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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，由于各成分之间的热膨胀和拉伸/弯曲应力的差异而产生的热应力。在运行过程中也施加洛伦兹力。这些应力静态地和周期性地作用于复合超导体。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。本文试图了解应力损伤的产生、生长和积累与临界电流的关系，并获得多丝Bi_2Sr_2Ca_2Cu_3O_x/Ag（以下简称Bi2223/Ag）、Nb_3Al/Cu和Nb-Ti/Cu超导复合导线和带保持原始临界电流的力学条件。主要研究结果总结如下。在恒定拉伸应力作用下，Bi2223、Nb_3Sn、Nb_3Al和Nb-Ti长丝的断裂应变分别为0.09 ~ 0.13、0.5 ~ 1.2、0.6 ~ 1.0和2%左右。保持原始临界电流的基本条件是使用低于该应变水平的复合超导体。重要的是，可以通过引入残余应力来延迟细丝的断裂。对于低断裂应变的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，施加应变可达0.25%左右，即最小断裂应变和残余应力之和，外加弯曲应变可达0.4%左右。在循环应力作用下，当应力循环达到疲劳寿命的70 ~ 90%左右时，包覆铜的疲劳裂纹开始向核心区域扩展。当这种情况发生时，临界电流减小。为了保持原来的临界电流，使用复合超导体是有效的低于这种应力循环。少