Simulating the Failure Behaviour of Ceramic Components Under Gas Turbine Conditions

Advanced monolithic ceramics have a good potential to survive under the severe thermal and mechanical loading conditions which are present in stationary gas turbines. Long term volume stability and high creep resistance are hard to achieve from a materials point of view but comparatively easy to verify. Resistance against thermal shock loading, on the other, has to be tested in a test rig, and test results obtained in the lab have to be scaled up to provide a database for a reliable design. This implies that advanced methods of fracture statistics have to be used. In this paper, failure probabilities under thermal shock loading are calculated using a modified version of the Weibull theory which takes the pronounced stress gradients into account. The basic idea is to determine the stress intensity factors of the natural flaws using weight functions. The new approach is used to estimate the failure probability in a thermal shock experiment which is designed to simulate critical gas turbine conditions. The predicted value of the failure probability is lowered by a factor of about 5 if the stress gradients are taken into considerations. The agreement between theory and experiments is very good.Copyright © 2002 by ASME