Creep-Rupture and Fatigue Behavior of a Notched Oxide/Oxide Ceramic Matrix Composite at Elevated Temperature

The inherent resistance to oxidation of oxideoxide ceramic matrix composites makes them ideal for aerospace applications that require high temperature and long life under corrosive environments. The ceramic matrix composite CMC of interest in the study is the Nextel tm 720Alumina N720A which is comprised of an 8-harness satin weave of Nextel tm fibers embedded in an alumina matrix. One of the top applications for N720A is in the combustion section of a turbine engine. This will require mounting and shaping the material with rivets and possibly sharp edges thereby introducing geometry based stress concentration factors. Sullivans research concentrated on the effects of central circular notches with a notch to width ratio 2aw of 0.33. This study expands upon his research to include the creep and fatigue response to double edge notch geometry with the same notch to width ratio of 0.33. In short, 12.0 mm wide rectangular specimens with two edge notches of 2 mm depth and 0.15 mm width were subjected to creep and fatigue loading conditions in 1200 deg. C of air. All fracture surfaces were examined by an optical microscope and a scanning electron microscope. Sullivans research concluded that specimens with a central circular notch were insensitive to creep but slightly more sensitive to fatigue than unnotched specimens. In contrast, this study showed significant creep and fatigue life reductions for double edge notch specimens.