Les composites 3D C/C sont utilisés dans l’industrie aérospatiale ou nucléaire pour leurstrès bonnes propriétés mécaniques à haute température. Afin d’assurer une intégrité optimaledes structures, la connaissance du comportement mécanique du composite, et plus particulièrementde ses mécanismes de rupture, est essentielle.Dans ce but, ce travail présente une modélisation de l’endommagement d’un composite3D C/C à température ambiante. Pour cela, une approche de modélisation à l’échelle mésoscopiquea été adoptée. A cette échelle, le composite 3D C/C présente deux types deconstituants : les baguettes de fibres de carbone et la matrice carbonée. Le comportement dechacun de ces méso-constituants est modélisé par une loi de comportement élastique endommageable(isotrope pour la matrice, orthotrope pour les baguettes) nécessitant un nombrede paramètres restreint. L’identification de ces paramètres repose sur des données expérimentalestirées de travaux antérieurs ainsi que celles issues d’une campagne expérimentale,menée durant la thèse, visant à compléter la connaissance du comportement mécanique ducomposite 3D C/C à l’échelle mésoscopique. Par ailleurs, des essais macroscopiques ont étéréalisés afin de valider le modèle développé. Les réponses expérimentales d’essais de flexion4 points et de flexion 3 points sont notamment bien reproduites par le méso-modèle. / 3D C/C composites are commonly employed in aerospace industry due to their outstandingmechanical properties at high temperatures. In order to ensure the integrity of structures,knowledge of the composite mechanical behaviour and fracture mechanisms is crucial.For this purpose, damage modeling of a 3D C/C composite, at room temperature, isproposed in which a meso-scale approach is considered. At this description scale, 3D C/Ccomposites are made of two materials : carbon fibers yarns and carbon matrix. Each materialbehavior is modeled by an elastic damage law (isotropic for matrix, orthotropic for yarns)with a limited number of parameters.The parameters identification process is based on experimentaldata obtained from previous work and from an experimental campaign carried outthrough this thesis work. This campaign aimed to a greater understanding of the materialmechanical behavior at mesoscopic scale. Furthermore, experimental tests were carried outto validate the composite modeling. It is shown that experimental reponses obtained fromfour-point and three-point bending tests are particularly well described from the proposedmesoscopic model.

Les composites 3D C/C sont utilisés, entre autres, comme bouclier thermique dans le domaine aérospatial en raison de leurs propriétés thermomécaniques et de leur résistance à l’ablation à haute température. Si leur comportement macroscopique a déjà été largement étudié par le passé, aucun modèle ne permet actuellement de relier de manière satisfaisante le comportement des constituants au comportement effectif du composite. En particulier, les modèles phénoménologiques ne permettent pas d’anticiper l’effet d’un éventuel changement de constituant. De plus, le rôle des interfaces dans le comportement hors-axe du composite reste à déterminer. L’objectif de ce travail est donc d’établir un modèle multi-échelle du comportement thermomécanique d’un 3D C/C en s’intéressant plus particulièrement au rôle des interfaces à haute température. Ce travail s’articule autour de la caractérisation de la morphologie et du comportement thermomécanique du matériau et de ses constituants. Le développement d’un dispositif original de push-out a notamment permis de mesurer les propriétés des interfaces baguette/baguette et fibre/matrice en température. Ces données expérimentales ont été intégrées à un modèle numérique du matériau à l'échelle mésoscopique. Un modèle de zone cohésive ad hoc a été développé afin de prendre en compte le comportement spécifique des interfaces. Les simulations éléments finis ainsi réalisées ont permis de reproduire avec succès le comportement non-linéaire du matériau de même que l'évolution de ses propriétés effectives avec la température. Ce modèle permet ainsi de relier les mécanismes d’endommagement observés aux échelles inférieures au comportement macroscopique du 3D C/C. / C/C composites are used as shield for aerospace applications since they display beneficial thermo-mechanical properties at high temperature, as well as high resistance to ablation. Though the macro-scale behavior was thoroughly studied in the past, no model can efficiently tie the properties of the constituents at the meso-scale to the effective macroscopic behavior. In addition, the phenomenological models proposed so far cannot predict a change in the composition. Besides, the interfaces influence on the out-of-axis mechanical behavior of the composite is yet to be evaluated. Thus, the goal of this work is to build a multi-scale model for the thermo-mechanical behavior of a 3D C/C, with a particular focus on the interfacial properties and its evolution with temperature. This study is based on the morphological and thermo-mechanical characterization of the material and its constituents. An original push-out test device has been developed to conduct high-temperature interfacial characterization at two scales (yarn/yarn and fiber/matrix interfaces). Collected experimental data were used for modeling purposes at the meso-scale. A cohesive zone model has been developed to take into account the specific behavior of the interfaces. Finite element simulations were successfully performed to reproduce the non-linear behavior of the material including the effective properties evolution with temperature. This model allowed to effectively link the damage mechanisms observed atthe lower scale to the 3D C/C macro-scale behavior.

In 1803, the Louisiana Purchase doubled the territory of the fledgling United States. Taking control of and defending the new territory, especially the culturally heterogeneous city of New Orleans occupied much of the administration's time. Most of the burden for establishing the defense policy rested on William C. C. Claiborne, a staunch Jeffersonian, former member of Congress from Tennessee, and previous governor of the Mississippi Territory. By working with local business leaders with a stake in American success, observing the local customs and traditions, and gradually encouraging political participation, Claiborne successfully introduced the American militia system to a culture far different from that of his native Virginia. Claiborne's policies reduced the likelihood that local dissidents and foreign powers such as Spain and Great Britain could conspire to subvert American government in Louisiana by rebellion and invasion.

Ansamycin natural products have historically been a rich source of new drugs for the treatment of bacterial infections and cancer. The C17-benzene ansamycins in particular have shown excellent preclinical results as potential anti-fungal and anti-cancer medicines. However, their thorough clinical evaluation has been hampered by the absence of a concise synthetic strategy. In order to address this issue, recently developed hydrogenative carbon-carbon bond forming methods were applied toward a short total synthesis of C17-benzene ansamycins. This class of natural products provides a challenging testing ground for these methods while facilitating the further development of compounds which may be used as treatments for life threatening diseases. In the first synthetic approach to the C17-benzene ansamycins key bond formations include direct iridium catalyzed carbonyl crotylation from the alcohol oxidation level followed by chelation-controlled dienylation to form the stereotriad, which is attached to the arene via Suzuki cross-coupling. The diene-containing carboxylic acid is prepared using rhodium catalyzed acetylene-aldehyde reductive C-C coupling mediated by gaseous hydrogen. Finally, ring-closing metathesis delivers the cytotrienin core. The second approach toward triene-containing C17-benzene ansamycins resulted in the syntheses of trienomycins A and F, which were prepared in 16 steps (longest linear sequence) and 28 total steps. The C11-C13 stereotriad was generated via enantioselective ruthenium-catalyzed alcohol CH syn crotylation followed by chelation-controlled carbonyl dienylation. Finally, diene-diene ring closing metathesis to form the macrocycle. The present approach is 14 steps shorter (LLS) than the prior syntheses of trienomycins A and F, and eight steps shorter than any prior synthesis of a triene-containing C17-benzene ansamycin. / text

Texte remanié de: Doct-diss.--Philos.--London, 1977. / Bibliogr. p. 377-383. Index.

The research work focuses on implementing intelligent measurement and diagnostic techniques for the non-destructive evaluation (NDE) of aircraft carbon composites. The outcome of this research work developed reliable and faster techniques to aid in the rapid assessment of defects in anisotropic carbon composites by applying ultrasonic and infrared thermography NDE methods. To fulfill the requirement of the intelligent non-destructive evaluation methods, this research is divided into four sub-researches: fuzzy logic based delamination detection, super-resolution image reconstruction for ultrasonic C-scan, ultrasonic 3D reconstruction, and polynomial fitting techniques for infrared thermography inspection. These researches focus on the improvement and optimization of current ultrasonic testing and infrared thermography inspection. They are independent but interrelated component, and they all serve the same goal which is to interpret data correctly and provide detailed information about the region of interests (ROI) for intelligent non-destructive measurement and evaluation. Details of these researches are presented in Chapter 2, 3, 4, and 5 respectively. For the ultrasonic testing, a fuzzy inference classifier will be used to generate the rule base and knowledge base for different kinds of defects in composites. It will automatically manage large amounts of signal data sets and extract the important information. Data features and NDE expert knowledge are seamlessly combined to provide the best possible diagnosis of the potential defects and problems. As a result, the outcome of this research work will help ensure the integrity and reliability of carbon composites. The C-scan image resolution of ultrasonic testing system was improved by applying super-resolution algorithms to overcome the inherent resolution limitations of the existing ultrasonic system. It greatly improves the image quality and allows for more detailed inspection of the ROI with high resolution, making defect evaluation easier and more accurate. The ultrasonic 3D reconstruction technique will be able to provide NDE inspectors with more detailed information on defect depth, volume, and 3D structure, as well as help them make quick, accurate, and reliable decisions. For the IR inspection, the thermography methods based on the thermal contrast are strongly affected by non-uniform heating which due to the heat source alignment and specimen thickness variation. The proposed polynomial curve fitting and surface fitting techniques were applied to eliminate the non-uniform heating effect by subtracting the estimated non-uniform heating pattern from the corrupted IR images. Mainly, aircraft composite material: carbon fiber reinforced polymer (CFRP) panels will be considered for this research work. Based on the preliminary study, delamination defects due to impact damage and foreign object inclusions artificially embedded in CFRP panels were successfully detected by immersion ultrasonic testing (UT) and IRT inspection. Therefore, the next step will be in improving the detection algorithm and developing an intelligent quality inspection technique for NDE testing. Powered with multiple image processing techniques and mathematical algorithms, the research result will provide high resolution images and detailed information about defect areas. In addition, it will also capable of identifying the type, shape, size, and the distribution of defect.

No description available.

The work described in this thesis documents the development of new rhodium(I)-catalysed methodologies within two areas of research. The first examines the use of carbonyls as chelating groups in hydroacylation to produce synthetically valuable ketones and enones. The second area explores new carbon-carbon bond activation methodologies. Chapter 1 presents a literature review of the historical development of rhodium-catalysed hydroacylation, with a focus on chelating groups that can currently be used to suppress decarbonylation. A brief review of methodologies that avoid the requirement for a tether is also included. Chapter 2 describes the development of a novel hydroacylation methodology employing carbonyl-based functional groups as tethers on aldehyde substrates. The chapter begins with the optimisation studies for the hydroacylation of β-formyl amides with terminal and internal alkynes, allenes and terminal alkenes, and subsequently explores the substrate scope for each case. The chapter then outlines the investigations undertaken with 1,4-dicarbonyl and 1,5-dicarbonyl systems, N-formyl amides, β-formyl esters and finally β-formyl ketones. A detailed description of the routes undertaken to synthesise each starting material is also presented. Chapter 3 presents a short review surveying the key milestones in the development of carbon-carbon activation methodologies. The chapter begins with a theoretical comparison to carbon-hydrogen activation and a discussion of the unique challenges that are faced. An overview of the major strategies employed to enact these processes is subsequently presented for both strained and unstrained substrates. Chapter 4 outlines the attempts undertaken to develop a novel carbon-carbon bond activation methodology. The work evaluates sulfur-, nitrogen- and alkene-based chelating groups, known to be successful in hydroacylation, in analogous ketone substrates. Chapter 5 discusses the conclusions from this work and the potential for further work. Chapter 6 presents the experimental procedures and data.

AN ABSTRACT OF THE THESIS OFChristoph Michael Goettler, for the Master of Science degree in Mechanical Engineering, presented on Nov 6, 2020, at Southern Illinois University Carbondale. TITLE: EFFECT OF DENSITY ON FRICTION AND WEAR PERFORMANCE OF CARBON-CARBON COMPOSITE MATERIALSMAJOR PROFESSOR: Dr. Peter FilipCarbon-carbon (C/C) composite materials exhibit high thermal conductivity, high thermal stability, low density, and high mechanical strength. Due to these properties, C/C composites are ideal for use in high performance braking systems. However, C/C composites are incredibly expensive to manufacture, and thus improving the longevity of these materials is vital. C/C composite materials inherently have a density gradient due to manufacturing limitations. By determining the effect of density on friction and wear performance of C/C composite materials, manufacturers could use that data to alter manufacturing methods to improve the lifespan of C/C composites. In this study, the effect of density on friction and wear performance of C/C composite materials was studied. Friction tests were conducted through use of a universal mechanical tester (UMT) manufactured by Bruker and subsequent analysis was done through use of scanning electron microscopy, energy dispersive x-ray spectroscopy, and polarized light microscopy. Numerous samples from depths of 0 mm and 5 mm were taken from two C/C composite materials with varying matrices and friction tested at varying conditions to determine friction properties, friction surface characteristics, microstructure just below the friction surface characteristics, friction layer characteristics, and wear characteristics. Density, apparent density, and apparent porosity gradients were also measured to be able to correlate observations to density differences. It was observed that while density does not seem to be the main cause in differences in friction and wear performance of C/C materials at depths of 0 mm and 5 mm, there still existed significant differences in friction performance, wear performance, and post friction test material characteristics when comparing 0 mm samples to 5 mm samples. In conclusion, density was not found to be a significant cause in variations in friction performance. However, friction surface depth was found to have a significant effect on friction performance, wear performance, and the friction surface. Further research is needed to be able to determine the exact cause of the variations in performance at depths of 0 mm and 5 mm. Keywords: carbon-carbon, composite, C/C, density, friction, wear, brake

Methane is an abundant resource existing in the form of natural and shale gas, and molybdenum-based catalysts, including molybdenum oxides and carbides, are the commonly used components in catalysts for converting methane to value-added chemicals. Therefore, understanding the catalytic mechanism underlying the methane conversion over molybdenum-based catalysts is key to designing highly efficient catalysts and optimizing the operating conditions. In this dissertation, I focus on the structural evolution from oxide to carbides and catalytic reactivity of the molybdenum-based catalysts for methane conversion based on the result from density functional theory (DFT) computational studies.First, the surface chemistry and reactivity of α-MoO3 toward C-H bond activation of methane by breaking the first C-H bond on the MoO3 (010) surface were used to evaluate various functionals of the DFT method. Our results indicate that surface reduction of α-MoO3 (010) occurs preferably through releasing the terminal oxygen atoms, generating oxygen vacancies while exposing the reduced Mo centers. These oxygen vacancies tend to be separated from each other at a higher density due to the repulsive interactions. Furthermore, the reduced α-MoO3 (010) surface promotes methane activation kinetically and thermodynamically by reducing the activation barrier for the first C-H bond breaking and stabilizing the product state as compared with those on the stoichiometric surface. There is a synergy between the reduced Mo active site and surface lattice oxygen for C-H bond cleavage. In addition, the performance of different functionals, including the pure-GGA PBE functional with the semi-empirical vdW correction and the meta-GGA SCAN functional, has been investigated. With the meta-GGA functional, we can predict the bulk structure of α-MoO3 more accurately while reproducing the thermal chemistry of MoO3. On the other hand, the reactivity based on the PBE functional is qualitatively consistent with that from the SCAN functional.We then conducted a systematic study of methane activation and conversion over the Mo-terminated surfaces derived from different phases of Mo2C carbides, i.e. the (001) surface of α-Mo2C and the (100) surface of β-Mo2C. The results show that Mo-terminated Mo2C with lower carburization in its subsurface (β-Mo2C) possesses a superior reactivity toward methane activation, resulting in a complete dissociation of methane to carbon adatom on the surface. This carbon adatom causes further carburization of the surface, lowering the reactivity toward methane activation. Moreover, the carburization occurs more easily in the near surface layers of Mo2C than in the bulk. Although carburization lowers the activities for methane activation, it promotes C-C coupling for dimerization of the (CH)ad species, resulting in (C2H2)ad on the Mo-terminated surfaces. On the deep carburized molybdenum carbide (MoC) surfaces, we mapped out the elementary steps of CH4 dissociation and possible mechanisms for forming the C2 species. The results indicate that the Mo-terminated MoC surfaces derived from different bulk phases (α- and δ-) of MoC possess a similar mechanism to that on the noble-metal surfaces for methane dissociation, i.e., CH4 dissociates sequentially to (CH)ad with both kinetic and thermodynamic feasibilities while breaking the last C-H bond in (CH)ad is highly activated. As such, C-C coupling through dimerization of the (CH)ad species occurs more readily, resulting in (C2H2)ad on the Mo-terminated surfaces. Such (C2H2)ad species can dehydrogenate easily to other C2 adsorbates such as (C2H)ad and (C2)ad. Consequently, these C2 species from CH4 dissociation will likely be the precursors for producing long chain hydrocarbons and/or aromatics on molybdenum carbide based catalysts.