Design Methodology for Ceramic Structures

Unique design techniques are required to successfully take advantage of the superior high temperature structural strength of ceramic materials. The design methodology described here combines the results of a finite element stress analysis with a statistical analysis in order to predict the probability of failure of a ceramic structure. The strength degradation of a ceramic material as a result of subcritical crack growth under constant and cyclic loading conditions is incorporated into the methodology. Critical material properties such as strength, Weibull modulus, and the strength degradation exponent are discussed. A tapered disk and a wedge specimen are analyzed. When subjected to thermal shock, these specimens simulate the stresses in critical regions of structures such as the trailing edge of a gas turbine vane. Finally, applications of the design methodology to ceramic transition pieces are discussed where similar probabilities of failure are obtained for single-piece and four-piece designs.