Chapter 72. Creep Rupture Behavior of Oxide/Oxide Nextel ™720/AS and MI SiC/SiC Composites with Effusion Holes

Summary

Woven Oxide/Oxide and SiC/SiC ceramic matrix composites (CMC) are targeted for high-temperature aerospace applications such as combustors, combustor liners, exhaust washed structures, exhaust nozzle flaps and seals, and blade outer air seals. Some of these components contain stress concentration sites such as holes and attachment points. Components such as combustors may also include effusion holes, which are used to lay down a film of cooling air on the hot wall to create a boundary layer effect and to cool the component by providing more internal surface area. During service, these locations will be subjected to long-term exposures and thermal stresses. Hence, the knowledge of the effect of sustained (creep) loading on the deformation and rupture of notched oxide/oxide and SiC/SiC composites is required for durability assessment. The results from creep tests of unnotched and notched Nextel^TM720/Alumina-Silica (Nextel^TM720/AS-0) and Melt Infiltrated (MI) SiC/SiC are discussed in this paper. Nextel^TM720/AS-0 was evaluated at 1100°C and SiC/SiC at 982°C and 1200°C in laboratory air. In the case of large notches, i.e., notch length greater than average tow size, the notch-sensitivity increased significantly under sustained loading for both composite. Under sustained loading, the effusion hole (diameter less than tow size) specimens also exhibited notch-sensitivity comparable to that of specimens with large notches.