Critical Current and Strain Tolerance of Bi-2223/Ag Multifilament Tapes

Abstract

Multifilament Bi-2223/Ag composite tapes are candidates for large-scale applications in power transmission and power devices for operation at or below liquid nitrogen temperature. To withstand the handling and winding operations during device fabrication, the tapes must have a strain tolerance or irreversible strain limit ε _irr ≥ 0.3%.

We report the results of a comprehensive investigation of the effects of bend strain, e, on the critical current, _Ic (77 K), of a 27-filament Bi-2223/Ag tape. The strain was applied by single-bend and double-bend tests, and by up to one hundred cyclic double-bend tests by bending specimens to a radius of curvature from ∞ (straight tape) to 10 mm (ε = 0–1.5%). In general, the irreversible strain limit, ε _irr , decreases from 0.4% for single-bend tests to 0.2% for double-bend tests. At 0.4% strain, I _cε/I _{c0 o} = 95% for single-bend tests and 60% for double-bend tests. The I-V characteristics near I_c obey the relation V ∞ I ⁿ where n decreases with increasing strain from about 20 for zero strain to about 4 for 1.5% strain.