A standardized measurement method and data analysis for the delamination strengths of YBCO coated conductors

Abstract

Of crucial importance for the application of high temperature superconducting coated conductors (CCs) is the delamination strength due to thermal stress and Lorentz force during their operation. This paper reports the mechanical delamination strengths of YBCO CCs at room temperature and 77 K, as well as the electro-mechanical delamination strength form a modified anvil tensile method. Compared to previous measurement setups, our anvil device only has one degree of freedom of transverse tension. Moreover, we use a vertical soldering technique to ensure the data reliability. Since we eliminate the influence of the measurement method on the experimental results, a naturally discrete property of the delamination strength is obtained. To describe these experimental data, a three-parameter Weibull distribution function has been suggested and a new criterion for determining delamination strength is proposed from the reliability function, which can be conveniently referred to for engineering design.

Measurement of Transverse Tensile Interfacial Strength of REBCO-Coated Conductors

“…The mean value was 2.34 MPa, with a maximum relative error of 7.3%. The data dispersion was smaller than those tested based on anvil and pin-pull transverse tension [23,24,26,27]. This is because the non-interface elastic-plastic mechanical deformation and overflowed solder appearing in the anvil and pin-pull transverse tension tests were removed in this study.…”

“…Figure 4b shows the morphology of the the delaminated interface of one of the valid specimens. A clearly uniform debonding surface appeared on both interfaces, differing from the results of anvil or pin-pull transverse tension [21][22][23][24][25][26][27]. Traces of black REBCO distributed well on the interface without the matrix, whereas the other interface presented a significantly different morphology.…”

“…In the transverse delamination test, a uniaxial tensile load was applied to the specimen at 0.2 mm min −1 until the tape delaminated. Experimental studies indicated that the delamination strength of an REBCO CC tape was almost independent of temperature [27]; therefore, the experiment was performed at room temperature in this study. The transverse tensile delamination strength was obtained when the load decreased abruptly in the force-displacement curve.…”

“…Once the transverse stress on the CC tape is greater than its interfacial delamination strength, severe degradation occurs irreversibly. Some testing methods have been used to investigate the delamination behaviour of REBCO CC tapes, including the anvil and pin-pull transverse tensile tests [21][22][23][24][25][26][27], peel tests [28,29], cleavage tests [30], and anvil shear tests [31]. Among them, the anvil and pin-pull transverse tensile tests are widely used to determine the transverse tensile delamination strength.…”

“…A systematic study pertaining to the delamination of REBCO CC tapes performed by Shin et al [23][24][25] indicated significant variations in the delamination strength for both RCE-DR and MOCVD tapes; the variations were caused by the slit edge location effect and the inhomogeneity of the CC tapes. To describe these scattered experimental data of the delamination strength, a three-parameter Weibull distribution function was suggested and a new criterion for determining the delamination strength was proposed based on the Weibull distribution function [27]. In our previous study [32], we presented a three-dimensional (3D)/two-dimensional (2D) mixed-dimensional multi-scale finite element (FE) model to overcome the meshing difficulties typically encountered in modelling laminated thin-film multilayers in full-3D FE models.…”