Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 254-264).

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 129-132). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Washington, 1992. / Vita. Includes bibliographical references (leaves [267]-272).

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (leaves 177-196). Also available in electronic version.

Includes bibliographical references (p. 115-124).

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Suresh G. Advani, Dept. of Mechanical Engineering. Includes bibliographical references.

Élaboration et caractérisation de polymères nanocharges / Elaboration and characterization of nanocharged polymers

Cette étude porte sur un composite de tissu de chanvre et matrice époxy. Des essais ont d’abord été réalisés sur les constituants. Ils ont montré que le comportement des fils imprégnés par de la résine est plus représentatif du comportement dans le composite que celui des fils secs. Ces essais ont aussi permis de déterminer les paramètres matériaux nécessaires pour l’élaboration d’un modèle par éléments finis d’un pli du composite. Ce modèle est basé sur une simplification de la représentation du tissu. La variabilité des propriétés des constituants a été prise en compte. Les champs de déformation ont été comparés avec ceux mesurés par la technique de DIC à la surface des composites. Des essais de fatigue ont été réalisés sur les composites [0°/90°]7 et [±45°]7. L’échauffement a été mesuré par caméra IR, les endommagements ont été suivis par EA et par une caméra haute résolution. Des observations ont été effectuées par microscopie et par microtomographie X. Une analyse approfondie des mécanismes d’endommagement a été réalisée. Un modèle de courbe SN de fatigue a été adapté aux composites chanvre/époxy étudiés. La tenue à l’impact et le comportement mécanique postimpact du composite chanvre/époxy [0°/90°]7 ont été étudiés. Les résultats ont montré l’influence d’un impact non destructif sur la durée de vie en fatigue de ce composite, et l’évolution de l’endommagement a été analysée. Il a été montré que le modèle des courbes S-N de fatigue peut s’appliquer aux éprouvettes impactées. Il est ainsi possible de prédire la durée de vie en fatigue du composite impacté à partir de sa contrainte à rupture en traction et du comportement en fatigue du matériau sain. / This study focuses on a woven hemp/epoxy composite. Tests were first conducted on its components. They showed that the behaviour of resin impregnated yarn is more representative of the yarn behaviour in the composite than the dry yarn usually studied. These tests were also used to determine the material parameters necessary for the development of a finite element model of a composite ply. This model is based on a simplified representation of the fabric. Variability of properties of the components was taken into account. Strain fields were compared with those measured by the DIC technique on the surface of the composites. Fatigue tests were conducted on composites [0°/90°]7 and [±45°]7. Heating was measured by IR camera; the damage was followed by AE and high resolution camera. Observations were made by microscopy and X-ray microtomography. A detailed analysis of damage mechanisms was performed. A model of S-N fatigue curve was adapted to the studied hemp/epoxy composite. The resistance to impact and the post-impact mechanical behaviour of the [0°/90°]7 hemp/epoxy composite were studied. The results showed the influence of a non-destructive impact on the fatigue life of the composite, and the evolution of the damage was analyzed. It has been shown that the model of S-N fatigue curve can be applied to impacted specimens. It is thus possible to predict the fatigue life of the impacted composite from the tensile strength and fatigue behaviour of the non-impacted material.

Dans le domaine des matériaux de structure destinés à des applications thermomécaniques sous conditions extrêmes, les carbures métalliques et, plus particulièrement, ceux de la famille de métaux de transition (i.e. titane, zirconium, hafnium) sont de bons candidats étant donné la nature à la fois métallique et covalente de leurs liaisons. De plus, parmi les céramiques non-oxydes, le carbure de silicium est le plus employé dans la réalisation de composites particulaires du fait de son bon comportement à l’oxydation à haute température. Les composites de type SiC/ZrC seraient de bons candidats pour des applications à haute température dans des atmosphères oxydantes car ils sont susceptibles de développer des propriétés thermostructurales intéressantes. Cependant, l’élaboration de composites particulaires, avec un bon contrôle de la distribution respective des deux phases carbures au sein de la microstructure, n’est pas parfaitement maîtrisée. En particulier, l’amélioration ou l’optimisation des performances thermomécaniques de ces céramiques avancées, exige le contrôle de leur composition chimique à l’échelle atomique et de leur nanostructuration. L’approche « Precursor Derived Ceramics » (PDCs) permet notamment de moduler la composition du matériau à l’échelle moléculaire et d’obtenir des matériaux de formes diverses et complexes (nanomatériaux, fibres, dépôts, composites). Cette méthode, appliquée au système Si/C/Zr, est basée sur la synthèse de polymères précéramiques par chimie click et hydrosilylation. Des poudres ultrafines obtenues après le traitement thermique par spray pyrolyse laser des précurseurs pourront suivre des étapes ultimes de mise en forme, de consolidation et de densification. / In the field of structural materials for thermomechanical applications under extreme conditions, metal carbides, and more specifically, those of the transition metal family (i.e. titanium, zirconium, hafnium) are good candidates thanks to the nature of the both metallic and covalent bonds. Further, among the non-oxide ceramics, silicon carbide is the most used in the elaboration of particulate composites because of its good oxidation behavior at high temperature. SiC/ZrC composites would be good candidates for high temperature applications in oxidizing atmospheres thanks to their ability to develop interesting thermostructural properties. However, the development of particulate composites, with good control of the respective distribution of the two carbides phases in the microstructure is not well controlled. Particularly, improving or optimizing the thermomechanical performances of these advanced ceramics, requires to control the chemical composition at the atomic scale and their nanostructuration. The "Precursor Derived Ceramics" approach (PDCs) notably allows to modulate the composition of the material at the molecular level and to obtain materials of various and complex shapes (nanomaterials, fibers, deposits, composites). This method, applied to the Si/C/Zr system is based on the synthesis ofpreceramic polymers by click chemistry and hydrosilylation. Ultrafine powders obtained after laser spray pyrolysis heat treatment could be shaped, consolidated and densified.

M.Tech. / The mining industry exerts ever increasing demand for components with high wear resistance to the extent that plain ferrous alloys are falling short. Innovative metal-matrix composites nonferrous metals have been widely researched and used. Casting composites based on ferrous alloys pose monumental challenges in casting. Firstly, the density differential results in large resistant forces on the ceramic such that unless a rigid structure is configured, the less dense ceramic floats on the metal stream. Secondly, the poor wetting properties between metal and ceramic will result in inferior bonding of the matrix, hence separation of solids in service.This study presents the feasibility of manufacturing ceramic based metal matrix composites (MMC) for multi-purpose industrial application including wettability and the bonding between the matrix and the composite. The cold rods of alumina positioned in the mould prior to casting cracked as soon as they came in contact with hot metal. Because of the density difference between ceramic and liquid metal the alumina tended to float under the influence of Ferro static pressure. Infiltration of zirconia (ZrO2) and alumina (Al2O3) in ferrous matrix was investigated. Infiltration of liquid metal in ceramic filters increased with porosity of filters i.e. greater infiltration occurred in filters with larger pore volume fraction measured in terms of number of pores per linear inch (ppi). Thus, there was high infiltration in casting with 10ppi followed by 30ppi and there was poor infiltration in 50ppi ceramics. Infiltration increased with increasing temperature of the ceramics. A temperature of 1000oC was found to be superior to 800oC. The wetting behaviour of molten iron on the substrates of Al2O3 was investigated. Titanium in high chromium white cast iron was found to improve the wetting characteristics on alumina. The wetting angle decreased with increased titanium content. The wear properties of ferrous alloys used were not significantly improved by the ceramic used to make the composite. Filters are produced by a deposition process and hence are not densified for the purpose of manufacturing hard composites