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

Critical current, I_c, 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_c 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_c -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_irr cannot be solely explained by the coefficient of thermal expansion difference among constituent layers.