Superconductors always operate under high electromagnetic fields at extremely low temperature, and the critical properties of witch depend on the transport current, the magnetic field, the temperature, and the stress (strain) state within the superconducting sample. Thus, investigations on the intrinsic properties and the safety-and-stability issues of superconductors are basic subjects for the application of superconducting devices. Starting from the macroscopic and microscopic perspective, the stress (strain) state and the intrinsic properties of superconducting materials under mechanical, thermal and electromagnetic field, the vortex dynamical behaviour and the flux pinning mechanism, the flux avalanche behaviours of the superconductors triggered by the themomagnetic instability are investigated in this thesis.
Firstly, the mechanical behaviours and the critical properties of two promising candidates (the Nb3Sn superconducting strand and the second generation YBCO coated conductor) under mechanical-thermal-electromagnetic field are modeled and analyzed. A 3D theoretical model based on the Mori-Tanaka method in the micromechanics theory are proposed to analyze the stress (strain) state within the superconducting filaments and the overall effective properties of the Nb3Sn strand. Influences of the twisting of Nb3Sn filaments are considered in the simulation. In addition, the mechanical behaviours of the second generation high temperature superconducting coated conductor subjected to cooling and electromagnetic force are analyzed based on the thin film theory. The influences of the physical parameters and the geometry factors on the stress distribution in the film and at the film-substrate interface are discussed.
Secondly, the vortex dynamics and flux pinning behaviour of the superconductors under magnetic fields are investigated within the Ginzburg-Landau theory. The coupling between lattice deformation and the superconducting electrons nucleation and its influences on the critical parameters of the deformable superconducting cylinder are investigated based on the modified Ginzburg-Landau equation. The effects of coupling parameters, the pressure and the geometry of the superconducting cylinder are considered in the analysis. The flux pinning effect of the secondary normal inclusion are also investigated. In addition, the magnetic domain patterns and superconducting vortices nucleation evolution in the superconductor/ferromagnet hybrid bilayer thin f...