Numerical Study On Crack Propagation Of REBCO Superconducting Laminated Tapes Considering The Behavior Of Interfacial Failure

The second generation(2G)high temperature superconducting(HTS)tapes,RareEarth-Barium-Copper-Oxide(REBCO)coated conductors(CCs),have become a research hotspot in the field of superconductivity technology and applications widely used in high-tech industry such as energy,transportation and medical treatment based on the high critical magnetic field,high current density and superconducting state realized in their liquid nitrogen environment.As a multilayer brittle composite,however,the interface delamination and superconducting film fracture are easy to happen due to the brittle characteristic of REBCO layer.Thus,the superconductivity and even the structure failure are affected.In this thesis,the interface delamination and superconducting film fracture of REBCO CCs are numerically studied.Finite element(FE)model for crack propagation analyses based on a bilinear cohesive zone model(CZM)and the extended finite element method(XFEM)are established considering the behavior of interfacial failure.The fracture characteristics and crack propagation behavior of REBCO superconducting laminated tapes under mechanical force and thermal mismatch stress accumulated during cooling process are studied respectively.The calculated results show that: the delamination between superconducting layer and the adjacent layers and the fracture of REBCO superconducting film influence each other.The higher the interface strength is,the more difficult the delamination is induced.The longer the initial crack is,the more likely it is to fracture.The thickness of copper layer obviously effects the delamination and fracture behavior within a certain range.The influence of thermal mismatch stress accumulated during cooling process from room temperature to 77 K on the interface delamination and superconducting film fracture behavior of the laminated tape was studied based on the FE model.Results showed that the superconducting laminated tape tends to fail more easily when the effect of thermal mismatch stress was considered.The model established in this thesis can qualitatively explain some experiment results in the literature.The progressive failure mechanism caused by the interaction of interfacial delamination and superconducting film fracture has been revealed.The results of correlation quantitative analyses can provide some theoretical guidance for the engineering applications and mechanical failure of REBCO superconducting tapes under complicated environments.