Dolinska I. The determination of the constructions elements life-time under the variable in time loadings and high temperatures

The thesis consideres the development of mathematical models for description of kinetics a creep-fatigue crack growth in deformable solids. The mathematical model for research a creep-fatigue crack growth in construction materials under cyclic loads and high temperature has been formulated. It based on the first law of thermodynamics concerning to mechanics of solids slow fracture. The mathematical model for determination of creep-fatigue crack initiation period in plates with stress concentrator has been built. The calculation model for research a high temperature creep crack growth under long-term static breaking in time load has been formulated (maneuvering regime exploitation). As a result the differential equation with initial and eventual conditions has been obtained. It is a mathematical model for determination of kinetics and sub critical growth period of higt temperature creep crack in construction materials. The criterion of high temperature cyclic strength of thin-walled construction elements with cracks has been formulated. The formulation of the problem about sub critical creep-fatigue crack growth has been made. Approximate solutions of the problem with creep-fatigue crack in the wall of the steam pipeline and in the disk and shaft of steam turbine are obtained and in such way the residual lifetimes has been estimated.