Influence of pore size on fracture strength of porous ceramics

Porous ceramics possess the excellent penetration and adiabatic characteristics, etc., and are used as heatproof filter materials for environmental equipments, etc. Moreover, porous ceramics controlled with porosity and pore size in the wide range have been actively developed. However, how the strength characteristics of porous ceramics are influenced by porosity and pore size of the material are not understood still enough. In this research, the evaluation tests on fracture strength, fracture energy and fracture toughness of porous alumina ceramics specimens which porosity are almost equal, while pore sizes are different mutually were performed, and the relation between the pore size and the fracture strength was obtained. The tests results show that the dispersion of fracture strength data is few though fracture strength of porous ceramics is lower than that of highdensity ceramics. Moreover, the relation based on linear fracture mechanics between the defect size and the fracture strength is valid when the one that a pore accompanies with the peculiar defect observed in fracture surface of the material was assumed to be a defect size. In addition, fracture energy increases with the increase of pore size, and this seems based on a crooked propagation path of a crack. Finally, the process zone fracture model by considering the effect of the pore and grain size of the material are presented. According to this model, for all pore size and crack length, it was shown that the fracture strengths of cracked specimens are evaluated.