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Fibre reinforced polymer matrix composites are used frequently in aerospace applications. Manufacturers of aerospace components favour composites over traditional metallic alloys due to their light weight, high modulus, corrosion resistance and fatigue resistance. Advantages of composites for non-structural interior components over metallic include: ease of manufacturing for single parts of complex geometry as opposed to assemblies, cheaper manufacturing of a limited series of parts and composites greatly reduced noise, vibration and harshness. However, manufacturing interior composite components requires critical attention to detail during the preforming stages and handling of dry fabric textiles. Since these components are handmade they often yield lower profits and therefore efficient preforming is critical. Designing draping strategies for industrial liquid composite moulding processes requires a significant amount of time and testing, in simulation and also working on physical moulds. Mould and part surfaces are often defined by a number of geometric features, labelled base surfaces in the context of this thesis, which can be used to quickly probe multiple draping strategies and identify the best one. Traditionally, trial and error work is performed over a full mould surface until a working or acceptable draping strategy is found, rarely identifying the best strategy. The work in this thesis presents the initial development stages for a draping predictive tool aimed at quickly probing multiple draping scenarios in simulation prior to receiving moulds and identifying the best draping strategy for industrial non-structural aerospace composites. A multi-parameter remodelling tool – the conical frustum – was developed for uniformly identifying base surfaces through 12 geometric parameters linked into a database of in-plane shear and yarn orientations results. The development of the database is discussed, detailing Taguchi methods of experimental design used for developing linear functions from the database results, which allow interpolation of results on base surfaces that do not directly exist within the database. This thesis also includes major developments for the core draping algorithm used for linking individual base surface results together when probing draping strategies. Further investigations were performed on unique elements of in-plane shear behaviour that are encountered during draping, so that these could ultimately be considered during the development of this version of the draping algorithm whilst others may be included in future developments.

The present research aims at engineering design of military helmet shells with continuous 3D woven fabric reinforcements for improved protection at a lighter weight and a reduced cost. The research was carried out using both the experimental and numerical methods. The results proved that the designed 3D woven wadded through-the-thickness angle interlock (TTAI) fabrics can be successfully moulded as continuous reinforcements for the doubly curved military helmet shells; therefore, costs in pattern cutting in the current composite helmet making process are eliminated. An improved ballistic performance was also demonstrated in the continuously reinforced composite structures. The wadding yarns added into the conventional TTAI fabrics enhanced the mechanical properties along the warp direction significantly. Improved composite in-plane isotropy was achieved by using the wadded TTAI fabrics as reinforcements. The locking angle method was modified based on the deformation behaviour of TTAI fabrics and was used to predict and evaluate the mouldability of both conventional and wadded TTAI structures. Mouldability factor, defined from the locking angle, assists the design and selection of continuous reinforcements that are of the appropriate mouldability. The mouldability limit of a PASGT (Personnel Armour System for Ground Troops) helmet shell was determined as 25.54. Thus, TTAI fabrics with mouldability factor no larger than this value are capable of continuously reinforcing the doubly curved shape. Ballistic tests and post-mortem examinations through ultrasonic C-scan and X-ray computed tomography (CT) demonstrated the advantages of the continuously reinforced composite in energy absorption. Up to 19.3% more of the kinetic energy was absorbed by the continuously reinforced panel through generating a delamination volume that was twice as large as that of the discontinuously reinforced one, and the delamination damages were distributed over a wider area. Under the same level of fabric mouldability and composite areal density, the panels reinforced with fewer plies of heavier fabrics performed better. The wadded TTAI reinforced composite panel demonstrated the optimal ballistic resistance by showing a 25.5% thickness increase and 55.3% penetration through the thickness. The 3D wadded fabric and 2D plain weave fabric continuously reinforced flat panels presented an equivalent ballistic performance. Meanwhile, further numerical analyses were conducted based on the digitally obtained geometry of a PASGT helmet. Although the ballistic limits varied from location to location, an equivalent ballistic limit of the helmet shell was noticed for the PASGT shell when compared to its flat counterparts. The military helmet shells reinforced by 3D wadded TTAI fabrics continuously offer improved ballistic performance. This is attributed to the preserved reinforcement continuity and the enhanced through-the-thickness properties. The research provides a novel reinforcing strategy for the construction of future composite military helmet shells.

In this study structural design, analysis and composite manufacturing applications for a tactical UAV, which was designed and manufactured in Aerospace Engineering Department of Middle East Technical University (METU), is introduced. In order to make an accurate structural analysis, the material and loading is modeled properly. Computational fluid dynamics (CFD) was used to determine the 3D pressure distribution around the wing and then the nodal forces were exported into the finite element program by means of interpolation from CFD mesh to finite element mesh. Composite materials which are mainly used in METU TUAV are woven fabrics which are wetted with epoxy resin during manufacturing. In order to find the elastic constants of the woven fabric composites, a FORTRAN code is written which utilizes point-wise lamination theory. After the aerodynamic load calculation and material characterization steps, linear static and dynamic analysis of the METU TUAV&rsquo / s wing is performed and approximate torsional divergence speed is calculated based on a simplified approach. Lastly, co-cured composite manufacturing of a multi-cell box structure is explained and a co-cured multi-cell box beam is manufactured.

Dans le cadre de cette thèse, une modélisation par éléments finis continue renforcée discrète est développée. Le modèle est basé sur le concept de la cellule élémentaire, avec utilisation de connecteurs pour prendre en compte la rigidité en tension de la structure, et modéliser l'anisotropie du tissu et un élément coque pour décrire la rigidité en cisaillement et gérer le frottement et le contact avec les outils lors de la simulation du procédé de préformage. Les différents éléments de ce maillage spécifique sont générés automatiquement à l'aide des scripts pythons. Associés à ce choix de modélisation, les caractéristiques du comportement sont déterminées à l'aide d'essais expérimentaux conduits sur le renfort et d'une démarche de méthode inverse. Le comportement de ces différents éléments est choisi d'être linéaire élastique en premier lieu, et par la suite à évoluer pour devenir non linéaire. Ces développements numériques sont réalisés dans le logiciel Abaqus/ Explicit. Dans un second temps le modèle développé est utilisé dans le cadre de simulation de l'étape de préformage des renforts secs. A ce titre un démonstrateur expérimental développé dans le cadre de la thèse sert à obtenir des résultats expérimentaux pour corréler ces travaux de simulations. Des comparaisons avec des simulations mono-couche, hémisphérique, permettre de mettre en évidence l'influence des paramètres de simulations mises en jeu. Dans le cadre de préformages de plusieurs plis, l'influence des caractéristiques du contact / frottement est mise en évidence. Finalement une procédure d'automatisation afin de rendre la simulation plus ergonomique dans un contexte industriel est présentée. Cette procédure consiste à générer le maillage spécifique et mettre la simulation en donné dans Catia. Les simulations peuvent ainsi se réaliser sans le passage par Abaqus/CAE. / In this work, a discrete approach for the simulation of the preforming of dry woven reinforcementis proposed. A “unit cell” is built using elastic isotropic shells and axial connectors instead of bars and beams used in previous studies. Shell elements are used to take into account the in-plane shear stiffness and to manage contact phenomenon with the punch and die. Connectors reinforce thestructure in the yarn directions and naturally capture the specific behavior of the fabric. To identify the material parameters, uniaxial tensile tests and bias tests have been employed. A numerical algorithm,coupling Matlab and Abaqus/Explicit, is used to determine the shear parameters by an Inverse method. The model has been implemented in Abaqus to simulate hemispherical stamping.Experimental results are compared to numerical simulations, good agreement between both resultsis shown for the case of single layer forming.This model has been then used to simulate a multilayer performing and a numerical study of the effect of fiction coefficient has been performedFinally a tool which interfaces a CAD Software to the Abaqus/code has been developed.

Flame retardant chemicals were used to make flammable fibres or fabrics flame retardant. Flame retardants protect the flammable material from fire by delaying or preventing the ignition process. The problem with flame retardants is unreliable durability when applied physically or bonded chemically on the surface of the fibre or fabric. This thesis project investigated the implementation of inherently flame retardant fibres as a shield form flame for flammable fibres. The most widely used flammable textiles fibres (cotton and polyester) were mixed with inherently flame retardant fibres (modacrylic and Lenzing FR) pairwise at fibre level for non-woven fabric and both fibre & yarn level for knitted fabric. The vertical flame test, where the fabric hung vertically and burned from the bottom, was used to characterise their burning behaviour. With the vertical flame test, it was found that flame shielding ability of inherently flame retardant fibres towards flammable fibres improves with an increasing proportion of inherently flame retardant fibres in the fabric. Also, fabric structure influences the shielding properties of the flame retardant fibres. A comparison between fibre and yarn level mixing for knitted fabric yarn level mixing was found to have better flame shielding properties. Thesis work points out the issue with flame retardant chemical and presents an alternative approach for conventional flame retardant.

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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.

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