Estimation of the coefficient of thermal expansion of Bi2223 at low temperature

Abstract

The evaluation of the coefficient of thermal expansion (CTE) of each constituent in Bi2223 composite tape is essential since the thermal residual strain exerted on Bi2223 during cooling from annealing temperature gives the important effect on the strain endurance of critical current (Ic). In the present study, the thermal expansion of Ag, Ag alloy and the composite tapes was measured during heating from 7 K to RT by means of Nyilas type extensometers. Mechanical properties of Ag and Ag alloy such as Young's modulus and yield stress were measured at RT and 7 K because they are also necessary for the analysis based on the rule of mixture. Comparing the measured thermal expansion of Ag tape with the reference data of Ag bulk, it is confirmed that the present technique is useful, even for the thin tape. From the analysis taking yield of the Ag into account, CTE of Bi2223 in the multifilamentary tapes were determined. It was found that CTE of Bi2223 in the present study locates between the reported data of αab and αc, which represent the CTE parallel to the ab-plane and c-axis. These are the first results on CTE measurement of Bi2223 at low temperature by the indirect method.

Direct measurement of mechanical properties of Bi2223 filament using Ag alloy removed tape

“…The composite superconductors used in this study were multifilamentary Bi2223/Ag/Ag-Mg-Ni tapes (VAM3, Nordic Superconductor Technologies), which were supplied as the standard samples for the VAMAS round-robin program [9,13]. The critical current under the self-field was about 36 A, and the critical current density was about 16 kA/cm 2 .…”

“…The total length of the specimen was 80 mm and the distance between two grips was 50 mm. A pair of lightweight extensometers designed by Nyilas was used for strain measurements [13,15].…”

“…The a Bi values were reported to be between 14 and 15 · 10 À6 K À1 in the temperature range of between 573 and 1123 K along the a-and b-axis [5,[11][12][13]. When the value used in Fig.…”

Determination of mechanical and thermal properties of electrical insulation material at 4.2 K

“…For further standard mechanical tests like tensile or compression [8], thermal investigation of expansion [9] and conductivity [10] specimen were cut and tested in warp (direction of the glass fabric plane) and normal direction from G10 material. On the left, a schematic view of the test configuration using two steel bars with defined surface preparation and 5 sheets of glass fabric impregnated with given epoxy.…”

“…Mainly mechanical tests like full-size component tests up to 630 kN, fracture mechanic or fatigue tests on small size specimen in a temperature range from room temperature down to 4.2 K are performed. Beside this, a dedicated test rig was implemented in the past to measure thermal expansion of specimen up to 50 mm · 5 mm · 20 mm maximum size [9]. A Physical Property Measurement System (PPMS) by Quantum Design is used for thermal conductivity experiments [10].…”