Study On Comprehensive Properties And Influencing Factors Of YBCO Superconducting Tape Joint

Second-generation high-temperature superconducting material(REBCO)represented by the YBCO coated conductor has excellent characteristics,such as high current density,high critical transition temperature and high critical magnetic field.Therefore,it has a wide range of application potential in the fields of electric power,transportation,energy and medical treatment.However,during the actual use of YBCO tapes,it is inevitable to connect multiple superconducting tapes or multiple sets of superconducting coils.Therefore,it is of great practical significance to continuously improve the manufacturing technology and performance evaluation methods of connection joints to meet the actual needs in the manufacturing process of superconducting equipment.In this thesis,the welding process of YBCO tapes,the superconductivity,mechanical properties and DC impact characteristics of the joint and their influencing factors are studied to avoid the harm caused by joints in practical application.Firstly,this thesis introduced the welding process of YBCO tapes and studies the welding factors that affect the joint resistance.Based on the reliable and stable joints prepared by automatic welding machine for superconducting tapes,the influence law of welding pressure,welding length and welding angle on joint resistance is mastered.And The optimal welding parameters are 6MPa,2.5cm and 30°.For straight-cut and miter-cut joints,the current distribution characteristics in the joint area with different welding angles are explored.The results show that the current flow mainly occurs at both ends of the joint.Secondly,the mechanical properties of YBCO tape joints under bending,stretching,twisting and stretching twisting are studied,and the attenuation law of joint critical current is obtained.By experiments,the critical stress and strain values of joints with different welding angles and different welding lengths are determined.And the tensile properties of straight-cut joints are simulated and analyzed.The results show that the smaller the welding angle and the shorter the welding length,the better the mechanical properties of the joint.In addition,the difference of critical current attenuation law of miter-cut joints under single tensile load and combined tensile and twisting load is analyzed and compared.Finally,this thesis analyzed the DC impact characteristics of YBCO tape joints.The influence of different welding angles and welding lengths on the direct current impact characteristics of joints was studied,and the simulation analysis of direct current impact was carried out for straight-cut and miter-cut joints.The results show that the longer the welding length,the better the DC impact characteristics of the miter-cut joints.In addition,the difference of DC impact characteristics of miter-cut joints between normal state and twisted state is analyzed and compared.The above results provide experimental basis and theoretical guidance for the superconducting cable project of our research group.