Nb_(3)Sn复合超导体中复杂形貌晶粒及晶界的力学变形分析

Mechanical deformation analysis of Nb_(3)Sn composite superconductor with complex grain structure

Nb_(3)Sn复合超导体中的晶粒具有复杂的形貌,本文基于密排纤维增强复合材料的相关理论与多晶体有限元分析方法,建立Nb_(3)Sn复合超导体中晶粒及晶界变形的尺度耦合计算模型,该模型能较为真实地反映细观尺度下Nb_(3)Sn复合超导体的结构特征;利用该模型研究Nb_(3)Sn复合超导体在轴向拉伸与压缩加载模式下柱状晶区和等轴晶区的微观局部应力以及晶粒与晶界变形特征,并分析荷载下Nb_(3)Sn复合超导体中沿晶界的弹性变形变化特点。研究结果表明:在拉压加载条件下,Nb_(3)Sn多晶体的Mises等效应力表现出非均匀分布的特征,Nb_(3)Sn等轴晶晶界处以及柱状晶区域与等轴晶交界处为主要的应力集中区域;局部应力与加载应力的比值范围集中在0.11~1.28并沿晶界波动变化,变化幅值依赖于晶粒形貌和复合材料结构。相关结果有助于理解和揭示极低温环境下Nb_(3)Sn复合超导体的变形和其超导电性能力学效应的起源。

A scale-coupled calculation model of grains and grain boundaries deformation in superconducting Nb_(3)Sn composites is built on the basis of the elastic theory of closely packed fiber-reinforced composites and the polycrystalline finite element method.The model effectively describes the complex architecture of Nb_(3)Sn composites.The relationship between the microstructure of the Nb_(3)Sn composites and the local stress distribution(stress map of grains and grain boundaries in uniaxially strained superconducting Nb_(3)Sn composites)are comprehensively studied.The stress along the grain boundary in the Nb_(3)Sn composites is carefully examined with the aid of the proposed model.The results show that the equivalent Mises stress in the Nb_(3)Sn composites is sharply non-uniform.The high stress concentration always occurs at intersections between multiple equiaxed grains,and the interface between the regions of Nb_(3)Sn columnar grains and equiaxed grains.The ratio of the local stress to the applied axis stress ranges from 0.11 and 1.28(in uniaxial tensile and compressive loading modes).The stress fluctuates along grain boundaries,and the magnitude of the variation depends on the grain morphology and the composite structure.The results are helpful to understand the deformation behavior of Nb_(3)Sn composites at the extremely low temperature and to reveal the origin of the strain sensitivity of Nb_(3)Sn.