In situstrain measurements by neutron diffraction and residual stress estimation in Ag-sheathed Bi2223 superconducting composite tapes

Abstract

Heretofore, an accurate residual stress in Ag-sheathed superconducting composite tape could not be obtained from a measurement using conventional low energy x-rays due to the large x-ray absorption in Ag phase. Therefore, we developed a method for evaluating the residual strain in the filaments using neutron diffraction and finite element method (FEM) analysis, measuring the mechanical curvature. As for the residual strain of the Ag phase and Bi phase in a high strength type specimen, the Bi phase has a compressive longitudinal strain, and the Ag phase has a tensile strain; these are thermally balanced residual stresses at room temperature that depend on the mismatch of the coefficient of thermal expansion (CTE). On the other hand, there was very little thermally induced stress at the room temperature in the high Ic specimen. The numerical residual strain obtained by the FEM analysis agrees with experimental neutron method results. In a high critical current (Ic) type specimen, the existence of a stress relaxation mechanism during the heat treatment is suggested.

Improvement of Reversible Strain Limit for Critical Current of DI-BSCCO Due to Lamination Technique

“…The residual strain of Bi filaments was determined by comparing the lattice constant of the powder samples extracted from the same insert tapes investigated in the present study. The details of the strain measurement will be reported elsewhere [6].…”

“…The precise lattice constant for BSCCO (220) was measured under the geometry as the scattering vector is parallel to the longitudinal axis of the tape and to the tape surface. So the change of lattice constant was detected parallel to the longitudinal axis of the tape as the details are reported at [6]. In order to measure the lattice constant in the zero strain state, the powder sample was provided.…”

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

“…This observation, if inspected from Fig. 4, corresponds to ε = 0.30 %, a value that falls well beyond the reach of any measurable [2][3][4] I /(ε). Catastrophic fracture strain, ε is previously reported at C f 0.22% for similar wire.…”

“…The improvement in I c is ascribed to filament densification, second phase reduction, and voids, pores, and defects elimination from the final product. On one hand side, intriguing methods have recently been View Article Online employed to estimate the residual strain in Bi -2223 filaments of the [2][3][4][5] composite wires. An in situ synchrotron x -ray technique is used 2 for the estimation of temperature induced residual strain at 77 K. Elastic constant of the Bi -2223 phase is measured under tensile load by a defractometer for residual stress analysis, (RESA) and the resulting data is compared with that obtained from a reference 3 sample at RT.…”

Non-destructive magneto-strain analysis of YB2Cu3Oy superconducting magnets using neutron diffraction in the time-of-flight mode

“…11 Several researchers have investigated residual strains in a variety of high-T c materials, including bulk form, first generation silver sheathed Bi-2223 or second generation Y-123 wire. [12][13][14] The cryogenic loading frame was also developed for the neutron diffraction strain measurements, 15 capable of 10 kN load and reaching temperature as low as 4.8 K. The investigators point out that the developed cryogenic load frame can be applied to the study of stress-strain effects in high-T c materials over a wide range of cryogenic temperatures. Until now there have been published no reports on neutron diffraction experiments on melt-processed superconductor bulks at lower temperatures with a trapped magnetic field.…”