Strain dependence of critical current and self-field AC loss in Bi-2223/Ag multi- filamentary HTS tapes: a general predictive model

It is well known that mechanical deformations have a strong impact on the critical current (I-c) of Bi-2223/Ag multi-filamentary high-temperature superconducting (HTS) tapes, and a remarkable I-c degradation is induced, which results in a significant AC loss. In this paper, a general predictive model based on the strain dependence of the Weibull distribution function of statistical damage of superconducting filaments and the Norris formula is developed to explore the influence of the uniaxial, bending and torsional deformation on I-c degradation and self-field AC loss of Bi-2223/Ag HTS composite tapes. A unified strain dependence of the I-c formula is suggested, which is extended in view of the I-c degradation mechanism of Bi-2223/Ag HTS tapes under a uniaxial deformation with an introduction of longitudinal strain to unify the strain in uniaxial, bending and torsional deformation modes. Then, a modified Norris formula is deduced in light of the unified strain dependence of the I-c model to predict AC loss of Bi-2223/Ag HTS tapes. With a set of appropriate model parameters determined by the tested data of I-c under uniaxial deformation, the presented model can well predict both I-c degradation and AC loss behaviors under not only a uniaxial deformation mode, but the bending and torsional ones. The proposed model indicates that the significant increase of AC loss for a deformed tape is presented due to the notable degradation of I-c.