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 thermo-mechanical loads during normal gas turbine operation and II) transient thermal shock loading during a turbine trip. Thermal shock testing of alumina disks were 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.

Tensile Creep and Rupture of Silicon Nitride

“…Previous references to the creep and rupture of the silicon nitride of this study can be found in the literature. [15][16][17][18][19][20][21][22][23] The data from this study are part of a much larger engineering study of the suitability of monolithic silicon nitride for gas turbine engine applications. 24…”

Reliability of a Conceptual Ceramic Gas Turbine Component Subjected to Static and Transient Thermomechanical Loading

“…The 7IS specimens were prepared by NGK and were machined in a direction parallel to the loading axis. The 71S flexure data from 90 tests were evaluated to estimate temperature-independent Weibull moduli and temperaturedependent Weibull scale parameters for two volume-distributed fracture origins, pores and large grains (Rajiyah et al, 1995).…”

“…A life-limiting condition for ceramic gas turbine components is fast fracture during a full load turbine trip. An atmospheric thermal shock test rig was constructed for the purposes of proof test development and reliability model validation (Rajiyah et al, 1995). The rig consisted of an electric furnace, an air-fluidized bed of alumina particles and an elevator apparatus which rapidly transferred the specimen from r ",...""........"",...,…”

“…Stress and reliability analyses for the conceptual shroud were performed using ANSYS and CARES/LIFE, respectively, for two cases: 1) steady-state thermomechanical loads during baseload gas turbine operation and 2) transient thermal shock loading during a full load turbine trip. The analysis methods were described previously (Rajiyah et al, 1995). The method for predicting component reliability during a turbine trip was validated via thermal shock analyses and experiments.…”