| As a kind of new intelligent material,high-temperature superconductors have been widely used in magnetic levitation,nuclear magnetic resonance,tokamak and other smart devices,and further promote the rapid development of electric power,communication,transportation,aerospace and so on.It is well known that superconducting materials are brittle materials and they are highly sensitive to the defects such as holes and cracks.Due to the service environment of superconducting materials is filled with the complex electromagnetic field and strong electromagnetic force,the stress concentration is usually dramatic in defects,which will lead to the failure and destruction of the superconducting structures.In order to have a better cognition of the performance of high temperature superconductors and design a better usage,it is necessary to study the effects of defects on the electromagnetic properties and mechanical behaviors of superconducting materials under the applied electromagnetic fields.Based on the magnetic energy minimization method and finite element method,the electromagnetic properties and mechanical behaviors of the defected superconducting films will be investigated in this paper.The details are as follows:First,the stress distribution of a rectangular superconducting film with a centric rectangular and elliptic hole under applied magnetic field is numerically studied respectively.Based on the Bean critical state model,the distribution of magnetic flux density and current density under the applied magnetic field is obtained by using the minimum magnetic energy method.And according to Lorentz theorem,the electromagnetic body force is derived.Then the stress distribution in the film is obtained by finite element method.The effects of shape of hole,applied magnetic field and shape of film have been discussed.Then,the stress distribution and stress concentration of superconducting film with a centric rectangular hole are further analyzed.Unlike the previous chapter,the superconducting film has three regions of diffierent critical current densities.As the same method,the Bean critical state model is introduced.The effects of shape of hole,applied magnetic field and critical current density on hole edge stress are discussed.Finally,the centric crack problem is investigated for a superconducting film with regions of different critical current densities under electromagnetic forces.With the similar processes and methods,the stress intensity factors at the crack tips under the applied magnetic field are calculated.The effects of shape of the film,applied magnetic field and critical current density on fracture properties are analyzed. |
