Effect of the Bending Strain on the Inhomogeneity of Critical Current for YBCO Coated Conductors

Hall sensor system was used to measure the local critical current of YBCO tape with high spatial resolution under in-situ tensile stress. The hot spot generation and minimum quench energy of YBCO tape, which depended on the local critical current, was calculated through the thermoelectric coupling model. With the increase in tensile stress, the cracks which have different dimensions and critical current degradation arose more frequently and lowered the thermal stability of the YBCO tape.

Section: Methodsmentioning

confidence: 99%

Study of the inhomogeneity of critical current underin-situtensile stress for YBCO tape

Zhu

Chen

Zhang

et al. 2018

“…In the irreversible region, the Weibull distribution function was firstly used to describe the irreversible I c degradation of Bi-2223 tapes by Kiss et al [53]. Then, the Weibull distribution function has been proven to be an effective method for depicting the irreversible degradation of I c of BSCCO tapes [54][55][56] and REBCO tapes [56][57][58] under mechanical loads. In our previous investigations [48,59], a phenomenological model of I c combining the Ekin power-law formula and Weibull distribution function was established to depict the strain dependence of I c in both reversible and irreversible regions under uniform axial loads.…”

Section: Strain Dependence Of I C Modelmentioning

confidence: 99%

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

Pan¹,

Gao²

2023

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.

“…Meanwhile, many experimental results showed that the deformation of REBCO CCs could lead to the degradation of the critical current density [8,9]. The critical current may even decrease irreversibly when the applied strain exceeds the critical value (0.45 ± 0.05%) [10][11][12]. In addition, REBCO CC is a typical laminated multi-layer structure which has a potential risk of transverse delamination [13,14].…”

Section: Introductionmentioning

confidence: 99%

3D numerical investigation on delamination behavior of the epoxy impregnated REBCO pancake coil

Shen,

Chen,

Peng

et al. 2023

Superconducting coils made of Rare-Earth-Barium-Copper-Oxide (REBCO) coated conductor (CC) exhibit superior electromagnetic performance. Employing epoxy impregnation can improve the structural integrity and mechanical property of the superconducting coils. However, due to the extreme work environment and weak adhesion strength of REBCO CC, the delamination induced by radial thermal stress and electromagnetic force significantly affects the electromagnetic property and the reliability of the superconducting coil. This study proposes a three-dimensional (3D) thermal-electromagnetic mechanical delamination model that incorporates the cohesive zone model (CZM) to investigate the delamination mechanisms in epoxy impregnated REBCO pancake coils during the cooling and coil operation processes. The simulation employs a three-parameter Weibull distribution to account for the inhomogeneity of transverse tensile strength in the CCs. The delamination behavior and mechanisms of the coils under different conditions are analyzed. The simulation results show that the model considering random adhesion strength proves to be more effective in representing the delamination behavior of the coil. And large tensile radial stresses caused by thermal stresses and electromagnetic forces lead to the delamination behavior of the coil during cooling and operation. The main reason for the tensile radial stress is the mismatch in the thermal contraction among components of the coils during cooling process. Furthermore, we investigate the influence of the thermal expansion coefficient (CTE) and thickness of the mandrel, the CTE and prestress of the overband and the initial localized damage. The results indicate that these factors significantly affect the tensile radial stress and the extent of delamination in the windings. And the extent and distribution of delamination is related to the stress release caused by delamination to a certain degree.