Study On Mechanical Behavior Of Superconducting Strip Coating Structure Excited By Electromagnetic Field

High temperature superconductor materials have high critical transition temperature,high current carrying capacity and low AC loss.Therefore,they are paid more attention by the scientific and superconducting engineering fields,which makes it the most promising superconductor material for the application of high-power in liquid nitrogen temperature zone.It is expected to be obtained in the future in power equipment such as superconductor cable,superconducting generator,superconducting transformer,superconducting current limiter,STATCOM and other power equipment It has been widely used.However,the multi-layer structure properties of superconducting strip and the local debonding problems in application are easy to cause the degradation of transmission performance and mechanical properties.Therefore,the research on the electrical and mechanical properties caused by local debonding is very important.Based on this,this paper has carried out the following two research work.Firstly,the electromagnetic mechanical response of YBCO High temperature superconducting tape excited by external magnetic field after local debonding of superconducting layer is studied.Based on the superconducting critical state bean model and the elastic plane strain method,the governing equations of the normal stress in the superconducting film and the shear stress at the substrate interface are given.The variation of the normal stress in the superconducting film and the shear stress at the substrate interface with the external magnetic field is studied numerically.The results show that the normal stress in the superconducting film and the shear stress at the substrate film interface increase sharply near the debonding region,which can easily cause further debonding of the superconducting layer.At the same time,the maximum shear stress appears at the edge of the structure.The properties of the substrate material,especially young's modulus,have a significant effect on the stress in the structure.In the soft substrate structure,there is a large normal stress in the superconducting film,while when the substrate material is hard,there is a large shear stress at the interface between the substrate and the film.These factors will cause the degradation of the mechanical and electrical properties of the superconducting coating structure.Secondly,the mechanical properties of YBCO superconducting tape under local magnetic field are studied.Based on the critical state bean model,using the linear elastic theory and the plane strain method,the distribution characteristics of the current and magnetic induction intensity in the superconducting film under the same proportion of the rising and falling transmission current and the external magnetic field are given.By analyzing the stress state of the substrate film structure under the magnetic flux pinning force,the mechanical equilibrium equation in the substrate film structure is given,Then,the normal stress in the superconducting film and the shear stress at the substrate film interface are calculated by numerical calculation.The effects of the change of electromagnetic field,the existence of local debonding of superconducting coating and different substrate materials on the distribution of normal stress and shear stress at the interface are discussed in detail.The results show that: when the superconductor is only affected by the transmission current or the external magnetic field,the normal stress and the interfacial shear stress in the superconductor are symmetrically distributed on both sides of the structure except for the debonding region;when the transmission current and the external magnetic field act together,the normal stress and the interfacial shear stress in the superconductor film on the right side are significantly larger than those on the left side;and for the superconductor film with high conductivity,the normal stress and the interfacial shear stress are more symmetrical For the superconductors with hard substrate,the normal stress in the superconductors decreases,while the shear stress at the interface increases.In addition,due to the existence of local debonding,the normal stress and the shear stress at the interface change rapidly near the superconductors,resulting in the phenomenon of stress concentration,which may lead to the further propagation of cracks,and then lead to the formation of superconductors The current carrying characteristics of the tape change.