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

Abstract

Mechanical and electromagnetic stresses are exerted on Bi2223∕Ag∕Ag alloy superconducting composite tapes during fabrication∕winding and operation, which cause reduction in critical current when the Bi2223 filaments are damaged. In the damage process, the thermally induced residual strain and fracture strain of the Bi2223 filaments play a dominant role. The aim of the present work was to propose a comprehensive method for estimation of these strain values and a quantitative description method of the relation of critical current to the applied bending∕tensile strain, and to examine the accuracy of the method in comparison with the experimental results. The residual strain of Bi2223 filaments in the composite tape was measured by the x-ray diffraction method. The measured residual strain value was used for analysis of the load-strain curve, from which the intrinsic fracture strain of filaments was estimated. The relation of critical current to applied bending∕tensile strain was predicted by the proposed calculation procedure, in which the estimated strain values were input. The predicted critical current-applied strain relation agreed well with the experimental results, suggesting that the present method is a useful tool for prediction∕description of tensile∕bending applied strain dependence of critical current of multifilamentary-type conductors.

Critical current of laminated and non-laminated BSCCO superconducting composite tape under bending strain

“…3 shows the measured stressstrain curves. Concerning the influence of the fracture of filaments on the stress-strain curve, the following features have been revealed [10,11]: (1) The stress carrying capacity of a composite is reduced when filaments are fractured. Accordingly, the slope of the stress-strain curve is reduced in comparison with the extrapolation of the slope in a region where no filaments are fractured.…”

“…It has been shown that the Weibull distribution is a useful tool for description of a critical current distribution [10,[13][14][15]. In this section, first, whether the critical current distribution of the nonlaminated and laminated samples is described by this function or not was examined, and, based on the result, influences of lamination on the distribution of the critical current were studied.…”

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

“…Because the " r is negative (compressive) in the Bi2223 composite tape, as has been demonstrated by X ray diffraction analysis, 7,8) the actual fracture strain of the filaments in the composite tape is by À" r higher than the intrinsic fracture strain " f of the filaments alone. 2,4,[6][7][8]11,14) The " f À " r value is different from location to location within a specimen as well as from specimen to specimen. In the preceding works, 11,12) the heterogeneous damage behavior was formulated by the distributed " f À " r values and was correlated to the distribution of critical current values.…”

“…[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.…”

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

“…In order to describe the critical-current degradation of Bi2223/Ag composite tapes from bending strain, some empirical formulae based on experimental observations were presented [10][11][12][13][14][15][16][17][18]. Haken et al [10] first investigated the critical-current I c , as a function of axial strain in Bi-2212/Ag superconducting composite wires, and a descriptive model based on experimental data was proposed and further utilized to analyze the bending deformation influence on the critical-current in pre-strained wires within different tension/compression strain regimes.…”