Strain Effect on Critical Current Degradation in Bi-Based Superconducting Tapes With Different Deformation Modes

A 77-K cryostat system combined with different mechanical loading fixtures has been designed and fabricated to provide various strain modes for Bi-based superconducting tapes. The relations of the corresponding critical current of superconducting tapes and the applied strains are measured. The observations show that the critical current degradation of Bi-2223 superconducting tapes under small strains for different deformation modes is recoverable. While the deformation of tapes increases and exceeds some certain strain values, it is clarified that the critical current and n-value degrade significantly with an irreversible process. The degradation of critical current in Bi-2223 tapes under tension strain is much greater compared to those of bending and torsion strains. To quantitatively predict the degradation dependence upon strains of superconducting tapes, a generalized empirical degradation model based on Ekin's exponential model and Weibull's distribution function is developed for capturing the critical current degradation behavior under different deformation modes. The theoretical predictions exhibit quite good agreement with the experimental data for the critical current degradation of Bi-2223 superconducting tapes under axial, bending, and torsion strains, respectively.