Influence of Tensile Stress on Superconducting Properties in Ag/Bi2223 Monocore Tapes

Abstract

The influence of tensile stress on superconducting properties in Ag/Bi2223 monocore tapes has been investigated, especially at the initial stage of fracture. The fracture of oxide core was found to start at the stress lower than the macroscopic fracture strength of oxide observed as the drop in the stress. Stress and electric voltage were measured simultaneously during the tensile test at 77K. A gradual increase of voltage was observed at the stress fairly lower than that of macroscopic fracture as a stress-strain curve deviated from elastic behavior and its slope began to decrease. These results suggested that the initiation of microcracks occurs in the oxide before the macroscopic fracture. Both I_c and n-value decreased with increasing stress, but the change of n-value was more drastic than that of the I_c. The V-I curves before and after loading were analyzed by assuming that the generation of voltage was dominated by the nonsuperconducting transition of grain boundaries.