銀合金シース Bi-2223超伝導テープ材の臨界電流の曲げひずみ効果試験法

Abstract

Results of three test methods were compared among different laboratories to determine a standard measurement method of critical current (Ic) as a function of bending strain for Ag alloy-sheathed Bi-2223 superconductor tapes. The die-press, the weight-wind, and the bending-rig methods were used. Specimens were bent at room temperature and the Ic values were measured at 77 K and in the self-field. After Ic measurement of an unbent specimen, bending of the specimen and subsequent Ic measurements were done from 0.2% to 1.0% in 0.2% steps of strain on single specimens. Both Ic and Ic/Ic0 values start to decrease from 0.4% strain and continue to decrease up to 1.0% strain. Moreover, data scattering starts to increase stepwise at 0.4% strain, being a function of the magnitude of Ic and Ic/Ic0 values with strain for all the test methods. Regarding the statistical analysis on the data, results showed that the data obtained using the die-press method were reasonable and no serious defects were associated with this method. On the other hand, results of the bending-rig method showed a lower Ic/Ic0 degradation rate with bending strain than those of other two methods, which exhibited nearly the same degradation rate. The use of solder for the current contact induced extra thermal strain in the specimens. Consequently, the data for the irreversible strain scatter. Examining the difference in the resistance of the current contact part between the method using solder and the way a specimen is mechanically clamped, the mechanical method is useful and does not affect the test results. Results show that the mechanical method for the current contact increases the test method's effectiveness and reliability.