Transport properties of multifilamentary Ag-sheathed Bi-2223 tapes under the influence of strain

Current-voltage (I-V) characteristics in multifilamentary Ag/Bi2223 tapes are investigated as a function of mechanical strain. As is well known, the critical current, I_c, in axially elongated tape remains almost constant up to a strain around 0.5%, then is followed by a sharp reduction. However, for larger elongations, a long tail in the I_c-strain curve is observed, i.e., around 20% of the initial I_c still remains even at 0.8% strain. The irreversible I_c reduction indicates that the degradation comes from the breakdown of superconducting filaments. However, it is observed that the rupture risk probability reduces as the strain is increased in the long tail. This anomaly suggests that the measured strain of the whole tape is not identical to that of the HTS filaments inside the tape. We propose a model to describe the mechanical properties of the tape. It is shown that (1) the breakdown probability of the filaments is well described by the Weibull function if we calculate the influence of shearing between the superconducting filaments and the surrounding Ag sheath, (2) the I_c-strain properties can be described accurately by the model, (3) transport I-V characteristics can also be described simultaneously as a function of strain