Nemanezhyn Y. Development of methods for calculating the high-temperature strength of gas turbine blades under static and dynamic loading

The dissertation is devoted to the study of high-temperature strength characteristics of gas turbine engine turbine blades under static and dynamic loading. Object of research is the process of development of elastic deformation and creep in operating modes of turbine blades made of single-crystal nickel heat-resistant alloys. The subject of research is the characteristics of high-temperature strength of turbine blades under static and dynamic loading with consideration of anisotropic properties of single-crystal alloys. The purpose of the dissertation is to develop theoretical and experimental approaches to determining the characteristics of high-temperature strength of turbine blades under static and dynamic loading, taking into account the peculiarities of the complex volume-stressed state of the blades, loading in places of stress concentration and anisotropy of elastic and other mechanical properties of nickel heat-resistant alloys. The introduction provides the rationale for choosing the topic of the dissertation, provides information on the subject and object of the investigation, research methods, and indicates the scientific novelty of the presented work. There is information about the approbation and implementation of the results, as well as the applicant's contribution to published scientific works. In the first chapter, a review of scientific and technical sources of information related to modern approaches to assessing the high-temperature strength of turbine blades was performed. The peculiarities of mathematical modeling of the anisotropy of heat-resistant alloys and its influence on the strength characteristics of turbine blades are substantiated. The information on modern and fundamental research in the field of creep, long-term and fatigue strength of nickel single-crystal heat-resistant alloys is systematized. In the second chapter, the influence of the anisotropy of the elastic properties of single crystals on the natural frequencies and vibration modes of GTD turbine blades is investigated. A method for determining the elastic characteristics of single crystals for different temperatures is developed and described. A method for calculating the elastic properties of heat-resistant single-crystal alloys is proposed to estimate changes in the natural frequencies of turbine blades vibrations when the crystallographic systems of single-crystal directions are rotated. A modal analysis of the turbine blade was performed. The construction of Campbell diagrams is performed, the main dangerous harmonics of the exciting forces are determined, and an example of detuning from dangerous resonant modes and vibration frequencies of the blade is given. The verification process of the calculated discrete mathematical model of the blade is substantiated. The third chapter is devoted to the process of modeling the stationary creep of GTE turbine blades. A mathematical model of single-crystal alloy creep is developed, as well as a method for calculating creep constants at the stationary stage. The fourth chapter describes a method for assessing the influence of the anisotropic properties of single-crystal heat-resistant alloys on the durability of gas turbine blades. Using the developed method, based on the modeling of the distribution of the Larson-Miller parameter, a numerical experiment was conducted to determine the time to turbine blade failure for different single-crystal CGOs. The fifth section is devoted to the numerical and experimental study of the high-temperature multi-cycle fatigue strength of single-crystal turbine blades. The conclusions summarize the results, describe the main scientific tasks that were solved in the course of the study. Scientific novelty of the thesis: For the first time, a method for modeling the effect of changing the orientation of crystallographic directions on the natural vibration frequencies of turbine blades made of single-crystal alloys has been developed. For the first time, the results of the modal analysis were verified by experimental study of the first and second frequencies of resonant vibrations of a cooled blade of a high-pressure turbine of an aircraft engine. For the first time, experimental studies of the fatigue strength of single-crystal gas turbine blades under high-temperature multi-cycle loading were carried out. For the first time, a mathematical model of anisotropic creep of single crystals with cubic symmetry and a procedure for identifying material creep constants were constructed. For the first time, a numerical-analytical method for calculating the long-term strength of single-crystal turbine blades under centrifugal force loading was developed. The results of research confirm, with an act of implementation at “Ivchenko-Progress” SE, Zaporizhzhia, the practical and theoretical value of the developed methods, provide practical recommendations on the application of the developed methods and consider the prospects for their further improvement.