Analysis on Stress/Strain Tolerances of $I_{\rm c}$ in Externally Laminated GdBCO CC Tapes

Abstract

Critical current, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , in REBCO coated conductor (CC) tapes may increase or decrease reversibly within the reversible region with stress/strain but degrade permanently beyond the irreversible limits due to cracking of the superconducting film. Analyzing quantitatively the stress/strain tolerances of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is of importance on the possibility to suppress the onset of cracking on the REBCO coating film. In this study, the stress/strain tolerance of GdBCO CC tapes was experimentally measured from <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -strain measurement test at 77 K. The improvement in the irreversible strain limit in CC tapes was analyzed by calculating the pre-compression induced by additional layers. The increase of about 0.10%-0.15% in irreversible strain limit with additional Cu and brass laminate is much larger compared with the measured 0.03%-0.06% residual strain due to thermal contraction difference among constituent layers. This result showed that the improvement in the ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">irr</sub> cannot be solely explained by the coefficient of thermal expansion difference among constituent layers.