Thermal shock of monolithic ceramics

Equation (15.24) shows that, for high resistance to crack initiation, high strengths combined with low stiffness and CTE are required. Under mild thermal shock conditions (e.g. in a boiling water quench) the thermal conductivity also becomes important, and (15.24) is modified to give  

The resistance to crack propagation is characterised by the following parameter  

Different parameters impose different requirements on ceramic materials depending on whether fracture resistance or crack propagation resistance is of prime importance. The values of the above parameters for a range of ceramic materials are presented in Table 15.1, where the property dependence of thermal shock behaviour can be observed. A variety of other parameters 

Cracks are unstable between those limits for which  

Evans (1975), Evans and Charles (1977), and Emery (1980) performed more refined fracture mechanics studies regarding the onset and arrest conditions Bahr et al. (1988) and Pompe (1993) extended this work and considered the propagation of multiple cracks while Swain (1990) found that materials showing non-linear deformation and A-curve behaviour have a better resistance to thermal shock. More specifically, the behaviour of a crack in the thermal shock-induced stress field was deduced from the dependence of the crack length on the stress intensity factor. Unstable propagation of a flaw in a brittle material under conditions of thermal shock was assumed to occur when the following criteria were satisfied  

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