Stress–Strain Relationship, Critical Strain (Stress) and Irreversible Strain (Stress) of IBAD-MOCVD-Based 2G HTS Wires Under Uniaxial Tension

The mechanical behavior of a REBCO-coated conductor wire under uniaxial tension is largely determined by the two thickest component layers in the architecture, namely, the substrate and the stabilizer. A rather complicated stress-strain relationship is often observed when the composite conductor is under uniaxial tension, which is the result of the differences in elastic modulus and yield stress between the Hastelloy substrate and the electroplated Cu stabilizer. In this paper, the stress-strain relationships of a free standing Cu stabilizer and a bare REBCO wire, i.e., a tape without any stabilizer, were measured. The results are utilized for the calculation of the stress-strain relationships of electroplated Cu stabilized wires using a two-component composite model. Given the thicknesses of the substrate and stabilizer, the calculated results agree well with the measured stress-strain curves, which can be well fitted with the Ramberg-Osgood equation. The tensile strain (stress) dependence of the critical current (I _c ) was measured at 77 K in liquid nitrogen. Depending on whether the critical current was measured with the wire under a stress or after unloading, a critical strain (stress) and an irreversible strain (stress) were determined, respectively.