Experimental studies and modeling of mechanical behavior for Nicalon(TM)/silicon carbide and Nextel(TM)/Blackglas(TM) fiber fabric-reinforced ceramic-matrix composites

Fully understanding the mechanical behavior of continuous fiber-reinforced ceramic composite (CFCC) material systems will provide guidelines for material selection, component design, computation of the safety factor, maintaining the safe service condition, and predicting the residual life. Since most of CFCCs were invented within the last decade, the database for their mechanical behavior is still under construction. Many aspects are even left completely blank. The extensive application of CFCCs by industry is still hampered by insufficient understanding of the mechanical behavior and the lack of a well-developed and widely accepted design philosophy, in addition to the high production costs. There is an urgent need to understand the scientific principles controlling mechanical behaviors of woven fabric-reinforced CFCCs.; In this dissertation, mechanical behaviors were experimentally and theoretically studied for two commercially available 2-dimensional woven fiber fabric-reinforced CFCCs, namely, the plain-weave Nicalon fabric-reinforced SiC matrix composite fabricated by ORNL and the crowfoot Nextel fabric-reinforced Blackglas composites manufactured by Northrop Grumman.; A fundamental and scientific understanding of the correlation among microstructures, fracture mechanisms, and load-bearing capabilities for the two woven fabric-reinforced ceramic composites were provided. Effects of oxidation and porosity on flexural strengths of the Nicalon/SiC CFCC were experimentally investigated. Analytical methods were formulated, and computer-aided models and FORTRAN programs for the quantification of the fabric stacking sequence effects on elastic stress distributions, laminate effective elastic moduli, and flexural strengths for the plain-weave Nicalon/SiC laminated composite were established. Nondestructive evaluations (NDE) by ultrasonics and x-ray computed tomography (CT) were performed on the low-cost Nextel/Blackglas CFCC. Fiber orientation effects on the flexural strength of the Nextel/Blackglas CFCC were experimentally investigated. Damage mechanisms of the Nextel/Blackglas composite were analyzed by the scanning electron microscopy (SEM) and SEM energy dispersive x-ray spectroscopy (EDXS) as well as SEM/EDXS line-scan and mapping techniques.; Among them, one unique breakthrough is that a methodology and computer-aided modeling were provided that help to pave a way to optimize the design and process of CFCCs through an in-depth and systematic study of the laminate layup and lamina stacking sequence effects on elastic behaviors of woven CFCCs. Suggestions for future work were also provided.