Two basic concepts of brittle fracture are considered: the first involving stage-by-stage interatomic bonds decohesion at the crack tip, the second - microcrack coalescence. Quantitative evaluation has been made of the material threshold and minimal fracture toughness values which correspond to the above concepts. The paper presents the analysis of methods for the experimental evaluation of two main structure parameters, which govern the material fracture, and discloses their physical meaning. These are the characteristic distance and cleavage stress. It also considers the methods of a priori express-evaluation of the materials fracture toughness from their conventional mechanical characteristics.
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