Analysis of Irradiation Swelling and Irradiation Creep Models with the Stress Effect Account in the Problems of Inelastic Strain Mechanics. Part 1. Formulation of Constitutive Equations

Modern models of irradiation swelling and irradiation creep are considered, in which the damaging dose, irradiation temperature, and influence of stress state on swelling and creep of irradiated material are taken into account. Using these models, constitutive equations of material behavior are formulated, which makes it possible to describe the non-isothermal processes of inelastic strain, taking into account irradiation swelling and irradiation creep strains. The loading process is broken down into separate computational stages, and for each of them the equations of plastic flow and irradiation creep are integrated within the loading stage. Through integration, constitutive equations for the full stress and strain components are derived, which allows the processes of active loading, unloading, and reloading to be described. The irreversible strains in these equations include accumulated plastic strains, irradiation swelling, and irradiation creep strains. The derived equations are treated as constitutive equations for irradiation creep, in which creep strain is defined as strain that includes instantaneous plastic strain and creep strain. Elastic-plastic strain curves that take into account the accumulated damaging dose and irradiation temperature are transformed into a functional dependence that describes the strain of irradiated material depending on the intensity of irradiation creep strain growth during the loading stage. The application of the formulated equations to the solution of practical problems contributes to the persistence of computational processes that makes it possible to use extended loading stages for calculations. At the same time, the study of the properties of the obtained constitutive equations is considerably simplified in comparison with the analysis of plasticity and creep equations in finite increments. Initial prerequisites for the formulation of constitutive equations of irradiation creep based on the full model of swelling, which takes into account the accumulated irreversible strain, are outlined.