Thermal Shock Analysis and Testing of Simulated Ceramic Components for Gas Turbine Applications

Abstract

A ceramic gas seal for a utility gas turbine was designed and analyzed using ANSYS and CARES/LIFE. SN-88 silicon nitride was selected as the candidate material. The objective was to validate the failure prediction methodology using rectangular plates, which were thermally shocked in a fluidized bed. The failure prediction methodology would then be applied to the representative component geometry. Refined ANSYS finite element modeling of both the plate and component geometries was undertaken. The CARES/LIFE reliability analysis of the component geometry for fast fracture was performed for two cases: (I) steady-state thermomechanical loads during normal gas turbine operation and (II) transient thermal shock loading during a turbine trip. Thermal shock testing of alumina disks was performed in order to gain confidence in the testing and analysis procedures. Both notched and unnotched SN88 plates were then tested. Failure modes were identified through flexure tests and data censoring was performed using SAS. Weibull modulus was assumed to be invariant with temperature and the scale parameter was assumed to vary through a scaling variable such that multiple data could be pooled.