Novel two-step procedure for measuring I c vs. tensile stress of commercial REBCO tape

This paper presents a novel two-step procedure for measuring the critical current (I c) properties as a function of tensile stress. The proposed method completely eliminates the possible negative effect of the voltage tap used during the tensile procedure, allowing the actual I c irreversible degradation stress to be clearly determined. Six different commercial REBCO tapes from five manufacturers were tested. The I c value does not degrade until the stress reaches the 'inflection area' in the tensile curve, which corresponds to the most pronounced transformation step from elastic to plastic deformation. This allows easy estimation of the stress corresponding to I c irreversible degradation by a simple and accurate cryogenic tensile curve instead of complicated in-situ I c tensile measurement. A feasible composite-material tensile model is established to explain the phenomenon. In addition, fatigue measurements on a commercial REBCO tape from Shanghai Superconductor technology show that the tape can withstand 10 000 cycles under 580 MPa and over 5000 cycles under 695 MPa, which also is consistent with the proposed composite-materials tensile model and is confirmed by the EBSD experiments on the Hastelloy substrate. This research provides better insight and tools for designing and fabricating extremely high-field magnets.

Automated summary

This paper presents a novel two-step procedure for measuring the critical current properties as a function of tensile stress. The proposed method eliminates the negative effect of the voltage tap used during the tensile procedure, allowing the determination of the actual irreversible degradation stress. The results show that the critical current value does not degrade until the stress reaches the 'inflection area' in the tensile curve. A feasible composite-material tensile model is established to explain this phenomenon. Fatigue measurements and EBSD experiments confirm the proposed model.