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

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Abstract
The bend strain characteristics of Bi‐Pb‐Sr‐Ca‐Cu‐O/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 (∞−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%.