Comparison of bending strain effect on the critical current degradation of Bi-2223 tapes through different measurement techniques

Abstract

Unlike in the tests under tension, transverse compression and torsion, the bending test of HTS tapes requires lots of time and effort since the sample should be bent or mounted successively onto sample holders having different bending radius at room temperature, and then cooled down to measure the critical current, Ic, up to 77K at each step. In this process, the effect of repeated thermal cycle on the Ic degradation can not be ignored. The establishment of a practical and effective measurement method of the critical current as a function of bending strain for HTS tapes should be considered. A ρ-shaped sample holder which provides a series of bending strains to HTS tapes was newly devised. In this case, the connection of Bi-2223 tapes to current terminal blocks was done mechanically. Using this sample holder, the bending strain effect on the Ic degradation behavior in Bi-2223 tapes in the easy bending mode was investigated, and discussed them comparing with other data obtained by different testing methods, namely, the conventional bending method using FRP sample holders and the Goldacker-type continuous bending test rig. Commercially available Bi-2223 tapes which have different reinforcing structures were supplied for this study. By using the newly devised ρ-shaped sample holder, it was possible to obtain a bending strain characteristic of Ic in Bi-2223 tapes at one time cooling which lessened the testing time significantly when compared with other testing methods and supply good reproducible data. The Ic degradation behavior in Bi-2223 tapes was similar to the cases using FRP sample holders although it showed slightly higher Ic values.