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Defects created during the manufacture of an oxide/oxide and two non-oxide (SiC/SiNC and MI SiC/SiC) ceramic matrix composites (CMCs) were categorized as follows: (1) Intra-yarn defects such as dry fibers, (2) Inter-yarn defects such as those at crossover points, matrix voids, shrinkage cracks and interlaminar separation, and (3) Architectural defects such as layer misalignment. Their impact on elastic properties was analytically investigated using a stiffness averaging approach considering the defects to have volumetric and directional influences. In-plane tensile and shear moduli as well as the through-thickness compressive modulus were experimentally evaluated. Results of analytical model were around 7% on average from the mean value of the experimental data. It was observed that interlaminar separation drastically reduced the through-thickness modulus by about 63% for the SiC/SiNC, 40% for the MI SiC/SiC and around 32% for the oxide/oxide composites. Shrinkage cracks in oxide/oxide composite reduced the in-plane tensile and shear moduli by 14% and 8.8%, respectively., Journal article published in Composites: Part B 55 (2013) 167-175. The original document contains color images.

This final report details progress made on various topics related to advanced metallic, advanced metallic composites and ceramic materials. The development and sustainment of Air Force systems depends on both the optimal performance of traditional materials and the continued exploration of materials technologies. Major requirements driving the research into these new technologies include: 1) reducing the weight of engineering components of aircraft, 2) increasing the operating temperatures of engines, 3) providing advanced materials for thermal protection systems, and 4) producing geopolymer-based material for space mirror applications. Research was carried out three different classes of materials, advanced metallics, advanced metallic composites, and ceramics. In the latter case, both monolithic and fiber-reinforced materials were evaluated, along with geopolymers. The process-microstructure-property relationships were extensively and critically assessed for these material classes. Much of this research has been published elsewhere in the open literature as journal articles and papers.