Change of theV–Icurve and critical current with applied tensile strain due to cracking of filaments in Bi2223 composite tape

Abstract

The critical current at 77 K of multifilamentary Bi2223 composite tape was studied under applied tensile strain experimentally and analytically. Beyond the irreversible strain, the critical currents (I C ) decreased significantly with increasing applied tensile strain (ε c ), due to the enhanced cracking of the Bi2223 filaments. The voltage generation in the voltage-current relation was calculated by the current share model in which the transport current is shared by the Bi2223 filament and Ag near the cracked portion. Then the critical current was estimated with a 1 μV cm −1 criterion. By the application of the current share model to the experimental result, the effective crack length responsible for the reduction in critical current was estimated, with which the change of critical current could be described satisfactorily as a function of applied strain.

Influences of cracking of coated superconducting layer on voltage-current curve, critical current, and n-value in DyBCO-coated conductor pulled in tension

“…17,19,20 However, whether s = 0.1 m is suitable for the present DyBCO conductor or not is not sure. In this subsection, the influence of s-value on the result of analysis is discussed below.…”

“…Shin et al 19 have applied this model to the measured V-I curves of the BSCCO filamentary composite tape under applied tensile strain. They found that the measured V-I curves and change in I c as a function of T can be described with this model by using an effective relative crack size ͑ratio of the cracked cross-sectional area to overall transverse cross-sectional area͒.…”

“…In calculation, s was taken to be 0.1 m as in the preceding works. 17,19,20 The influence of s-value on the result of analysis is discussed in Sec. V D. The voltage V d in Eq.…”

“…The good agreement of calculation results with experimental results for V-I curves, I c , n-value, and correlation of n-value to I c indicates that the conversion of arrayed multiple cracks to a single equivalent crack can give a good description of superconducting properties and is useful for analysis of influence of cracking of superconducting layer on V-I behavior in coated conductors as well as for analysis of that in filamentary conductors. 19,20 B. Shunting current I s and voltage V s "=V d … developed in the cracked region at I = I c Figure 8͑a͒ shows an example of the measured and analyzed V-I curve and variation in shunting current I s with overall current I. In this example, the data at T = 0.411% is picked up representatively.…”

Effects of Crack Size Distribution and Specimen Length on the Correlation between <i>n</i>-Value and Critical Current in Heterogeneously Cracked Superconducting Tape

“…Both coated-and lamentary-conductor tapes are subjected to thermal, mechanical and electromagnetic stresses/strains during fabrication and operation. When the superconducting layers/ laments are cracked by such stresses, the critical current I c and n-value both of coated [1][2][3][4][5][6][7][8][9][10] and lamentary [11][12][13][14][15][16][17][18][19] conductor tapes are reduced. In ordinary cases, cracking of the coated layer/ lament takes place heterogeneously.…”