Axial tensile and compressive strain effects on the critical current of Bi-2223 superconducting tapes

The effects of axial strains ε_a on the critical current of Bi-2223/Ag and Bi-2223/AgMn tapes produced by the powder-in-tube method have been studied at 77 K. The normalized critical current I_cn vs axial strain ε_a curves I_cn(ε_a), and its empirical formulae as I_cn=1-(ε_a/a)^b, where a and b are constants, have been obtained. The critical current degrades more rapidly under large axial tensile strains than under axial compressive strain. The irreversible strain limit of 19-filament, 37-filament Bi-2223/Ag and 61-filament Bi-2223/AgMn superconducting tapes are 0.23-51%, 0.30-36% and 0.43-0.54%, respectively. Strain rate has influence on the irreversible strain limit. The whole I_cn(ε_a) curve is divided into four ranges: Compressive strain regime, first tensile strain regime, second tensile strain regime, third tensile strain regime.