Coupled thermo-mechanical analysis of stress-strain response and limit states of structural materials taking into account the cyclic properties of steel and stress concentration

Two groups of governing equations have been obtained due to the extensive theoretical and experimental studies in the field of mechanics of deformable solids conducted worldwide: (1) constitutive equations and criteria for damage and fracture in an isothermal formulation and (2) relationships between elastoplastic deformations and dissipative heat release. The paper considers the problems of the coupling between the processes of deformation and fracture and the kinetic effects of self-heating of the material due to the development of deformations. These problems are quite complex in the experimental and theoretical terms for relatively limited (up to 0.1), increased (up to 0.2) and large (up to 0.5) strains both under uniform and nonuniform states stresses and strains (with stress concentration factors ranging from 1 to 3). This leads to an essentially nonlinear formulation of coupled thermo-mechanical problems. The paper focuses on the scientific and methodological aspects of the formation of constitutive equations for the structural materials subjected to static and cyclic elastoplastic loading, and on determining the relationship between the processes of deformation and self-heating of the material due to internal heat release that occurs at limited operational strains that are close to isothermal ones as well as large static and cyclic strains that are close to the fracture ones and are accompanied by intensive (up to 500-600 degrees C) self-heating. The results of the experiments performed on specimens made of two different structural steels with different mechanical properties (heat-resistant and radiation-resistant low-alloy chromium-molybdenum-vanadium steel and austenitic stainless chromium-nickel-titanium steel) are presented. Precision measurements of temperatures of thematerial at various levels of strainswere taken during static and cyclic tests that were carried on smooth and notched specimens under high-vacuum conditions using thermal imaging systems and high-sensitivity thermocouples. The results of the performed computational and experimental studies can be used for the estimation of strength and service life of highly loaded structural components of nuclear reactors, rocket engines, supersonic aircraft and other complex technical systems.