Influence of test methods on critical current degradation of Bi-2223/Ag superconductortapes by bending strain

Abstract

The results of two test methods were compared among three laboratoriesto determine a standard measurement method of critical current(Ic) as a function of bending strain for Ag-sheathed Bi-2223 superconductors. The VAMASround-robin-test method (RRT) and the bending-rig method developed by Goldacker were used. TheIc degradation started with less bending strain for RRT than for bending-rig. Average irreversible strains(εirr) were 0.30% for RRT and 0.37% for bending-rig. Another test identified parameters thataffected the results. A modified RRT method, with a current connection between the sampleand the electrode, was used to avoid some thermal stresses of the test procedure. Theεirr values increased to the level of the bending-rig, but the modified RRTIc degradation rate with bending strain was higher. The stress states during sample bendingdiffered between these methods. The shear stress was examined as a source of theIc degradation rate differences with strain in terms of the crack propagation and delaminationdefects of oxide filaments from the Ag sheath.