Investigation On Eletromagneto-Mechanics Behaviors And Characteristics Of Some Inhomogenous High-Temperature Superconducting Materials And Structures

High temperature superconductors have promising applications due to their high critical temperature, larger critical current density and strong trapped magnetic field properties. With the born of the high temperature superconductors, it attaches great importance to scientific community and the characteristics of them arouse public attention. However, the mechanical stability of the fragile superconductor restricts its application seriously, the stress induced by the electromagnetic field in the superconductor materials needs to be considered seriously and the material’s inhomogeneous effection on the magnetic and mechanical properties becomes a key factor which couldn’t be neglected. This thesis mainly aims to study the inhomogeneous effect on the magnetic properties of the inhomogeneous high temperature superconductor structure and its mechanical behaviour induced from the flux pinning force is investigated in detail.Firstly, the stress and magnetostriction of an infinite hollow superconducotor cylinder which is placed in a magnetic field is investigated based on the critical exponent model and the current density and magnetic flux density are obtained analytically. With the linear elastic theory and the plane strain method, the flux pinning induced magnetic force and stress is calculated analytically. In order to avoid the stress concentration which appears at the hollow verge, a filling method is adopted and the non-superconductive elastic materials are filled into the central hole of the cylinder. The stress and magnetostriction of the composite superconductive cylinder are formulated and the magnetoelastic behaviors are characterized analytically. The obtained results show that the filling material provides effective way to remedy the stress state at the verge of the hollow in the superconductive cylinder and an optimal stress state is received by adjusting the filling material’s Young modulus without change of the magnetization characteristic of the superconductor. Secondly, the stress and magnetostriction induced by flux pinning in a functionally graded rectangular superconductor slab is discussed analytically based on an extended exponent model of superconductivity. The magnetic field distributions as well as the stress and strain are calculated analytically with a graded distribution of the critical current density and Young modulus. Special emphasis is put on the maximum stress variation under different applied magnetic field condition, and the influence of the material graded index a for the critical current density and β for the Young modulus both on the magnetic stress and its location is investigated in detial. The obtained results show that electromagnetic characteristics as well as the mechanical properties are strongly influenced by the graded of the material. The magnetic field distributions under an increasing or decreasing magnetic field receive greart alteration with the changed graded index a and the strain and magnetostriction of the cylinder are reduced by increasing the graded index β.Thirdly, the mechanical stress induced by flux pinning in a functionally graded rectangular superconductor strip with transport current in a perpendicular magnetic field is investigated analytically. The demagnetization effect is taken into account and the current and magnetic field distributions in the strip are analyzed exactly. With the basic theory of the elastic mechanics, the analytical expression of the stress induced by the flux pinning is firstly obtained. The body force and stress distributions along the strip are presented exactly under the zero-field cooling condition and the influence of the material graded index on the stress and magnetostriction of the strip is investigated. The obtaiend results show that the flux distribution in the strip is not symmetric anymore since the different flux fronts at both sides of the strip under combined transport current and applied magnetic field action and the flux pinning induced stress is larger than the one induced by one field magnetized condition. The stress distribution of the strip is obviously different due to the restraint of the strip. A tensile stress appears at which larger magnetic flux are trapped and it’s easy to get a crack occurs in the frangile superconductor strip. The graded index β about the Young modulus has the direct bearing on the magnetostriction of the strip and the hysteresis loop is observed for the combined transport current and applied magnetic field, while for the only transport current condition, the hysteresis loop is dispeared and a hysteresis curve is received.Finally, a substrate-superconductor structure is investigated with the combined transport current and applied magnetic field. The shear stress between the substrate and superconductor is considered at this moment and the stress in the superconductor strip is investigated. The force balance equation between the normal stress in the superconductor strip and the interface shear stress is obtained. The numerical results show that the trapped magnetic flux receive unsysmmetrical distribution in the superconductor strip under combined transport current and magnetic filed and a tensile stress which leads to a crack occur easily in the fragile strip appears at both sides of the superconductor strip. The tensile stress at where more magnetic flux present in the strip is obviously larger than the one at the other side, this tensile stress always restricts the maximum of the trapped magnetic field and the stress distribution in the strip which is influenced by the Yong mudulous of the substrate obviously.This thesis aims to study the magnetic force behavior of the HTS material and structure due to its application and it makes some significant progress in research on the magnetic force characteristics and multi-field behaviour of inhomogeneous superconductor material and structure. The obtained results can guide a better application of the inhomogeneous superconductor material and structure under multi-field circumstance.