静水压作用下Nb3Sn多晶体超导临界温度退化的耦合模型

Nb3Sn超导材料主要用于强磁场超导磁体的制造。力学变形诱导的其超导临界性能退化给强磁场超导磁体装置的电磁性能指标和安全运行造成了极其不利的影响。针对静水压作用下，Nb3Sn单晶体和多晶体表现出的不同退化行为，本文基于Maki De Gennes（MDG）关系式，建立了描述Nb3Sn单晶体变形-超导临界温度耦合响应的本构关系，并借助于多晶体有限元方法，对静水压作用下Nb3Sn多晶体超导临界温度退化响应进行了预测，预测结果与实验结果定性吻合。模型实现了从Nb3Sn单晶体到Nb3Sn多晶体变形-超导临界温度退化响应曲线的一致性预测。研究结果有助于提高对Nb3Sn高场超导材料变形-超导电性能耦合行为的认识，为发展描述运行工况下Nb3Sn超导材料力-电磁-热多物理场多尺度耦合行为的建模与数值计算方法提供了一定的基础；同时，相关结果对于特殊工况下高场超导磁体性能的评估和高应变耐受性超导材料的制备也具有一定的指导作用。

A coupling model for hydrostatic pressure induced critical temperature degradation of Nb3Sn polycrystalline superconductors

Nb3Sn superconducting material has promising application prospect in high-field magnet. In the material application in the high-field magnet design and manufacture, strain induced superconducting performance degradation of Nb3Sn is of great importance and significance. In order to reveal the different degradation responses of Nb3Sn single crystal and Nb3Sn polycrystal under hydrostatic pressure, we establish a constitutive relation characterizing the electro-mechanical coupling behavior in Nb3Sn single crystal. The constitutive relation is based on maki de Gennes (MDG) relation. By using the relation, we predict the hydrostatic pressure induced critical temperature degradation response of Nb3Sn polycrystalline superconductor, whose deformation is modeled by polycrystalline finite element method. The predicted results are qualitatively consistent with the experimental observations. The proposed relation can consistently describe the hydrostatic pressure induced degradation responses of both Nb3Sn single crystal and Nb3Sn polycrystal. The results are helpful to improve the understanding of the electro-mechanical coupling behavior of Nb3Sn superconducting material and to lay a foundation for modeling and simulation methods for multi-field and multi-scale characterization of Nb3Sn in extreme serving environment. At the same time, the results can be used to evaluate high field superconducting magnet design and to give insight on how to fabricate superconducting materials with high strain resistance.