High temperature superconducting (HTS) conductors, represented by Rare Earth-Barium-Copper-Oxide (REBCO) conductors, are promising for high energy and high field superconducting applications. In practical applications, however, the HTS conductors experience different stresses and strains, including residual stresses due to thermal mismatch and tensile stresses due to Lorentz forces, resulting in some circumstances to a reduction in the load-carrying capacity as well as the risk of degradation in conductor critical current. In this study a mixed-dimensional high-aspect-ratio laminated composite finite element model for REBCO conductor is developed for stress and strain analyses in the processes of fabricating and cooling, as well as tensile testing. The model includes all the major constituent layers of a typical REBCO conductor and is experimentally validated. First, the thermal residual stresses and strains accumulated during the fabrication and cooling processes are analyzed by a multi-step modeling method that emulates the manufacturing process. Then, with the residual stresses and strains as initial stresses and strains, the mechanical behavior under a tensile load is studied. Lastly, a phenomenological critical current-strain model based on the Ekin power-law formula and the Weibull distribution function is combined with the mixed-dimensional conductor model to predict the strain dependence behavior of critical current in the reversible and irreversible degradation strain ranges. Simulation results show that the multi-step modeling is an effective method for stress and strain analyses of REBCO conductors during the fabrication and cooling processes and under and tensile loads. Compressive thermal residual stress generated on the REBCO layer during fabrication and cooling strongly affects the subsequent mechanical and current-carrying properties. Stress–strain curves generated by tensile loads are analyzed and experimentally validated at both the conductor and constituent-layer levels. Simulation results for the strain dependence of critical current are in good agreement with experiment data in both the reversible and irreversible degradation stages.

Rare-earth barium copper oxide (REBCO) high-temperature superconducting-coated conductor (CC) tapes are potential conductors for high-field magnets. In an operating high-field magnet, REBCO CC tapes are bent into coils and simultaneously subjected to hoop electromagnetic forces. Under these combined bending-tension loads, the critical current ( I c ) of the REBCO CC tapes is at risk of irreversible degradation. Therefore, investigating the mechanical behavior and electromechanical properties of REBCO CC tapes under combined bending-tension loads is necessary. In this study, the mechanical behavior of REBCO CC tapes was analyzed using a finite element model (FEM). First, in the fabrication-cooling process of REBCO CC tapes, the thermal residual stress/strain accumulated in the constituent layers was analyzed. Then, considering the thermal residual stress/strain as the initial stress–strain state, the mechanical behavior of REBCO CC tapes under various mechanical loads, such as axial tension, bending, and combined bending-tension at 77 K, was analyzed. Furthermore, a phenomenological model of the internal strain in the REBCO films dependence of I c was developed for analyzing the electromechanical properties of REBCO CC tapes under combined bending-tension loads at 77 K. Calculated results showed that the compressive thermal residual strain in REBCO films at 77 K was −0.25%, and the internal strain in the REBCO films corresponding to the irreversible degradation of I c was 0.45% under axial tension loads, which was verified by experimental results. Under bending and combined bending-tension loads, the distribution of the internal strain in the REBCO films along the width direction was non-uniform owing to the Poisson effect, and the onset of the irreversible degradation of I c occurred at the outer edge of the REBCO films. The phenomenological model was experimentally verified to be effective in I c degradation behavior prediction under combined bending-tension loads, and model predictions based on the FEM results indicated that the electromechanical properties were significantly influenced by the bending modes (tensile bending or compressive bending) of the REBCO CC tapes.

It is well known that mechanical deformations have a strong impact on the critical current ( I c ) of Bi-2223/Ag multi-filamentary high-temperature superconducting (HTS) tapes, and a remarkable I c degradation is induced, which results in a significant AC loss. In this paper, a general predictive model based on the strain dependence of the Weibull distribution function of statistical damage of superconducting filaments and the Norris formula is developed to explore the influence of the uniaxial, bending and torsional deformation on I c degradation and self-field AC loss of Bi-2223/Ag HTS composite tapes. A unified strain dependence of the I c formula is suggested, which is extended in view of the I c degradation mechanism of Bi-2223/Ag HTS tapes under a uniaxial deformation with an introduction of longitudinal strain to unify the strain in uniaxial, bending and torsional deformation modes. Then, a modified Norris formula is deduced in light of the unified strain dependence of the I c model to predict AC loss of Bi-2223/Ag HTS tapes. With a set of appropriate model parameters determined by the tested data of I c under uniaxial deformation, the presented model can well predict both I c degradation and AC loss behaviors under not only a uniaxial deformation mode, but the bending and torsional ones. The proposed model indicates that the significant increase of AC loss for a deformed tape is presented due to the notable degradation of I c .