Теоретичні та експериментальні методи визначення характеристик міцності лопаток турбін при термомеханічному навантаженні

Abstract

The subject of this article is the methods of research and evaluation of the properties of turbine blades of a cooled structure under thermomechanical loading. The purpose of the article is to review the world achievements of leading enterprises and research institutions in the issue of fatigue tests of turbine blades under complex loading (cyclic temperature exposure, dynamic and static loading), as well as an overview of the state of this topic at SE "Ivchenko-Progress" and suggestions for its further studying. As a result of the analysis of publications and scientific articles, it can be concluded that specialized research institutes and leading aircraft engine-building enterprises from the end of the twentieth century are studying the properties of turbine blades in the conditions of their operation as part of an engine. In world practice, there are calculated and experimental methods for thermomechanical testing of turbine blades. These tests are aimed at determining the most damaging loads, establishing the flight cycle modes at which these loads are recorded. As a result, it was found that the greatest threat to the strength of the turbine blades is carried by transient modes of engine operation, which are short in time (measured in seconds), but at which there is a change in the parameters of the temperature field, loads from axial and centrifugal forces. And it is the cycling of these parameters that leads to a decrease in the cyclic durability of the turbine blades, especially of the cooled structure (the presence of perforations, internal cooling channels, and other structural elements leads to a complication of the volumetric stress state of the blades). The article analyzes various crystallographic structures of blades and their relationship with the volumetric stress state; examples of studies that were carried out at SE "Ivchenko-Progress" and their results are given, which emphasize the need for further experiments in the field of assessing strength characteristics under complex cyclic loading. An example of an installation for testing blade joints and samples of gears is considered, which can be adapted for testing blades with three-component loading (temperature, dynamic loads, and imitation of the effect of centrifugal forces). It is concluded that when using exclusively computational methods, it is impossible to reliably estimate the level of stresses and their distribution since the calculations are limited by the boundary conditions, which are set according to the capabilities of a particular computational model. Summing up, it can be noted that it is advisable to start assessing the strength of blades under thermomechanical loading with several series of tests of samples of blade material to study the effect of temperature and power cycles of loads, the effect of the orientation of the load vector concerning the crystallographic orientation of the blade. It is noted that tests of full-scale blades under thermomechanical loading are also important since the features of the volumetric stress state of the material during real operation of the blades as part of an engine are not reproduced during testing of samples. The above entails the development of methods and specialized installations for thermomechanical testing.