Complementary analysis of the results of a bending strain effect round robin-test on the critical currents of Ag alloy-sheathed Bi-2223 tapes

As a result of the first round robin-test (RRT) on the bending strain effect in Ag alloy-sheathed Bi-2223 superconducting tapes, it has been found that the scatter in the critical current data reported from 12 participant laboratories is not very large; the coefficient of variation (COV) is, for example, less than 6% at a bending strain of 0.6%. However, the bending strain limit, which is practically a more important parameter and is defined as a strain where the critical current degrades by 10%, has been found much scattered (17% in COV) in the first RRT. To clarify the origins of data scatter and finally reduce it, complementary analysis and tests on the effects of thermal stress relating to the sequences of the bending of the specimen and critical current measurements have been carried out. Additionally, it has been found that the sample inhomogeneity in mechanical properties contributes to some part of data scatter.