GRAIN-BOUNDARY TOUGHNESS EFFECTS ON CRACK-PROPAGATION IN BRITTLE POLYCRYSTALS

Quasi-static crack advance has been statistically analysed as a functi on of interfacial toughness using a randomized two-dimensional. polycr ystalline model. The average macroscopically observable toughness is c alculated to be a strong function of interfacial toughness if the inte rfaces, grain boundaries in this case, have a fracture resistance less than approximately 1/2 that of the grains. Alternatively, the relativ e amount of crack deflection, as indicated by the percentage of interf acial failure, is a relatively homogeneous function of the interfacial toughness if interfacial fracture resistance is higher than about 0.3 Gamma(int). Combining these predictions gives a quantitative measure of both the expected material strength and resulting fracture surface roughness. Results exhibit good agreement with a similar analytical mo del which considers a deterministic approach for a similar geometry. F inally, the method employed here is general enough to be used for any polycrystalline ceramic.