Les matériaux composites ont connu ces dernières années une forte croissance, croissance aujourd'hui renforcée par les nouvelles normes européenne visant à diminuer les émissions CO2 d'ici 2020. La réalisation de pièces complexes peut poser de nombreuses problématiques de fabrication comme la formation de zones sèches, ou la création de distorsions géométriques. Les origines de ces problématiques sont souvent liées à un manque de connaissance et de maîtrise des phases d'imprégnation des renforts et de cuisson du matériau. L'amélioration de la robustesse des procédés nécessite d'avoir une connaissance fine des phénomènes physiques qui ont lieu lors de l'élaboration. Dans cette perspective, les procédés d'élaboration de matériaux composites ont été étudiés à travers la mise en place d'un démonstrateur de laboratoire dans le cadre du projet LCM Smart. Ce pilote d'injection a permis de valider des solutions d'instrumentation, à partir de capteurs innovants (OFS) développés en partenariat avec le laboratoire d'optique Hubert Curien.L'application de cette instrumentation dans le cadre du suivi du procédé RTM a démontré les capacités des OFS pour le suivi des caractéristiques physiques de la pièce (le front d'écoulement, la température, les déformations résiduelles et le degré de cuisson). La comparaison des caractéristiques mesurées avec des simulations numériques effectuées en collaboration avec ESI, a montré une bonne corrélation.Enfin, l'instrumentation a permis de mettre en évidence l'intérêt d'un outillage composite en HexTool pour la réduction des contraintes résiduelles liées à l'interaction outil/pièce.

Cette thèse s’intéresse à la fabrication de pièces composites par le procédé Resin Transfert Molding (ou RTM), appliquée à des tubes de protection thermiques. Plus particulièrement, cette thèse vise à démontrer la faisabilité d’utiliser ce procédé pour la fabrication cette pièce complexe. La phase d’imprégnation de préformes sèches est plus particulièrement étudiée. Après mise en oeuvre, cette pièce peut présenter des défauts tels que de la porosité ou des déplacements de plis constituant la préforme. L’objectif de cette thèse est donc de comprendre l’origine de ces défauts et de minimiser voire de d’empêcher leur apparition. Pour cela, une démarche expérimentale a été mise en place. Celle ci comprend la réalisation d’un pilote de laboratoire permettant d’appliquer différentes conditions d’imprégnation aux préformes considérées. La perméabilité des renforts considérés a aussi été évaluée à différentes échelles grâce à l’utilisation de moyen dédiés à l’échelle macroscopique (banc de perméabilité planaire et transverse), et grâce à l’utilisation d’un code de calcul se basant sur des images de tomographie synchrotron à l’échelle microscopique. Enfin, une analyse de la qualité des prototypes réalisés a été menée en suivant des procédures mises en place lors de ce projet et les résultats analysés et mis en relation avec les conditions de mise en oeuvre. Cette approche expérimentale est couplée aux simulations numériques de la phase d’imprégnation que nous avons aussi mise en oeuvre au cours de cette thèse. Par l’utilisation combinée de la simulation numérique et des essais expérimentaux, nous avons défini des critères estimant le risque d’apparition des défauts. Ces critères ont montré leur efficacité sur les solutions innovantes que nous avons proposées puisque répondant aux exigences du cahier des charges industriel. / This work concerns the manufacturing of composite parts using the Resin Transfer Molding (RTM) process. A major goal of this study is to test the feasibility of using this process to manufacture a thick tubular part with a complex shape. This study concerns the different stages of the process with an important focus on the injection step of dry preforms. The goal of this thesis is to understand the generation of manufacturing defect (mainly porosity and preform deformation) that possibly takes place during the injection step to avoid them. An experimental procedure is proposed. An experimental setup was developed to study the influence of the different process parameters on the quality of the composite parts. The determination of the longitudinal and through the thickness permeabilities was conducted experimentally on sheared and un-sheared samples. An alternative technique to estimate the permeability is presented based on simulation software using X-ray tomography images at the microscale. At last, a quality control procedure was developed and applied to the tubes manufactured within this project. This experimental work was compared to numerical simulations of the injection stage. Using both numerical simulations and experiments, criteria on process and material parameters to predict the quality of the tailored parts are presented. Those criteria are successfully compared to experimental data and were applied to design innovative injection solutions that meet industrial specifications.

This diploma thesis called „Aileron Design of Composite Materials” deals with the technologies of production used in aricraft industries. It shows appropriate conceptions of composite structures for the airplane aileron of Aero L-159A/B as well as a proposal of an accetable structure for RTM process.

Resin infusion of composite parts has continually been reaching to achieve laminate quality equal to, or exceeding, the quality produced with prepreg in an autoclave. In order for this to occur, developers must understand the key process variables that go in to producing a laminate with minimal void content. The purpose of this research is to continue efforts in understanding 1) the effect of process conditions on the resultant void content, with a focus on resin infusion flow rate, 2) applying statistical metrics to the formation, location and size of voids formed, and 3) correlate these metrics with the local mechanical properties of the composite laminate. The variation in dispersion and formation of micro-voids and macro-voids varied greatly between the rates of flow the infusion occurred, especially in the non-crimp carbon fiber samples. Higher flow rates led to lower volumes of micro-voids in the beginning section of the carbon fiber laminates with macro-voids being introduced approximately half-way through infusion. This was determined to have occurred decreasing pressure gradient as the flow front moved away from the inlet. This variation in void content per location on the laminate was more evident in the carbon fiber samples than the fiberglass samples. Micro-voids follow void formation modeling especially when coupled with a pressure threshold model. Macro-void formation was also demonstrated to correlate strongly to void formation models when united with void mobility theories and pressure thresholds. There is a quick decrease in mechanical properties after the first 1-2% of voids signaling strength is mostly sensitive to the first 0-2% void content. A slight decrease in SBS was noticed in fiberglass laminates, A-F as v0 increased but not as drastically as represented in the NCF laminates, G and H. The lower clarity in the exponential trend could be due to the lack of samples with v0 greater than 0% but less than 1%. Strength is not well correlated to void content above 2% and could possibly be related to void morphololgy.

This investigation completed the verification of a three-dimensional resin transfer molding/resin film infusion (RTM/RFI) process simulation model. The model incorporates resin flow through an anisotropic carbon fiber preform, cure kinetics of the resin, and heat transfer within the preform/tool assembly. The computer model can predict the flow front location, resin pressure distribution, and thermal profiles in the modeled part. The formulation for the flow model is given using the finite element/control volume (FE/CV) technique based on Darcy's Law of creeping flow through a porous media. The FE/CV technique is a numerically efficient method for finding the flow front location and the fluid pressure. The heat transfer model is based on the three-dimensional, transient heat conduction equation, including heat generation. Boundary conditions include specified temperature and convection. The code was designed with a modular approach so the flow and/or the thermal module may be turned on or off as desired. Both models are solved sequentially in a quasi-steady state fashion. A mesh refinement study was completed on a one-element thick model to determine the recommended size of elements that would result in a converged model for a typical RFI analysis. Guidelines are established for checking the convergence of a model, and the recommended element sizes are listed. Several experiments were conducted and computer simulations of the experiments were run to verify the simulation model. Isothermal, non-reacting flow in a T-stiffened section was simulated to verify the flow module. Predicted infiltration times were within 12-20 percent of measured times. The predicted pressures were approximately 50 percent of the measured pressures. A study was performed to attempt to explain the difference in pressures. Non-isothermal experiments with a reactive resin were modeled to verify the thermal module and the resin model. Two panels were manufactured using the RFI process. One was a stepped panel and the other was a panel with two `T' stiffeners. The difference between the predicted infiltration times and the experimental times was 4 to 23 percent. / Master of Science

This investigation explored the feasibility of recently developed toughened cyanate ester networks as candidate materials for high performance composite matrix applications. The resin investigated was a Bisphenol-A cyanate ester toughened with hydroxy functionalized phenolphthalein based amorphous poly(arylene ether sulfone). The thermoplastic modified toughened networks exhibited improvement in the fracture toughness over the base cyanate ester networks without significant reductions in mechanical properties or glass transition temperature. Void free, unidirectional carbon fiber prepreg was successfully manufactured with the toughened cyanate resin using a solventless hot-melt technique. The resin mass fraction of the prepregs was between 31 and 35%. The carbon fiber, toughened cyanate ester prepreg was fabricated into composite panels for mechanical and physical testing. The cure cycle used to manufacture the composite laminates was developed with the aid of a process simulation model developed by Loos and Springer. In order to accurately simulate the resin curing and flow processes, the cure reaction kinetics and melt viscosity was characterized as a function of temperature and degree of cure and input into the simulation model. The model generated cure cycle was used in the manufacture 8-ply unidirectional and 16-ply quasi-isotropic composite laminates. The manufactured laminates were well consolidated to the specified fiber volume fraction between 59 and 60%. Photomicrographs showed that the laminates are void free, the fiber and resin distribution is uniform and fiber wet-out is very good. Mechanical tests were performed to measure the impact damage resistance and shear properties of the toughened cyanate ester resin composites. The results show improvements in impact damage resistance compared with the commonly used hot-melt epoxy resin composites. The influence of processing on performance was observed from the results of shear tests. Carbon fabric composite panels were manufactured by liquid molding processes (resin transfer molding and resin film infusion), with a series of four toughened cyanate ester resins generated by varying the concentration and the molecular weight of the toughener. The panels were subjected to physical, damage tolerance, and fracture toughness tests. The results of physical testing indicate consistently uniform quality, and the void content was found to be less than 2%. The toughened cyanate ester composites exhibited significantly improved impact damage resistance and tolerance compared with hot-melt epoxy systems. Marked increase in the mode II fracture toughness were observed with an increase in the concentration and the molecular weight of the toughener. / Ph. D.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Vacuum assisted resin transfer moulding (VARTM) belongs to the category of resin infusion techniques that use lower than atmospheric pressure to infiltrate a reinforced cavity. This technique has various advantages; however, manufacturing costs can be relatively high due to more difficult shapes fabricated and a lack of knowledge regarding cost driving factors. The objective of this study was to develop a cost model for composite parts. Such a model allows the estimation of manufacturing costs of shapes of different geometries. Therefore, it provides a comparison to alternative manufacturing techniques, such as metal forming or composite spray lay-up and helps to avoid unnecessarily expensive design features. The proposal was made to split complex shaped composite parts into individual basic shapes, which are further investigated here. For the basic shapes, an experimental approach was used where the manufacturing times of each process step are measured and then statistically analysed. Infusion simulation software was used to obtain additional filling times to complete the design of experiments. This method allows the estimation of manufacturing times of composite parts with different geometries. The manufacturing times were validated to that of a complex shaped industrial part, with reasonable results. Finally, a flexible cost model was developed to compare different manufacturing techniques and to estimate the manufacturing costs. / AFRIKAANSE OPSOMMING: Vakuumgesteunde harsinspuitingsgietwerk (VARTM) behoort tot die kategorie harsinspuitingstegnieke wat laer-as-atmosferiese druk gebruik om ʼn versterkte holte binne te dring. Hierdie tegniek hou verskeie voordele in. Tog kan vervaardigingskoste betreklik hoog wees wanneer dit by ingewikkelder vorms en ʼn gebrek aan kennis met betrekking tot kostesnellers kom. Die doelwit van hierdie studie was om ʼn kostemodel vir saamgestelde onderdele te ontwikkel. Die model maak voorsiening vir die raming van die vervaardigingskoste vir verskillende afmetings. Sodoende bied dit ʼn vergelyking met alternatiewe tegnieke, en help voorkom onnodig duur ontwerpkenmerke. Daar is voorgestel dat dele met ingewikkelde vorms in individuele basiese vorms verdeel word, wat dan hier verder ondersoek word. Vir die basiese vorms word ʼn eksperimentele benadering gebruik waar die vervaardigingstye in elke prosesstap gemeet en statisties ontleed word. Voorts word inspuitingsimulasiesagteware gebruik om komplementêre inspuitingstye te bepaal ten einde die eksperimentele ontwerp te voltooi. Hierdie metode maak dit ook moontlik om die vervaardigingstye vir saamgestelde materiaal onderdele van verskillende afmetings te raam. Die vervaardigingstye word dan bevestig aan die hand van dié van ʼn kompleks gevormde industriële onderdeel, met redelike resultate. Uiteindelik word ʼn buigsame kostemodel ontwikkel om verskillende vervaardigingstegnieke te vergelyk en die vervaardigingskoste te raam.

Neste trabalho propôs-se a construção de um tubo de material compósito híbrido, com fibra de vidro e fibra de carbono, para utilização como prolongador de prótese de membro inferior a serem fabricadas pela AACD - Associação de Assistência à Criança Deficiente. O objetivo é avaliar as solicitações da prótese para otimizar custo e reduzir a massa. Fez-se inicialmente um levantamento das propriedades dos materiais comerciais utilizados para a fabricação do prolongador para referenciar o desenvolvimento do componente da prótese. Utilizou-se modelagem por elementos finitos para otimizar o componente em função dos esforços biomecânicos a que a prótese é submetida. Nesta modelagem, estudaram-se várias disposições, quantidade e material das camadas de forma a atender às solicitações e minimizar os custos. O levantamento bibliográfico permitiu encontrar uma rota de menor custo para a fabricação de compósito que utiliza um processo de transferência de resina auxiliado a vácuo e pré-formados de vidro e carbono. Como referência, foi fabricado um componente pelo processo de bobinagem filamentar que produz materiais compósitos de qualidade reconhecida. O processo de moldagem por transferência de resina assistido à vácuo, apesar de ter alguns insumos importados, pela sua simplicidade pode ser realizado na própria AACD e se mostrou capaz de obter componentes com custo que viabiliza sua produção sem grandes investimentos em equipamentos. Apesar da redução de algumas das propriedades em relação à peça de referência, o tubo apresentou vantagens na redução de massa e na absorção de impacto. / In this work it was considered a construction of a pipe of hybrid composite material, with carbon and glass fibre, for use as prosthesis extension of inferior member to be manufactured for the Associação de Assistência à Criança Deficiente AACD. The objective is to evaluate the requests of prosthesis to optimize cost and to reduce weight. A survey of the properties of the commercial materials commonly used for the manufacture extension became initially a reference to the development of the final component. A finite element modeling was used to optimize the component in the biomechanics function related to the efforts which the prosthesis is submitted. In this modeling some disposals and numbers of layers, amount and material have been studied to take care of the requests and to minimize the cost. A bibliographical survey allowed finding a shipper route for the manufacture of composite that uses a process of vacuum assisted resin transfer molding and preforms of glass with carbon. As reference, a component was produced using filament winding process to compare the quality of the obtained composite pipe. The process, although to have some imported feed-stock, can be proper carried out by AACD and if it showed capable to produce components with cost that makes possible its production internally. Despite the reduction of some of the properties in relation to the reference part, the component presented advantages such as weight reduction and the impact absorption.

Le procédé Resin Transfer Molding est une technologie de fabrication de pièces en matériaux composites. Une compréhension et une modélisation des phénomènes physiques qui interviennent dans certaines étapes de la fabrication apportent une contribution importante à la maîtrise de ce procédé. Les travaux abordés dans cette étude se situent dans le cadre d'un programme plus général visant le contrôle et le pilotage du RTM. Tout d'abord, une caractérisation de la perméabilité des renforts dans la direction perpendiculaire aux plis va compléter les résultats obtenus dans des études préalables sur les perméabilités planes. Ensuite, nous étudierons de près les transferts thermiques durant l'injection et la cuisson. Pour cela, plusieurs étapes sont nécessaires: caractérisation des propriétés thermiques (avec notamment le développement d'un montage destiné à mesurer les conductivités thermiques dans le plan des fibres), étude théorique et étude expérimentale à l'aide d'un moule instrumenté. Des simulations numériques permettront alors de valider les modèles développés. Ces travaux devront ensuite servir de base à l'amélioration du logiciel de simulation LCMFLOT. Enfin, une première étape vers l'optimisation du remplissage a été réalisée afin de pouvoir piloter les machines d'injection en imposant une vitesse d'imprégnation constante pendant le remplissage. Cette optimisation est basée sur l'exploitation des résultats de simulation.

Baigiamajame magistro darbe suprojektuotos ir pagamintos dviejų rūšių šviesos koncentratorinės sistemos: jungtinė parabolinė ir sistema su Frenelio lęšiu. Atlikta saulės elementų efektyvumo analizė, išnagrinėtos šviesą koncentruojančių sistemų rūšys bei aptarti jų optiniai parametrai. Frenelio lęšis ir koncentratorinių sistemų laikančiosios konstrukcijos pagamintos vakuuminio formavimo būdu, ieškant pigesnės gamybos technologijos. Baigiamajame darbe atlikti optinio pralaidumo ir lūžio rodiklio, matomos šviesos bangų ilgių ruože, tyrimai bei saulės elementų, esančių šviesos koncentratorinėse sistemose,voltamperinių ir voltvatinių charakteristikų tyrimai. Iš tyrimų rezultatų nustatyti šviesos koncentravimo laipsniai. Darbe diskutuojama apie pigių optinių sistemų galimus pritaikymus ir jų tobulinimo būdus. Išnagrinėjus teorinę ir praktinę dalis, pateiktos išvados ir pasiūlymai. Darbą sudaro 8 dalys: įvadas, saulės elementų efektyvumo ribos, saulės šviesos koncentratoriai ir jų panaudojimas fotoelektrinėse sistemose, eksperimentinių tyrimų metodika, prototipų gamyba, eksperimentiniai tyrimai, išvados, literatūros sąrašas. Darbo apimtis – 82 p. teksto be priedų, 95 pav., 13 lent., 22 bibliografiniai šaltiniai. Atskirai pridedami darbo priedai. / Concentrated PV systems (compound parabolic and Fresnel CPV) have been designed and investigated. The efficiency of solar cells and the types of light concentrated systems have been analyzed and their optical parameters have been discussed. Fresnel lens and the CPV system holding structure have been fabricated by means of vacuum forming machine in this way making the technology of production less expensive. Optical transmittance and refractive index of Fresnel lens were measured in the range of visible light wavelengths. Current-voltage and voltage-power characteristics of solar cells built inside the CPV systems were investigated, based on results the degree of light concentration by Fresnel lens and compound parabolic CPV has been determined. Some discussions regarding possible applications of concentrated PV systems containing the Fresnel lens as well as possible ways of CPV design improvements are given in current work. After analysed theoretical and practical parts, conclusions and suggestions are proposed. Thesis structure: introduction, theoretical and experimental parts, results of experiments, conclusions and references. Thesis consist of: 82 p. text without appendixes, 95 pictures, 13 tables, 22 bibliographical entries. Appendixes included.