Numerical analysis of stress distribution in Cu-stabilized GdBCO CC tapes during anvil tests for the evaluation of transverse delamination strength

Abstract

Rare-earth-Ba-Cu-O (REBCO) based coated conductors (CCs) are now being used for electric device applications. For coil-based applications such as motors, generators and magnets, the CC tape needs to have robust mechanical strength along both the longitudinal and transverse directions. The CC tape in these coils is subjected to transverse tensile stresses during cool-down and operation, which results in delamination within and between constituent layers. In this study, in order to explain the behaviour observed in the evaluation of c-axis delamination strength in Cu-stabilized GdBCO CC tapes by anvil tests, numerical analysis of the mechanical stress distribution within the CC tape has been performed. The upper anvil size was varied in the analysis to understand the effect of anvil size on stress distribution within the multilayered CC tape, which is closely related to the delamination strength, delamination mode and delamination sites that were experimentally observed. The numerical simulation results showed that, when an anvil size covering the whole tape width was used, the REBCO coating film was subjected to the largest stress, which could result in low mechanical delamination and electromechanical delamination strengths. Meanwhile, when smaller-sized anvils were used, the copper stabilizer layer would experience the largest stress among all the constituent layers of the CC tape, which could result in higher mechanical and electromechanical delamination strengths, as well as high scattering of both of these delamination strengths. As a whole, the numerical simulation results could explain the damage evolution observed in CC tapes tested under transverse tensile stress, as well as the transverse tensile stress response of the critical current, I c .

Delamination Characteristics in Wide REBCO Coated Conductor Tapes Under Transverse Loading

“…It occurred due to the stress distribution when a relatively smaller size upper anvil than the tape width was used. In this case, the Cu layer was subjected to the maximum stress induced on the CC tape and singularities occurred on the edges of the upper anvil as reported elsewhere [18]. Similar delamination mechanism was also observed at the edge case of the superconducting layer side as shown in Fig.…”

“…Van der Laan et al showed the effect of slit on the CC tape which adopts metal organic deposition (MOD) on rolling assisted biaxially textured substrate (RABiTS) process [14]. While Dizon et al reported that the SC film experienced most of the transverse stress when edges of the CC tape were included [18]. In our case, the mechanical delamination strength of the CC tape loaded at the edge part of its superconducting layer side ranged from 38 MPa to 122 MPa (open circle symbol) with an average of 90.6 MPa (closed circle symbols).…”

“…[15]. Recently, our group made efforts in characterizing the delamination behaviors in GdBCO CC tapes adopting the Hastelloy substrate and reinforced the experimental data through Weibull analysis and finite element method (FEM) [15]- [18]. In coil applications, using a wider tape to obtain the desired magnetic field can be more effective as compared to a narrow counterpart [4].…”

Delamination behaviors of GdBCO CC tapes under different transverse loading conditions

“…It is also possible that work hardening of the Cu stabilizer might have occurred. In this anvil configuration, stress concentration is greatest on the Cu stabilizer among the CC tape constituent layers [15]. On the other hand, the stress distribution changes and the maximum transverse tensile stress shifted to the superconducting film in the case of wide upper anvil (4 mm x 8 mm) which covers the whole width of the CC tape [15].…”

Delamination Strength of the Soldered Joint in YBCO Coated Conductors and Its Enhancement

“…This phenomenon has been observed not only the YBCO CC but also the GdBCO CC samples [12]. So far, there are few numerical simulations that could interpret this experimental phenomenon, since the recently published article by Dizon et al [13] in this year. Here, a 3-D numerical simulation by using ANSYS is presented, in which the bonded restraint between the multilayers was conducted, and the solid 186 hexahedral element with 20 nodes was used.…”