No description available.

The present work has been produced as part of an on-going collaboration between the University of Manchester and Amec, with the primary aim of furthering mechanistic understanding of corrosion processes in zirconium alloys out-of-reactor. Zirconium alloys are used as cladding material for nuclear fuel pellets, and correct understanding of the corrosion process in autoclave is essential to predicting material behaviour in-reactor. This EngD thesis is composed of five proposed papers that investigate observations and hypotheses under the theme of mechanical degradation in oxides formed on zirconium alloys in autoclave. First investigations concern observed stress relaxation in zirconium oxide. Finite element analysis is used to capture mechanical aspects of the corrosion process and apply this to stress behaviour determined previously using synchrotron x-ray diffraction. The results indicate that a mechanism other than creep or hydrogen induced lattice strain must be present to account for the observed stress relaxation. One such potential mechanism is crack formation; statistical analysis of scanning electron microscopy images has been used to identify a link between the development of roughness at the metal-oxide interface, crack formation in the oxide and transition points or acceleration in the corrosion kinetics. Parameters such as the median radius of curvature and profile slope (Rdq) have been applied, as these parameters do not require the definition of a periodic wavelength or amplitude. These and other parameters are related to information in literature to indicate that for samples of Zircaloy-4 and ZIRLOTM, which go through transition, the interface roughness changes in a way that would increase localised stress concentrations. The third material is an experimental low tin alloy, which under the same oxidation conditions, and during the same time period, does not appear to go through transition and does not develop an interface roughness in the same way. A critical assessment of finite element analysis applied to oxidising non-planar interfaces shows the significant limitations in the existing mechanism for representing oxidation expansion and stress formation. Autoclave oxidation experiments of artificially roughened samples of Zircaloy-4 were carried out to further understand the impact of out-of-plane stress generation. The results indicate a divergence based on surface roughness after ~86 days oxidation. SEM examination of images in cross section highlighted accelerated oxidation above surface roughness peaks, and an increased crack area in rougher samples. Finally, finite element analysis of the tetragonal to monoclinic phase transformation showed that biaxial compressive stress relaxation, or the tri-axial tensile stress associated with an advancing crack tip, could reduce the transformation strain energy and destabilise the tetragonal phase. The volumetric expansion and shear strain associated with the phase transformation produces stress in the surrounding oxide sufficient to generate nano-scale cracks perpendicular to the metal-oxide interface. This would allow fast ingress routes for oxygen containing species, and therefore acceleration in the corrosion kinetics.

No description available.

A ce jour, la fabrication additive est développée avec plusieurs procédés qui sont capables de fabriquer les pièces en plastique ou en métallique. De plus, la FA a des avantages qui sont des limites pour la technologie traditionnelle. Par exemple, grâce à la liberté de la forme de la pièce, il n’y pas besoin des outillages spécifiques. Mais la FA a aussi des inconvénients, par exemple, la qualité de surface de la pièce, normalement faible, le cout, de la fabrication, notamment à cause de l’investissement pour la machine de fabrication et aussi la matière première. Il y a beaucoup de différences entre la FA et les technologies traditionnelles. Nous considérons donc qu’il est nécessaire d’avoir un nouveau processus de conception pour la fabrication additive On étudie une méthode de conception pour la fabrication additive qui nous permet de fabriquer une pièce ou un mécanisme de manière optimale.Notre travail de thèse est appuyé sur les deux questions de recherche :• Quel modèle pour le processus de conception d’une pièce par fabrication additive ?o Comment tirer les profits de l’avantage de la FA, par exemple, la liberté de la forme ?o Comment intégrer des caractéristiques du procédé de FA dans le processus de conception ?• Quelle est l’influence de la représentation intermédiaire dans le processus de conception pour la fabrication additive ?o Les types de représentations intermédiaires avec la FAo Le choix du type de représentation intermédiaire pour évaluer le produit dans un moment spécifique du processus de conception pour la FA.En première temps, nous avons développé une modèle de processus qui permet de prise en compte la caractéristique des procédés, ainsi de tirer les profits de l’avantage de fabrication additive.En deuxième temps, nous avons déterminé une méthode de choix qui nous permet de choisir entre les types de représentations intermédiaire pour évaluer le produit dans un processus de conception pour la FA. Cette méthode est basé sur Case Based Reasoning. / To date, additive manufacturing is being developed with several processes that are capable of manufacturing plastic or metal parts. In addition, the FA has advantages that are limitations for traditional technology. For example, thanks to the freedom of the shape of the part, there is no need for specific tools. But the FA also has disadvantages, for example, the surface quality of the part, normally low, cost, manufacturing, especially because of investment for the manufacturing machine and also the raw material. There are many differences between AF and traditional technologies. We therefore consider it necessary to have a new design process for additive manufacture. A design method for additive manufacturing is being studied which allows us to manufacture a part or mechanism in an optimal way.Our thesis work is based on the two research questions:• Which model for the design process of a part by additive manufacturing?O How to draw the benefits of the FA advantage, for example, freedom of form?O How to integrate AF process characteristics into the design process?• What is the influence of intermediate representation in the design process for additive manufacturing?O Types of intermediate representations with FAO The choice of intermediate representation type to evaluate the product at a specific time in the design process for the FA.In the first phase, we have developed a process model that takes into account the characteristic of the processes, thus taking advantage of the additive manufacturing advantage.As a second step, we determined a method of choice that allows us to choose between the types of intermediate representations to evaluate the product in a design process for FA. This method is based on Case Based Reasoning.

The goal of the thesis is to find general nonlinear geometric transformation, which compensates irregular deformation of images, so that they could be registered. In the introductory part, necessary mathematical tools are stated, especially convolution, correlation and Fourier transform. In the next part, method of phase correlation is stated, followed by algorithms used for finding the geometric transformation. Those algorithms are implemented in computer program, that is included.

This work is aimed at deposition of fibers, which are able to penetrate deeper in the human respiratory airways and cause health hazards. Opening chapters are dedicated to classification of aerosols, human lung anatomy basics and methods for measurement of micrometer-sized aerosols. An experiment was carried out to investigate the deposition of fibers. Fibers were delivered into the silicon cast of the human airways and data of deposition fraction and efficiency were acquired. A new method was established to acquire the data. This method works on a principle of image analysis. Results of the new method were compared with a standard method, which follows a methodology NIOSH 7400.

The intentions of the so-called "More Electrical Aircraft" (MEA) are higher efficiency and lower weight. A main topic here is the application of electrical instead of hydraulical, pneumatical and mechanical systems. The necessary power electronic devices have intermediate DC-links, which are typically supplied by a three-phase system with active B6 and passive B12 rectifiers. A possible alternative is the B6 diode bridge in combination with an active power filter (APF). Due to the parallel arrangement, the APF offers a higher power density and is able to compensate for harmonics from several devices. The use of the diode bridge rectifier alone is not permitted due to the highly distorted phase current. The following investigations are dealing with the development of an active power filter for a three-phase supply with variable frequency from 360 to 800 Hz. All relevant components such as inductors, EMC-filters, power modules and DC-link capacitor are designed. A particular focus is put on the customized power module with SiC-MOSFETs and SiC-diodes, which is characterized electrically and thermally. The maximum supply frequency slope has a value of 50 Hz/ms, which requires a high dynamic and robustness on the control algorithm. Furthermore, the content of 5th and 7th harmonics must be reduced to less than 2 %, which demands a high accuracy. To cope with both requirements, a two-stage filter algorithm is developed and implemented in two independent signal processors. Simulations and laboratory experiments confirm the performance and robustness of the control algorithm. This work comprehensively presents the design of aerospace rectifiers. The results were published in conferences and patents. / Hauptziele des sogenannten "More Electrical Aircraft" (MEA) sind Effizienzerhöhung und Gewichtseinsparung. Ein Schwerpunkt hierbei ist die Nutzung von elektrischen statt hydraulischen, pneumatischen und mechanischen Systemen. Die notwendigen Leistungselektroniken haben DC-Zwischenkreise, welche mittels aktiven B6 und passiven B12 Gleichrichtern aus dem Dreiphasennetz gespeist werden. Eine mögliche Alternative ist die B6 Diodenbrücke in Kombination mit einem aktiven Netzfilter, welcher aufgrund der parallelen Anordnung eine höhere Leistungsdichte aufweist und darüber hinaus mehrere Geräte gleichzeitig entstören kann. Die alleinige Nutzung einer Diodenbrücke ist aufgrund des hohen Anteils von Stromharmonischen nicht zulässig. Diese Arbeit beschäftigt sich mit der Entwicklung eines aktiven Filters für ein Dreiphasensystem mit variabler Frequenz von 360 bis 800 Hz. Es werden alle relevanten Bauteile wie Induktivitäten, EMV-Filter, Leistungsmodule und Zwischenkreiskondensator ausgelegt. Besonderes Augenmerk liegt auf dem kundenspezifischen Modul mit SiC-Dioden und SiCMOSFETs, welches vollständig elektrisch und thermisch charakterisiert wird. Die Änderung der Netzfrequenz beträgt bis zu 50 Hz/ms, was eine hohe Dynamik und Robustheit von der Filterregelung verlangt. Weiterhin ist im statischen Fall eine hohe Genauigkeit gefordert, da die 5. und 7. Harmonische auf unter 2% geregelt werden müssen. Um beiden Anforderungen gerecht zu werden, wird ein zweistufiger Regelungsalgorithmus entwickelt der auf zwei digitalen Signalprozessoren implementiert wird. Simulationen und Labormessungen bestätigen die Robustheit des Regelungskonzeptes. Diese Arbeit stellt umfassend die Entwicklung von Luftfahrtgleichrichtern dar. Die Ergebnisse wurden in Konferenzen und Patenten veröffentlicht.