Les procédés additifs, auxquels appartient la fusion laser de poudres métalliques, ont la capacité de créer des structures à géométries complexes, avec la possibilité d'intégrer des formes creuses, par exemple des canaux de refroidissement assurant un contrôle thermique optimum. Ce procédé permet de fabriquer des pièces réelles à partir de poudres métalliques, par fusion du matériau, couche par couche, en accord avec le modèle CAO. Au cours du procédé, de nombreux cycles thermiques et d'importants gradients thermiques se produisent dans la pièce au cours de sa fabrication. Ces gradients de température induisent des déformations plastiques hétérogènes et de ce fait des contraintes résiduelles. Ces contraintes peuvent nuire à la qualité de la pièce obtenue, par exemple sa résistance mécanique. Ces travaux ont pour objectifs de proposer un modèle numérique, s’appuyant sur la méthode des éléments finis afin d'étudier l'apparition des contraintes résiduelles lors du procédé de fusion laser de poudres métalliques. Le logiciel multiphysique ABAQUS® a été utilisé pour effectuer les analyses thermiques et mécaniques. La technique « d'ajout et de suppression des éléments » a été utilisée afin de simuler la fusion et la solidification de la matière au cours du procédé. Les propriétés mécaniques dépendantes de la température de l'acier maraging, utilisé dans notre cas, ont été obtenues à l’aide d’essais expérimentaux de caractérisations et intégrées dans le modèle. Les calculs sont réalisés de manière découplée, dans un premier temps le calcul thermique est effectué, puis les résultats sont utilisés pour réaliser le calcul mécanique et finalement prédire les champs de contraintes. Dans le cadre de ce travail, une méthode originale s'appuyant sur la technique de mesure des contraintes résiduelles par enlèvement de couches successives a été mise au point pour mesurer ces contraintes en direct au cours du procédé. Les résultats renseignent sur le niveau et la distribution des contraintes dans la pièce créée et le support. Deux paramètres ont été testés afin d'étudier leur influence sur le niveau des contraintes résiduelles : le temps d’étalement de la poudre entre deux couches successives et la hauteur des couches. Le modèle numérique paramétrable permet d'analyser les effets de paramètres liés au procédé sur la répartition des contraintes résiduelles dans les pièces fabriquées. Les résultats montrent que la variation de l'épaisseur du support n'affecte pas la répartition des contraintes dans la pièce créée. Le préchauffage du support à une température de 800°C réduit les contraintes résiduelles L'étude de quelques trajectoires laser montre leurs influences sur la répartition des déformations plastiques cumulées ainsi que la hauteur des couches de poudres ou de la forme du support (embase, colonnes). / The Selective Laser Melting process, belonging to Additive processes , have the ability to create structures with complex geometries , with the possibility of including cavities, such as cooling channels providing optimum temperature control. This process enables the manufacture of three-dimensional parts from metal powders by melting the material , layer by layer, in agreement with the CAD model. In the process , high temperatures and thermal gradients cycles occur in the part during the process. These temperature gradients induce heterogeneous plastic strain and residual stresses. These residual stresses may affect the quality of the part obtained, for example the fatigue life. This work aims to propose a numerical model , based on the finite element method to study the appearance of residual stresses during laser melting process of metallic powders . The ABAQUS® Multiphysics software was used to perform the thermal and mechanical analyzes. The movement of the laser beam and the resolution of the thermal problem can predict the evolution of the temperature in the part and support. The "birth and death elements" technique was used to simulate the melting and solidification of the material during the process. Dependent mechanical properties of the temperature of the maraging steel used in this case were obtained using experimental testing and characterization and were established in the model. The calculations are decoupled : initially thermal calculation is performed and the results are used to perform mechanical calculations and finally predict the residual stress fields. In this work, a novel method based on the technique of measuring residual stresses by removing layers was developed to measure these stresses directly in the process. The results provide information on the level and distribution of stresses in the created part and support. Two parameters were tested to study their influence on the level of residual stress : time to spread the powder between two successive layers and layer height. The model is used to analyze the effects of process parameters related to the distribution of residual stresses in the manufactured parts. The results show that the variation of the thickness of the support does not affect the distribution of stresses in the part created. Preheating the substrate to a temperature of 800 °C reduces the residual stresses. The study of some laser strategies shows their influence on the distribution of plastic strain thus the height of the layers of powder or in the form of support (base, columns).

Les polymères semi-cristallins à chaînes semi-rigides, bien qu’abondamment utilisés dans la vie quotidienne, représentent des systèmes complexes qui ne sont pas encore parfaitement compris. Parmi les nombreux domaines de recherche sur cette famille de polymères, l’étude de la morphologie semi-cristalline et des processus de cristallisation et de fusion de ceux-ci restent des sujets très importants. L’investigation de la morphologie semi-cristalline est rendue difficile car elle présente une structure hiérarchique composée de plusieurs niveaux d’organisation, dont le plus petit est observable à une échelle très réduite de quelques nanomètres. De plus, les aspects liés à la cinétique des processus de cristallisation et de fusion n’ont pas toujours permis de bien les mettre en évidences, les rendant ainsi par très bien compris. Cependant, les nouvelles avancées technologiques dans le domaine de la physique expérimentales ont beaucoup profité à la science des polymères. <p>Dans ce travail, une contribution originale est apportée à cette étude, et cela en combinant diverses techniques expérimentales permettant des mesures calorifiques et structurales en températures et temps réels. L’intérêt c’est porté sur les polymères linéaires aromatiques tels que le polyéthylènes teréphthalate, PET, et le polytriméthylène téréphthalate, PTT, caractérisés par une température de transition vitreuse supérieure à l’ambiante ( Tg > 50°) et une température de fusion élevée (Tm>220°C), offrant ainsi une assez large gamme de température de cristallisation (Tm-Tg). L’étude de la structure semi-cristalline du PET à l’échelle du nanomètre et de la relaxation des phases amorphes présentes dans sa structure est facilitée par l’utilisation d’un diluant amorphe tel que le polyétherimide (PEI), qui forme un mélange miscible avec le PET. <p>L’utilisation de microscopie de force atomique AFM à haute température a permis d’observer la cristallisation isotherme de PET en temps réel et de décrire ainsi la cristallisation secondaire comme un processus d'épaississement des piles lamellaires. De plus, l’analyse de la structure semi-cristalline du PET et du PTT, dans l’espace direct, sont en faveur d’un modèle structural homogène, où l’épaisseur lamellaire moyenne est légèrement inférieure à l’épaisseur moyenne des régions amorphes interlamellaires. Ces résultats ont permis, d’une part, d’apporter une meilleure interprétation aux données obtenues par diffusion des rayons X aux petits angles (SAXS), et d’autre part, d’ interpréter le comportement de fusion multiple caractéristique des polymères semi-cristallin à chaînes semi-rigides par le seul processus de fusion-recristallisation. Dans l’étude investiguée sur les mélanges PET/PEI et sur le PTT pur, on montre que la cinétique d’un tel processus est particulièrement rapide comparée à la cristallisation. De plus, les observations par AFM et par microscopie optique de même que les mesures SAXS en temps réel ont montré la simultanéité et la compétition existant entre la fusion des cristaux et leur réorganisation durant la chauffe. Par ailleurs, la relaxation des régions amorphes interlamellaires, souvent considérées comme rigides, a pu être mise en évidence par les mesures AFM et SAXS réalisées à haute température sur des échantillons de PET/PEI semi-cristallins.<p> / Doctorat en sciences, Spécialisation physique / info:eu-repo/semantics/nonPublished

The thesis focuses on exploring the sub-grain structure in stainless steel 316L prepared by additive manufacturing (AM). Two powder-bed based AM methods are involved: selective laser melting (SLM) and electron beam melting (EBM). It is already known that AM 316L has heterogeneous property and hierarchy structure: micro-sized melt pools, micro-sized grains, nano-sized sub-grain structure and nano-sized inclusions. Yet, the relation among these structures and their influence on mechanical properties have not been clearly revealed so far. Melt pool boundaries having lower amount of sub-grain segregated network structures (Cellular structure) are weaker compared to the base material. Compared with cell boundaries, grain boundaries have less influence on strength but are still important for ductility. Cell boundaries strengthen the material without losing ductility as revealed by mechanical tests. Cellular structure can be continuous across the melt pool boundaries, low angle sub-grain boundaries, but not grain boundaries. Based on the above understanding, AM process parameters were adjusted to achieve customized mechanical properties. Comprehensive characterization were carried out to investigate the density, composition, microstructure, phase, magnetic permeability, tensile property, Charpy impact property, and fatigue property of both SLM and EBM SS316L at room temperature and at elevated temperatures (250°C and 400°C). In general, SLM SS316L has better strength while EBM SS316L has better ductility due to the different process conditions. Improved cell connection between melt pools were achieved by rotating 45° scanning direction between each layer compared to rotating 90°. Superior mechanical properties (yield strength 552 MPa and elongation 83%) were achieved in SLM SS316L fabricated with 20 µm layer thickness and tested in the building direction. Y2O3 added oxide dispersed strengthening steel (ODSS) were also prepared by SLM to further improve its performance at elevated temperatures. Slightly improved strength and ductility (yield strength 574 MPa and elongation 90%) were obtained on 0.3%Y2O3-ODSS with evenly dispersed nanoparticles (20 nm). The strength drops slightly  but ductility drops dramatically at elevated temperatures. Fractographic analysis results revealed that the coalescence of nano-voids is hindered at room temperature but not at elevated temperatures. The achieved promising properties in large AM specimens assure its potential application in nuclear fusion. For the first time, ITER first wall panel parts with complex inner pipe structure were successfully fabricated by both SLM and EBM which gives great confidence to application of AM in nuclear industry. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.</p>

Background: Critically ill patients are at particular risk of developing bloodstream infection. Such infections are associated with the development of sepsis, leading to a marked increase in mortality rate. Early detection of the causative organism and appropriate antibiotic treatment are therefore critical for optimum outcome of patients with nosocomial infection. Current infection diagnosis is based on standard blood culture techniques. However, microbiological culture has a number of limitations, not least that it takes several days to confirm infection and is therefore not useful in directing the early treatment with antibiotics. New techniques based on the detection of pathogen DNA using real-time polymerase chain reaction (PCR) technology have the potential to address these limitations but their clinical utility is still to be proved. Objectives: Develop and evaluate novel PCR-based approaches to bloodstream infection diagnosis in critical illness based on detection and identification of bacterial and fungal DNA in blood. Methods: A range of commercial and 'in-house' PCR-based assays for detection of bacterial and fungal DNA were developed and/or optimised for use in clinical blood samples. These included LightCycler SeptiFast, a CE-marked multi-pathogen assay for common bloodstream pathogens, BactScreen and GramScreen, broad spectrum bacterial assays based on 16S rRNA gene and real-time PCR assays developed to detect a range of clinically important fungal pathogens. Novel approaches to speciation of pathogen DNA using melting temperature (Tm) profiling and high resolution melting analysis (HRMA) were developed. Clinical evaluation of assays was either on blinded clinical isolates or blood samples from critically ill patients with clinical suspicion of bloodstream infection against conventional microbiological culture. Several techniques aimed at improving extraction of pathogen DNA from blood were also investigated. Results: The CE-marked commercial assay SeptiFast showed analytical sensitivity and specificity of 79% and 83% respectively. Concordance with positive culture results was good but high levels of 'false positives' were detected possibly attributed to detection of free pathogen DNA not associated with viable pathogens. The predictive value of a negative SeptiFast test was 98% suggesting that absence of pathogen DNA is a strong indicator of absence of infection. Further studies were aimed at detailed optimisation and validation of 16S rRNA gene real-time PCR assays for bacterial DNA. BactScreen and GramScreen were able to detect a broad range of clinically important bacteria down to <50 CFU/ml blood. A preliminary comparative evaluation against SeptiFast showed BactScreen gave excellent concordance with blood culture results with minimal false positive results compared to SeptiFast. Efficient extraction of pathogen DNA was shown to be a key factor in determining analytical sensitivity and several protocols were evaluated. Low cost approaches to speciation of bacterial DNA were developed by combining broad range real-time PCR with HRMA. A novel HRMA method based on Tm profiling was shown to identify 89% and 96% of blinded clinical isolates at species or genus level respectively. Real-time PCR/HRMA approaches were also successfully developed for detection and identification of fungal pathogens including a range of Candida and Aspergillus species associated with bloodstream fungal infection. Conclusions: These studies have highlighted some of the key factors that need to be considered when developing and validating PCR based assays for pathogen DNA detection in blood. A set of novel tools have been developed for rapid detection and identification of bacterial and fungal pathogens that could address the challenges of infection diagnosis based on pathogen DNA detection. Further work is required, not least in development of more efficient pathogen DNA extraction and detailed clinical validation but the tools described here have the potential to provide cost effective solutions to aid infection diagnosis that would be complementary to current culture-based methods. The provision of time critical information could have a positive impact on clinical decision-making leading to more effective management and treatment of patients with suspected bloodstream infection.

The thesis deals with optimization of the manufacturing process of the muzzle device designed for assault rifle. The most common titanium alloy named Ti-6Al-4V was chosen for this task. The introduction summarizes previously existing types of muzzle devices and further describes the SLM technology with a special focus on titanium alloys processing. The optimization methods and their follow-up testing were designed according to theoretical knowledge that is summarized in the theoretical part of this work. Firstly, the aim was to describe the optimization of the manufacturing process with attention to preserving the relative density of the parts. Secondly, the mechanical properties of the parts that underwent different heat treatment were tested.The obtained data were then used to design and manufacture a muzzle device that underwent further testing in real condition afterwards.

This diploma thesis describes the design of filling element with trabecular structure for revision implant of total knee arthroplasty. Design of the filling element is created by the digital data of the patient tissue. Production of a functional sample is performed using additive technology Selective Laser Melting. This work also include analyze of the accuracy of this technology for the production of titanium alloy Ti6Al4V.

>Magister Scientiae - MSc / As human beings we are curious about our origin and ancestry. A curiosity has led to an investigation of human evolution and expansion across the world by means of population genetics and phylo-genetics by evaluating a region in Southern Africa that is largely unknown. The objective of this study was to develop a quick, inexpensive and accurate hierarchical diagnostic screening system of the MtDNA phylogenetic tree, AI-SNPs in the mtDNA genome by using High Resolution Melting analysis to evaluate the population composition and ancestral haplogroups of Southern African populations in Limpopo. The admixture between the ‘Khoesan’ hunter-gatherers, herders and the Bantu speaking populations led to population growth and expansion in Limpopo. This has contributed to populations settling in Limpopo and has thus shaped the ancestral contemporary populations. No research on these individuals residing in Limpopo has been done before, thus an investigation of their ancestral origin was necessary. A total of 760 saliva samples were collected from individuals residing in Limpopo. Only 500 saliva samples were extracted by means of an optimized salting out technique. Five hundred extracted genomic samples were genotyped by means of a quick, inexpensive High-resolution melting analysis. Of the 500 samples, the genotyping results showed 95 individuals derived for the L3 haplogroup which gives a 19% ratio of individuals screened with Multiplex 1. Only 56 individuals were derived for the L1 haplogroup, which gives a percentage of 11%. A total of 249 individuals were derived for the L0 haplogroup, making up a 50% of the total individuals genotyped. Only 100 samples were derived for L0a, making up 20% of individuals screened with Multiplex 1. Of the 95 samples derived for the L3 haplogroup, the results showed 87 individuals to be ancestral for both M and N, making up 91.57% of individuals screened with Multiplex 2. http://etd.uwc.ac.za/. In population genetics using SNPs to infer population history and ancestral origin has become significant, this study allowed researchers to evaluate population groups by investigating their genetic markers and the application of the results allowed for downstream analyses. Finally, this study provides a quick and simple screening method for the selection of lineages that are of interest for further studies.

The aluminium industry is anticipated to witness a surge in demand, with projectionsof a two to three-fold increase by 2050. Meeting environmental objectives andaddressing the growing emphasis on sustainability from both the industry andconsumers seeking eco-friendly products present significant challenges. Energyefficiency will be crucial in addressing these concerns. While primary aluminiumproduction consumes the majority of energy in the industry, the die-casting sector, asan energy-intensive segment, offers opportunities for enhancing energy efficiency. Inhousealuminium smelting in high-pressure die-casting (HPDC) foundries, primarilyemploying gas-fired shaft furnaces with preheating for improved energy efficiency, isa significant energy user.This research examines energy efficiency in High-Pressure Die Casting (HPDC)foundries, particularly in-house aluminium smelting. Utilizing literature reviewsand expert interviews, the study reveals efficient technologies, drivers and barriersto energy efficiency, and the importance of sustainability. The current absence ofwell-defined Best Available Techniques (BAT) and the absence of validated claims bymanufacturers in the HPDC sector emphasize the urgent need for extensive researchand empirical verification.The results from this study show that using gas-fired shaft furnaces is the optimalchoice for the next decade, with waste heat recovery as the primary energy efficiencymethod, supplemented by the implementation of energy management systems andstrategies. Induction furnaces may emerge as a viable future technology, contingenton significant electricity network expansion and low energy prices.

Additive Manufacturing (AM) using the Powder Bed Fusion (PBF) is a relatively new manufacturing method that is capable of creating shapes that was previously practically impossible to manufacture. Many think it will revolutionize how manufacturing will be done in the future. This thesis is about some aspects of when and how to Design for Additive Manufacturing (DfAM) when using the PBF method in metal materials. Designing complex shapes is neither easy nor always needed, so when to design for AM is a question with different answers depending on industry or product. The cost versus performance is an important metric in making that selection. How to design for AM can be divided into how to improve performance and how to improve additive manufacturability where how to improve performance once depends on product, company and customer needs. Using advanced part shaping techniques like using Lattices or Topology Optimization (TO) to lower part mass may increase customer value in addition to lowering part cost due to faster part builds and less powder and energy use. Improving PBF manufacturability is then warranted for parts that reach series production, where determining an optimal build direction is key as it affects many properties of PBF parts. Complex shapes which are designed for optimal performance are usually more sensitive to defects which might reduce the expected performance of the part. Non Destructive Evaluation (NDE) might be needed to certify a part for dimensional accuracy and internal defects prior use. The licentiate thesis covers some aspects of both when to DfAM and how to DfAM of products destined for series production. It uses design by Lattices and Topology Optimization to reduce mass and looks at the effect on part cost and mass. It also shows effects on geometry translation accuracies from design to AM caused by differences in geometric definitions. Finally it shows the effect on how different NDE methods are capable of detecting defects in additively manufactured parts.

The isothermal crystallization and melting temperatures of poly(ε-caprolactone) were correlated using fast differential scanning calorimetry. The melting kinetics was found to be independent of isothermal crystallization temperature and time. The conventional Hoffman-Weeks method could not be used to determine the equilibrium melting temperature because the observed melting temperatures were greater than the crystallization temperatures by a constant, so the Gibbs-Thomson method was used instead, yielding an equilibrium melting temperature of 103.4 ± 2.3°C. A modification was proposed to the non-linear Hoffman-Weeks equation that included a non-linear undercooling dependence for the kinetic fold surface free energy upon crystallization and permitted accurate modeling of the observed melting behavior. The isothermal crystallization rates of four narrow molecular weight poly(ethylene oxide) fractions were characterized using fast differential scanning calorimetry for crystallization temperatures spanning 100°C range with the lower limit approaching the glass transition. A transition from homogeneous to heterogeneous primary nucleation was observed at −5°C. The kinetic analysis suggested that the crystal growth geometry depends strongly on temperature, where rod-like structures begin to appear near the glass transition temperature, highly branched solid sheaves grow throughout the homogeneous primary nucleation temperature range, and spherulites grow in the heterogenous primary nucleation range. Poly(δ-valerolactone) was synthesized using microwave-assisted techniques. Narrow molecular weight fractions were obtained using successive precipitation fractionation. Preliminary isothermal crystallization studies suggest that conventional thermal analysis methods are not adequate to measure the melting temperatures accurately due to reorganization during heating. / Doctor of Philosophy / Plastics may be classified into two general categories: those which form ordered domains upon solidification, i.e. undergo crystallization, and those which remain disordered upon solidification, i.e. form glasses. This work is focused on studying the crystallization and melting processes in two linear polymers, poly(ε-caprolactone) and poly(ethylene oxide), using new experimental technology. In the case of poly(ε-caprolactone), the experimental data could not be rationalized by existing theories, and we have proposed modifications to these theories that explained the results. In the case of poly(ethylene oxide), the application of new experimental technology resulted in previously unreported data that indicated novel behavior at very low crystallization temperatures. In the last portion of this work, poly(δ-valerolactone) was made using a novel approach. Conventional experimental approaches to measuring the crystallization and melting behavior were shown to be inadequate.