International round-robin test for electromechanical properties of HTS wires under uniaxial tension at liquid nitrogen temperature

Abstract As superconducting wires have become more prevalent, it has become increasingly important to establish reliable and standardized methods for evaluating their electromechanical properties (EMPs) at cryogenic temperatures. An international round-robin test (RRT) was conducted to assess the EMPs of four commercially available high-temperature superconducting (HTS) tapes as an activity to establish a standard for the EMP test method. Six laboratories participated in the RRT, adhering to the guidelines. During tensile testing of the HTS wires at 77 K, critical current ( I c ) measurements were performed using a stress-based test method. This method streamlined the testing procedure by changing stress intervals from broad to narrow as the applied stress approached the I c degradation point while eliminating the need for dedicated extensometers. The EMPs of the reversible stress limit ( R rev ) and retention stress limit ( R ret ) for I c degradation were defined based on specific criteria for 99% I c0 recovery and 95% I c0 retention. Once the RRT participants reported their test results, statistical analysis tools such as ANOVA were employed to identify sources of variation and assess their magnitude in the results. The primary source of the relative standard uncertainty was the effect of inter-laboratory scattering. The RRT results are utilized to develop an international standard for evaluating EMPs of HTS wires through I c measurements under uniaxial tension at liquid nitrogen temperature. These RRT analysis results offer valuable insights into potential sources and magnitudes of measurement uncertainties, ultimately contributing to standardized test procedures for accurate and reliable EMP characterization of HTS wires.