Additive Manufacturing (AM) has demonstrated great potential to advance product design and manufacturing, and has showed higher flexibility than conventional manufacturing techniques for the production of small volume, complex and customised components. In an economy focused on the need to develop customised and hi-tech products, there is increasing interest in establishing AM technologies as a more efficient production approach for high value products such as aerospace and biomedical products. Nevertheless, the use of AM processes, for even small to medium volume production faces a number of issues in the current state of the technology. AM production is normally used for making parts with complex geometry which implicates the assessment of numerous processing options or choices; the wrong choice of process parameters can result in poor surface quality, onerous manufacturing time and energy waste, and thus increased production costs and resources. A few commonly used AM processes require the presence of cellular support structures for the production of overhanging parts. Depending on the object complexity their removal can be impossible or very time (and resources) consuming. Currently, there is a lack of tools to advise the AM operator on the optimal choice of process parameters. This prevents the diffusion of AM as an efficient production process for enterprises, and as affordable access to democratic product development for individual users. Research in literature has focused mainly on the optimisation of single criteria for AM production. An integrated predictive modelling and optimisation technique has not yet been well established for identifying an efficient process set up for complicated products which often involve critical building requirements. For instance, there are no robust methods for the optimal design of complex cellular support structures, and most of the software commercially available today does not provide adequate guidance on how to optimally orientate the part into the machine bed, or which particular combination of cellular structures need to be used as support. The choice of wrong support and orientation can degenerate into structure collapse during an AM process such as Selective Laser Melting (SLM), due to the high thermal stress in the junctions between fillets of different cells. Another issue of AM production is the limited parts’ surface quality typically generated by the discrete deposition and fusion of material. This research has focused on the formation of surface morphology of AM parts. Analysis of SLM parts showed that roughness measured was different from that predicted through a classic model based on pure geometrical consideration on the stair step profile. Experiments also revealed the presence of partially bonded particles on the surface; an explanation of this phenomenon has been proposed. Results have been integrated into a novel mathematical model for the prediction of surface roughness of SLM parts. The model formulated correctly describes the observed trend of the experimental data, and thus provides an accurate prediction of surface roughness. This thesis aims to deliver an effective computational methodology for the multi- objective optimisation of the main building conditions that affect process efficiency of AM production. For this purpose, mathematical models have been formulated for the determination of parts’ surface quality, manufacturing time and energy consumption, and for the design of optimal cellular support structures. All the predictive models have been used to evaluate multiple performance and costs objectives; all the objectives are typically contrasting; and all greatly affected by the part’s build orientation. A multi-objective optimisation technique has been developed to visualise and identify optimal trade-offs between all the contrastive objectives for the most efficient AM production. Hence, this thesis has delivered a decision support system to assist the operator in the "process planning" stage, in order to achieve optimal efficiency and sustainability in AM production through maximum material, time and energy savings.

Le développement récent des technologies de fabrication additive par couches (Additive Layer Manufacturing) a généré de nouvelles opportunités en termes de conception. Généralement, une étape d'optimisation topologique est réalisée pour les structures ALM. Cette tâche est aujourd'hui facilitée par des progiciels commerciaux, comme Altair OptiStruct ou Simulia TOSCA. Néanmoins, la liberté accordée par l’ALM est seulement apparente et des problèmes majeurs empêchent une exploitation complète et généralisée de cette technologie.La première lacune importante provient de l'intégration directe du résultat d'un calcul d’optimisation topologique dans un environnement CAO approprié. Quoi qu'il en soit, la géométrie optimisée résultante n'est disponible que sous une forme discrétisée, c'est-à-dire en termes d'éléments finis (FE) obtenus à la fin de l'optimisation. La frontière de la géométrie optimisée n'est pas décrite par une entité géométrique, par conséquent la topologie résultante n'est pas compatible avec les logiciels de CAO qui constituent l'environnement naturel du concepteur. Une phase de reconstruction CAO longue est nécessaire et le concepteur est obligé de prendre une quantité considérable de décisions arbitraires. Souvent la topologie CAO compatible résultante ne répond plus aux contraintes d'optimisation.La deuxième restriction majeure est liée aux exigences technologiques spécifiques à l’ALM qui doivent être intégrées directement dans la formulation du problème d'optimisation: considérer la spécificité de l’ALM uniquement comme un post-traitement de la tâche d’optimisation topologique impliquerait des modifications si importantes de la pièce que la topologie optimisée pourrait être complètement différente de la solution optimisée.Cette thèse propose une méthodologie générale pour résoudre les inconvénients mentionnés ci-dessus. Un algorithme d’optimisation topologique innovant a été développé: il vise à fournir une description de la topologie basée sur des entités NURBS et B-Spline purement géométriques, qui sont nativement CAO compatibles. Dans ce cadre, les analyses éléments finis sont utilisées uniquement pour évaluer les réponses physiques du problème étudié. En particulier, une entité géométrique NURBS / B-Spline de dimension D + 1 est utilisée pour résoudre le problème d’optimisation topologique de dimension D.L'efficacité de cette approche a été testée sur certains benchmarks 2D et 3D, issus de la littérature. L'utilisation d'entités NURBS dans la formulation de l’optimisation topologique accélère considérablement la phase de reconstruction CAO pour les structures 2D et présente un grand potentiel pour les problèmes 3D. En outre, il est prouvé que les contraintes géométriques, comme par exemple les épaisseurs minimale et maximale de matière, peuvent être efficacement et systématiquement traitées au moyen de l'approche proposée. De plus, des contraintes géométriques spéciales (non disponibles dans les outils commerciaux), par exemple le rayon de courbure local de la frontière de la phase solide, peuvent être formulées également grâce à la formulation NURBS. La robustesse de la méthodologie proposée a été testée en prenant en compte d'autres grandeurs mécaniques, telles que les charges de flambement et les fréquences naturelles liées aux modes de vibration.Enfin, malgré la nature intrinsèque de l'algorithme d’optimisation topologique basé sur les NURBS, certains outils ont été développés pour déterminer automatiquement le contour des pièces 2D sous forme de courbe et sous forme de surface dans le cadre 3D. L’identification automatique des paramètres des courbes 2D a été entièrement développée et un algorithme original a été proposé. Les principes fondamentaux de la méthode sont également discutés pour l'identification des paramètres des surfaces limites pour les pièces 3D. / The recent development of Additive Layer Manufacturing (ALM) technologies has made possible new opportunities in terms of design. Complicated shapes and topologies, resulting from dedicated optimisation processes or by the designer decisions, are nowadays attainable. Generally, a Topology Optimisation (TO) step is considered when dealing with ALM structures and today this task is facilitated by commercial software packages, like Altair OptiStruct or Simulia TOSCA. Nevertheless, the freedom granted by ALM is only apparent and there are still major issues hindering a full and widespread exploitation of this technology.The first important shortcoming comes from the integration of the result of a TO calculation into a suitable CAD environment. The optimised geometry is available only in a discretised form, i.e. in terms of Finite Elements (FE), which are retained into the computational domain at the end of the TO analysis. Therefore, the boundary of the optimised geometry is not described by a geometrical entity, hence the resulting topology is not compatible with CAD software that constitutes the natural environment for the designer. A time consuming CAD-reconstruction phase is needed and the designer is obliged to make a considerable amount of arbitrary decisions. Consequently, often the resulting CAD-compatible topology does not meet the optimisation constraints.The second major restriction is related to ALM specific technological requirements that should be integrated directly within the optimisation problem formulation and not later: considering ALM specificity only as post-treatment of the TO task would imply so deep modifications of the component that the optimised configuration would be completely overturned.This PhD thesis proposes a general methodology to overcome the aforementioned drawbacks. An innovative TO algorithm has been developed: it aims at providing a topology description based on purely geometric, intrinsically CAD-compliant entities. In this framework, NURBS and B-Spline geometric entities have been naturally considered and FE analyses are used only to evaluate the physical responses for the problem at hand. In particular, a NURBS/B-Spline geometric entity of dimension D+1 is used to solve the TO problem of dimension D. The D+1 coordinate of the NURBS/B-Spline entity is related to a pseudo-density field that is affected to the generic element stiffness matrix; according to the classical penalisation scheme employed in density-based TO methods.The effectiveness of this approach has been tested on some 2D and 3D benchmarks, taken from literature. The use of NURBS entities in the TO formulation significantly speeds up the CAD reconstruction phase for 2D structures and exhibits a great potential for 3D TO problems. Further, it is proven that geometrical constraints, like minimum and maximum length scales, can be effectively and consistently handled by means of the proposed approach. Moreover, special geometric constraints (not available in commercial tools), e.g. on the local curvature radius of the boundary, can be formulated thanks to the NURBS formulation as well. The robustness of the proposed methodology has been tested by taking into account other mechanical quantities of outstanding interest in engineering, such as buckling loads and natural frequencies.Finally, in spite of the intrinsic CAD-compliant nature of the NURBS-based TO algorithm, some support tools have been developed in order to perform the curve and surface fitting in a very general framework. The automatic curve fitting has been completely developed and an original algorithm is developed for choosing the best values of the NURBS curve parameters, both discrete and continuous. The fundamentals of the method are also discussed for the more complicated surface fitting problem and ideas/suggestions for further researches are provided.

Cette recherche vise à proposer une approche intégrée permettant la prise en compte simultanée des paramètres Produits / process dans le cadre d’une fabrication par ajout de matière. Le développement produit est en profonde mutation, prenant en compte les contraintes de personnalisation, de temps de mise sur le marché de plus en plus court, la volonté d’une approche eco-responsable etc. Ce changement de paradigme conduit à s’intéresser au choix du couple matériau /process dès la phase de conception afin de prendre en compte les contraintes liées au procédé identifié. Cette approche multi critère s’intéresse à la fois au couple matériau procédé mais prend en compte les aspect fonctionnels de la pièce. Ainsi ce travail de thèse présente une méthodologie de décision générique, basée sur des outils de prise de décision multicritères, qui peut non seulement proposer une solution satisfaisant les contraintes liées aux matériaux, processus et processus par addition de matière, mais propose également de servir de guide aux concepteurs permettant un choix raisonné basé sur des combinaisons matériau-machine orientées conception et obtenu à partir d’une base de données de 38 fournisseurs internationaux de machine de fabrication par ajout de matière. / The doctoral research focuses to build an integrated approach that can simultaneously handle the product and process parameters related to additive manufacturing (AM). Since, market dynamics of today are constantly evolving, drivers such as mass customization strategies, shorter product development cycles, a large pool of materials to choose from, abundant manufacturing processes, etc., have made it essential to choose the right compromise of materials, manufacturing processes and associated machines in early stages of design considering the Design for AM guidelines. As several criteria, material attributes and process functionality requirements are involved for decision making in the industries, the thesis introduces a generic decision methodology, based on multi-criteria decision-making tools, that can not only provide a set of compromised AM materials, processes and machines but will also act as a guideline for designers to achieve a strong foothold in the AM industry by providing practical solutions containing design oriented and feasible material-machine combinations from a database of 38 renowned AM vendors in the world today.

Automatic altitude compensation has been a holy grail of rocket propulsion for decades. Current state-of-the-art bell nozzles see large performance decreases at low altitudes, limiting rocket designs, shrinking payloads, and overall increasing costs. Aerospike nozzles are an old idea from the 1960’s that provide superior altitude-compensating performance and enhanced performance in vacuum, but have survivability issues that have stopped their application in satellite propulsion systems. A growing need for CubeSat propulsion systems provides the impetus to study aerospike nozzles in this application. This study built two aerospike nozzles using modern 3D metal printing techniques to test aerospikes at a size small enough to be potentially used on a CubeSat. Results indicated promising in-space performance, but further testing to determine thermal limits is deemed necessary.

This thesis set out to find a blend of thermoplastics that had better combustion properties than the current ABS (acrylonitrile butadiene styrene) plastic or “Lego TM plastic” used by Utah State University. The current work is in an effort to eliminate toxic propellants from small space applications. High and low density polyethylene plastics were used because they are common plastic waste items. In this way rocket fuel can be made from these items to reduce the waste found in landfills. Three plastics were considered for replacement and as mixture components with the ABS plastic, namely low and high density polyethylene, and high impact polystyrene. These plastics failed to have superior combustion properties when used in rockets designed to achieve 12 pounds or less of thrust compared to the current ABS plastic.

To evaluate potential uses for friction stir welding in additive manufacturing, two separate parts were fabricated, one of 2195-T84 and the other 2219-T87, utilizing fixed pin techniques and additive lap welds. The parts were cut into samples, artificially aged and subjected to Rockwell hardness (HRB), Vickers hardness, micrographic photography, and metallographic imaging on both pre- and post- heat treatment. Additionally, tensile testing was performed on the heat-treated samples. A comparisons of test results showed a minimal increase in the yield strength of the 2195-T84 samples compared to as-welded tensile results obtained from a previous project. The ultimate tensile strength was reduced by approximately 16%. Further testing will be required to determine the nature of this reduction. No previous results were available for the as-welded 2219-T87, but UTS of the artificially aged samples was approximately 91% that of the parent material.

This research project primarily focuses on three major aspects: synthesis and inclusion of silver microparticles and nanowires within a polymer matrix, extrusion of composite filaments and, three-dimensional (3D) printing of multifunctional polymer composites. Since very few studies have explored the inclusion of silver nanoparticles in 3D printing materials, the findings from this study can be significant for additive manufacturing technology. Over the past few decades, the applications of additive manufacturing has been expanding considerably in several industries like automobile, biomechanics, aerospace, hardware engineering, to name a few. We are particularly interested in silver particles and nanowires because of their enhanced antimicrobial, mechanical and optical properties. The unique antimicrobial properties of the silver-polymer composite will especially be applicable in the food and meat industry, where microbial infection is a major concern because of the exposure of microbes in the polymer belts that are used to transfer and package the items in the factory. It costs the industries a considerable amount of time, money and labor to regularly clean and sanitize those belts. If we are able to develop polymer belts with embedded antimicrobial properties, it could have tremendous applications in the food and meat industries. The morphology of the particles will be studied using scientific techniques like Transmission electron microscopy (TEM) and Scanning Electron Microscopy (SEM). The idea is then to nanoparticles will be incorporated into PLA polymer pellets and extruded into composite filaments that can be used for 3D printing of dog-bone test structures. After the fabrication process, tensile tests and fracture surface analysis will be conducted to study the extent of enhancement of the mechanical properties as compared to neat polymer 3D printed specimens. The critical challenge in this project would be to ensure homogenous distribution of the nanoparticles throughout the polymer filaments. This project will integrate concepts and applications from three different fields: nanotechnology, material science, and additive manufacturing.

La fusion laser sélective d’un lit de poudres (Selective Laser Melting – SLM) connait un véritable essor depuis quelques années,notamment en ce qui concerne la production de pièces métalliques. La faible densité des alliages d’aluminium, conjuguée à l’optimisation de conception rendue possible grâce aux procédés de fabrication additive, assure un gain de masse des structures conséquent, ce qui intéresse fortement les industriels des domaines automobile et aéronautique. Cependant, les propriétés finales des pièces aluminium fabriquées par SLM dépendent des nombreux défauts sont générés lors de la fabrication (porosités, fissuration à chaud, état de surface, …). Cette thèse s’intéresse aux moyens de mieux maîtriser ces problèmes en explorant trois axes : Une identification et sélection des méthodes de caractérisations adaptées aux spécificités des matériaux métalliques élaborés par les procédés de fabrication additive « lit de poudre » a été mise en place. Par exemple, la comparaison de différentes méthodes de détermination de la densité relative de pièces nous a permis de montrer les avantages et inconvénients de chacune des techniques employées ; Une étude du moyen de fabrication SLM a mis en évidence l’influence de différents facteurs (flux de gaz, position des éprouvettes sur le plateau de construction, méthodes de dépôt de la poudre) sur les propriétés finales des pièces produites.Ces éléments ont un impact sur la densité des pièces, leurs propriétés de surface et leurs propriétés mécaniques. Nous avons ainsi constaté que la façon de positionner une pièce sur le plateau est une étape de la préparation d’une fabrication à ne pas négliger ; Les études paramétriques menées sur deux types d’alliages d’aluminium, AlSi7Mg0,6 et AM205, ont montré que la composition chimique de l’alliage d’aluminium employé influence de façon non négligeable le jeu de paramètres opératoires à appliquer pour fabriquer une pièce de manière optimale. La densité d’énergie volumique ψ, rapport de la puissance laser avec le produit de la vitesse de lasage, de la distance inter-cordons et de l’épaisseur de couche, est utilisée de façon classique pour l’optimisation des conditions opératoires en SLM. Nos études expérimentales à différentes échelles (1D et3D) ont permis de mettre en évidence les limites de ce critère. La combinaison de ces résultats à la simulation numérique du lasage d’un cordon de poudre a servi de base à la définition d’un premier modèle dont l’objectif sera à terme d’optimiser le choix des paramètres de fabrication. / Interest in selective laser melting (SLM) has been growing in recent years, particularly with regard to the production of metal parts.The low density of aluminum alloys, combined with the possible design optimization enabled by additive manufacturing processes,ensures a significant decrease in the mass of structures which is very interesting for manufacturers in the automotive and aerospaceindustries. However, it is difficult to control the final properties of aluminum parts manufactured by SLM because many defects, suchas porosity, hot cracking, and surface roughness, are generated during the process. To better understand how to optimize theperformance of SLM aluminium parts, several studies were conducted during this work: An identification and selection of characterization methods well-adapted to the specificities of metallic materials developedby powder bed additive manufacturing processes was established. For instance, the comparison of different methods ofdetermining the relative density of parts showed the advantages and disadvantages of each of the techniques; A study of the SLM machine highlighted the influence of various factors (gas flow, positions of specimens on the constructionplate, or methods of depositing the powder) on the final properties of the produced parts. These elements have an impacton the density of the parts, their surface properties, and their mechanical properties. We found that the positioning of a pieceon the tray is a critical step in the preparation of a build that is not to be neglected; Parametric studies carried out on two types of aluminum alloys—AlSi7Mg0,6 and AM205—have shown that the chemicalcomposition of the aluminum alloy used has a significant influence on the set of operating parameters required tomanufacture an acceptable aluminum alloy part. The energy density, ψ, which is the ratio of the laser power to the productof the lasing speed, the hatching distance, and the layer thickness, is conventionally used for the optimization of the operatingconditions in SLM. Our experimental studies performed at different scales (1D and 3D) have shown the limits of this criterion.The combination of these results with the numerical simulation of the lasing of a single powder bead served as a basis forthe definition of an initial model, the final objective of which will be to optimize the choice of manufacturing parameters.

Digital innovations are about to overtake the supply chain systems and revolutionize the way of producing products. With the use of technology in the value chain a sustainable development can be generated and developed. The usage of digital tools for manufacturing can minimize waste and further develop sustained processing. 3D printing is a technology that produces products by adding layer by layer of material. The additive manufacturing process theoretically produces no waste and aims for a sustainable and efficient processing. The textile and sportswear industry adopted this process for high fashion or functional performance products. Especially in the sportswear sector the process shows great potential. Brands like Adidas, Nike and Underarmour adopted the process in order to create midsoles for performance shoes. This research aims to identify the potential of 3D printing for the textile and sportswear industry. The purpose of this research is to explore the advantages and disadvantages of 3D printing within the textile industry and sportswear value chain, to survey where are potential solutions to reduce waste. The qualitative research consists of a theoretical and empirical part. The study begins with a systematic literature review that presents the state of the art of 3D printing in the textile and sportswear industry. In order to add empirical data, interviews with five experts from academia and industry have been conducted. The experts work with 3D printing and three of them with 3D printing and textiles. The case study methodology was chosen in order to compare a small number of cases and their approaches. In order to answer the research questions, the empirical data was thematically analyzed and one overarching theme and seven sub themes emerged. The sub themes were compared to the effects and challenges of 3D printing for the textile and sportswear value chain that emerged from the literature review. The findings show that there are several advantages as design freedom and customization and disadvantages as slow production speed and costs. 3D printing is mostly used as an additional process when implementing the process in the textile and sportswear value chain.

O trabalho trata do desenvolvimento de processo de fabricação de compósitos de fibras longas através da tecnologia de manufatura aditiva, possibilitando a criação de peças com maior resistência mecânica através da combinação adequada de materiais com diferentes propriedades mecânicas. Os processos de manufatura aditiva consistem na obtenção de um objeto sólido a partir de um modelo digital de três dimensões, através do fatiamento deste modelo e da adição sequencial de material com o objetivo de criar suas respectivas camadas, permitindo a reprodução real do modelo digital escolhido. Um compósito é a combinação de materiais com diferentes propriedades para a obtenção de um novo material com características específicas, permitindo a criação de melhores arranjos de propriedades através da escolha adequada dos materiais a serem combinados. Os materiais que formam um compósito podem ser divididos em matriz e reforço, entre os quais, os materiais de reforço são responsáveis por suportar os carregamentos transmitidos pela matriz. O uso de materiais poliméricos reforçados resulta em um material com baixo peso e elevada resistência mecânica. A adição de fibras longas nos processos de manufatura aditiva é foco do estudo, no qual foi utilizada a tecnologia Fused Deposition Modeling devido à sua simplicidade e facilidade de acesso a equipamentos de baixo custo para fins de validação de conceito. Foi desenvolvido e construído um cabeçote de deposição contínua de fibras longas, adequado ao uso no processo de deposição por camadas, através do qual foram manufaturados corpos de prova, que foram ensaiados mecanicamente conduzindo a resultados satisfatórios, validando a técnica e indicando que a fabricação de polímeros reforçados através da tecnologia de manufatura aditiva é um processo promissor. / The work deals with the development of long fiber composite manufacturing process through additive manufacturing technology, enabling the creation of parts with higher mechanical strength through proper combination of materials with different mechanical properties. Additive manufacturing processes consist in obtaining a solid object from a three dimension digital model through the slicing of the model and the sequential addition of material layer by layer allowing the real reproduction of the digital model. A composite is a combination of materials with different properties to obtain a new material having specific characteristics, allowing the creation of the best arrangement of properties through the choice of materials to be combined. The materials that form a composite can be divided into matrix and reinforcement, where the reinforcing materials are responsible for supporting the loads transmitted by the matrix. The use of reinforced polymeric materials results in a material with low weight and high mechanical strength. The addition of long fibers in the additive manufacturing process is the focus of this study, where the Fused Deposition Modeling process was used due to its simplicity and facility to access low-cost equipment in order to validate the concept. The system developed was used to manufacture specimens which have been mechanically tested leading to satisfactory results, indicating a very promising process for the production of reinforced polymers by additive manufacturing technology.