Mechanical Behavior Laws for Multiscale Numerical Model of Nb3Sn Conductors

Low-temperature superconductors are widely used in high field magnets, mostly within Rutherford-type cables. Cables are multiscale composite structures including strands composed of superconducting filaments twisted in a metallic matrix. Mechanical effects at the filament scale affect magnetic performance, especially with strain-sensitive superconductors such as Nb3Sn. During operation, the conductor is subject to a complex combination of axial and transverse loads. It is thus necessary to build 3-D models at the cable scale. Previous work has presented a numerical approach for 3-D Finite-Elements (FE) modeling of Rutherford cables at the scale of the strand considered bi-metallic. In this paper, representative behavior laws for the different components of the strand model are identified, based on experimental results. Copper is modeled with a non-linear elastic-plastic behavior accounting for isotropic and kinematic hardenings. Homogenization of the superconducting filamentary area is carried out numerically using a FE representative volume element. Underlying parameters are identified from microstructural characterization and tensile tests on superconducting strands using an optimization routine. The strand model is compared to monotonic and cyclic tensile tests performed on Nb3Sn strand manufactured with the Powder-In-Tube method.