Prediction of thermal fatigue life of ceramics

Abstract

On the assumption that the thermal fatigue life of ceramics is determined mainly by the duration over which a crack reaches a small critical length, a prediction of the life was made by application of fracture mechanics to ceramics based on subcritical crack growth. Approximated formulae, such asN/N′≃(ΔT _N′ /ΔT _N )ⁿ, were derived, whereN andN′ are the lives for temperature differences of ΔT _N and ΔT _N′ , respectively, andn is a material constant. Experimental examination showed that the formulae proved to be valid for glass, sintered mullite under moderate shock severity, and zirconia. Data given by other authors also prove their validity. The deviation of the life from the formulae for sintered mullite under a thermal shock of extremely low severity, suggests that a certain mechanism, for example strengthening, is needed to understand the life of the sintered mullite. Moreover,n determined from the thermal shock experiments is comparable with that given in data determined by a mechanical method.