MULTISCALE SIMULATION OF MECHANICAL DEFORMATION EFFECTS ON CRITICAL PROPERTIES OF Nb₃Sn HIGH FIELD COMPOSITE SUPERCONDUCTORS

A15 superconducting Nb₃Sn has shown great promise for applications in the international thermonuclear experimental reactor, and high energy physics. In these high field applications, the stress/strain arises from the cool-down and operation process of the superconducting magnet, inducing the performance degradation of the Nb₃Sn cable-in-conduit conductors, which is a critical issue in the superconductivity applications and developments. Due to the complex multi-scale structure of Nb₃Sn composite, the electromechanical coupling responses at different scales are intrinsically interrelated. On the basis of the micro-meso-macro frame analysis, this paper intends to study the effects of strain induced variations of the characteristic parameters of material microstructure on the superconducting properties of Nb₃Sn and establish the constitutive model which accounts for the multiscale coupling in strained Nb₃Sn. A framework for micro-to-macro transitions for multi-scale analysis of multifilamentary superconducting composites is developed. Using this model, we respectively predict the critical properties degradation responses of Nb₃Sn polycrystal under hydrostatic pressure and Nb₃Sn composite under axial loading, the predicted results are in qualitative agreement with the experimental observations.. This study reveals the multiscale coupling mechanism of electromechanical effects in Nb₃Sn high-field superconducting composite.With the aid of the study, the multiscale features in electromechanical coupling behavior in Nb based A15-type compounds are identified. The study will promote the material engineering application process, and the results of which are promising to engineer optimized large-scale superconducting high magnetic field systems. It is helpful to improve the understanding and description of the strain sensitivity of Nb₃Sn, and to provide a solid theoretical support for the manufacture of high-field superconducting magnets. The developed simulation model provides a basis for the detailed description of strain effects on the superconducting properties of Nb₃Sn. Furthermore, the developed multiscale model lays foundation for understanding the empirical relation given by the experiment and opens the way for the parameterization of the strain effects on the superconducting Nb₃Sn.