Miniature round robin test on the bending strain characteristics of Ag/Bi(2223) tapes at room and liquid nitrogen temperatures

In order to supplement the VAMAS round robin test (RRT) on the bending strain dependence of critical current, Ic, of Ag/Bi-2223 tapes conducted in 2001, a miniature bending RRT at 77 K and room temperature, RT, participated by three laboratories has been conducted. Three devices developed by Goldacker of Karlsruhe, which allow continuous change of the bending radius of the sample and measurements of Ic at 77 K have been used. The onset strains for steep Ic degradation, εirr , at 77 K, 0.55%, was larger than that at RT, 0.37%. This is due to an additional pre-compression in Bi-2223 filaments for the bending at 77 K. The comparison of the present results bent at RT with those in the VAMAS-RRT showed that the scatters in the degradation behaviors were substantially small in the present results. εirr of the former was larger than that of the latter. These appear to be explained by the different thermal histories. Based on the results, some attempts to reduce the scatter of bending test results were tried.