Thermally induced residual strain accumulation in Bi2223/Ag/Ag alloy composite superconductor

Abstract

A method to estimate the thermally induced residual strain accumulation under varying temperature in a Bi2223/Ag/Ag alloy composite superconductor was presented, in which the mechanical property values measured from the stress-strain curves of the samples with different residual strain states, the residual strain value of Bi2223 filaments in the composite tape at room temperature measured by x-ray diffraction and the reported coefficients of thermal expansion of the constituents (Bi2223, Ag and Ag alloy) in the relevant temperature range were incorporated. This method was applied to estimate the change of the residual strain of all constituents of the high critical current type composite tape fabricated by American Superconductor Corporation as a function of temperature. The residual strain value at 77 K estimated by this method and the reported fracture strain of Bi2223 filaments accounted well for the measured strain tolerance of the critical current at 77 K.

Effect of fatigue loading on critical current in stainless steel–laminated DI-BSCCO superconducting composite tape

“…The procedure to calculate the residual stress/strain has been previously reported by our group [10]. For the residual stress/strain analysis, here, the temperature for the residual stress/strain to start accumulating and that for soldering are assumed to be 563 K and 506 K, respectively [13,10].…”

Effect of epoxy impregnation on strain distribution of materials in Bi2223 superconducting coils by using synchrotron X-ray diffraction

“…The value of s h is 20 MPa that is same with the tensile stress in the coil winding process. The value of Y w for the Bi2223 wire is about 110 GPa [11,12].…”

“…Comparing the maximum strains in the Bi2223 filaments between the two coils, the strain of 0.1e0.2% was decreased by the epoxy impregnation. Using the Young's modulus Y w of 110 GPa [11,12], the reinforced tensile strength s r of the Bi2223 wire is 100e200 MPa, by the following formula,…”

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].…”