Multiscale electromechanical framework for elastoplasticity and interface failure in high-field NI REBCO magnets

Abstract

No-insulation (NI) rare-earth barium copper oxide (REBCO) superconducting coils, owing to their high current density and intrinsic self-protection capability, have emerged as a key technological option for insert coils in ultra-high-field superconducting magnets. However, under high background magnetic fields, Lorentz forces induced by non-uniform electromagnetic field subject REBCO tapes to complex and high electromagnetic–mechanical stresses, leading to elastoplastic deformation, interfacial damage, and critical current (Ic) degradation that constrain reliable magnet operation. To address these challenges, this paper proposes an electromagnetic–mechanical coupled multiscale modeling framework for large-scale NI REBCO coils. The approach is based on an orthotropic elastoplastic homogenization theory, in which the multilayer REBCO composite tape is represented as an equivalent continuous medium. Building on existing multiscale mechanical formulations, this work introduces bidirectional coupling between the homogenized U–T–A electromagnetic formulation and the elastoplastic mechanical model through a strain-dependent Ic relation. Inter-turn contact behavior is further considered, and a U–T–A formulation is employed to achieve efficient coupled computation of current distribution and electromagnetic forces. The homogenized elastoplastic constitutive response is calibrated and assessed against uniaxial tensile data of REBCO coated conductors, while the coupled coil-level response is further compared with strain measurements from a small-scale NI coil. It is then applied to the numerical analysis of a REBCO insert coil in the 45.5 T hybrid magnet at the National High Magnetic Field Laboratory. The results indicate that non-uniform Lorentz forces induced by screening currents lead to hoop-stress concentration in the end regions of the REBCO insert coil and driving local plastic deformation of the tapes. It further modifies the internal current distribution, resulting in severe and irreversible Ic degradation. At mesoscale, markedly different mechanical responses are observed in different materials. Moreover, internal interface degradation and delamination were observed in the conductors. This framework provides an effective numerical tool for elucidating failure mechanisms and supporting structural safety assessment and optimized design of high-field superconducting magnets.