Thermal shock residual strength of functionally graded ceramics

When subjected to severe thermal shocks functionally graded ceramics (FGCs) suffer strength degradation due to microcrack growth, coalescence and macrocrack propagation induced by the shocks. This paper presents a thermo-fracture mechanics model to study the residual strength behavior of thermally shocked FGCs. It is assumed that thermal shock damage mainly results from the extension of a pre-existing edge crack initially located at the thermally shocked surface of an FGC specimen. Thermal shock threshold, or the critical thermal shock that causes precipitous strength drop, is determined. The paper describes applications of the model to calculate the thermal shock residual strength of FGCs as a function of thermal shock severity. Two FGC systems, i.e., Al2O3/Si3N4 and TiC/SiC FGCs are considered in the numerical studies. The numerical results show that material gradation profile has a pronounced effect on the thermal shock threshold and the thermal shock residual strength of FGCs.