Progress of Evaluation Techniques for Electromagnetic and Mechanical Properties of High Temperature Composite Superconductors

Abstract

Synopsis:Remarkable progresses in the development of high temperature superconductors (HTS) such as BSCCO-2223 tapes and YBCO coated conductors have been achieved in recent years, where very high engineering critical current densities (J e ) were reached in long conductor length. It is however necessary to realize simultaneously high strain tolerance of J e , low AC losses and high mechanical strength in order to apply them for practical uses. In the first part of the present review, some critical techniques to improve microstructures for achieving total performance of BSSCO tapes as well as YBCO coated conductors are suggested. In the major part, the recent progress of evaluation techniques of mecahno-electromagnetic properties is introduced. The HTS's are typical composite material consisting of essentially five components. Here the analytical technique is proposed to make clear the mechanical properties based on the rule of mixture, while the quantitative experimental method to measure tensile properties is introduced. The critical current is very sensitive on strain. The strain dependency could be divided into two regions. In the reversible region, the critical current decreases monotonously for BSCCO tapes. On the other hand, YBCO coated conductors give a so-called Ekin's intrinsic behavior for the change of critical current, where a maximum of critical current appears during the process of increasing tensile strain. In order to understand fully the strain dependences of critical current, it is absolutely necessary to elucidate the strain state exerted on the superconducting component in the composite. Recently the direct measurements of local strain have been succeeded by means of diffraction techniques using neutron and synchrotron radiation. Their interesting results including a new science are reported in the present review.

Stress–strain behavior under static loading in Gd123 high-temperature superconductors at 77K

“…The compressive stress is removed by tensile loading. Further loading results in fracture of filaments and degradation of critical current density [11].…”

“…Since RE-Ba-Cu-O (RE: Y or rare-earth elements) HTS materials have intrinsic brittleness, evaluations of the mechanical properties are crucial. The homogeneities of various properties such as high fracture strength, high fracture toughness, high critical current density and low alternating current loss in long HTS conductors are indispensable for the practical application of superconducting devices [10][11][12].…”

“…It has been reported that the mechanical properties of HTS conductors are excellent because of the excellent mechanical properties of metal substrates such as Ni-based alloy [9,11]. Evaluations of the mechanical properties of RE123 materials are informative for further improvements of the mechanical properties of HTS conductors.…”

“…Evaluations of the mechanical properties of RE123 materials are informative for further improvements of the mechanical properties of HTS conductors. With regard to the mechanical properties of RE123 materials, investigations about the residual strain in the RE123 materials of HTS conductors have been reported [11,12].…”