Testing Ceramic Matrix Composites for Gas Turbine Combustion Chamber Panels

Over the last 15 years, aircraft engine manufacturers and research centers have conducted many demonstration tests of combustion chambers made of ceramic matrix composites (CMC’s). However, even though some deterioration... [ view full abstract ]

Over the last 15 years, aircraft engine manufacturers and research centers have conducted many demonstration tests of combustion chambers made of ceramic matrix composites (CMC’s). However, even though some deterioration modes have been described and reported in the literature, relatively small amount of data is available for predicting life and reliability of CMC’s in such hot section static components. Up to now, in laboratories, most material characterization tests have simulated tensile loading, which is typical of rotating components.

In a goal of better understanding durability of CMC’s under the cyclic thermal stresses of a combustion chamber, this paper proposes a simple test procedure for subjecting the materials to similar conditions in laboratory. An experimental apparatus was assembled that produces a temperature gradient across the thickness of a CMC sample, while holding the sample at its two extremities, in order to simulate the bending stress that would be observed in a combustor panel. The material sample is heated on one face with an infrared lamp heating system, and cooled on the opposite face by radiation and forced convection. The shape of the sample is designed to maximise bending stresses and concentrate potential damage at its center. Bending response of the sample is monitored periodically in order to observe damage initiation and progression, either interlaminar rupture or in-plane cracking.

Validation tests were performed where an oxide-oxide CMC sample was heated up to about 1200 degrees C on surface. Test conditions achieved with the proposed experiment are compared to real engine conditions by analysis. Even though the simplified material sample is subjected to bending stress in one direction only, and its stress distribution does not represent all possible combustor panel geometries and conditions, it is expected to show deterioration modes that are representative of typical gas turbine static components.