Probalistic Structural Analyses of Ceramic Gas Turbine Components

Abstract

Tokyo Electric Power Company (TEPCO), with the cooperation of gas turbine manufacturers and ceramic component manufacturers, has conducted research to apply ceramic components to the hot parts of gas turbines, such as the combustors, the stator vanes and the rotor blades.

Although ceramics have a very attractive combination of physical and mechanical properties at high temperatures well over 1300°C, their toughness is very low, and their strength shows wider scatter compared to metal materials. These undesirable properties cause the necessity of “design by analysis” of ceramic components.

As a part of TEPCO’s project, therefore, the authors have conducted research to develop a strength evaluation system of structural ceramic components using a probabilistic approach. A computer program,GFICES (Gas turbine - FIne Ceramics Evaluation System), was developed on the basis of statistical strength theory using the two parameter Weibull probability distribution. This program is coupled as a postprocessor to the general purpose structural analysis program MSC/NASTRAN and the dynamic stress analysis program DYNA3D. Main analytical functions of GFICES are the reliability analyses corresponding to fast fracture, static fatigue, dynamic fatigue and the effect of proof testing. The time dependent fracture analyses are based on the assumption of subcritical crack growth (SCG). In addition, several supplemental functions are added in GFICES such as the application of bi-modal Weibull probabilistic theory, the evaluation of aging degradation effects of ceramics on fast fracture, and the reliability evaluation of components subject to non-proportional transient stress history. Bimodal Weibull probabilistic theory is incorporated to take account of both volume distributed flaws and surface distributed flaws of ceramic components.

As an application of GFICES, the reliability of a ceramic rotor blade subject to thermal stress and centrifugal stress is analyzed. It is shown that GFICES can very effectively evaluate the strength reliability of ceramic components.