60277 - Life Limiting Aspects of an Mi Sic/sic Ceramic Matrix Composite (Cmc) in Interlaminar Shear at Elevated Temperature 

Life limiting behavior of an MI SiC/SiC ceramic matrix composite (CMC) was determined under interlaminar shear at 1316^oC in air using double-notch-shear (DNS) test specimens. The three different interlaminar-shear loading configurations of dynamic fatigue, static fatigue, and cyclic fatigue were employed to assess their individual respective life behaviors. The MI SiC/SiC CMC exhibited low susceptibility to fatigue (‘slow crack growth’) regardless of loading configuration, indicating that resistance to interlaminar slow crack growth of the CMC was substantially high. A Life prediction model for interlaminar shear in cyclic fatigue was developed based on the fracture mechanics framework using a power-law crack growth formulation. This cyclic fatigue life-prediction model as well as the previously developed dynamic and static fatigue models were all in good agreement with the experimental data. This indicates that the governing failure mechanism under interlaminar shear was consistent, independent of fatigue loading configurations, which can be formulated with a power-law type of crack growth law. Microstructural analysis was also done to assess how cracks interacted with adjacent material constituents of fibers, matrices, interfaces, defects, etc. The interlaminar life-limiting aspects of the MI SiC/SiC were also compared with those of different SiC/SiC CMC material systems as well as with oxide/oxide CMCs.