Fracture mechanics analysis including the butt joint geometry for the superconducting conductor conduit of the National Centralized Tokamak

This paper presents the dependence of the stress intensity factor on a geometrical factor estimated by fracture mechanics analysis around the defect in the butt joint weld of a cable-in-conduit conductor (CICC) of a superconducting coil. The stress intensity factor can be estimated by the Newman–Raju equation applied to the CICC section, but the effect of the difference between the geometry assumed in the equation and the actual CICC geometry has not been clarified yet. Therefore, the three-dimensional finite element method (3D-FEM) is performed to estimate the geometrical factor. As a result, the Newman–Raju equation is considered to be applicable for the assessment of the fracture toughness of the rectangular-shaped conduit because the maximum stress intensity factor by 3D-FEM is only 3% larger than that determined by the Newman–Raju equation for the maximum postulated defect.