3D textile performs offer a high potential to increase mechanical properties of composites and they can reduce the production steps and costs as well. The variety of woven structures is enormous. The algorithms based on the conventional weaving notation can only represent the possible woven structures in a limited way. Within the scope of this dissertation, a new weaving notation was developed in order to analyze the multilayer woven structures analytically. Technological solutions were developed in order to guarantee a reproducible preform production with commingled hybrid yarns. Terry weaving technique can be utilized to create vertical connections on carrier fabrics, which makes it suitable for the development of complex profiles. A double rapier weaving machine was modified with electronically controlled terry weaving and pneumatic warp yarn pull-back systems. Various spacer fabrics and 3D profiles were developed. A linear take-up system is developed to assure reproducible preform production with a minimum material damage. Integrated cutting and laying mechanisms on the take-up system provides a high level of automation.

Three-dimensionally woven composites are a relatively new class of material that offer improved out-of-plane performance by including through-the-thickness mechanical reinforcement compared to traditional laminated composite structures. The mechanical properties are highly dependent upon the weave architecture as this dictates the nature of the through the thickness reinforcement and its effect in improving out-of-plane shear strength. A comparison of two testing methods, Short Beam Strength, and Five Point Bending was conducted over a range of span to thickness ratios with the latter found to be more consistent at producing shear failure over a greater range of span to thickness ratios, although evidence of matrix crushing was present in both, and flexural failure in the Short Beam Strength test. Two weave architectures, the orthogonal and angle weave were subjected to the Five Point Bending test and the failure and damage progression behaviour of both weave architectures were characterised using Digital Image Correlation analysis to measure the edge strain through the thickness of the specimens. This testing showed the angle weave architecture had in general a higher failure strength, and more gradual failure due to longer debonding cracks. The orthogonal weave architecture showed a characteristic post-failure response indicative of crack bridging with discrete load recovery and load drop phases. A numerical model developed from previous work builds on the mosaic modelling method and was modified to include cohesive elements in order to simulate interface debonding via the maximum stress criterion. The simulations are consistently 15 20% greater in failure loads, and 8 - 12% greater in failure shear stresses than those found from the averaged experimental results over the range of tested span to thickness ratios. Post failure response was not modelled. The work presented in this thesis is another step towards gaining a thorough understanding of the mechanical properties of 3D woven composite structures, focussing in particular on out of plane shear strength. The modified mosaic modelling method used showed it is effective at modelling the out of plane testing of orthogonal 3D woven composite structures, and offer the potential to predict the failure of larger composite structures of the same construction and 3D woven architecture although developments are still needed in modelling the post failure response.

The character of woven textiles is dependent on both the materials and the loom technology used. While digitally-controlled jacquard looms are a major development in weaving technology, they have mostly been used in developing representational and pictorial weaving. Such three-dimensional weaving as exists, utilises materials in predictably similar ways. Here, through systematic experimentation, three shrinking and two resisting yarns have been combined in multi-layer weaves in order to explore their potential for form-generating behaviour. Three-dimensional form occurs when the shrinking yarn/s place the resisting yarn/s under tension. To relieve this tension, the resisting yarn moves within the weave, creating waves or folds. The resulting form is highly sensitive to variation, demonstrating emergent behaviour, and identifying the woven textile as a complex system. Demonstrating the variety of form possible from a limited number of materials, the results represent a small body of work aiming to re-form weaving. The exploration of synergistic material combinations is therefore shown to be an exercise of value to fields from art textiles through to industry. It demonstrates that there is great development potential in woven textiles. Understanding the behaviour of materials is fundamental to furthering form-based weaving.

Les pales d’hélicoptère sont des structures composites soumises à un chargement cyclique multiaxial, et leur criticité impose de porter une attention particulière à la tolérance aux dommages. Leur revêtement peut potentiellement présenter des criques suite à certains évènements (impact, défaut, foudre). Ces travaux se focalisent sur un matériau de revêtement donné (tissu de verre) et concernent l’étude de la propagation de coupure (crique) sous chargement cyclique. Les sollicitations de service ont amené à considérer la traction et le cisaillement plan. Une étude expérimentale a été menée afin d’étudier les modes d’endommagement du matériau et sa résistance à la propagation de coupure pour différentes sollicitations (en traction et en cisaillement) et pour les drapages les plus courants. Elle a permis de dégager les mécanismes d’endommagement mis en jeu, et a fourni un ensemble important de propriétés matériau et de données quantitatives de vitesse de propagation. Elle a par ailleurs guidé vers une modélisation par éléments finis adaptée à l’architecture du matériau, et la manière dont il se dégrade en fatigue. Ce modèle repose sur un maillage à l’échelle de la mèche, et la prédiction de la propagation est obtenue par l’utilisation d’une courbe de fatigue S-N. La simulation a été évaluée par comparaison des faciès de rupture, des vitesses de propagation et de l’étendue des zones d’endommagement avec les essais réalisés sur éprouvettes. / Helicopter blades consist of composite structures which have to sustain multi-axial cyclic loading. Because of their criticality, damage tolerance has to be considered carefully. Their skin is subjected to environmental events like impact, flaw, lightning which can cause through-thethickness cracks. The present work focuses on one given skin material (woven glass fabric) and concerns the study of the through-the-thickness crack growth under cyclic loading. In-flight loading lead to consider tension and shear. An experimental study has been carried out to study damage in the material and its crackgrowth resistance under different loadings (tension and shear) and for usual stacking sequences. It highlighted damage mechanisms and provided an important set of material data and crack growth speeds. Besides, this led to a finite element approach adapted to the woven fabric architecture, anddamage feature under fatigue loading. This modeling is based on a bundle scale mesh, a semidiscrete damage modeling and an S-N curve to predict fiber failure. Numerical simulations of crack growth tests were carried out, and results were compared with experiments in terms of crack direction, crack growth speed, and size of damaged area.

Ce travail concerne l'étude théorique, expérimentale et numérique du comportement mécanique de matériaux tissés et de toiles laminées à base de fibres synthétiques, destinés à la fabrication des voiles, comme le polyester ou le Kevlar. Une approche théorique originale a été proposée ; elle permet une prise en compte du comportement spécifique des fils, de l'enduction et de leurs interactions. La modélisation, qui en résulte, permet de décrire le comportement biaxial des matériaux tissés et des toiles, en chargements cycliques complexes, avec une prise en compte des déformations finies, des effets visqueux non linéaires, de l'irréversibilité indépendante du temps et de l'anisotropie. Une mise en œuvre de cette modélisation a été effectuée dans un code d'Eléments Finis, afin de produire un outil opérationnel pour le calcul des voiles. L'approche théorique proposée a été validée grâce à une étude expérimentale détaillée, qui a été réalisée sur le Dacron SF HTP Plus. Ainsi, nous avons réalisé sur ce matériau différents essais de tractions monotones et de tractions ondulées, contrôlés en déformation et en force. Certains de ces essais comportent des séquences de relaxation. Ces essais ont été réalisés dans les axes du matériau, dans le sens chaîne ou dans le sens trame, ainsi qu'en hors axes avec des orientations par rapport à la direction chaîne allant de 5° à 45°. Des résultats expérimentaux complémentaires ont également été obtenus sur une toile laminée en Kevlar X15 et sur un Dacron SF HTM simple. Enfin, une simulation de l'essai de traction biaxiale a été réalisée et a permis d'étudier l'homogénéité des champs de contrainte et de déformation de trois formes d'éprouvette différentes. / This work deals with theoretical, experimental and numerical studies of the mechanical behavior of woven materials and laminated fabrics, made with synthetic fibers, for the manufacture of sails, such as polyester or Kevlar. An original theoretical approach was proposed, it allows taking into account the specific behavior of yarns, of coating and their interactions. The resulting modeling allows describing the behavior of woven materials and laminated fabrics, in the case of complex cyclic biaxial loadings, taking into account finite deformations, nonlinear viscous effects, time-independent irreversibility and anisotropy. The implementation of this modeling was performed in a finite element code, in order to produce an operational tool for the design and calculation of sails. The proposed theoretical approach has been validated through a detailed experimental study, which was conducted on material “Dacron SF HTP Plus”. Thus, we performed various monotonous and cyclic tensile tests, which were strain or load-controlled. Some of these tests include relaxation sequences. These tests were conducted in the axes of the material, in the warp and weft directions, as well as off-axis or bias orientations, from 5 ° to 45 ° with respect to the warp direction. Further experimental results were also obtained on a laminated “Kevlar X15” and a woven “Dacron SF HTM simple” fabrics. Finally, numerical simulations of the biaxial tensile test were performed and were used for studying homogeneity of the stress and the strain fields in the cases of three different contours of biaxial-tensile samples.

O método convencional de ensaios para a obtenção das curvas de fluência de geossintéticos pode necessitar de períodos de até 10.000 horas. Entretanto, a utilização de ensaios acelerados têm se mostrado bastante eficiente, especialmente para avaliar rapidamente a qualidade do material. Estudos bem sucedidos realizados por diversos autores, utilizaram o método Stepped Isothermal Method (SIM) para acelerar a fluência nos geotêxteis. Neste trabalho, com base neste método foi estimada a fluência de dois geotêxteis com 300 g/m² do tipo não tecido de poliéster (PET) de fibra curta e contínua. Neste estudo, foi analisada a fluência causada por carregamentos de 5, 10, 20, 40 e 60% da carga que causa a ruptura do material. Com base nos resultados conclui-se que os valores de deformação por fluência obtidos são satisfatórios, pois as previsões de alcance de até 355 anos estão próximos aos valores encontrados na literatura internacional. Ainda, para o tempo de 100 anos ficou evidenciado que para o geotêxtil não tecido do tipo PET, de fibra curta ou contínua, o comportamento mecânico do geotêxtil é mais influenciado pela deformação inicial do que pela fluência. / The conventional method of tests to achieve the geosynthetic creep curves may require times of up to 10,000 hours. However, the use of accelerated tests have shown to be very effective, especially for rapidly assessing the quality of the material. Successful studies by various authors used the Stepped Isothermal Method Method (SIM) to accelerate creep in geotextiles. In this work, based on this method was estimated creep of two non-woven geotextiles of polyester with 300 g/m², short or continuous fiber. In this study, creep caused by loads of 5, 10, 20, 40 and 60% of the rupture load of the material was analyzed. Based on the results, it is concluded that the creep strain values obtained are satisfactory, because up to 355 years range forecasts are close to those found in the literature. Still, for the 100-year time, it became evident that for the nonwoven geotextile type PET with short or continuous fiber, the mechanical behavior of the geotextile is more influenced by the initial deformation than by creep.

En contrôle non-destructif par ultrasons, la simulation présente un intérêt majeur en permettant à la fois d’optimiser les configurations de contrôle des pièces et de simplifier l’analyse des données acquises. Cette thèse traite de la modélisation de la propagation des ultrasons dans les matériaux composites tissés. Ces matériaux sont constitués de fibres de Carbone (micrométriques) regroupées en mèches (millimétriques) qui sont ensuite tissées pour former une couche de matériau : leur structure est donc hétérogène à deux échelles distinctes. L’étude à l’échelle du tissage nécessite la connaissance préalable des propriétés mécaniques des mèches. Nous proposons deux méthodes visant à effectuer l’homogénéisation dynamique du matériau à l’échelle microscopique. Une première consiste à identifier les rigidités complexes d’un milieu effectif représentatif de la mèche en comparant les nombres d’ondes des modes guidés s’y propageant à ceux calculés dans un milieu hétérogène de même géométrie ; nous avons développé un algorithme génétique permettant de faire correspondre les jeux de nombres d’onde, dont l’application permet d’identifier certaine des rigidités recherchées. La seconde consiste à étendre un modèle existant permettant d’homogénéiser la structure de la mèche en tenant compte de la diffraction multiple des ondes de volume par les fibres. Le modèle initial (modèle à trois phases) ne traitant que le cas de l’incidence normale aux fibres est étendu au cas plus complexe de l’incidence oblique : un calcul de la diffraction multiple en incidence oblique par un réseau dense de fibres et tenant compte de l’anisotropie des différents milieux est donc proposé. Comme pour la première méthode, on utilise un algorithme génétique pour effectuer l’identification des rigidités effectives. Les résultats obtenus nous amènent à remettre en cause certaines hypothèses de base faites pour effectuer cette homogénéisation dynamique ; particulièrement, la dépendance des résultats à l’angle d’incidence semble remettre en cause le choix de la loi de Hooke comme loi fondamentale pour effectuer une homogénéisation dynamique des composites à structures complexes. / The simulation of nondestructive examinations is of great interest to optimize testing configurations and to help interpreting collected data. This thesis deals with the modeling of ultrasonic propagation into woven composite materials. These materials are made from Carbon fibers (micrometric) assembled into bundles (millimetric) which are woven to form a layer; their structure is thus heterogeneous at two scales. To study the material at the weave scale, one first needs to know the mechanical properties of bundles. We propose two methods aiming at dynamically homogenize the material at this scale. The first one achieves identification of complex rigidity coefficients of the effective material by comparing the wave numbers of guided waves propagating in the effective materials with those of guided waves propagating in the heterogeneous composite. A genetic algorithm is developed to match the sets of wave numbers, allowing to identify some of the coefficients. The second method extends an existing model that homogenizes bundles and takes into account multiple scattering of bulk waves on fibers. The existing model (3-phase model) was limited to waves at normal incidence; the extension deals with oblique incidence. For this, the problem of multiple scattering of waves under oblique incidence on fibers is solved; the solution takes into account the anisotropy and viscoelasticity of the various phases. A genetic algorithm (as already used in the first homogenization method) allows one to identify the complex effective rigidity coefficients. Results obtained using this method finally brings us to question some of the basic hypotheses made to proceed to dynamic homogenization.

Ce travail de thèse s’inscrit dans le cadre de la modélisation multi-échelle des matériaux composites à renfort tissé dans le but de prévoir leur comportement mécanique et leur tenue. Les objectifs de cette étude sont de caractériser et de modéliser de manière discrète les mécanismes d’endommagement à l’échelle mésoscopique (échelle du renfort de fibres) afin d’évaluer leur influence sur le comportement mécanique macroscopique des matériaux composites tissés. La démarche adoptée consiste tout d’abord à caractériser expérimentalement les mécanismes d’endommagement d’un matériau composite tissé à renfort de fibres de verre et matrice époxy. Les mécanismes observés sont des fissures intra-toron et des décohésions inter-torons en pointe de fissure. Afin de modéliser ces mécanismes d’endommagement, une géométrie représentative du composite, obtenue par simulation du procédé de compaction du renfort, et un maillage conforme de cette géométrie sont choisis. Les fissures et les décohésions sont modélisées de manière discrète dans le maillage à éléments finis de la cellule élémentaire représentative du composite. L’amorçage des endommagements dans le composite est déterminé en utilisant un critère couplant une condition en contrainte et une condition en énergie. La propagation de ces endommagements dans le matériau est évaluée à l’aide d’une approche basée sur la mécanique de la rupture incrémentale. L’approche proposée permet de prévoir l’amorçage et la propagation des endommagements en prenant en compte les possibles couplages entre les endommagements, et de faire le lien entre les endommagements observés à l’échelle mésoscopique et le comportement mécanique macroscopique du matériau. / The topic of this PhD thesis is multi-scale modeling of woven composites with the aim of predicting their mechanical behavior and strength. The objectives of the presented work are the experimental characterization and numerical modeling of damage at the mesoscopic scale (scale of the reinforcing fabric) in order to evaluate its influence on the macroscopic mechanical behavior of woven composites. First, the characteristic damage mechanisms of a woven composite made of glass fibers and epoxy matrix are determined experimentally. Intra-yarn cracks and decohesions between yarns at the crack tips are observed. In order to model these damage mechanisms at the mesoscopic scale, a geometry representative of the composite, obtained from numerical simulation of the dry fabric compaction, and a conformal mesh of this geometry have been selected. Discrete cracks and decohesions are inserted into the finite element mesh of the composite unit cell. Crack initiation is studied using a coupled criterion based on both a stress and an energy condition. The propagation of cracks and decohesions is modeled using a method based on Finite Fracture Mechanics. The proposed approach allows evaluating of the influence of the damage mechanisms observed at the mesoscopic scale on the macroscopic mechanical behavior of the studied material.

The present research focuses on analyzing the possibility of implementing three dimensional woven composite (3DWC) materials in hip implants. The integration of 3DWCs in hip implants has the possibility to both extend the life-time and improve patient outcomes; by spatially varying mechanical properties to meet both biological needs as well as required mechanical loading. In this study, the bulk material properties of 3DWCs were varied based on woven composite architecture and determined using physics based models, which reflect the realistic geometries of fibers in compaction and preform. The multi-digital chain method combined with Extended Finite Elemental Analysis (XFEA) are adopted in this micro-analysis for composite design. Four different woven architectures with a combination of different existing biocompatible fiber and resins are considered in this study. The main objective is to assess the mechanical response of these biocompatible materials in the design of 3D woven architectures and determine their ability to match the required modulus at different regions of a hip implant. Results obtained show 3DWCs are viable candidates for this application. Multiple architectures and materials chosen, were able to achieve the desired mechanical response. Additional studies can use these results as a starting point and framework for further mechanical and biological testing.

Deployable structures made from ultra-thin composite materials can be folded elastically and are able to self-deploy by releasing the stored strain energy. Their lightness, low cost due to smaller number of components, and friction insensitive behaviour are key attractions for space applications. This dissertation presents a design methodology for lightweight composite booms with multiple tape-spring hinges. The whole process of folding and deployment of the tape-spring hinges under both quasi-static and dynamic loading has been captured in detail through finite element simulations, starting from a micro-mechanical model of the laminate based on the measured geometry and elastic properties of the woven tows. A stress-resultant based six-dimensional failure criterion has been developed for checking if the structure would be damaged. A detailed study of the quasi-static folding and deployment of a tape-spring hinge made from a two-ply plain-weave laminate of carbon-fibre reinforced plastic has been carried out. A particular version of this hinge was constructed and its moment-rotation profile during quasi-static deployment was measured. Folding and deployment simulations of the tape-spring hinge were carried out with the commercial finite element package Abaqus/Explicit, starting from the as-built, unstrained structure. The folding simulation includes the effects of pinching the hinge in the middle to reduce the peak moment required to fold it. The deployment simulation fully captures both the steady-state moment part of the deployment and the final snap back to the deployed configuration. An alternative simulation without pinching the hinge provides an estimate of the maximum moment that could be carried by the hinge during operation. This moment is about double the snap-back moment for the particular hinge design that was considered. The dynamic deployment of a tape-spring hinge boom has been studied both experimentally and by means of detailed finite-element simulations. It has been shown that the deployment of the boom can be divided into three phases: deployment; latching, which may involve buckling of the tape springs and large rotations of the boom; and vibration of the boom in the latched configuration. The second phase is the most critical as the boom can fold backwards and hence interfere with other spacecraft components. A geometric optimisation study was carried out by parameterising the slot geometry in terms of slot length, width and end circle diameter. The stress-resultant based failure criterion was then used to analyse the safety of the structure. The optimisation study was focused on finding a hinge design that can be folded 180 degrees with the shortest possible slot length. Simulations have shown that the strains can be significantly reduced by allowing the end cross-sections to deform freely. Based on the simulations a failure-critical design and a failure-safe design were selected and experimentally verified. The failure-safe optimised design is six times stiffer in torsion, twice stiffer axially and stores two and a half times more strain energy than the previously considered design. Finally, an example of designing a 1 m long self-deployable boom that could be folded around a spacecraft has been presented. The safety of this two-hinge boom has been evaluated during both stowage and dynamic deployment. A safe design that latches without any overshoot was selected and validated by a dynamic deployment experiment.