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INVESTIGATION TO RETAIN HIGH CRITICAL CURRENT OF COMPOSITE SUPERCONDUCTORS FROM MECHANICAL VIEWPOINT

从力学角度研究复合超导体高临界电流的保持

基本信息

批准号：
14350360
负责人：
OCHIAI Shojiro
金额：
$ 10.75万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

Thermal stresses arising from the difference in thermal expansion among the constituents and tensile/bending stresses are exerted during fabrication and winding. Also Lorentz force is exerted during operation. These stresses are statically and cyclically given to the composite superconductors. Therefore, it is one of the most important research subjects to reveal the mechanical behavior of the composites and its influence on superconducting properties, and, based on such results, to clarify the condition to retain high superconducting properties under applied stresses. The present work attempted to understand the relation of the initiation, growth and accumulation of the stress-induced damages to critical current and to obtain the mechanical condition to retain the original critical current for the multifilamentary Bi_2Sr_2Ca_2Cu_3O_x/Ag (hereafter noted as Bi2223/Ag), Nb_3Al/Cu and Nb-Ti/Cu superconducting composite wires and tapes. Main results are summarized as follows.Under the sta … More tically applied tensile stresses, the fracture strains of the Bi2223,Nb_3Sn,Nb_3Al and Nb-Ti filaments were around 0.09-0.13,0.5-1.2,0.6-1.0 and 2%, respectively. The rough condition to retain the original critical current is to use the composite superconductors below such strain levels. It is important that the fracture of the filaments can be delayed by introducing residual stresses. In the case of Bi2223 composite with low fracture strain, the introduction of residual stress is very effective. Based on the experiments and analysis, the applied strain is allowable up to around 0.25% which is the sum of the minimum fracture strain and residual stress and applied bending strain up to around 0.4%. Under the cyclic stresses, the fatigue crack initiates in the clad cupper and it propagates to the core region when the stress cycles reaches around 70-90% of the fatigue life. When such situation arises, the critical current is reduced. To retain the original critical current, it is effective to employ the composite superconductors below such stress cycles. Less

在制造和缠绕过程中，由于组件之间的热膨胀差异而产生的热应力和拉伸/弯曲应力被施加。此外，在操作过程中还会施加洛伦兹力。这些应力是静态地和循环地施加给复合超导体的。因此，揭示复合材料的力学行为及其对超导性能的影响，并在此基础上阐明在外加应力下保持高超导性能的条件是最重要的研究课题之一。本工作试图了解应力损伤的萌生、扩展和积累与临界电流的关系，并获得多芯Bi2Sr2Ca2Cu3Ox/Ag(以下简称Bi2223/Ag)、Nb_3Al/Cu和Nb-Ti/Cu复合线材和带材保持原始临界电流的力学条件。主要研究结果总结如下：在Sta…下在较高的拉应力作用下，Bi2223、Nb_3SN、Nb_3Al和Nb-Ti纤维的断裂应变分别为0.09-0.13、0.5-1.2、0.6-1.0和2%。保持原始临界电流的粗略条件是使用低于这种应变水平的复合超导体。通过引入残余应力可以延缓纤维的断裂，这一点很重要。对于断裂应变较低的Bi2223复合材料，残余应力的引入是非常有效的。根据实验和分析，最小断裂应变和残余应力之和允许的外加应变约为0.25%，外加弯曲应变约为0.4%。在循环应力作用下，疲劳裂纹在覆铜板上萌生，当应力循环达到疲劳寿命的70-90%左右时，疲劳裂纹扩展到芯区。当出现这种情况时，临界电流减小。为了保持原始的临界电流，在这样的应力循环下使用复合超导体是有效的。较少