Three-Directional FEM Analyses of Pre-Bending Effects for Nb3Sn Composite Wires

Pre-bending effects of Nb₃Sn composite wires, enhancement in J_c at the as-cooled condition and J_c peak, J_cm, against applied tensile strain, are well known in especially Cu-Nb reinforced Cu stabilized Nb₃Sn wire. In an attempt to understand the effects, three directional strain analyses using FEM were studied by considering thermally-induced residual strain due to temperature difference between the reaction temperature and the cryogenic temperatures including the pre-bending process at room temperature for three types of Nb₃Sn composite wires. To evaluate effects of change in three directional strain, the von Mises strain was introduced. As a result, the minimum von Mises strain against the applied tensile strain corresponded to J_cm; low strain shows J_cm enhancement by the pre-bending for Cu-Nb reinforced Nb₃Sn wire. It was found that there is a direct correlation between the minimum von Mises strain and J_cm related to the pre-bending.