International round robin test for mechanical properties of REBCO superconductive tapes at room temperature

Abstract

An international round robin test was promoted to establish a test method for room temperature mechanical properties of commercial REBCO superconductive tapes. Seven laboratories practiced a tensile test under the direction of guideline REBCO13 for four different kinds of REBCO tape. From the stress versus strain curve, the modulus of elasticity and the 0.2% proof strength were measured. The scatter of measured values was analyzed by evaluating the RSU (relative standard uncertainty). To judge the major contribution to scattering, an F test was applied. The major source of RSUs was estimated to be the influence of inter-laboratory scattering. In order to reduce the overall scattering, it is suggested that the REBCO13 guideline should be modified with respect to the following three experimental factors. The window determining acceptable data should be narrowed, and the initial strain rate should be suppressed to less than 1 × 10 −4 (s −1 ). Repeated thickness measurement is recommended to reduce the standard uncertainty.

International round robin test for tensile testing HTS wires at cryogenic temperatures

“…Uncertainty budget calculation for proof strength for sample C2-05 tested in lab G.for REBCO wires the number of unqualified results become 14.7%. That is in good agreement with the results obtained with the room temperature RRT[10].5. ConclusionsThe international RRT for tensile testing HTS wires at liquid nitrogen temperature was performed for six commercially available HTS wires.…”

“…where L g is the grip length, and L LG is the gauge length of the extensometer. L x is the free gap distance between grip and extensometer and is given by the condition [10]:…”

“…In order to indicate the major scatter source, analyses of variance (ANOVA) were performed for all RRT results. In these analyses the inter-laboratory estimate s a a 2 n ( ) and the intra-laboratory estimate s b b 2 n ( ) (see formulas in [10]), where J 1 a n =and J K 1 , RRT configuration. Based on this comparison, a conclusion about the major scatter source on the data can be obtained.…”

“…A number of RRTs for tensile testing at room temperature have been already successfully completed for Nb 3 Sn [8], BiSCCO [9], and REBCO [10] wires. Following this experience, an international RRT for tensile testing HTS wires at cryogenic temperatures was promoted by the Versailles Project on Advanced Materials and Standards and supported by the International Electrotechnical Commission.…”

‘Defect-irrelevant’ behavior of a no-insulation pancake coil wound with REBCO tapes containing multiple defects

“…REBCO (RE-Ba 2 -Cu 3 -O x , RE: rare Earth) coated conductor has been regarded as one of the most viable high-temperature superconductor (HTS) options for next-generation high field magnets, mainly owing to its large in-field current carrying capacity and mechanical robustness. Commercial REBCO tapes show a 95% critical current (I c ) retention strain of 0.5% or higher, which corresponds to a tensile stress of 550-850MPa depending on the tape's architecture [1][2][3][4][5][6][7][8].…”