Degradation of critical current by the mixed strain of bending and tension in Bi-2223/Ag HTS tape

Influences of the mixed strain mode of bending tension on Ic degradation at the bent region of a commercially available Bi-2223 tape without external reinforcement were investigated and discussed. The Ic degradation behaviors were examined at 77 K in each and in the mixed strain mode. A newly devised sample holder, which provides a mixed strain mode, ε(t+b), of bending tension to the HTS tape by applying tension to bent tapes, was used. Some variations in the Ic degradation existed in the Bi-2223 tape resulting from non-uniform deformation in the tension mode. In the mixed strain mode, the Ic degradation was expressed as a function of the total strain derived by the superposition principle. The irreversible strain, εirr.(b+t), for the onset of Ic degradation at the mixed strain mode region of the tape was larger as compared with the simple bending case. For strains larger than the εirr.(b+t), the Ic at the bent region of the tape degraded gradually as compared with the simple tension case. As the initially imparted bending strain to the tape increased, the εirr.(b+t) of the tape increased. It was found that the friction between the tape and the mandrel at the mixed strain mode region of the tape contributed to improve the apparent strain tolerance of Bi-2223 tapes at the bent region.