The Hardening Type Influence of Pressure Vessel Ratcheting in Case of Thermal Cyclic Loads

Classical studies of the ratcheting of pressure vessels under thermocyclic loading assume that the structural material is elastic-plastic without hardening (ideal plasticity). This allows for an analytical solution to the problem, which is typically presented in the form of a "Brie diagram" plotted on the axes of mechanical and thermal stresses. The actual behavior of a material under cyclic thermo-mechanical loading requires more complex mathematical models that consider isotropic, kinematic, or mixed isotropic-kinematic hardening effects. These additional factors significantly affect the adaptability characteristics of the structure. Modern Russian and international design standards (PNAE, GOST, ASME, RCC-MR) for nuclear power plant reactor installations (reactors using liquid metal coolants, high-temperature gas-cooled reactors, etc.) allow for the occurrence of plastic deformation in the material but limit the accumulation of these deformations over the lifespan of the structure. Specifically, these standards regulate the use of both a simplified method based on the classic Bree solution for perfectly plastic materials and a direct finite element analysis of the structural life cycle under conditions of plastic deformation and high-temperature creep. In this paper, we investigate the problem of thermal cycling of a pressure vessel using different hardening models. We have developed a numerical algorithm to construct and analyze the evolution of adaptation diagrams depending on the number of cycling loads. We perform a specific numerical calculation for the cyclic thermal force loading of a steel pressure vessel with known parameters for elastic-plastic deformation models. This is done in the context of predicting the design life based on current regulations and standards for the design of nuclear power plant equipment.