FEM analysis of three directional strain states under applied tensile stress for various composite superconductors

Composite superconductors such as Cu/Nb₃Sn and Ag/Bi-oxides are subjected to thermally-induced residual strain by other component materials due to the around 1,000 K temperature difference between the reaction temperature and the cryogenic temperatures, and to applied tensile strain by the hoop stress of longitudinal (z) direction during the coil operation. To clarify especially the radial (r) and tangential (θ) strain behaviors including z-strain, we analyzed elastic-plastically multi-core model by computing of FEM for various composite conductors. As a result, applied tensile stress on the z-direction of the composite conductor gave monotonous decrease of thermally-induced r- and θ-strains, which changed tensile to compressive strain. With increase in the z-strain effective strain showed the minimum value, not zero, at around z -strain-free state. Moreover it was found that all conductors are classified into three types by combination of component materials.