Extreme-value statistics analysis of fracture strengths of structural ceramics failing from pores

The relation between pore-size distribution and the fracture-strength distribution was investigated for two structural ceramics, 2 m% Y2O3-TZP and silicon nitride, using the theory of extreme-value statistics. Specimens of Y-TZP with a controlled distribution of artificial pores were fabricated from a commercial powder in which spherical polymeric particles were mixed and burned out prior to sintering. On the other hand, the commercial sintered silicon nitride failed exclusively from pore/agglomerate defects intrinsic to its processing. The pore-size distributions in as-sintered specimens were measured using an automatic image analyzer. Specimens were fractured in three-point bending under inert conditions. The sizes of the fracture initiating pores (flaws) were measured from SEM fractographs. The initial pore-size distributions and the resultant fracture-strength distributions were then correlated using linear elastic fracture mechanics models of cracks around pores. The applicability of extreme-value statistics in the fracture behaviors of the two materials is discussed