Magister Scientiae - MSc / This study reports on the changes in the structural properties of a tungsten-filament when exposed to a methane / hydrogen ambient for different durations at various filament-temperatures. / South Africa

I och med att additiv tillverkning blir allt vanligare i dagens samhälle kommer dess ekologiska, samt ekonomiska effekter bli alltmer tydliga och viktiga att ta i beaktning. Tekniken utvecklas och är numera tillgänglig för i stort sett alla. Detta har gjort att 3D-skrivare bland privatpersoner blivit vanligt förekommande. Det har lett till att mer filament går åt till användning av 3D-skrivare, vilket också leder till att mer material går till spillo. Ett av de vanligaste filamentmaterialen inom detta område är PLA. PLA har många fördelar när det kommer till 3D-skrivning, en av nackdelarna är dock svårigheten med att ta till vara på spillmaterialet då det är svårt att återvinna. Detta bidrar till ett ökat behov av att kunna återvinna filamentet själv, och vad kan då vara bättre än att göra det till nytt filament som kan användas igen? Detta är bra ur både ekonomiska och ekologiska hållbarhetsaspekter. Av denna anledning har en extruderingsmaskin designats så att privatpersoner och mindre aktörer ska kunna bygga en egen. På så sätt kan de ta hand om sitt spillmaterial på ett vis som närmar sig en cirkulär ekonomi. Projektet inleddes med en bakgrundsundersökning för att undersöka befintliga lösningsalternativ som redan finns och för att få tips och inspiration. Sedan genomfördes en idégenereringsprocess för att ta fram så många idéer som möjligt för att därigenom förbättra möjligheterna till att hitta en exceptionell lösning. När ett koncept hade valts gjordes jämförelser mellan olika komponenter. Sedan gjordes beräkningar på de valda komponenterna. Detta för att kunna dimensionera dem, delvis för att vara säker på att den håller, men även för att veta hur mycket värme och mekanisk energi som kommer att behöva tillföras i maskinen för att den ska fungera som tänkt. Ett komplett designförslag har tagits fram tillsammans med dimensioner på komponenter för att underlätta för ett eventuellt privat byggprojekt av denna extruderingsmaskin. Vissa ändringar kan göras beroende på budget och tillgänglighet av komponenter. De ändringar som görs kan leda till att även beräkningar behöver göras om eller justeras. Flera av måtten och dimensionerna på vissa komponenter kan ses som överdrivna, detta är på grund av att de ska klara det högsta tryck och krafter som kan uppstå. Dessa uppstår enbart när det satt stopp i matrisen. Att det sätter stopp helt och hållet kommer troligtvis vara ovanligt, men om det händer är det viktigt att maskinen klarar av ett sådant stopp. Till sist kommer alla inställningar behöva justeras och testas på egen hand. Detta är på grund av att maskinen inte har byggts, utan enbart är ett koncept. Dessutom kommer den troligtvis fungera lite annorlunda för alla som bygger den då det kommer att vara skillnader i montering och komponenter. / In today's society additive manufacturing is getting more and more common. The technique is developing and is within reach for almost everyone. It is within the private sector the biggest growth of popularity can be seen. The increased usage of this technology has led to increased usage of plastic within this field. This means that the waste has increased as well. One of the most common materials for 3D-printing is PLA, this is because of a few different benefits. Although it has its cons, one of the bigger drawbacks is that it is hard to recycle. There are very few recycling facilities that can take care of PLA. This means that it is necessary to find another way to handle the otherwise wasted PLA. One way to do this is by making it possible for people to do it themselves, therefore the goal of this project, to develop an extruder for individuals. The extruder is supposed to use old PLA-prints to make new filament. This is good from an ecological perspective as well as an economic one. The extruder is designed to make it possible for the user to assemble it on their own. The project started with a background search, this was to get a better picture of the problem, but also to see what alternative solutions already exists. After this the phase of brainstorming as many ideas as possible started. When a concept had been chosen it was developed even further and calculations were done to ensure that it would work as intended. The calculations contained aspects such as strength of the base and pipe, but also the amount of energy needed from the motor and heaters to fulfill their respective functions. A complete design proposal for the extruder has been established, this together with supporting calculations and measurements for the different components. A few changes can be done to modify the machine for individual needs, however the calculations might have to be adapted depending on the changes that are made. A few of the dimensions on certain components might seem exaggerated. This is because they need to be able to handle the highest pressures and forces that may occur. These pressures and forces are only reached when the machine gets clogged up. The machine clogging should be unusual, but once it happens it might break without proper dimensions. At last smaller adjustments might have to be made by the user. This is because the machine has not been built, it is just a concept. Also, there will be differences depending on what specific component is chosen and the individual assembling process.

Advanced composites are extremely strong, rigid, and light, even when compared with advanced metals. Advanced composites are replacing high-tech metals as the material of choice for aerospace engineering. However, the processes used to manufacture advanced composites generally lose some of the properties of the materials by their process limitations. One process that keeps the theoretically awesome qualities of the composite materials in tact is filament winding. Filament wound parts are used as rocket shells, bicycle frame tubes, drive shafts, pressure vessels, etc. Filament winding is an automated process and makes reliable parts to close tolerances. If a straight tube were to be made by all the existing composites manufacturing processes, filament wound tubes would be significantly better than any other. However, filament winding is generally limited to making straight tubes. A new process based on filament winding is proposed; one that can wind complex shapes of the same high quality as conventional filament winding. This process has achieved this by winding continuous, uncut, and aligned fibers. This process is called Lotus Filament Winding.

La fabrication additive est un procédé d’élaboration permettant la mise en forme d’une pièce par ajout de matière, par empilement de couches successives. Bien que de plus en plus de polymères puissent être mis en œuvre par cette technologie, les polymères chargés en sont quasiment absents, alors qu’ils sont largement utilisés dans les autres types de procédés de mise en forme. Les objectifs scientifiques et technologiques du projet concernent (i) une meilleure compréhension des relations entre le comportement rhéologique de systèmes polymères et leur aptitude à la mise en forme par les technologies de fabrication additive FDM, (ii) le développement de formulations de base de polymères bio-sourcés adaptées à ces technologies et apportant une multifonctionnalité. Le premier objectif nécessitera tout d’abord d’identifier les conditions (température, gradients de vitesse, nature des contraintes, …) imposées par les procédés considérés puis de mettre en place et/ou d’adapter les moyens de caractérisation du comportement rhéologique des systèmes polymères dans ces conditions. Le comportement rhéologique en cisaillement mais aussi en élongation pourra être considéré. Il conviendra en particulier d’identifier les compromis nécessaires entre comportement adapté à l’écoulement en filière ou en buse et aptitude à la fusion et à la consolidation couche par couche. Enfin, l’effet des différentes voies de fonctionnalisation envisagées sur le comportement rhéologique et thermique et donc sur l’aptitude à la mise en forme devra être analysé. De façon à adapter les polymères bio-sourcés à un large panel d’applications, diverses voies de fonctionnalisation seront considérées, basées sur le compoundage avec des charges particulaires. / Additive manufacturing process is a preparation for the forming of a workpiece by the addition of material, by stacking successive layers. Although more and more polymers can be implemented by this technology, the filled polymers are practically absent, so they are widely used in other types of shaping methods. The scientific and technological objectives of the project are (i) a better understanding of the relationship between the rheological behavior of polymer systems and their ability to shaping by additive manufacturing technologies FDM, (ii) the development of polymer-based formulations biosourced adapted to these technologies and providing multifunctionality. The first goal will require first of all to identify the conditions (temperature, velocity gradients, nature constraints ...) imposed by the processes considered then to implement and / or adapt the means of characterization of the rheological behavior of polymer systems under these conditions. The rheological behavior in shear but also in elongation may be considered. It should in particular identify the necessary compromise between behavior adapted to the flow at the die or nozzle and meltability and consolidation layer by layer. Finally, the effect of different ways of functionalization considered on the rheological and thermal behavior and thus on the ability to formatting will be analyzed. In order to adapt the bio-sourced polymers for a wide range of applications, various routes of functionalization will be considered based on compounding with particulate fillers.

Estudos recentes em medicina regenerativa utilizam estruturas de crescimento celular conhecidas como scaffolds: um scaffolds é uma estrutura porosa feita de material biodegradável. Essas estruturas ajudam na formação e reconstituição de novos tecidos, servindo como suporte para o crescimento e proliferação celular. Esses podem ser fabricados utilizando processos de manufatura aditiva (MA). O processo utilizado na pesquisa foi o FFF (Fused Filament Fabrication), que se baseia em fundir polímero e extrudá-lo em forma de filamento para produção de peças tridimensionais para confecção dos scaffolds. O polímero utilizado na pesquisa foi o ácido poliláctico (PLA), por ser biocompatível. Uma possível forma de aumentar a rugosidade de superfície é gerar uma geometria diferente na seção transversal do filamento extrudado que forma o scaffold. Assim, o scaffold adquiriria a micro-rugosidade ou nanorrugosidade (rugosidade superficial do material utilizado e inerente do processo), e a macrorrugosidade (geometria gerada ao longo de seu comprimento): a micro-rugosidade, para fins deste trabalho, será considerada como a rugosidade (acabamento de uma superfície); a macrorrugosidade (ou macrogeometria) será considerada, para fins deste trabalho, como a textura que se apresenta na forma de uma seção transversal de um filamento extrudado. Para gerar essa macrotextura, é necessário gerar na ferramenta bico extrusor uma geometria diferente na saída do bico. Geralmente, na saída do bico extrusor é feito um furo de geometria circular. Foi proposto neste estudo utilizar uma geometria diferente de um círculo na saída do bico, geometria essa a ser transferida ao filamento durante o momento da extrusão. A alteração desta geometria requer a utilização de técnicas não convencionais de usinagem. Neste projeto foram produzidos filamentos modificados a fim de melhorar a citocompatibilidade no scaffold. A morfologia foi analisada in vitro e o novo bico gerou filamentos impressos com diferenças na citocompatibilidade e com mudanças nos aspectos morfológicos das células quando comparadas àquelas aderidas aos filamentos convencionais. / Recent studies in regenerative medicine use cell growth structures known as scaffolds: a scaffold is a porous structure made of biodegradable material. These structures aid in the formation and reconstitution of new tissues, serving as a support for cell growth and proliferation. They are manufactured using additive manufacturing (AM) processes. The technology executed in this research was the FFF (Fused Filament Fabrication), which is based on melting polymer in the form of a filament and extruding it for the production of three-dimensional parts for the manufacture of scaffolds. The polymer used in this research was the polylactic acid (PLA), which was used because it is biocompatible. One possible way to increase surface roughness is to generate a geometry in the cross section of the extruded filament forming the scaffold. Thus, the scaffold would acquire the micro-roughness or nano roughness (surface roughness of the material used and inherent in the process), and the macro-roughness (texture generated along its length): the micro-roughness, for purposes of this work, will be considered a roughness (surface finish); The macro-roughness (or macro-geometry) will be considered, for purposes of this work, as the texture which is in the form of a cross-section of an extruded filament. To generate this texture (macro-roughness) it is necessary to generate a macro-geometry in the nozzle extruder tool. Usually at the exit of the extruder nozzle is made a hole of circular geometry. It was proposed in this study to use a geometry different from a circle at the exit of the nozzle to be transferred to the filament during the moment of the extrusion. Altering this geometry requires the use of non-conventional machining techniques. In this project modified filaments were produced in order to improve cytocompatibility and for cell differentiation in the scaffold. The morphology was tested in vitro and the new nozzle was able to generate printed filaments with differences in cytocompatibility and with changes in the morphological aspects of the cells when compared to those adhered to the conventional filaments.

Cette thèse est consacrée à la mécanique et à la mécanique statistique de biofilaments/biopolymères et de leur modèle le plus répandu le Worm-Like Chain (WLC) qu’il s’avère nécessaire d’étendre. Nous étudions WLC à 2-d en présence d’obstacles plus proches que la longueur de persistance. Nous caractérisons le mouvement aux temps courts par des simulations numériques complétées par des calculs analytiques. Des concepts similaires servent à décrire des ADN greffés balayés par le front d’une vésicule en cours d’étalement, l’adhésion de la vésicule est promue par des paires biotine/streptavidine qui contraignent les molécules d'ADN sur des chemins étroits où ils peuvent être imagés. Les microtubules (MT) ici stabilisés au taxol, présentent par contre certains comportements qui échappent au WLC et doivent être ramenés à leur structure interne : i)les déflexions latérales d’un MT attaché par un bout correspondent à une longueur de persistance apparente qui augmente avec la longueur ii) les MT adoptent des formes super-hélicoïdales. Ces deux points sont établis au moyen d’analyses de forme des MT. Des transitions de forme corrélées le long du MT mises en évidence sont compatibles avec un modèle basé sur la bistabilité du dimère de tubuline. Finalement un modèle de chaîne super-hélicoïdale comprenant une courbure et une torsion spontanées élargi le WLC. Confiné à 2-d, HWLC peut adopter un état fondamental circulaire ou sinueux caractérisé par le nombre de points d’inflexion où se concentre la torsion (twist-kink). Dans le cas circulaire, il existe des états métastables proches, à petit nombre de twist-kinks, hyperflexibles. / This PhD is devoted to the mechanics and statistical mechanics of biofilaments and their most widespread model, the Worm-Like Chain (WLC) model, which, as it turns out, needs to be extended. We study the WLC in 2-d in the presence of obstacles closer than their persistence length. We characterize the short time motion by numerical simulations complemented by analytical calculations. Similar concepts serve to describe grafted DNAs swept by the front of a spreading vesicle whose adhesion is promoted by biotin/streptavidin bonds, which constrain the DNAs on narrow paths where they can be imaged. Microtubules (MT), here stabilized by taxol, show features which cannot be rationalized by the WLC and shall be related to their internal structure : i)lateral deflections of a clamped MT correspond to an effective persistence length growing with the MT size ii) MT adopt super-helical shapes. These two points are proven by refined image analysis. We analyze shape transitions correlated along the MT which are compatible with a model based on dimer bi-stability. Finally, a super helical chain model (HWLC) allowing for spontaneous curvature and twist is developed which extends the WLC. When confined to 2-d, the HWLC can adopt a ground state which is circular or wavy with inflection points where twist accumulates, so-called twist-kinks. In the circular case there exist close metastable states, with a small number of twist-kinks, which are hyperflexible.

Vortex breakdown is an important phenomenon observed in swirling flows involving the development of a stagnation point on the axis of the vortex followed by a region of recirculation when the swirl increases beyond a particular level. It has been studied extensively over past 50 years and various theories have been proposed to explain its various aspects. However, a single model explaining all the aspects together is yet to emerge. Numerical simulations of breakdown have been performed using a variety of grid-based as well as vortex methods. Vortex methods are a Lagrangian alternative to grid-based methods wherein the motion of the vorticity is determined by the local fluid velocity convection, with models for viscous effects when considered. The fluid velocity is obtained from the vorticity field. Only the rotational regions of the flow need to be considered leading to significant economy of computational effort for simulations of vorticity dominated flows, such as vortex breakdown. The inviscid vortex filament method has been used to simulate several aspects of the vortex breakdown phenomenon. The vortex filament method however, cannot easily simulate viscous effects. To simulate the viscous effects the viscous vortex particle method needs to be used. This work was intended to be a first step towards this end by initially evaluating the effectiveness of the inviscid version of the vortex particle method in simulating the breakdown phenomenon. The inviscid vortex particle method was found to satisfactorily simulate most qualitative aspects involved in the formation of vortex breakdown such as the retardation of axial velocity along centerline, radial swelling of the vortex core, formation of stagnation points, creation of azimuthal vorticity gradient from axial vorticity gradient and the turning of vortex lines along with the formation of a bubble-like structure with recirculating flow within. The effect of a wall placed adjacent to the vortex core was simulated by using image vortices. The wall was not found to influence the location of breakdown. However, the initiation of the spiral mode was found to occur earlier when a wall was present. For a quantitative assessment, a simulation of the experimental results of Faler and Leibovich (1978) was attempted. The simulation managed to predict the location of the breakdown and the extent of the bubble. The shape and height of the bubble obtained however were not in accord with the experimental observations. A single vortical cell was obtained in the interior of the bubble.

The idea underlying the present study was to apply twisting in order to introduce different levels of transverse pressure. The modified structure affected both the bonding level and the evolution of the damage in the yarn. In order to isolate this effect in a broader context, additional parameters were included in the experiment design, namely effects of loading rate, specimen length and filament diameter (directly linked to the fineness of the yarn). These factors have been studied in various contexts by several authors. Some related studies on involved factors will be briefly reviewed.

Many active processes in cells are driven by highly specialised motor proteins, which interact with the cytoskeleton: a network of filamentous structures, e.~g.~ actin filaments and microtubules, which organises intracellular transport and largely determines the cell shape. These motor proteins are able to transduce the chemical energy, stored in ATP molecules, to do mechanical work while interacting with a filament. Certain motor proteins, e.~g.~members of the KIN-13 kinesin subfamily, are able to interact specifically with filament ends and induce depolymerisation of the filament ends. One important role for KIN-13 family members is in the mitotic spindle, a microtubule structure that is formed in the process of cell division and is responsible for separation and distribution of the duplicated genetic material to the forming daughter cells. The aim of this work is to develop a theoretical framework capable of describing experimentally observed behaviour and shed light on underlying principles of motor induced filament depolymerisation. We use two different theoretical approaches to describe motor dynamics in this non- equilibrium situation: On the one hand we use phenomenological continuum equations which themselves are to a large extent independent of the underlying molecular details of the system. Molecular details of the system are incorporated in the equations through the specific values of macroscopic parameters which are determined by the underlying details. On the other hand, we use one- and two-dimensional discrete stochastic descriptions of motors on a filament. These kind of descriptions enable us to investigate the effects of different microscopic mechanisms of filament depolymerisation, and to investigate the role of fluctuations on the dynamic behaviour of motor proteins. We additionally discuss filament depolymerisation in the case where motors are not free to move but are fixed to a common anchoring point and depolymerise filaments under the influence of applied forces, mimicking the situation in the mitotic spindle. Our results can be related to recent experiments on members of the KIN-13 subfamily and predictions made in our theory can be tested by further experiments. Although motivated by experiments involving members of the KIN-13 subfamily, our theory is not restricted to these motors but applies in general to associated proteins which regulate dynamics of filament ends.

O objetivo deste trabalho foi estudar o comportamento mecânico de cilindros de compósito polimérico reforçado com fibras. Para isso, foram produzidos cilindros com extremidades abertas reforçados com fibra de basalto e fibra de vidro, utilizando a técnica de enrolamento filamentar (filament winding). Estes cilindros foram submetidos a ensaio hidrostático com carregamento circunferencial, ensaio de ruptura de anel (split disk test) e ensaio de resistência ao cisalhamento interlaminar (ILSS). Uma placa do compósito de fibra de basalto foi produzida por enrolamento filamentar, para caracterização por ensaio de resistência à tração. Todos cilindros submetidos ao ensaio hidrostático apresentaram fratura localizada em uma faixa de altura do cilindro, com extensas delaminações das camadas circunferenciais. Os compósitos epóxi/fibra de basalto superaram ou igualaram os de compósito epóxi/fibra de vidro nas comparações entre resultados dos valores das propriedades mecânicas avaliadas, nas porcentagens: resistência à tração aparente de ruptura de anel em 45% e 43% em resistência específica; ILSS, em 11%; resistência/tensão de membrana de ruptura no ensaio hidrostático, em 55%. / The aim of this work was to study the mechanical behavior of fiber reinforced polymer composite cylinders. For this purpose, cylinders reinforced with basalt and glass fibers were produced, with open-ended geometry, using filament winding technique. These cylinders were submitted to hydrostatic test under circunferential loading, split disk (ring segment) test and interlaminar shear strength (ILSS). A basalt fiber composite plate was produced by filament winding for characterization by tensile strength test. All cylinders submitted to hydrostatic test presented fracture located in the height range of the cylinder, with extensive delamination of the circumferential layers. The epoxy/basalt fiber composites overcame or equated the epoxy/glass fiber composites in comparisons between results of the mechanical properties, tensile strength in split disk, in 45% and 43% in specific strength; ILSS in 11%; membrane tensile strength in the hydrostatic test, in 55%.