INFLUENCE OF MECHANICAL STRAIN ON CRITICAL-CURRENT DENSITY AND MICROSTRUCTURE OF SILVER-SHEATHED BI(PB)2223 SUPERCONDUCTING TAPES

The influence of mechanical strain on the critical current density J(c ) (77 K) of single- and multi-filament silver-sheathed Bi(Pb)2223 (Bi2 -xPbxSr2Ca2Cu3O10-y) superconducting tapes was investigated by cyclic double-bend tests. The in;eversible strain limits epsilon(irr) determi ned were compared with those measured using single-bend tests. II was found that the decrease in the J(c) is determined primarily by the ben ding radius while cyclic stress caused further deterioration. However, a large percentage of the J(c) is retained at large strain (much grea ter than epsilon(irr)) and through repeated bending. Scanning electron microscopy revealed that the deterioration resulted from microstructu ral damage in the form of cracks. At strains just beyond the irreversi ble strain limit, cracks developed only on the sides of the samples su bjected to tensile strains. At large strains, cracks also were found o n the compressive sides. The magnetic field dependence of the J(c) was measured on samples subjected to various strain levels. The results s uggest that the effect of strain on the J(c) is extrinsic and that mic rostructural damage is the only cause of the deterioration.