Local variations in the critical current degradation of Ag/Bi2223 tape by tensile and bending strains

Abstract

Using two types of tensile testing device, we have measured the strain dependence of Ic in AgMgNi-sheathed Bi-2223 57 core tapes at 77 K. The Ic degradation onset strains for the specimens with a short gauge length of 17.6 mm varied from 0.40 to 0.78%. In the relatively long samples with seven voltage terminals 5 mm apart along the gauge length of 60 mm, the smallest strain for the initiation of Ic degradation for the sections was 0.26%. The Ic in some other sections, however, began to degrade at larger strains and no degradation was found in another section even at 0.36%, which by far exceeds the strain corresponding to the yield stress of this tape. The local elongation in the first damaged section occupies most of the total elongation in the sample, while the net strain in the latter section is thought to be significantly less than average and no damage occurred there. The bending tests using several mandrels showed considerably consistent Ic degradation behaviour with increasing strain in all the sections, indicating that the strain distribution is uniform in the longitudinal direction.

Residual and fracture strains of Bi2223 filaments and their relation to critical current under applied bending and tensile strains in Bi2223∕Ag∕Ag alloy composite superconductor

“…1-27 For description of damage behavior of Bi2223 filaments that transport superconducting current, two important parameters have been mentioned. 4,13,14,16,19,21,27 One is the intrinsic fracture strain Bi,f and another is the residual strain Bi,r . If the Bi2223 filaments are tested alone, they fracture at the intrinsic fracture strain Bi,f .…”

Theory analysis of critical-current degeneration in bended superconducting tapes of multifilament composite Bi2223/Ag

“…The mechanical properties are among the most important parameters for HTS tapes [1][2][3]. The relation of deformation and fracture behavior of multi-filamentary Bi2223/Ag composite tapes to the superconducting property has been studied widely [4][5][6][7][8][9]. It was revealed that the critical-current in the superconducting composite tapes under bending deformation decreases seriously beyond an irreversible strain, and once the applied strain exceeds such the irreversible strain, the critical-current never returns to the original value even when the applied strain is released [4][5][6].…”

“…The relation of deformation and fracture behavior of multi-filamentary Bi2223/Ag composite tapes to the superconducting property has been studied widely [4][5][6][7][8][9]. It was revealed that the critical-current in the superconducting composite tapes under bending deformation decreases seriously beyond an irreversible strain, and once the applied strain exceeds such the irreversible strain, the critical-current never returns to the original value even when the applied strain is released [4][5][6]. The influence of strain on the damage of superconductor filaments in Bi2223/Ag composite tapes was also observed in the experiment study by the scanning electron microscopy (SEM) [7,8].…”

Applicability of Weibull Distribution to Description of Distributed Normalized Critical Current of Bent-Damaged Bi2223 Composite Tape

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Heterogeneous damage occurs, and the damage evolution behavior differs from specimen to specimen and from location to location within a specimen. [9][10][11][12][13][14] Accordingly, when a number of specimens are tested, the critical current differs from specimen to specimen.…”