Construction of a Strain-Hardening Diagram to Analyze the State of Stress in the Fuel-Element Cladding Material

—A method is described for constructing a strain-hardening diagram (SHD) for ChS68-ID cladding steel in the unirradiated state using the results of compressive tests of circular specimens in the longitudinal direction of a pipe to low strains in order to construct the initial section of the diagram and tensile tests to failure of preliminarily ovalized specimens to construct the section of the SHD corresponding to large strains. The approximation coefficients of the SHD model are found by minimizing the root-mean-square deviation of the experimental data from the calculated ones. Finite element analysis of the state of stress in the cladding made of ChS68-ID steel in the unirradiated state using the obtained SHD demonstrates good convergence of the estimated strength properties with those obtained experimentally and a significant difference in the plastic shear strains.