The concept of limiting equilibrium in the theory of brittle fracture. The condition of finiteness of stresses and smooth elosinfl and its relation to the energetieal conditions of equilibrium. Some experimental grounds. Cohesion forces for an ideally brittle body and quasi-brittle body. Cohesion modulus and surface energy. Non-linear problem of the equilibrium of a body with cracks. Stability of creeks. Analysis of the conditions of fracture. Strength limits for a brittle body.
Time processes in fracture: statistical breaking of bonds, rheological processes of the deformation of bonds. The possibility of taking time processes into account only in the edge region of cracks. Kinetical characteristics of processes of variation and deformation of bonds.The dependence of the cohesion modulus and of the surface energy on the rate of crack extension. Changes in the statement of the non-linear problem of equilibrium of a body with cracks when taking time processes into account in the edge-region of the crack. The time of rupture under fixed load and under fixed rate of loading. The general set of equations for the cohesion modulus and the length of the edge region. Tile full transformation of bonds in the edge region, elastic deformation of bonds. The derivation of the Zhurkov formula for the time of rupture. The derivation of the rule of Bailey. Some questions concerning the development of cracks under fatigue fracturing. Some questions of nucleation and propagation of cracks under the action of laser radiation on transparent dielectrics: some experimental facts and dements of the theory.