Strain tolerance of multifilament Bi-Pb-Sr-Ca-Cu-O/silver composite superconducting tapes

The bend strain characteristics of Bi-Pb-Sr-Ca-Cu-O/silver composite tapes were determined from measurements of the critical current, Ic(77 K), as a function of bend strain (0%–2%) or radius of curvature (∞−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, εirr, for the onset of bend strain damage, increases with the number of filaments from εirr=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%.