Strain Dependent Transport and Mechanical Characteristics of High-current and High-Strength Type Ag/Bi2223 Composite Superconductors

Abstract

Tensile strain dependence of electromechanical characteristics of high-current, (Hic) and highstrength, (Hs) type Ag/Bi2223 composite tapes measured at room temperature, RT and 77K is investigated. Mechanical strength of composites revealed strain-hardening signature in Bi2223 filaments due to plastic strain above the elastic limit. Critical current, I c maintained constant value up to the elastic limit then decreased slowly before finally dropped to about 10% at 0.19% and 0.39% strain, signaling a three-stage limitation. Microstructure observations and electromechanical response of the composites suggest that limited longitudinal, transverse, interfacial, granular and transgranular microcracks formed during gradual imposition of strain hardening in Bi2223 filaments may be responsible for the slow reduction of I c in the initial mechanical stage.

Modulated Rate (Time) – Dependent Strain Hardening of Ag/Bi2223 Composite Wire Flattened in a Low – Strength AgMg Alloy Matrix

“…In this work however, when the stress value responsible for first macroscopic fracture is attained at σ = 138.5 MPa , the stress immediately decreases 4.0 % from that value before picking up again. It's apparent that the abrupt transition from elastic to plastic state of the low -strength Ag/AgMg -alloy matrix coupled with concurrent sequential macroscopic fracture formation in the (11)…”

“…4, fortunately or unfortunately this is not the case. A subtle residual strain scatter is so results from [2][3][4][5][6][7][8][9][10][11][12][13][14][26][27][28][29][30][31][32] each experiment. Note that the above estimation is a rough one but nonetheless, the achieved σ -ε values from these tests were useful for describing the strain hardening and the pre-compressive force features of this composite wire.…”

“…Normalised stress -strain curves for a matrix with the Ramberg -Osgood hardening. (a) Solid symbols ( ) indicate an elastic -perfectly plastic flow in the matrix estimated by equation(11). Open symbols ( ) are the strain hardening feature in the composite.…”