Evaluation of the electromechanical properties in GdBCO coated conductor tapes under low cyclic loading and bending

The effects of low cyclic loading on the critical current, I-c, under uniaxial and transverse loadings, and bending deformations in GdBCO coated conductor (CC) tapes were evaluated. Under monotonic continuous bending deformation, CC tapes exhibit a high tolerance of I-c up to the lowest bending diameter of 12 mm using the Goldacker bending test rig. However, when the CC tape was subjected to alternate tension-compression bending, a lower irreversible bending strain limit was measured. This was also observed when cyclic bending was applied to the CC tapes which showed a significant decrease in I-c just after 10 cycles of alternate tension-compression bending at 20 mm bending diameter. Such different I-c degradation behavior under different bending deformation procedures gave insight into the proper handling of CC tapes from manufacturing, coiling and up to operating conditions. In the case of uniaxial tension, when electromechanical properties of CC tape were evaluated by repeated loading based on a critical stress level obtained under monotonic loading, I-c also did not show significant change in its degradation behavior up to the irreversible stress limit. The GdBCO CC tape adopted can allow cyclic loading up to 100 cycles without significant irreversible degradation below the monotonic irreversible limit. In the case of the transverse cyclic test, with regard to the large scattering of data especially in the tensile direction, a different cyclic loading procedure was established. For 10 repeated loadings, the mechanical and electromechanical properties of the GdBCO CC tapes showed similar values within the reversible range under the monotonic loading. I-c degraded abruptly indicating that no delamination occurred at the REBCO film during the subcritical cyclic loading. Different fracture morphologies were observed under cyclic loading depicting branch-like patterns of the remaining REBCO layer on the substrate of the CC tape.