The distribution of elastic moduli is much different between discs with and without degeneration.

In this paper, we have investigated the Ic degradation behaviours in Ag alloy sheathed Bi-2223 superconducting tapes under bending and torsion strains. In particular, we have examined the homogeneity of Ic degradation along the longitudinal direction of tapes by adopting multiple voltage terminals. The bending modes influenced the Ic degradation behaviour in Bi-2223 tapes. A gradual and consistent decrease of Ic could be observed at all sections, which was a different behaviour from that under tensile loading. Up to εirr, Ic 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 εirr, some variations in the Ic 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 Ic in Bi-2223 tapes by torsion occurred gradually when the torsion angle exceeded 150°. However, the Ic degradation by torsion strain was small compared with other types of loading. Also, the Ic degradation behaviour at each section along the longitudinal direction of tapes was gradual and consistent, representing a uniform torsional deformation in the tapes.

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Using two types of tensile testing device, we have measured the strain dependence of Ic in AgMgNi-sheathed Bi-2223 57 core tapes at 77 K. The Ic degradation onset strains for the specimens with a short gauge length of 17.6 mm varied from 0.40 to 0.78%. In the relatively long samples with seven voltage terminals 5 mm apart along the gauge length of 60 mm, the smallest strain for the initiation of Ic degradation for the sections was 0.26%. The Ic in some other sections, however, began to degrade at larger strains and no degradation was found in another section even at 0.36%, which by far exceeds the strain corresponding to the yield stress of this tape. The local elongation in the first damaged section occupies most of the total elongation in the sample, while the net strain in the latter section is thought to be significantly less than average and no damage occurred there. The bending tests using several mandrels showed considerably consistent Ic degradation behaviour with increasing strain in all the sections, indicating that the strain distribution is uniform in the longitudinal direction.

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