Modeling analysis of the critical current of bent Bi2223 composite tape based on the damage strain parameter and the shape of the core

Abstract

We present a new modeling approach to describe the relation between the critical current and the applied bending strain of a multifilamentary Bi2223/Ag/Ag alloy superconducting composite tape. In the model, the shape of the superconducting core, in which the Bi2223 filaments that transport the superconducting current are embedded in Ag, and the damage strain parameter, defined as the difference between the intrinsic tensile fracture strain and the residual strain of the filaments in the sample length direction (= current transport direction), are combined with the exerted strain distribution in the bent sample. The extent of the damage to the core and the corresponding critical current are expressed as a function of bending strain. The present approach describes well the measured critical current–bending strain relation for the three different fabrication-route samples.

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

“…The strain at which the filaments in the present composite tape are damaged under applied tensile strain has been estimated to be around 0.25% from the change in the stress carrying capacity upon occurrence of the damage in the stress-strain curve. 6,19) The estimated value ð" f À " r Þ ave ¼ 0:25% in the present work coincides with this value.…”

“…The exerted tensile strain is dependent on the location; it increases with distance from the neutral axis. 6,11,12) Accordingly, the filaments farthest from the neutral axis, existing at y core ¼ y core,max (¼ y core,max ðSÞ and y core,max ðRÞ in Fig. 4(c) for Models S and R, respectively), have the highest tensile strain and are fractured first at Damage occurs first at the outermost filaments at the maximum value of y core (y core,max ) when the bending strain " B reaches the irreversible bending strain " B,irr .…”

“…[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.…”

“…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.…”

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.…”