Strain effects on the AC critical current of Bi-2223 superconducting tapes

Axial tensile strains effects on the AC critical current of Bi-2223/Ag and Bi-2223/AgMn tapes produced by the powder-in-tube method have been studied, at 77 K. 5 μV/cm field criterion was used to determine the AC and DC critical current. The degradation of AC critical current due to axial tensile strain is irreversible, the normalized AC and DC critical current I_cn vs tensile strain ε curves I_cn (ε) of Ag and AgMn/Ag sheathed Bi-2223 superconducting composite tapes are almost the same when the axial tensile strain is less than ε_0.9, when the axial tensile strain is larger than ε_0.9, the AC critical current I_cn decrease less rapidly than DC critical current I_cn, and at the same strain, the normalized AC critical current is greater than normalized DC critical current. This may be due to the greater relative increment in DC voltage than in AC voltage when the strain is large enough to deteriorate the transport capacity of the tape. The AC and DC I_cn (ε) curves have the same empirical formula as I_cn = 1 - (ε/a)^b, where a and b are constants.