Mechanism for the uniaxial strain dependence of the critical current in practical REBCO tapes

Abstract

In order to elucidate the effect of uniaxial strain on the critical current of practical REBCO tapes (REBa2Cu3O7−d, RE = Y and Gd) fabricated by Superpower and SuNAM, two types of critical current measurements were carried out. In the first, the tape sample was attached directly to a universal testing machine and pulled under a tensile load. In the second, the tape was soldered to a Cu–Be springboard and then attached to the testing machine and then pushed or pulled in order to apply both tensile and compressive strains to the tape sample. An inverse parabolic behaviour was observed for the uniaxial strain dependence of the critical current of both tapes. Using synchrotron radiation, the local strain exerted on the REBCO layer was measured at room temperature under the conditions used for the two techniques for making Ic measurements. On the basis of these room temperature data, the local strain exerted on the REBCO layer at 77 K was numerically evaluated. A one-dimensional chain model for current flow in the REBCO material with fractional lengths of A-domains and B-domains oriented along the uniaxial strain direction is proposed. The model can explain the parabolic strain behaviour of the critical current and shows that the strain at which the peak in Ic occurs, is not only determined by pre-compression or pre-tension on the superconductor at the operating temperature, but also by the ratio of the fractional amounts of the two domains.