N. V. Yavors’ka’s research while affiliated with Lviv University and other places

We formulate computational models used to determine the durability of plates with systems of cracks under the action of long-term static loads, high temperatures, and hydrogen-containing environments. These models are based on the first law of thermodynamics, i.e., on the balance of energy components and rates of their changes in metallic materials containing macrocracks and subjected to long-term tension, high-temperature field, and hydrogen-containing environments. We also consider specific cases of periodic and doubly periodic systems of cracks.

We proposed a computational model for the determination of the kinetics of propagation of hydrogen cracks in a body caused by high pressures in these cracks formed due to ultrahigh hydrogen concentrations in the body. The model is based on the deformation criterion of fracture mechanics with regard for the hydrogen concentration, the mechanism of jumplike propagation of hydrogen cracks, and the Fick laws of heat and mass transfer. Using this model, we investigate the kinetics of propagation of a hydrogen crack over the surface of fusion of the base materia with protective coating in the shell of an oilhydrocracking reactor.

We formulate a mathematical model for the determination of the effect of hydrogen on the period of initiation of creep-fatigue macrocrack in the vicinity of a stress concentrator in a plate. By using this model, we find the period of initiation of a macrocrack for a strip with two side notches under cyclic loads, high temperatures, and the action of hydrogen-containing medium. It is shown that hydrogen increases the rate of crack initiation in steel plates.

We propose a numerical model for the evaluation of the influence of hydrogen on the subcritical growth of high-temperature creep cracks in metallic materials. The model is based on the first law of thermodynamics specifying the energy balance and the rates of changes in the energy components in a metallic body weakened by a macrocrack and subjected to the action of long-term static tension, high-temperature field, and hydrogen-containing media.

We propose a computational model for the investigation of the process of growth of high-temperature creep cracks under long-term tensile static loads (dynamic mode of operation) and determine the residual service life of a steam pipe under these operating conditions. It is shown that the indicated loads may lead to the unpredicted fractures of structural elements.

A computational model is proposed for the determination of the service life of structural elements with concentrators under the conditions fatigue and high-temperature creep. The model is based on the energy approach and the representation of the service life of a structural element as the sum of the periods of initiation and subcritical growth of creep-fatigue cracks.