Distribution of normalized critical current of bent multifilamentary Bi2223 composite tape

Abstract

The distribution of the normalized critical transport current (critical current normalized with respect to the original value) of Bi2223/Ag/Ag alloy composite tape under bending strain of 0%–0.833% was studied experimentally and analytically. The experimental results were analyzed by a modeling approach based on the relation of the heterogeneous damage evolution to the distribution of the critical current. The main results are summarized as follows. (1) The measured distribution of the critical current values varying with bending strain was described well by the present approach. (2) When all specimens were damaged at high bending strains (0.338%–0.833% in the present work), the distribution of the critical current of the bent-damaged specimens was expressed by the three-parameter Weibull distribution function, the reason for which was revealed. (3) The distribution of the irreversible strain was estimated, with which the influence of the increase in the fraction of damaged specimens on the variation of critical current distribution in the low bending strain range (0%–0.35%) was elucidated.

Tape Length-Dependence of Critical Current and <i>n</i>-Value in Coated Conductor with a Local Crack

“…9,11,14,15) In our preceding work using specimens composed of three sections, 11) there arose two cases in the cracking behavior. In one case, three sections were cracked almost similarly, and in another case, one section was far severely cracked than the other sections.…”

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

“…The cumulative (F) and density ( f ) probability of the critical current (I c =I c0 ) values at " B ¼ 0:6, 0.8 and 1.0%, taken from Fig. 1(a 15) This function has been used to describe the transport critical current distribution [11][12][13][14] and the critical current distribution at weak links for analysis of V (voltage)-I (current) curve near the transition from superconducting to normal conductive state. 16,17) The three-parameter Weibull distribution function is characterized by three parameters (ðI c =I c0 Þ min is the minimum (lower limit) value of critical current, ðI c =I c0 Þ 0 is the scale parameter, and m is the shape parameter).…”

“…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.…”

“…11,12,14) In this approach, the " f À " r value, where " f is the fracture strain of the bare Bi2223 filaments and " r is the residual strain of the filaments in the current transport direction, was treated as a variable; using this value, the difference in damage amount among the specimens was expressed. The " f À " r value corresponds to the tensile strain at which the filaments embedded in the composite tape are fractured.…”

“…[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.…”