Statistical Fracture Analysis of Brittle Materials in Thermally Stressed Components

Abstract

Thermal stress fracture in brittle materials is treated with a Weibull statistical analysis technique. The probability of failure and size effect is predicted by combining a risk analysis with finite element heat transfer and stress analysis. In a thermal transient the maximum probability of failure can occur at times greater than the time of maximum thermal stress. In many situations the thermal stress in a structure increases with size while, due to the size effect, the strength of the structure decreases. Thermal shock tests of silicon carbide and alumina demonstrate the scatter in the fracture strength. The average fracture strength of alumina is well-predicted, but the strength of silicon carbide disks is apparently affected by a nonhomogeneous flaw population. Applications of the statistical analysis technique to thermal stress situations in gas turbine vanes and combustors are reviewed.