A Phenomenological Model And Analysis Of Relationship Between Strain And Critical-Current Degradation For Bi-Based High-Temperature Superconducting Tapes

Bi-based superconducting tape, as the first generation of high temperature superconducting materials, has high transition temperature and can be implemented successfully in liquid nitrogen temperature environment. Bi-based superconducting multi-filamentary composite tape has been widely used in the field of transportation, energy, scientific instruments, medical devices, national defense. But because the high-temperature superconducting material is brittle, its mechanical performance is often poor. Superconducting materials are always severely restricted in its performance and safety of structure due to the significant degradation of superconductivity with mechanical deformation.Based on the damage theory of brittle fiber reinforced metal matrix composites and weibull distribution function, a phenomenological model of relationship between strain and critical current degradation for Bi-based high-temperature superconducting tapes under axial load is proposed in present thesis. The relationship between strain and critical current degradation of superconducting tape with the axial strain in the processes of axial loading and unloading is given analytically. On that basis the degradation of the critical current of superconducting tape under the conditions of different initial damages and pre-strains is predicted theoretically. Then, the critical current model under axial strain is generalized and a phenomenological model of relationship between strain and critical current degradation for Bi-based high-temperature superconducting tapes under bending load is proposed. The relationships between strain and critical current degradation of superconducting tape in the processes of bend loading and unloading are obtained, and further the critical current degradation of superconducting tape are discussed under the conditions of different critical damage strains and different distribution of superconducting core. The theoretical predictions comparing with experiment results show that the phenomenological model we developed can predict and simulate well the degradation of critical current of the Bi-based superconducting multi-filamentary composite tape. The model parameters are easy to determine, resulting in simple and easy usage to engineering application. At the end of the thesis, a general analytic expression of relationship between strain and critical current degradation has been established for the superconducting cores with the asymmetric distribution. The theoretical predictions of the optimal distribution of the superconducting core for different critical damage strain are given. Theoretical calculations show that less superconducting filament distribution in the tensile side improves the mechanical properties and transmission stability of superconducting tapes, and critical damage strains have influence on the optimal location of superconducting core distribution and security domain of strain.The research and analysis result on strain dependences of critical current degradation in Bi-based HTS tape will provide theoretical guidance for prediction and evaluation of Bi-based HTS tape in practical industrial production.