση με τα γραφιτικά υλικά και τις μηχανικές τους ιδιότητες. Στο πρώτο μέρος της εργασίας, γίνεται μια εισαγωγή στους νανοσωλήνες άνθρακα και διεξάγεται μια βιβλιογραφική ανασκόπηση στο θέμα, με έμφαση στη μικροσκοπία Laser Raman ως μη-καταστρεπτική τεχνική μέτρησης μηχανικών ιδιοτήτων. Στο δεύτερο τμήμα, μελετώνται οι μηχανικές τους ιδιότητες με πειράματα εφελκυσμού σε πρωτότυπα ινίδια νανοσωλήνων, σε συσκευή δυναμικής μηχανικής ανάλυσης (DMA) και επίσης διεξάγονται μετρήσεις σε άλλα υλικά, όπως buckypapers και ίνες γραφίτη αλλά και αραμιδικές ίνες Kevlar®. Δίνεται ιδιαίτερη έμφαση στη διαδικασία παραγωγής ινιδίων νανοσωλήνων άνθρακα μονού τοιχίου με διηλεκτροφόρηση, την οποία ελπίζουμε να αναπαράγουμε στο μέλλον. / The main purpose of this thesis is to get acquainted with graphitic materials and their mechanical properties. The first part of the thesis is an introduction in carbon nanotubes and emphasis is put on Laser Raman spectroscopy as a non-destructive method to measure mechanical properties. In the second part, the mechanical properties of prototype carbon nanotube fibrils are measured in a dynamic mechanical analysis (DMA) machine and also measurements are carried out on other graphitic materials like buckypapers, graphitic fibres and aramidic polymer (Kevlar®) fibres. The production process of these carbon nanotubes fibrils via dielectrophoresis, which we hope to reproduce in the future, is specially stressed.

This study focuses on the effect of tufting on the mechanical and electrical properties of carbon composites using a variety of tuft materials, such as aramid, steel and copper. Several configurations were investigated based on a case study, involving the reinforcement of stiffener-to-skin interfaces of a tail cone. The effect of tuft and base composite material, tufting depth and inclination on the delamination resistance in mode I was evaluated, the associated bridging laws were determined and the failure mechanisms were identified. A simplified superposition model of the delamination response of tufted composites was developed. The electrical performance of tufted composites was determined in simulated lightning strike tests and set against the through-the-thickness electrical conductivity of the materials. The results of mechanical testing showed that the delamination performance depends strongly on the material response of the tufts, with both the bridging behaviour and final toughness levels influenced directly by the strength, ductility and ultimate strain of the tufts. Interactions between the tufts and the surrounding composite, such as interfacial shear and bridging induced by tuft pull-out, play a significant role in the overall behaviour generating a deviation from a simple superposition of the base material and tuft response. The balance between interfacial shear and tuft elongation results in a decreasing trend of delamination toughness with increasing tufting depth for low ductility materials, whilst the trend is reversed for the high ductility copper tufts. This balance is also affected by the properties of the base material, with tougher matrices leading to dominance of shear effects and a weaker enhancement introduced by tufting. Inclination of tufts leads to an increase in crack energy release rate due to the activation of a ploughing mechanism. Metallic and carbon tufts have a positive effect on lightning strike response, with copper tufting offering strike protection at an improved level compared to standard copper mesh solutions.

This diploma thesis focuses on composite pipes production by winding of composite fibres soaked in resin binder and feeding with additional third type material simultaneously. It also describes the production machine FWMS180 and all of its additional devices necessary for the composites production by filament winding. The production process of composite pipes on the production machine FWMS180 is described in this paper as well as detailed description of the winding method. Furthermore, the technological bend and vibration tests procedures conducted on pipes of different material composition are discussed with related results and comparison. The thesis proves that presence of the third type material in composite pipes structure has different influence depending on observed and evaluated property.

Manufacturing induced shape distortions is a common problem for composite materials. Due to the non-isotropic nature of carbon fibre reinforced polymers (CFRP) unavoidable deformations occur during part production. During fabrication of polymer composites, the material obtains its final shape at elevated temperatures. The curing process involves a transition from the liquid state to the solid, glassy state, allowing bonding between fibres and matrix. As the material cools the mismatch in thermal expansion coefficients and cure shrinkage obtained during the matrix polymerization leads to residual stresses on the mechanical level within composite part. There is a great interest from the aircraft and automotive industries, to increase the ability to understand development of shape distortions and residual stresses during the cure, since these deformations often lead to dissatisfaction of tolerances and it is essential to predict the deformations beforehand in order to compensate time and cost.  In this context, a study of residual stresses during the curing process of thermosetting resin composites is presented. A methodology is proposed for predicting the formation and development of manufacturing- induced residual stresses. The present project reports on a comprehensive experimental study on the dependency of different short curing cycles on the build-up of residual stresses in a carbon fibre/fast-curing epoxy system and evaluate of post-curing methods through induction heating and oven post-curing with unidirectional [904] and unsymmetrical [9020] laminates. It includes characterization in thermo-elastic properties and degree-of-cure of the material by Thermal bending test, thermal expansion test, mechanical tensile test and Differential Scanning Calorimetry (DSC) in non-post-cured and post-cured laminates. The results showed slight variation in the thermal properties and not effect in the mechanical properties at different cure and post-curing conditions. Analytical data by Laminate Analysis program validated the experimental thermo-elastic data with analytical simulations. In addition, it is shown improvements in the temperature distributions in the post-curing by induction heating with different experimental set-ups, however, oven post-curing showed a more systematic system, higher heat efficient a low cure temperature, with more consistent mechanisms of shape distortions and residual stresses compared to induction heating. These findings are relevant for the future development of prediction methods for process induced deformations of Fast Curing Epoxy Resins (FCER).

Die Textiltechnik ermöglicht den Einsatz von rezyklierten Kohlenstofffasern in thermoplastischen Faserverbundwerkstoffen mit hohen Festigkeitsanforderungen. Das Erreichen vergleichbarer mechanischer Eigenschaften entsprechender endlosfaserverstärkter Verbundwerkstoffe wird durch die Nutzung von Stapelfaser-Hybridgarntextilien realisiert. Die Anwendung von thermoplastischen Hybridgarntextilien für die Herstellung von mehr als 100.000 Bauteilen pro Jahr erfordert jedoch eine kurze Taktzeit zur Imprägnierung und Konsolidierung des textilen Halbzeugs. Diese ist in dem derzeitigen Stand der Technik nicht gegeben, sodass hier Forschungsbedarf besteht. Die vorliegende Arbeit präsentiert eine Methode zur Reduktion der Taktzeit zur Imprägnierung und Konsolidierung komplexer Bauteilgeometrien auf Basis leitfähiger Hybridgarntextilien von derzeitig mehreren Minuten auf unter eine Minute, mit Potenzial zur weiteren Minimierung. Dies erfolgt mittels In-situ-Erwärmung im formgebenden Werkzeug unter Nutzung der Widerstandsverluste bei Stromfluss durch die leitfähigen Verstärkungsfasern. Neben der Charakterisierung und Simulation der Erwärmung im Mehrlagengewebe wird eine Parameteranalyse an generischen Probekörpern durchgeführt, um die Machbarkeit zu demonstrieren. Genauso findet eine erfolgreiche Skalierung der Technologie durch Übertragung der Ergebnisse auf eine komplexe Bauteilgeometrie anhand einer innovativen Werkzeugtechnologie statt. Am Ende der Arbeit erfolgt eine wirtschaftliche Betrachtung der kompletten Prozesskette von der einzelnen Faser, über den Hybridroving und das Mehrlagengewebe, bis zum fertigen Bauteil. Die Arbeit zeigt eine Technologie zur wirtschaftlichen Fertigung von Bauteilen aus rezyklierten Kohlenstofffasern in unter einer Minute Taktzeit. Des Weiteren bieten sich Vorteile durch die geringen Materialkosten des Hybridrovings, den hohen Grad der Automatisierung und die energetisch effiziente intrinsische Erwärmung des Halbzeugs.

With increased use of carbon fibre (CF)-based textile-reinforced thermoplastic composites, the demand of hybrid yarns consisting of carbon filament yarns (CFYs) and thermoplastic filament yarns with improved properties is also high. Hybrid yarn manufacturing using commingling process by means of compressed air shows some distinct advantages over other hybrid yarn manufacturing processes. However, the potential of commingling process for the production of CF-based thermoplastic hybrid yarns is not yet fully explored. In this article, extensive investigations have been carried out for the development of commingled hybrid yarns manufactured from CFY and polyamide 6,6 (PA 6,6) filament yarns with improved adhesion properties between CFY and matrix in composites. Hybrid yarns are manufactured by varying air pressure and keeping overfeeds and delivery speed constant. Moreover, an additional heat treatment on CFY is done online for a better opening of CFY prior to the mixing with PA 6,6 filament yarn. The tensile properties of hybrid yarns as well as different mechanical properties of unidirectional composite, such as tensile, flexural, impact and interlaminar shear strength are investigated. The results show good potential for the development of hybrid yarns produced from CFY and thermoplastic filament yarns with improved adhesion properties for their application in textile-reinforced thermoplastic composites.

No description available.

Les matériaux composites présentent un intérêt dans des secteurs de pointe tel que l’aéronautique du fait de leurs propriétés. Dans le cas des composites à matrice organique renforcés par des fibres longues, les propriétés dépendent non seulement du renfort et de la matrice mais également de l’interface fibre/matrice (F/M). Ce mémoire fait état de travaux menés pour incorporer des nanotubes de carbone (NTC) alignés directement sur des fibres de carbone (FC) tissées de manière sécurisée afin d’élaborer un composite à matrice thermodurcissable et thermoplastique et d’évaluer l’effet des NTC introduits à l’interface F/M sur les propriétés électriques et mécaniques des composites. Pour cela, le procédé de dépôt chimique en phase vapeur (CVD) à partir d’aérosol mixte toluène/ferrocène a été développé pour la croissance de NTC alignés sur les FC, avec comme objectif la mise en place d’une procédure permettant d’éviter toute manipulation intermédiaire des produits. Il consiste à réaliser la synthèse de NTC en deux étapes successives qui sont le dépôt préalable d’une couche céramique de type SiO2 à la surface des fibres de carbone suivi de la croissance de NTC. Ce procédé a été ajusté pour permettre une croissance homogène de NTC alignés sur tissus de FC de taille suffisante pour permettre la préparation de matériaux composites. Les matériaux obtenus à l’issu de chacune des étapes ont été caractérisés en utilisant des techniques physico-chimiques complémentaires afin de comprendre le rôle de la sous-couche oxyde sur la croissance des NTC. Nous avons en particulier mis en évidence que cette dernière est modifiée lors de la croissance de NTC conduisant à la formation d’un oxyde mixte suite à l’incorporation de l’élément fer dans la sous-couche de type SiO2. Celle-ci joue alors le rôle de couche barrière de diffusion et permet une croissance de NTC alignés, denses et longs à la surface de substrats carbonés (carbone vitreux ou tissus de fibres de carbone). En outre, pour limiter les risques de dissémination de NTC dans l’atmosphère lors des manipulations des tissus de fibres recouverts de NTC pour l’élaboration des composites, nous avons réalisé une fonctionnalisation de surface des NTC afin d’encapsuler ces derniers sur le renfort fibreux. Enfin des mesures des propriétés mécaniques et électriques ont été réalisées sur les tissus présentant différents traitements et sur les matériaux composites incluant ces tissus. / Because of their properties, composite materials have attracted considerable interests in advanced technology such as in aeronautic field because of their properties. In the case of organic composite reinforced with long fibres, the properties depend not only on the reinforcements and the matrix but also on the interface between the fibre and the matrix (F/M). This thesis deals with the work led to integrate securely aligned carbon nanotubes (CNT) directly on carbon fibres (CF) in order to assess their effects on electrical and mechanical properties at the F/M interface in thermosetting and thermoplastic composite. To include aligned CNT directly on carbon substrates, the catalytic chemical vapour deposition synthesis method of CNT has been developed which consists in carrying out the synthesis in two steps in the same synthesis equipment avoiding intermediate handling. First, a deposition of oxide ceramic layer based on SiO2 is performed followed by the growth of CNT. The process has been adjusted in order to achieve a homogeneous growth of aligned CNT along the carbon fibre cloth compatible with industrial requirement for composite elaboration. Each material obtained from the different steps has been characterized with complementary physical and chemical analysis techniques in order to understand the ceramic sub-layer role on the growth of CNT. In particular, it has been pointed out that during the growth of CNT the sub-layer is modified by the incorporation of iron in the ceramic layer based SiO2, leading to the formation of mixed oxide which plays the role of diffusion barrier layer resulting in the growth of aligned, dense and long CNT on carbon substrates (glassy carbon, carbon fibre cloth). Besides, to avoid the dispersion of CNT in the atmosphere during the handling step for the elaboration of composite, a surface functionalization of CNT has been performed to encapsulate them. Finally, electrical and mechanical properties have been measured on carbon clothes exposed to different treatments and on composites reinforced with these clothes.

Ces travaux de thèse ont porté sur l’étude de nouveaux matériaux pour l’absorption électromagnétique en chambre anéchoïque. Ce sujet a été imaginé à partir de l’étude d’une nouvelle matrice jusqu’alors jamais utilisée pour les absorbants électromagnétiques : la mousse époxy. Cette dernière présente en effet de nombreux avantages par rapport aux matrices habituellement utilisées dans le commerce : possibilité de réaliser des formes complexes, piégeage de la charge au cœur du matériau… Nous avons associé cette matrice avec différentes charges carbonées (noir de carbone, graphite et des fibres longues de carbone). L’association de la mousse époxy avec des fibres de carbone millimétriques a montré d’excellentes performances d’absorption pour un taux de charge très faibles : 0,5 %wt (S11 ≈ -40 dB entre 4 et 18 GHz en incidences normale et oblique). En variant la longueur des fibres de carbone, nous avons mis en évidence qu’il était possible d’améliorer les performances d’absorption en basses fréquences en utilisant des fibres plus longues. Enfin, nous avons dirigé nos recherches sur la réalisation d’un matériau absorbant ‘Vert’ à partir d’une matrice de liège. Ces nouveaux matériaux, réalisés à partir de matières biosourcées, ont montré de meilleures performances d’absorption qu’un absorbant du commerce de mêmes dimensions en incidence normale (S11 = -53 dB et S11 = - 27 dB respectivement à 4,2 GHz) et en incidence oblique (S11 = -50 dB et S11 = -30 dB respectivement à 4,2 GHz) et constituent donc des candidats potentiels pour le remplacement des matériaux absorbants du commerce actuels. / This thesis work focused on the study of new materials for electromagnetic absorption in anechoic chambers. This subject arose from the study of a new matrix which was never used for electromagnetic absorbers until then: the epoxy foam. This foam has many advantages compared to the matrices usually used in the trade like the possibility of cutting complex shapes out of them or trapping the charge in the core of the absorber...This matrix was associated to different carbonaceous load (carbon black, graphite and carbon fibers). The combination of epoxy foam with millimeter carbon fibers has shown better absorption performance at very low loading rates: 0.5 %wt (S11 ≈ -40 dB between 4 and 18 GHz under normal and oblique incidences). The use of different fiber lengths showed that it is possible to improve absorption performance at low frequencies using long carbon fibers. Finally, we directed our work on the creation of an absorbent material from a cork matrix. These new materials, made from bio-based materials, have shown better absorption performance than a commercial absorber, with the same dimensions in normal incidence (S11 = -54 dB and S11 = - 27 dB respectively at 4.26 GHz) and oblique incidence (S11 = -51 dB and S11 = -30 dB respectively at 4.26 GHz) and are therefore potential candidates for the replacement of existing commercial absorbent materials.