Effect of pore clustering on the mechanical properties of ceramics

The reduction in strength and, to a lesser extent, Youngʹs modulus with increased amounts of discrete pores is frequently greater than that predicted by models based on a homogenous pore distribution. The effect of pore distribution has been examined in the present work by producing samples containing a non-homogenous distribution of pores and comparing the results with data reported for samples containing homogenously distributed pores. Youngʹs modulus and, to a greater extent, strength were shown to have stronger dependencies on the porosity content than would be predicted for homogeneous samples. By considering the material as a composite consisting of a pore-rich continuous phase containing a dispersion of pore-free material, various models were used to predict behaviour. It was found that the strength of the material is likely to be governed by the properties of the continuous phase, while the Youngʹs modulus is a function of the properties of the two phases, with the porous phase being described by the Spriggs equation. The implications of the different dependencies of strength and Youngʹs modulus in terms of the resistance to crack propagation following a thermal shock were then considered. Predictions of retained strength were in good agreement with those observed after water quenching.