Evaluation of Irreversible Strain/Stress Limits for Ic Degradation in Practical REBCO CC Tapes Under Uniaxial Tension

In various superconducting device applications such as power cables, magnets, and coils, the strain effect on the critical current I
_c
of coated conductor (CC) tapes including magnetic field B and cryogenic temperature T should be understood for a reliable design. Therefore, it is necessary to establish a standard measurement method to determine the electromechanical properties including mechanical properties of high temperature superconducting (HTS) CC tapes. In this study, some critical limits for the irreversible I
_c
degradation of CC tapes under uniaxial tension and at 77 K were evaluated. The irreversible strain/stress limits for four differently processed CC tapes were defined based on both criteria of the 99% I
_c
(ε) recovery and the 99% I
_c0
. The results showed that the criterion of the 99% I
_c
(ε) recovery produced higher limits as compared to the case of the criterion of 99% I
_c0
recovery in terms of the strain limits due to the reversible I
_c
degradation behavior and the residual strain induced in CC tapes. However, in terms of stress limits, they showed similar values for both criteria. As a result, it is important to consider the principles for both criteria in defining their reversible limits, whether will be normalized on the original state value or to consider the corresponding reversible degradation of I
_c
when it is unloaded.