Characterization of transverse tensile stress response of critical current and delamination behaviour in GdBCO coated conductor tapes by anvil test

Recent problems in superconducting devices operating at the high magnetic field regime include the possibility of substantial critical current, Ic, degradation due to the delamination of the coated conductor (CC) tapes. The delamination may originate from excessive tensile radial stress and cleavage stress developed due to epoxy curing, cool-down and Lorentz force generated. Therefore, it is necessary to investigate the Ic response under transverse loading and the delamination behaviour in REBCO CC tapes to predict its performance in practical device applications. In this study, using the anvil test method, the delamination strength and the transverse tensile stress response of Ic in GdBCO CC tapes were investigated. Under transverse tensile stress, the Ic degradation in GdBCO CC tapes showed both abrupt and gradual behaviours. A reversible Ic degradation behaviour was also observed which was similar to the case under uniaxial tension. The electro-mechanical and mechanical delamination strengths were determined, wherein both increased when a smaller-sized anvil was used during the delamination test. The electro-mechanical delamination strength was approximately half of the mechanical delamination strength in the GdBCO CC tapes tested. Four delamination modes were observed and well correlated with electro-mechanical delamination strength and Ic degradation behaviour. Lastly, delamination sites within the CC tapes were also correlated with the Ic degradation behaviour that had been observed.