Mamedov S. The physical nature of the local stress of brittle fracture of polycrystalline metal

The thesis is devoted to the investigation of the physical nature of local stress of fracture in polycrystalline metal. We elaborate the model of intensity of generating of crack nucleus and study the factors which have an influence on this. We found that the local scale effect is observed at the brittle fracture of metal in the vicinity of the stress concentrator. This effect manifests itself in the excess of local stress of fracture in the conditions of stress concentration over the level of brittle strength Rmc. We established that the dependence of the brittle fracture probability on the amount of crack nucleus which appear in the fracture initiating zone ("process zone") is the reason of the appearance of this effect. The value of the local scale effect is given by (i) the "process zone" volume and (ii) the relative value of the gradient of plastic deformation in this volume. It was demonstrated that the level of fracture toughness of reactor steels after neutron irradiation is caused by two main factors, namely by the radiation strengthening and the increasing of the intensity of crack nucleus generation in the irradiated metal.