Thesis(M.S.)--Auburn University, 2006. / Abstract. Includes bibliographic references.

Thesis (Ph. D.)--Lehigh University, 1997. / Includes vita. Includes bibliographical references (leaves 218-227).

Thesis (Ph. D.)--Lehigh University, 1999. / Includes vita. Library copy lacks abstract. PBL Includes bibliographical references (leaves 191-214).

Thesis (Master)--İzmir Institute Of Technology, İzmir, 2006. / Keywords: Hydroxiapatites, alumina ceramic, zirconium oxide, urea, precipitations. Includes bibliographical references (leaves. 73-75).

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references. Also available via the Internet.

Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2006. / Hamid Garmestani, Committee Member ; Arun M. Gokhale, Committee Member ; Rosario A. Gerhardt, Committee Chair.

No description available.

No description available.

Increasing use of fiber reinforced ceramic matrix composites (CMC's) materials is needed, especially for hostile environments such as elevated temperatures. However, some fundamental issues regarding how these materials should be made for optimized performance are far from being settled. This study focuses on the modeling of the tensile behavior of unidirectional CMC using statistical methods and micro-mechanical analysis, based on laboratory observations. The model can be used to examine the effect of performance-influencing parameters on the strength of unidirectional CMC, thus shed light on how such material should be put together. The tensile strength model was then modified such that the behavior of unidirectioal CMC under cyclic tensile load can be studied. Results from the tensile strength model suggest that the Weibull modulus, <i>m</i>, of the strength of the reinforcing fibers and the fiber/matrix interfacial shear stress both have significant effect on the strength and toughness of the unidirectional composite: a higher <i>m</i> value and a lower interfacial shear stress result in a lower strength; a lower value of <i>m</i> and a higher interfacial shear stress results in a higher strength but lower toughness. Calculations from the tensile fatigue model suggest that a lower <i>m</i> value results in a longer fatigue life. / Ph. D.

The forced—flow thermal gradient chemical vapor infiltration (FCVI) process for fabricating ceramic matrix composites (CMCs) was modeled and analyzed based on the finite element method (FEM). The modeling study was focused on the fabrication of silicon carbide (SiC) matrix composites from methyltrichlorosilane (MTS) precursors because of their high strength, high modulus and excellent oxidation resistance properties at high temperatures. Unlike other available FCVI models, which use lumped reaction schemes, both gas phase and surface reactions of the FCVI process were explicitly considered for the present FEM FCVI model. The kinetics of SiC deposition from MTS precursor were derived by analyzing our own deposition rate data as well as reported results. The SiC deposition process was modeled using the following reactions — (1) : gas phase decomposition of MTS molecules into two major intermediates, one containing silicon and the other containing carbon; (2) : adsorption of the intermediates onto the surface sites of the growing film; (3) : reaction of the adsorbed intermediates to form silicon carbide. The equilibrium constant for the gas phase decomposition process was divided into the forward and backward reaction constants as 2.0E+25 exp[(—448.2 kJ/mol)/RT] and 1.1E+32 exp[(-416.2 kJ/mol)/RT], respectively. Equilibrium constants for the surface adsorption reactions of silicon—carrying and carbon—carrying intermediates were determined to be 0.5E+11 exp[(—21.6 kJ/mol)/RT] and 7.1E+09 exp[(—33.1 kJ/mol)/RT], while the rate constant for the surface reaction of the intermediates was 4.6E+05 exp[(—265.1 kJ/mol)/RT]. Effects of the deposition temperature and vapor pressure variations on the density profiles of the composite preform were studied based on this FEM FCVI model. It was found that the advantages of the commonly used ambient—pressure FCVI process (APFCVI) are likely to be limited by the equipment and the accumulation of gaseous components around the entrance sides, which could render the deposition process to be mass transport limited. A conceptual multi-step FCVI process was proposed to alleviate this problem and obtain products of good final density profiles within reasonable processing times. This multi—step FCVI process involved deposition under ambient—pressure to improve the density profiles and shorten the processing times. This was followed by the sub ambient—pressure FCVI process (LPFCVI) process to overcome the mass transfer limitations caused by the entrance accumulation effect and possible limitations on the equipment. A balance between processing time and final density profile can be achieved through the use of this multi-step FCVI process. Advantages of this process has been demonstrated by studying the densification process in large size specimens. / Ph. D.