Hierarchy of strength criteria of structured brittle media. Satellite initiation of microcracks

The quasi-static growth of plane cracks in media with a regular structure is studied. The structures characterized by one linear dimension are considered. Consistent discrete-integral strength criteria for normal-rupture cracks for each structure are proposed. For three structures, the critical stress-intensity factor and the critical lengths of the normal-rupture cracks are estimated. For these critical parameters, a limiting passage is possible in the relations obtained where the stress-intensity factor and the crack lengths tend to zero (the classical relations do not admit this limiting passage). Modifications of the criteria proposed make it possible to describe the satellite initiation of a microcrack at the macrocrack tip if monocrystalline grains of the material are arranged in a special way in the vicinity of the macrocrack tip.