Strength/microstructure relation in Al sub 2 O sub 3 and TiO sub 2

It has been traditional to interpret the strength of ceramics in terms of the mean grain size. This paper investigates, critically, the use of strength vs mean grain size{sup {minus}1/2} plots and shows them to be inconsistent with fracture mechanisms theory. It is suggested that strength be plotted against maximum grain size{sup {minus}1/2} and interpreted by means of known fracture mechanics criteria. A model is presented based on the Griffith criterion which takes into account processing defects and the effect of large grains and which explains the experimental results.