Vibrations in engineering and technology

Bovsunovsky Anatoliy  – Doctor of Technical Sciences, Professor, Professor of the Department of Heat Power Engineering of National Technical University of Ukraine " Igor Sikorsky Kyiv Polytechnic Institute ", 03056, 37 Peremohy Ave., Kyiv, Ukraine; e-mail: apbovsunovsky@gmail.com).

Nosal Oleksandr  – PhD student of the Department of Heat Power Engineering of National Technical University of Ukraine " Igor Sikorsky Kyiv Polytechnic Institute ", 03056, 37 Peremohy Ave., Kyiv, Ukraine; e-mail: oleksandrnosal1998@gmail.com

In real operational conditions structural elements of steam turbines are subjected to a wide range of thermal and mechanical loading. Even substantial reserve of static and dynamic strength, laid down at the stage of turbine design, can not prevent the appearance of fatigue cracks in structural elements, which lead to catastrophic failures. One of the reasons of damage in structural elements of turbine is technological operations used in the process of manufacture (forging, turning, and milling, heat treatment), since they are accompanied with plastic deformation of material, which is the physical basis of the so-called distributed fatigue damage. It accumulates during long-term cyclic deformation and turns into local damage of a fatigue crack type. In addition, the appearance of cracks in turbine shafts is caused by complex geometry, that is, by the presence of fillets and grooves, which are stress concentrators and, therefore, potential areas of initiation and growth of fatigue cracks. The high pressure rotor of the K-200-130 steam turbine was used to simulate the process of crack growth at forced transverse vibrations of the rotor when it passes through the first critical speed. At this the amplitude-dependent energy dissipation typical for metallic materials was taken into account. There was estimated the maximum stresses arising in the rotor when it passed through the critical speed rotation and the number of loading cycles leading to the crack growth. It was assumed that a crack with a depth of about 1 mm has formed on the surface of the rotor, which is the maximum permissible depth according to the instructions for safe operation of the turbine. The growth rate of this crack is predicted based on the fracture mechanics approaches through the determined maximum stresses in the section with a crack and experimental dependences of the crack growth rate on the stress intensity factor range. Based on the model, the crack growth time is predicted until the rotor loses its bearing ability. Predictions are made for different scenarios of loading and mechanical properties of rotor steel.

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