高温超导MgB2线材体积成形有限元模拟:用金属和粉体的本构模型构建

Finite Element Simulation of Volume Forming of High-Temperature Superconducting MgB2 Wire: Construction Through Constitutive Models of Metals and Powders

摘要:

通过对内部镁扩散（IMD）-MgB₂单芯线用Cu管（加工态）、Nb管（软态）和Mg棒（挤压态）进行不同应变速率（0.001、0.01、0.07 s^-1）的室温拉伸力学试验和对B粉进行室温单轴单向和循环压缩力学试验以获得应力-应变曲线，建立了室温下3种金属的Johnson-Cook本构模型和B粉的弹性模量关于其相对密度的函数关系。同时，基于DEFORM有限元软件进行了室温下IMD-MgB₂单芯线材辊轧体积变形的模拟，分析了材料的变形行为和应力分布。结果表明，建立的3种金属材料的Johnson-Cook本构模型和B粉的弹性模量关于其相对密度的函数能够准确描述IMD-MgB₂单芯线用Cu、Nb、Mg的流变行为和B粉的弹性变形，DEFORM有限元模拟结果也能够有效反映IMD-MgB₂单芯线变形行为；辊轧工艺整体变形均匀，应力分布均匀，但表面存在缺陷。本研究为IMD-MgB₂超导线材的塑性成形工艺优化提供了理论依据。

Abstract:

Tensile mechanical tests at room temperature with varying strain rates (0.001, 0.01, and 0.07 s^-1) were conducted on Cu tubes (as-processed state), Nb tubes (soft state), and Mg rods (extruded state) used for internal magnesium diffusion (IMD)-MgB₂ single-core wires. Uniaxial unidirectional mechanical tests and cyclic compression mechanical tests at room temperature were performed on B powder to obtain the stress-strain curves. Based on the abovementioned analysis results, Johnson-Cook constitutive models for three metals at room temperature were established, as well as the function between the elastic modulus of B powder and its relative density. Furthermore, the bulk deformation of IMD-MgB₂ single-core wires during room-temperature rolling was simulated using the DEFORM finite element software, and the deformation behavior and stress distribution of materials were analyzed. Results demonstrate that the Johnson-Cook models established for three metals and the elastic modulus-relative density function of B powder accurately describe the flow behavior of Cu, Nb, and Mg in IMD-MgB₂ wires, as well as the elastic deformation of B powder. DEFORM finite element simulation results can also effectively reflect the deformation behavior of IMD-MgB₂ single-core wires. The overall deformation during the rolling process is uniform with a homogeneous stress distribution; however, the surface still has defects. This study provides a theoretical basis for optimizing the plastic forming process of IMD-MgB₂ superconducting wires.