Generalized sufficient strength criteria. Description of the pre-fracture zone

A generalized sufficient discrete–integral strength criterion is proposed for opening mode cracks in structured media. The criterion is constructed for materials of two types: an elastoplastic material with restricted deformability and an elastic ideal-plastic material. A detailed description of the pre-fracture zone is given. The cross-sectional dimension of the plastic zone near the tip of the initial crack is used as the cross-sectional dimension of the pre-fracture zone. It is assumed that the critical opening of the initial crack depends on the deformability of plastic materials. Based on the ratio of the length of the pre-fracture zone to the length of the initial crack, the following fracture types are distinguished: brittle, quasibrittle, quasiviscous, and viscous. For the first three types, the fracture curves are described in detail. Exact and approximate equations are proposed that relate critical parameters to the theoretical strength of a granular material, grain size, and parameters characterizing the averaging interval and the damage of the initial and deformed material.