STRAIN TOLERANCE OF MULTIFILAMENT BI-PB-SR-CA-CU-O SILVER COMPOSITE SUPERCONDUCTING TAPES

The bend strain characteristics of Bi-Pb-Sr-Ca-Cu-0/silver composite tapes were determined from measurements of the critical current, I(c)(77 K), as a function of bend strain (0%-2%) or radius of curvature (infinity-10 mm). The powder-in-tube method was used to prepare monofilament and multifilament (up to 49 filaments) tapes, 0.2-0.4 mm overall thickness, with 5-20 vol % superconductor. The irreversible strain limit, epsilon(irr), for the onset of bend strain damage, increases with the number of filaments from epsilon(irr)=0.2%-0.3% for monofilament tapes to values up to 1.5% for 49-filament tapes. Although strains beyond this limit cause irreversible damage in the form of microcracks and fracture of the superconductor filaments, multifilament tapes are exceptionally strain tolerant, with 49-filament tapes retaining 85%-90% of the initial critical current at strains of 2%.