Damage evolution under bending and tensile stress and its influence on critical current of Bi2223/Ag superconducting composite tape

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

“…In the existing literatures, some researches [5,[13][14]16] always utilized the simplified model of the tape in which the core shape was approximated to be rectangular one. In Ochiai's series works [17,20], the simplification of cross section was also used and there showed a reasonable results at high bending strain stage in comparison with the experiment data, while there was a little overestimation for critical current at low bending strain stage.…”

“…After determining the model parameters from experimental data by statistical analysis, they calculated the bending strain dependence of critical-current and resistances and explained the experiment observations. Among these theoretical analyses, the approach presented by Ochiai et al [13][14][15][16][17][18][19][20] analysis of distribution of critical-current based on the damage strain parameter defined as the difference between the intrinsic tensile fracture strain and the residual strain of the filaments was developed, and they obtained a good agreement of the theoretical results with the experimental ones. Based on the similar approach, Gou et al [21] recently presented a modified model for studying the bending strain dependence of the critical-current I c in Bi2223 superconducting composite tapes.…”

“…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.…”

Prediction of critical current–bending strain relation of Bi2223 composite tape using residual strain of filaments, load–strain curve and geometry of cross-section

“…It has been known that the critical current of Bi2223/Ag/Ag alloy composite tapes decreases with increasing applied tensile (e T ) and bending (e B ) strains beyond the irreversible strain due to the damage evolution of the Bi2223 filaments [1][2][3][4][5][6][7][8][9][10][11][12][13]. In the damage evolution process under the applied tensile strain, the residual strain e Bi,r of the filaments, which arises during cooling due to the difference in coefficient of thermal expansion among the Bi2223 filaments, Ag and Ag alloy [3,7,9,10,12] and tensile fracture strain e Bi,f of the filaments in the sample length direction (current transport direction) play a dominant role in the damage process.…”

“…In the damage evolution process under the applied tensile strain, the residual strain e Bi,r of the filaments, which arises during cooling due to the difference in coefficient of thermal expansion among the Bi2223 filaments, Ag and Ag alloy [3,7,9,10,12] and tensile fracture strain e Bi,f of the filaments in the sample length direction (current transport direction) play a dominant role in the damage process. Under the applied bending strain, they also play a dominant role since the damage is caused by the tensile strain in the sample length direction [10,13]. However, the damage process under bending strain is different from that under tensile strain, since the exerted tensile strain in the bent sample is dependent on the location and therefore the damage amount is dependent on the shape of the core, as will be shown later in detail.…”