Grain-size dependence of microcrack initiation in brittle materials

In this paper, the energy criterion is extended to predict the relationship between the temperature of microcrack initiation (T_MB) caused by thermal stressing in brittle materials and the grain size. The relation can be extrapolated to room temperature to provide an estimate of the critical grain size. When the relation was compared to literature data, it was found that: (1) the predicted inverse square root relation of T_MB to grain size is satisfied; (2) the room temperature intercept on the grain-size axis agrees well with the measured critical grain sizes. Also presented is a graphical method, based on the proposed relation, by which an engineering estimate of the critical grain size may be made from a minimal set of data.