The Critical Current Degradation of Bi-2223 Superconducting Tapes Due to Fatigue Cycles at Different Strain Range

The critical current (I_C) of high temperature superconductors is an important parameter for practical application, such as magnets, cables and transformers. The degradation of I_C under the tensile strain is measured at 77 K as well as under the compressive strain. It is found that the properties of Bi-2223 tapes are superior in the compressive strain to that in the tensile strain. The fatigue degradation behaviors of Bi-2223 tapes are studied in the symmetrical strain cycles and the unidirectional strain cycles. Both of the tests are conducted at 77 K. It is observed that the I_C after thousands of cycles in the unidirectional strain cycles is much higher than that of the symmetrical strain cycles. Finally, a round bending test is employed to determine the degradation of I_C when Bi-2223 tapes are wound around a mandrel. A critical radius of about 50 mm is found in the experiment.