A combination of failures of interfacial delamination and layer cracking in REBCO multilayered conductors

Abstract

Rare-earth barium-copper-oxide (REBCO) coated conductors (CCs) are kinds of multiphase, multilayer, and composited superconducting tapes, which are becoming promising candidates for abundant high-energy and high-field applications owing to their outstanding superconducting properties. However, the mechanical failures of REBCO CCs composites, such as cracks in the brittle ceramic layers, and delamination on interfaces among weak multiple layers, have become the essential issues threatening the capability and stable operation of REBCO-based superconducting devices, especially under extreme low temperature and complex electromagnetic fields. In this study, a failure modeling in combination of the interfacial delamination and layer fracture in REBCO CCs composites was established and analyzed numerically by the finite element method. To effectively treat with the two mechanical failure modes, the interfacial delamination response and the fracture behavior were respectively captured using the cohesive zone model and the extended finite element method for the multilayered superconducting CCs. The failures initiation and evolution in REBCO multilayered structures were implemented based on the stress criteria. The characteristics of two failure modes of the multilayered superconducting CCs under uniaxial tension and bending were investigated, and those during cooling process from room temperature to 77 K were then simulated in consideration of residual thermal stresses accumulated. The results illustrated that the progressive mechanical failure behaviors were presented in combination of the interfacial delamination and fracture damages in the REBCO multilayered structure. The crack propagation in the superconducting layer can cause the delamination failure at the corresponding position on the interfaces between the superconducting layer and its adjacent layers, while the delamination damage on the interfaces releases the constraint between the layers further enhances the crack propagation. The residual thermal stress accumulated during cooling was found to significantly affect the mechanical behavior of the REBCO CCs, and the low-temperature makes a failure occurrence earlier compared to that at room temperature.