Critical current degradation behaviour in Bi-2223 superconducting tapes under bending and torsion strains

In this paper, we have investigated the I-c degradation behaviours in Ag alloy sheathed Bi-2223 superconducting tapes under bending and torsion strains. In particular, we have examined the homogeneity of I, degradation along the longitudinal direction of tapes by adopting multiple voltage terminals. The bending modes influenced the I-c degradation behaviour in Bi-2223 tapes. A gradual and consistent decrease of I-c could be observed at all sections, which was a different behaviour from that under tensile loading. Up to epsilon(irr), I-c showed a nearly similar degradation at each section, due to a simultaneous initiation of cracks from defects indicating that uniform deformation occurred in tapes with bending. Over epsilon(irr), some variations in the I-c degradation occurred due to the difference of crack growth rates at each section. In particular, the behaviour appeared significantly with hard bending. The degradation of I-c in Bi-2223 tapes by torsion occurred gradually when the torsion angle exceeded 150degrees. However, the I-c degradation by torsion strain was small compared with other types of loading. Also, the I-c degradation behaviour at each section along the longitudinal direction of tapes was gradual and consistent, representing a uniform torsional deformation in the tapes.