Analysis Of Electromagnetic Mechanical Response Of High-temperature Superconducting Strip Coating Structure After Edge Debonding

Yttrium-Barium-Copper-Oxide(YBCO)high-temperature superconducting strips have become a research hotspot in the development and application of superconducting technology due to their high critical transition temperature and strong current carrying capacity,and are expected to be widely used in high-tech scientific and technological fields such as intelligent transportation,new energy,and modern medicine.However,as a typical multilayer electromagnetic functional composite material,one of the common failure modes in YBCO superconducting strips is "edge debonding",which seriously affects the stability of the structure.So,in this thesis,the mechanical behavior of high-temperature superconducting strips is investigated under three conditions,such as there is only magnetic field applied,or the strip only transport current and both transport current and magnetic field are applied.Considering the local debonding at the edge of the coating structure of YBCO high-temperature superconducting strips,firstly,the current and magnetic field distribution laws inside the superconducting film are obtained based on the superconducting critical state model by studying the cases of superconducting strips with only current-carrying or external magnetic field excitation perpendicular to the surface of the strip,respectively;the controlling equations of the positive and interlayer tangential stresses inside the ultra-thin film are given by the plane strain method.The control equations are solved numerically by using the properties of Chebyshev polynomials.The calculation results show that the positive stress in the film and the shear stress at the interface are symmetrically distributed along the center of the structure in the non-debonded region;At the separation point of the substrate-film interface on the debonding edge of the structure,an obvious stress concentration phenomenon occurs,and the sudden increase of the positive stress will easily cause further debonding of the coating structure or even the loss of super phenomenon;at the same time,the gradually increasing load-bearing current prompts the overall increase of the positive stress in the coating structure of the superconducting strip,which has an impact on the stable operation of the structure.When the strip structure is subjected to an external magnetic field,the distribution and variation pattern of the positive stresses in the superconducting film and the shear stresses at the film-substrate interface are similar to those in the current-carrying-only case: the superconducting coated structure also generates stress concentration in the edge debonding area,and when the debonding width on the debonded side of the strip increases,the positive stresses in the film on the non-debonded side of the structure increase significantly,which affects the stable operation of the structure.In addition,for structures with a small Young’s modulus of the substrate material,the value of the positive stress in the superconducting film is significantly greater than when the Young’s modulus of the substrate material is larger.The influence of these factors on the current-carrying capacity of superconducting strip structures cannot be ignored.Second,in the context of the application of superconducting strips in multi-field environments such as high currents and strong magnetic fields,the electromagnetic mechanical response within the coated structure of YBCO superconducting strips in the presence of edge debonding under joint current-magnetic field loading is systematically investigated in the paper.Firstly,the distribution of current density and magnetic induction intensity in the superconducting film is calculated for the cases of the same proportional increase and decrease of current and magnetic field,and then the relationship between the positive stress in the superconducting film and the tangential stress at the substrate-film interface is obtained by combining the basic equations of elastodynamics.The results of numerical analysis show that under the joint action of the carrying current and external magnetic field,the current density and magnetic induction intensity in the superconducting film change relative to a single physical field due to the interaction of the current and magnetic field,and the magnetic flux lines captured on both sides of the superconducting film are different,which results in an asymmetric distribution of the positive stress in the superconducting film along the width of the structure,and the tensile stress on the side of the superconducting film with more captured flux lines is significantly larger than that on the side with fewer captured flux lines.At the same time,the Young’s modulus of the substrate has a significant effect on the stress distribution in the structure,and the substrate material with a large Young’s modulus has a strong constraint on the superconducting film,which can effectively reduce the magnitude of the positive stress in the film.