Les travaux de recherche de ce manuscrit s’inscrivent dans le cadre d’une coopération scientifique avec la société STMicroelectronics de Tours concernant les interconnexions des prochaines générations de circuits intégrés. L’intégration de nanotubes de carbone comme connecteurs en microélectronique de puissance, limiterait sévèrement les effets d’échauffements dans les empilements de puces, permettant une meilleure dissipation de la chaleur. Ce travail de thèse avait pour objectif de déterminer un procédé de croissance reproductible de nanotubes de carbone d’au moins 20 dm de long, en tapis perpendiculaire au substrat, peu pollué par du carbone amorphe afin de réaliser un véhicule test permettant de mesurer les propriétés thermiques et électriques du tapis de nanotubes obtenu. Le dispositif expérimental présenté utilise l’ablation laser pour le dépôt de catalyseur (fer) la méthode de CVD assistée par plasma radiofréquence d’éthylène et d’hydrogène pour la croissance de nanotubes de carbone. Des conditions optimales d’obtention des tapis répondant aux critères de réalisation des démonstrateurs, ont été définies à la suite d’une étude paramétrée. Pour les mesures électriques, des plots d’or servant d’électrodes, sont déposés sur les tapis de nanotubes. Lors des tests électriques 4 pointes sur le démonstrateur réalisé, le comportement ohmique des tapis de nanotubes a été mis en évidence. Une puissance de 300 mW/mm2 est déposée sur les plots sans aucun dommage pour les nanotubes, et une résistivité de l’ordre de 10-3 L.m a été estimée. Pour les tests thermiques, une couche mince de titane absorbant l’énergie d’un faisceau laser UV pulsé représentant la source de chaleur, est déposée sur le tapis de nanotubes. Des valeurs de conductivité thermique apparente de 200 – 300 W/m/K et intrinsèque de 660W/m/K ont été déterminées par méthode de pyrométrie infrarouge résolue en temps. / This manuscript presents the research work done in the frame of scientific cooperation with the company STMicroelectronics in Tours concerning the interconnections for the next generation of integrated circuits. The integration of connectors based on carbon nanotubes in microelectronic would severely limits the effects of overheating in the stacks of chips, allowing a better heat dissipation. The aim of this PHD work was the determination of a reproducible carbon nanotubes carpet growth process at least 20 dm long, perpendicular to the substrate, slightly polluted by amorphous carbon in order to achieve a test vehicle for measuring thermal and electrical properties of carbon nanotubes carpet. The experimental device combines laser ablation process for the deposit of catalyst (iron) and RF plasma Enhanced CVD method with a mixture of ethylene and hydrogen gases for the growth of carbon nanotubes. Optimal conditions for obtaining carpet criteria for test vehicle realization have been defined from a parameterized study. For electrical measurements, gold layers as electrodes are deposited on nanotube carpets. Four probes electrical test is achieved and an ohmic behaviour of nanotube carpet is evidenced. A power of 300 mW/mm2 is deposited without any damage for the nanotubes and the carpet resistivity is estimated to be 2,99.10-3 L.m. For thermal testing, a titanium thin film is deposited on the carpet in order to absorb the UV pulsed laser beam representing the heating source. An apparent thermal conductivity value of 200 - 300 W/m/K and an intrinsic value of 660W/m/K were determined by time resolved infrared pyrometry method.

This work investigated the protection of mechanism of organic coatings on steel exposed to 3% sodium chloride solution at 50°C, coupled with the use of electrochemical impedance spectroscopy (EIS) to monitor progress of corrosion and degradation of coating. Unlike Walter, EIS measurement was conducted at 50°C as well as after cooling, and measurements at intermediate temperatures have been used to characterize the dependence of the process involved. The proposition that corrosion rate is controlled by the ionic resistance of an organic coating has been tested. EIS results were fitted to a model circuit and changes in the film resistance and charge-transfer resistance with temperature were analyzed to deduce activation energies for the processes involved. Surprisingly, the calculated activation energy for coating resistance is significantly lower than the activation energy for the charge transfer resistance. This suggests that ion conduction in the coating, as apparent in an AC measurement, cannot be controlling the corrosion rate. Potentiostatic pulse tests on coated metal enable iR-corrected polarization curves to be plotted at different temperatures. From this, the activation energy determined from the corrosion currents also higher matches the higher activation energy value calculated from the charge transfer resistance. However, measurements of coating resistance on free films of the same coating also generate higher activation energy values, leaving two possible models that can account for the results.

This thesis describes the assembly and integration procedures, methods and strategies used for the Generic Nanosatellite Bus (GNB) developed at the Space Flight Laboratory. The design of the interconnection medium routing will be presented and aspects of thermal testing such as thermal shock procedures and the satellite support structure design for the thermal vacuum testing. The compliance of the assembly, integration and testing requirements is demonstrated through validation and implementation. Step by step procedures are presented for GNB assembly, solar cell bonding and thermal tape application. The evolution of the integration design is described based on optimizing efforts and GNB design changes. Flexible circuits are presented as an alternative to the conventional harness for future missions. Finally, general assembly, integration and thermal testing recommendations are offered to add to the wealth of knowledge acquired by SFL in the proper design of nanosatellites.

This thesis describes the assembly and integration procedures, methods and strategies used for the Generic Nanosatellite Bus (GNB) developed at the Space Flight Laboratory. The design of the interconnection medium routing will be presented and aspects of thermal testing such as thermal shock procedures and the satellite support structure design for the thermal vacuum testing. The compliance of the assembly, integration and testing requirements is demonstrated through validation and implementation. Step by step procedures are presented for GNB assembly, solar cell bonding and thermal tape application. The evolution of the integration design is described based on optimizing efforts and GNB design changes. Flexible circuits are presented as an alternative to the conventional harness for future missions. Finally, general assembly, integration and thermal testing recommendations are offered to add to the wealth of knowledge acquired by SFL in the proper design of nanosatellites.

No description available.

<div> <p><a>Polymer nanocomposites are envisioned for use in many advanced applications, such as structural industries, aerospace, automotive technology and electronic materials, due to the improved properties like mechanical strengthening, thermal and chemical stability, easy bulk processing, and/or light-weight instigated by the filler-matrix combination compared to the neat matrix. In recent years, due to increasing environmental concerns, many industries are inclining towards developing sustainable and renewable polymer nanocomposites. Cellulose nanomaterials (CNs), including cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), have gained popularity due to their excellent mechanical properties and eco-friendliness (extracted from trees, algae, plants etc.). However, to develop CN-reinforced nanocomposites with industrial applications it is necessary to understand impact of hygroscopic swelling (which has very limited </a>quantitative study at present), aspect ratio, orientation, and content of CNs on the overall performance of nanocomposites; and overcome the low dispersibility of CNs and improve their compatibility with hydrophobic matrix. In this work, we attempt to understand the influence of single nanocrystals in the hygroscopic and optical response exhibited by nanostructured films; effect of CNCs on the properties of PVA/CNC fibers by experimental evidence with mathematical modeling predictions; and hydrophobized CNFs using a facile, aqueous surface modification to improve interfacial compatibility with epoxy. </p><p><br></p> <p>To evaluate the effect of CNC alignment in the bulk response to hygroscopic expansion, self-organized and shear-oriented CNC films were prepared under two different mechanisms. The coefficient of hygroscopic swelling (CHS) of these films was determined by using a new contact-free method of Contrast Enhanced Microscopy Digital Image Correlation (CEMDIC) that enabled the characterization of dimensional changes induced by hygroscopic swelling of the films. This method can be readily used for other soft materials to accurately measure hygroscopic strain in a non-destructive way. By calculating the CHS values of CNC films, it was determined that hygroscopic swelling is highly dependent on the alignment of nanocrystals within the films, with aligned CNC films showing dramatically reduced hygroscopic expansion than randomly oriented films. Finite element analysis was used to simulate moisture sorption and kinetics profile which further predicted moisture diffusion as the predominant mechanism for swelling of CNC films. </p> <p><br></p><p>To study the effects of different types and aspect ratios of CNCs on mechanical, thermal and morphological properties of polyvinyl alcohol (PVA) composite <a>fibers, CNCs extracted from wood pulp and cotton were reinforced into PVA to produce fibers by dry-jet-wet spinning. The fibers were collected as-spun and with first stage drawing up to draw ratio 2. </a>The elastic modulus and tensile strength of the fibers improved with increasing CNC content (5 – 15 wt. %) at the expense of their strain-to-failure. The mechanical properties of fibers with cotton CNC were higher than the fibers with wood CNC when the same amount of CNCs were added due to their higher aspect ratio. The degree of orientation along the spun fiber axis was quantified by 2D X-ray diffraction. As expected, the CNC orientation correlates to the mechanical properties of the composite fibers. Micromechanical models were used to predict the fiber performance and compare with experimental results. Finally, surface and cross-sectional morphologies of fibers were analyzed by scanning electron microscopy and optical microscopy.</p><p><br></p> <p>To improve the dispersibility and compatibility of CNFs with epoxy, CNFs were modified by using a two-step water-based method where tannic acid (TA) acts as a primer with CNF suspension and reacts with hexadecylamine (HDA), forming the modified product as CNF-TA-HDA. The modified (-m) and unmodified (-um) CNFs were filled into hydrophobic epoxy resin with a co-solvent (acetone), which was subsequently removed to form a solvent-free two component epoxy system, followed by addition of hardener to cure the resin. Better dispersion and stronger adhesion between fillers and epoxy were obtained for m-CNF than the um-CNF, resulting in better mechanical properties of nanocomposites at the same loading. Thermal stability and the degradation temperature of m-CNF/epoxy improved when compared to neat epoxy. </p> </div> <br>

Ermüdungsrissbildung ist ein gefährliches und kostenintensives Phänomen, welches frühzeitig erkannt werden muss. Weil kleine Fehlstellen jedoch hohe Testempfindlichkeit erfordern, wird die Prüfzuverlässigkeit durch Falschanzeigen vermindert. Diese Arbeit macht sich deshalb die Diversität unterschiedlicher zerstörungsfreier Oberflächenprüfmethoden zu Nutze, um mittels Datenfusion die Zuverlässigkeit der Fehlererkennung zu erhöhen. Der erste Beitrag dieser Arbeit in neuartigen Ansätzen zur Fusion von Prüfbildern. Diese werden durch Oberflächenabtastung mittels Wirbelstromprüfung, thermischer Prüfung und magnetischer Streuflussprüfung gewonnen. Die Ergebnisse zeigen, dass schon einfache algebraische Fusionsregeln gute Ergebnisse liefern, sofern die Daten adäquat vorverarbeitet wurden. So übertrifft Datenfusion den besten Einzelsensor in der pixelbasierten Falscherkennungsrate um den Faktor sechs bei einer Nutentiefe von 10 μm. Weiterhin wird die Fusion im Bildtransformationsbereich untersucht. Jedoch werden die theoretischen Vorteile solcher richtungsempfindlichen Transformationen in der Praxis mit den vorliegenden Daten nicht erreicht. Nichtsdestotrotz wird der Vorteil der Fusion gegenüber Einzelsensorprüfung auch hier bestätigt. Darüber hinaus liefert diese Arbeit neuartige Techniken zur Fusion auch auf höheren Ebenen der Signalabstraktion. Ein Ansatz, der auf Kerndichtefunktionen beruht, wird eingeführt, um örtlich verteilte Detektionshypothesen zu integrieren. Er ermöglicht, die praktisch unvermeidbaren Registrierungsfehler explizit zu modellieren. Oberflächenunstetigkeiten von 30 μm Tiefe können zuverlässig durch Fusion gefunden werden, wogegen das beste Einzelverfahren erst Tiefen ab 40–50 μm erfolgreich auffindet. Das Experiment wird auf einem zweiten Prüfkörper bestätigt. Am Ende der Arbeit werden Richtlinien für den Einsatz von Datenfusion gegeben, und die Notwendigkeit einer Initiative zum Teilen von Messdaten wird betont, um zukünftige Forschung zu fördern. / Fatigue cracking is a dangerous and cost-intensive phenomenon that requires early detection. But at high test sensitivity, the abundance of false indications limits the reliability of conventional materials testing. This thesis exploits the diversity of physical principles that different nondestructive surface inspection methods offer, by applying data fusion techniques to increase the reliability of defect detection. The first main contribution are novel approaches for the fusion of NDT images. These surface scans are obtained from state-of-the-art inspection procedures in Eddy Current Testing, Thermal Testing and Magnetic Flux Leakage Testing. The implemented image fusion strategy demonstrates that simple algebraic fusion rules are sufficient for high performance, given adequate signal normalization. Data fusion reduces the rate of false positives is reduced by a factor of six over the best individual sensor at a 10 μm deep groove. Moreover, the utility of state-of-the-art image representations, like the Shearlet domain, are explored. However, the theoretical advantages of such directional transforms are not attained in practice with the given data. Nevertheless, the benefit of fusion over single-sensor inspection is confirmed a second time. Furthermore, this work proposes novel techniques for fusion at a high level of signal abstraction. A kernel-based approach is introduced to integrate spatially scattered detection hypotheses. This method explicitly deals with registration errors that are unavoidable in practice. Surface discontinuities as shallow as 30 μm are reliably found by fusion, whereas the best individual sensor requires depths of 40–50 μm for successful detection. The experiment is replicated on a similar second test specimen. Practical guidelines are given at the end of the thesis, and the need for a data sharing initiative is stressed to promote future research on this topic.