芯丝断裂是造成Nb3Sn超导导体载流性能退化的关键因素，从而制约了其在高场磁体制造中的应用。目前国内外针对Nb3Sn超导股线内部芯丝断裂的研究，多数采用扫描或透射电镜对股线芯丝断裂进行微区表征，很难获得股线内部芯丝断裂的立体分布。且此方法在样品制备过程中还会对样品造成二次破坏，导致测试结果存在较大偏差。本项目旨在采用高分辨率的X射线断层扫描无损检测方法，实现对轴向拉伸应变导致Nb3Sn超导股线内部芯丝断裂的立体分布进行研究。掌握股线内部芯丝断裂和微孔缺陷的定量化分布规律，揭示轴向拉伸应变对Nb3Sn股线芯丝断裂的影响规律和载流特性衰减的物理机制，进而建立Nb3Sn低应变敏感性的股线结构模型，为Nb3Sn股线、导体及超导磁体设计提供参考。

Fracture of brittle filaments results in significant degradation of critical current density of Nb3Sn strand, which restricts its application in high field magnets. Conventional approach to analyzing the distribution of filament facture depends on fractographic analysis with SEM or TEM. However, it is impossible to obtain accurate spatial distribution of filament fracture in the Nb3Sn strand. Moreover, sample preparation process by polishing or etching will inevitably lead to filament fracture and thus result of filament fracture distribution is incredible. This project proposes investigation of filament fracture caused by tensile strain with a nondestructive testing technology, i.e. high resolution X-ray microtomography. The spatial distribution of filament fracture and other manufacturing cavities in the Nb3Sn strand will be quantitatively investigated. Based on this approach, the influence of axial, tensile strain on the filament fracture and then on the degradation mechanism of critical current density will be investigated. Moreover, the structure model of Nb3Sn strand with low strain sensitivity will be established. The results will provide a sound basis for optimization of Nb3Sn strand, conductor and magnet design.