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.