Modeling-Driven Optimization of Mechanically Robust REBCO Tapes and Wires

The bending properties of RE-Ba-Cu-O (REBCO, RE = rare earth) coated conductors are a stringent constraint for coil and cable applications. While the use of thinner substrates reduces the stresses/strains in the REBCO layer, it is also possible to enhance the mechanical properties of these tapes by optimizing the stabilizer thickness in order to reduce the distance between the neutral axis and the REBCO layer. In this paper, we present both experimental and analytical results showing a significant improvement in the critical current (I
_c
) retention at small bend diameters (less than 2 mm) for tapes with various substrate thicknesses by using an optimized copper thickness on the REBCO side only. The presented analytical method accounts for the neutral axis shift caused by the progressive plastic deformation in the various layers (Hastelloy, silver, and copper). The Ic dependence of different substrate tapes on the thickness of single-sided electroplated copper stabilizer was measured at bending diameters ranging from 0.81 to 12.5 mm by means of a single-turn helical winding on a cylindrical former. The strains were then calculated and an optimized copper thickness is determined for the various configurations. Based on these results, an optimal design for ultra-small diameter REBCO wires is also presented.