Effects of strain on the critical current of Bi-2223/Ag tapes

The influence of mechanical strain on the critical current (I_C) is investigated for multi-filamentary Bi-2223/Ag/Ag-0.2wt%Mg-0.3wt%Sb superconducting tapes at liquid nitrogen temperature, 77 K. Several kinds of Bi-2223/Ag tapes with different Ag/SC ratio (2.0, 2.2, and 2.6) and/or number of filaments (19 and 37) are examined. Bending and tensile deformation tests are performed. In the bending deformation tests, decrease of I_C is observed for the all samples with bending strain above 0.3% and 0.4% in the tests for bent samples and bent-and-re-straightened samples, respectively. The decrease of I_C is the most sensitive on the bending strain in the 19-filament samples with Ag/SC ratio of 2.0 and the least sensitive in the 37-filament samples with Ag/SC ratio of 2.2. Strain tolerance in the tensile deformation tests varies depending on the number of filaments, although the strain tolerance is similar for the samples with the same number of filaments and different Ag/SC ratio. Large decrease of I_C is observed for 19-filament and 37-filament samples with Ag/SC ratio of 2.2 at tensile strain above 0.17% and 0.23%, respectively (the tensile strain is the deformation from as-cooled state on Ti-6wt%Al-4wt%V holder). Higher Ag/SC ratio and fine filament are effective to improve the durability against deformation.