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DIN Standards Committee Materials Testing

Overview

Several types of composite superconductors have now been commercialised. Especially, high temperature superconductors such as Ag- and/or Ag alloy-sheathedBi-2223 (Ag/Bi-2223) and Ag- and/or Ag alloy-sheathed Bi-2212 (Ag/Bi-2212) tape-shaped or round wires are now manufactured in industrial scale. Commercial composite superconductors have a high current density and a small cross-sectional area. The major applications of composite superconductors are to build electrical power devices and superconducting magnets. While the magnet is being manufactured, complicated stresses/strains are applied to its windings and, while it is being energized, a large electromagnetic force is applied to the superconducting wires because of its high current density. It is therefore indispensable to determine the mechanical properties of the superconductive wires from which the windings are made. The Ag/Bi-2223 and Ag/Bi-2212 superconductive composite wires fabricated by the powder-in-tube method are composed of a number of oxide filaments with silver and silver alloy as a stabilizer and supporter. In the case that the external reinforcement of Ag/B i- 2223 and Ag/Bi-2212 wires by using thin stainless or Cu alloy foils has been adopted in order to resist the large electromagnet force, this standard shall be also applied. This part of the International Standard series IEC 61788 specifies a test method detailing the tensile test procedures to be carried out on Ag/Bi-2223 and Ag/Bi-2212 superconductive composite wires at room temperature. This test is used to measure the modulus of elasticity and to determine the 0,2 % proof strength. When the 0,2 % proof strength could not be determined due to earlier failure, the stress level at apparent strains of 0,05 %, 0,1 %, 0,15 %, 0,2 %, 0,25 % with increment of 0,05 % is measured. The values for elastic limit, fracture strength, percentage elongation after fracture and the fitted type of 0,2 % proof strength serve only as a reference. The sample covered by this test procedure should have a round or rectangular cross-section with an area of 0,3 mm² to 2 mm² (corresponding to the tape-shaped wires with width of 2,0 mm to 5,0 mm and thickness of 0,16 mm to 0,4 mm). The test consists of subjecting a sample to a tensile force, usually until fracture, to determine its mechanical properties. Depending on the method of strain measurement used, the measured values should be limited. When using a conventional single-strain extensometer, the determination is limited to certain values. In case of a double-strain extensometer, all values described can be determined since it is able to compensate bending and ensures a definite determination of modulus of elasticity. The responsible committee is DKE/K 184 "Supraleiter" ("Superconductors") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.

Document: references other documents

Responsible national committee

DKE/K 184 - Supraleiter