Feofentov M. The influence of changes of properties of surface layers of materials on the kinetics of the thermal stress state of structural elements under thermal cyclic loading conditions

The purpose of the work are the development and scientific justification of approaches to estimation of the impact of changes of properties of surface layers of materials on the kinetics of the thermal stress state of structural elements under thermal-cycle loading conditions in order to take such changes into account in methods for determining the residual operating life. The study object is the processes of damage and thermal stress state of elements of power and rocket systems under conditions of cyclic loading of high-temperature gas flows. Experimental methods and research techniques are used, in particular gas-dynamic stands equipped with modern information and measuring complexes, appropriate devices and methods of physics of metals research, methods of numerical modeling of thermal stress-strain state of models and structural elements based on standardized software designed for modern PCs, as well as the Space software package. The scientific novelty of the study is that the necessity of the consideration of the degradation of properties of surface layers of materials in problems of determination of the bearing capacity of structural elements that are operated under thermocyclic loading conditions is substantiated as a result of a complex of investigations of processes of the degradation and their influence on the kinetics of the thermal stress-strain state of structural elements. The practical significance of results of experimental and numerical studies is that established patterns of change of properties of a material of surface layers allow quantitatively evaluate the degree of damage of elements of structures that are operated under thermocyclic loading conditions and can be used in the performance of routine maintenance, repair, and the developed method of evaluation of thermal stress-strain state allows to increase the correctness of estimation of their residual service life time "by a technical condition". The developed methods are used in solving practical problems of simulating the conditions of aerodynamic heating of elements of rocket and space engineering structures according to orders of Yuzhnoye State Design Office.