Investigation On The Method Of Measurement And Data Analysis Of Delamination Strengths Of The ReBCO Second Generation High Temperature Superconducting Tapes

ReBCO(Re refers to Y,Gd,Dy and other rare earth elements)second generation high temperature superconducting tapes(Called ReBCO superconductor tapes for short)have higher irreversible magnetic field and better current carrying capacity at high field compared with low temperature superconducting wires.Compared with the first generation of high temperature superconducting tapes(referring to Bi superconducting material),ReBCO superconductor tapes have lower cost and wider temperature range.And they have important application prospects in superconducting magnets,superconducting cables,superconducting motors and other fields,and have become the main direction of the development of superconducting materials in the future.However,the ReBCO superconducting tapes are the typical laminated material,and the interlaminar peel(also known as delamination)will occur due to the action of electromagnetic force and thermal stress in the operation process.Existing research results show that delamination has become the most important damage form of ReBCO superconducting tapes delamination occur,the critical current of superconducting material will decrease rapidly,which brings safety risks to the operation of superconducting devices.For the manufacturers of superconducting materials,the delamination strength becomes one of the key indicators to evaluate their preparation process and product performance,and for the designers of superconducting devices,the delamination strength value is more critical and becomes the core index of structural safety and functional design.Considering the extremely low temperature,strong magnetic field and high current environment of ReBCO superconducting tapes,the research on the delamination strength of ReBCO superconducting tapes have both important scientific significance and broad engineering application background.For the measurement of ReBCO superconductor tapes' experiment of the delaminating strength,mainly have the following several ways: Peeling test,pin-pull test,anvil test,etc.Compared with the previous two methods,anvil test has the advantages of convenient operation,easy implementation of normal and low temperature testing,and the working condition is closest to the real stress characteristics of the tapes in the superconducting device.It is the most widely used test method of delamintion strength domestic and overseas.However,the difficulty of this method is that the fixture is difficult to ensure that it is perpendicular to the sample surface,so in the peel test process,inclined peel is easy to occur,resulting in small measurement results.Therefore,how to avoid inclined peeling from the design of peeling fixture becomes the first difficulty in peeling strength measurement of ReBCO superconducting tapes.In ReBCO superconductor tapes,the superconducting layer and buffer layer are ceramic materials,therefore they have low fracture toughness and discreteness and are very large.Therefore,the delamination strength data of the ReBCO superconducting tapes obtained in the traditional experiment are very discrete,and it is difficult to effectively describe the delamination characteristics by using the traditional data processing methods,i.e.average value and standard deviation,resulting in the difficulty of providing guidance and suggestions for material preparation and engineering design with this kind of experimental results.A new data processing mode is needed,which can not only characterize the delamination strength characteristics of ReBCO superconducting tapes,but also facilitate engineering application.In addition,the delamination strength of ReBCO is currently divided into two categories internationally.The first is the mechanical delamination strength,which is defined as the delamination strength in normal or low temperature(mainly liquid nitrogen temperature)and no electromagnetic environment.The second is the electromechanical delamination strength,which mainly refers to the delamination strength of superconducting materials when carrying current at liquid nitrogen temperature.Compared with the mechanical strength of delaminating,the testing process of electromechanical delamination strength requires a large number of samples,which leads to high experimental cost.Meanwhile,there is a problem that electrical criteria and mechanical criteria are not synchronized when loading in the current carrying process.Therefore,if the measurement process of electromechanical delamination strength can be simplified or even the mechanical delamination strength and electrical delamination strength can be unified,it will greatly promote the study of the delamination strength of superconducting materials.Finally,as the most promising superconducting material internationally recognized at present,there is no corresponding national standard for the testing and data characterization of the delamination strength of ReBCO superconducting tapes.On one hand,it is difficult to compare the measurement results of different laboratories,and on the other hand,it greatly restricts the engineering application of superconducting material.In view of the above problems,the research work of this master's thesis are as follows:1,Design and develop a set of vertical welding fixture of anvil drawing method,eliminate the inclined peeling phenomenon which is difficult to avoid in the process of anvil drawing before,and improve the reliability of test mathematics.The mechanical delamination strength and current-carrying delamination strength of ReBCO superconducting tapes are tested experimentally and the uncertainty of a single strength test is carried out.From the experimental data,it can be seen that there is indeed data dispersion,and the standard difference can reach about 1/3 of the average value of data.2,this paper proposes a three parameters weibull analysis data processing mode for a wide range of discrete delaminating strength test results into the effective statistical analysis,and gives the direct guide for engineering design of the reliability function,put forward the concept of permissible stress,implements the ReBCO superconductor tapes delaminating strength was evaluated.Then,the width of the anvil and the sample size of the statistical method are studied,and the minimum sample capacity is given and it is convenient for the measurement.3.The draft of the national standard for measurement of the delamination strength of ReBCO superconducting tapes has been formed,which has passed the vote of the National Technical Committee on Superconductivity of Standardization Administration,and is now submitting the project approval application to the Standardization Administration Committee of the State Administration for Market Regulation.4.Through mechanical analysis,it is found that if the test fixture is always perpendicular to the sample surface during the delamination experiment,the electromechanical delamination strength and mechanical delamination strength can be unified.After comparison,it can be seen that the difference between electromechanical delamination strength and mechanical delamination strength is no more than 5%,which greatly reduces the experimental cost and significantly improves the experimental efficiency.