The size-effect predictions from double-K fracture criterion, characterized by two parameters: the initiation toughness and the unstable toughness, are compared with the fictitious crack model or cohesive crack model for practical (laboratory) size range of three-point bend test notched specimens. Both the fracture models, although, adopt different crack propagation criteria, they yield indistinguishable crack initiation and unstable fracture loads for usual laboratory size specimens. Notable difference in the predicted crack initiation and unstable fracture loads are observed for asymptotic large size specimens and these loads are more conservative than those obtained using the fictitious crack model by ∼20 and 22%, respectively.
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