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Characteristics of fracture toughness of polycrystalline ceramics areinvestigated by numerical simulations and indentation fracture test for polycrystallinealumina ceramics. Generally ceramics fracture from a defect. A crack propagates fromthe defect stably under monotone increasing load before catastrophic fracture. Thisstable crack propagation determines the characteristics of fracture toughness ofceramics. In this study we perform crack propagation simulations by using boundaryelement method. The relationship between the micro crack extension resistance and themacro fracture toughness in polycrystalline ceramics is investigated. According to theresults, the crack extension area is wide and the standard deviation of the macrofracture toughness is large, so that the standard deviation of the micro crack extensionresistance is large. It is worth noticing that the aforementioned results obtained in thepresent paper might be useful also when stable crack propagation due to fatigueloading is investigated.