Tensile strain effects on critical current of Ag and Ag alloy-sheathed Bi-2223 superconducting tapes

The tensile stress-strain characteristics of Ag and AgMn alloy-sheathed Bi-2223 tapes have been studied, and the effects of sheath material, filament number and Ag/core ratio on the critical current of Bi-2223 tapes have been compared. Using the Ag-alloy tube as an outer sheath of Bi-2223 tapes can increase the residual thermal compressive stresses in the filaments, avoid a wavy interface between the Ag sheath and oxide core, and limit the stress concentrations induced by the interface inhomogeneity, thus the micro-crack will be formed at higher stress levels and the tensile strain tolerances of tapes can be improved remarkably. In this study, the critical tensile stress can be improved from 62 MPa to 124 MPa, and the irreversible tensile strain can be improved from 0.31% to 0.52% by using the AgMn-alloy as an outer sheath instead of pure Ag in 37-filamentary tapes. In addition, we found that Bi-2223 tapes can tolerate higher tensile strain level by increasing the filament number and Ag/core ration.