Effect of Bending Strain on the Current-Carrying Performance of Copper-Laminated REBCO Tape

Rare-earth barium copper oxide (REBCO) high-temperature superconducting (HTS) -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 (Ic) 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 Ic 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 Ic 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 Ic occurred at the outer edge of the REBCO films. The phenomenological model was experimentally verified to be effective in Ic 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.

Section: Introductionmentioning

confidence: 93%

Analysis of mechanical behavior and electromechanical properties of REBCO-coated conductor tapes under combined bending-tension loads using numerical methods

Pan¹,

Gao²

2023

“…A schematic of the testing device is shown in figure 4, and the specific operation process has been reported in [14]. First, secure the epoxy rod onto the base.…”

Section: Bending Test Of Individual Tapementioning

confidence: 99%

“…The analysis of the bending process in the single tape has already been analyzed [14][15][16][17][18][19][20][21]. Depending on the effect of strain on REBCO it can be divided into reversible and irreversible degradation zones.…”

Section: Introductionmentioning

confidence: 99%

“…The observation of the REBCO layer revealed that the receding of the I c was due to a fracture caused by irreversible strain. The electromechanical properties of the tapes were tested at 77 K in a self-field under a bending load, showing that the I c starts to decrease at a strain of about 0.4%-0.7% [14]. In order to explain the effect of mechanical deformation on the current-carrying capacity of REBCO tapes, several theoretical and numerical studies have been carried out to obtain the strain on the REBCO layer at different bending radii [22][23][24].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Bending characteristics of stacked REBCO cable under different stacking modes

Yuan

Dai

et al. 2023

Self Cite

High-temperature superconducting (HTS) tapes provide new materials for various high-current applications. The stacked tape cable (STC) is one of the promissing structure, which is based on the idea to stack single REBCO tapes. However, stacking the tapes increases the thickness of the cable and reduces its bending performance. In order to study the bending behavior of stacked tapes, bending tests of single tape was first made to analyze the strain of the REBCO layer at different bending radii, and the strain-current curves were obtained by empirical equations. The cables were stacked in both back-to-back and face-to-face modes. The strains of the REBCO layers in the tapes are calculated, and the critical currents of the cables are experimentally measured at various bending radii. The bending characteristics of the cable are analyzed using the fitted equation, and the experimental results demonstrate good agreement with the calculated results. The results indicate that the REBCO layer exhibits improved bending performance under compression, and thinner cables perform better. Therefore, we added copper tape to adjust the position of the neutral axis to optimize the bending performance. The results show that this method can effectively reduce the bending radius of the stacked cable.

“…During operation, they will be affected by a huge transverse compression electromagnetic force, which is the main reason for the degradation of the current-carrying capacity of CORC cables. Since the special eletromechanical properties of the second generation high temperature superconducting material composed of rare earth, barium, copper and oxygen (REBCO) elements layer in the HTS tape [32][33][34][35], it also determines the specificity of the transverse compression performance of the CORC cable. Once a CORC cable is subjected to a transverse compression load greater than a specific value, its currentcarrying capacity will decline irreversibly.…”

Section: Introductionmentioning

confidence: 99%

Analysis on the transverse compression performance of the CORC cable

Shi¹,

Dai²,

Ma³

et al. 2022

Self Cite

The conductor on round core (CORC) cable is considered as one of the best candidate cables for next generation fusion project due to its advantages of high current density, small cabling degradation and excellent magnetic ﬁeld performance. Nevertheless, the CORC cable will be aﬀected by huge transverse compression force during production and transportation, especially during operation in fusion project, which is the main reason that the current-carrying capacity of CORC cable will be irreversible degradation. There is little research on the transverse compression performance of CORC cables at present, and the inﬂuence rules of some cable parameters on its transverse compression performance are not clear yet. Therefore, in this paper, transverse compression tests are carried out on CORC cables of diﬀerent former sizes, materials and structure. The experimental results show that the larger the cable former size, the better its transverse compression performance. The transverse compression load limit of hollow tube former cable is larger than that of solid bar former cable. The performance of stainless steel bar former cable is similar to that of copper bar former cable. The limit value of transverse compression load of copper hollow tube former cable is larger than that of stainless steel hollow tube former cable. A 3D ﬁnite element model is also established to explain the internal reasons for the diﬀerences of current-carrying capacity decrease tendency of diﬀerent CORC cables. The research results can provide theoretical basis for the selection of former of CORC cable in the future. In addition, the inﬂuence of load block structure on the CORC cable’s transverse compression load limit is also studied in this paper. The results show that the arc block can signiﬁcantly increase the transverse compression load limit of CORC cable. The research results can provide a basis for the selection of the structure of support former when making cable in conduit conductor (CICC) and the structure of coil former when winding CORC coil magnet.