Zhierwinjay Bautista

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.

Note: Effective measurement of retained Ic in evaluating electromechanical properties of high temperature superconductor tapes by the voltage tap clipping technique

In this note, the effectiveness of voltage tap clipping technique was assessed in evaluating the electromechanical properties of high temperature superconductor (HTS) tapes in the aspect of practical device applications. In the four-probe transport I(c) measurement, instead of directly soldering the voltage lead wires onto the HTS samples, they were tapped to the sample by either just clipping or soldering them to the clips. This technique facilitated the simultaneous and repeated retained I(c) measurement test for multiple samples. Finally, the critical double bending diameter of HTS tapes and the electrical properties of jointed and striated coated conductor tapes could be easily determined.

Critical current degradation behaviour of GdBCO CC tapes in pure torsion and combined tension-torsion modes

Coated conductor (CC) tapes utilized in high-current-density superconducting cables are commonly subjected to different loading modes, primarily torsion and tension especially in the case of twisted stacked-tape cable. Torsion load can occur due to twisting along the length or when winding the CC tapes around a former, while tension load can occur due to pre-tension when coiled and as a hoop stress when the coil is energized. In this study, electromechanical properties of single CC tapes under torsion load were investigated using a new test apparatus. The results could provide basic information for cable designers to fully characterize stacked cables. Copper-electroplated and brass-laminated CC tapes fabricated with different deposition techniques were subjected to pure torsion and combined tension-torsion loading. The critical current, I c degradation behaviours of CC tapes under torsional deformation were examined. Also, the effect of further external lamination on the I c degradation behaviour of the CC tapes under such loading conditions was investigated. In the case of the combined tension-torsion test, short samples were subjected to twist pitches of 200 mm and 100 mm. Critical parameters including reversible axial stress and strain in such twist pitch conditions were also investigated.

Electro-Mechanical Properties of Single-Side Brass Foil Laminated Coated Conductor Tapes at 77 K Under Self-Field

The architecture of coated conductor (CC) tapes plays an important role in its overall mechanical and electromechanical performance characteristics. In this paper, mechanical and electromechanical properties of single-side brass foil laminated CC tapes were evaluated. Cu-stabilized CC tape was externally reinforced differently by soldering brass laminate just either on the superconducting layer side or the substrate one. Under uniaxial tension and double bending, the stress/strain dependences of critical current, Ic, in brass-foil-laminated CC tapes depending on the location of brass laminate have been examined and their irreversible limits are determined. Under uniaxial tension, CC tape samples where brass foil laminated on to the superconducting layer side showed a little high irreversible strain limit than the other one. Under double bending at RT, CC tapes brass foil laminated on superconducting layer side showed much smaller critical bending diameter. The location of the REBCO superconducting film with respect to the neutral axis on the cross-sectional area under bending deformation was important to achieve a much smaller critical bending diameter. In addition, the effect of brass laminate thickness on its Ic behavior under strain/stress was evaluated.

Characteristic Irreversible Critical Strain Limit of GdBCO Coated Conductor Tapes under Various Temperature and Magnetic Field Conditions

Superior mechanical and electromechanical properties of the coated conductor (CC) tapes made them a viable option for coil and magnet applications. In this study, investigation on the characteristics of <italic>I</italic>_c under different <italic>B</italic>, <italic>T</italic>, and <italic>ϵ</italic> conditions were conducted. Tensile load was applied using the Katagiri type test rig under different high magnetic field and low-temperature conditions wherein irreversible strain, <italic>ϵ</italic>_irr was determined. The <italic>I</italic> _c behavior with magnetic field of both reactive co-evaporation by deposition and reaction (RCE-DR) and metal organic chemical vapor deposition (MOCVD) processed CC tapes at different <italic>T</italic> and <italic>B</italic> were obtained. The critical irreversible strain limit <italic>ϵ</italic>_irr of Cu-stabilized REBCO CC tape increased with decreasing temperature from 65 K down to 20 K. This behavior was resulted from the increased yield strength of the CC tape due to thermal hardening effect.