极低温区循环载荷作用下Nb_(3)Sn复合超导体的变形损伤及其应变率效应数值模拟  

Simulation on Deformation Damage and Strain Rate Effect of Nb_(3)Sn Composite Superconductors under Cycling Load at Extreme Low Temperature

作　　者：黄敏 朱本浩 肖革胜 乔力 HUANG Min;ZHU Benhao;XIAO Gesheng;QIAO Li(Institute of Applied Mechanics,College of Mechanical and Vehicle Engineering,Taiyuan University of Technology,Taiyuan 030024,Shanxi,China)

机构地区：[1]太原理工大学机械与运载工程学院应用力学研究所,山西太原030024

出　　处：《高压物理学报》2024年第2期94-111,共18页Chinese Journal of High Pressure Physics

基　　金：国家自然科学基金(11772212,12272249);山西省基础研究计划资助项目(202303021211070)。

摘　　要：Nb_(3)Sn超导体在循环载荷下的变形损伤行为研究对揭示超导体临界性能不可逆退化背后的力学机制具有重要意义。采用分子动力学模拟方法研究了极低温条件下单晶和多晶Nb_(3)Sn/Nb复合材料在循环载荷下的变形损伤行为,同时分析了应变率对Nb_(3)Sn/Nb复合材料变形损伤和断裂行为的影响。结果表明:单晶Nb_(3)Sn/Nb复合材料在循环载荷作用后,Nb_(3)Sn层出现滑移,当滑移带交错处的局部应力大于材料强度时,在滑移带交错处微裂纹萌生,致使复合材料中Nb_(3)Sn层断裂失效;而多晶Nb_(3)Sn/Nb复合材料则由于晶界处应力在循环载荷下得不到松弛,当应力峰值超过晶界强度时,在晶界处萌生微裂纹,导致复合材料中Nb_(3)Sn层发生沿晶断裂。Nb_(3)Sn/Nb复合材料在不同应变率下表现出不同的断裂方式。随着应变率的增加,单晶Nb_(3)Sn层中的滑移带数量增加,导致单晶Nb_(3)Sn/Nb复合材料的韧性增强。而多晶Nb_(3)Sn/Nb复合材料中,晶界对材料强度的影响随着应变率的增加而降低,高应变率下,复合材料在Nb_(3)Sn层局部断裂后具有较大的剩余强度。研究结果将有助于理解Nb_(3)Sn/Nb复合材料在循环载荷下的损伤演化过程,为材料的性能优化设计提供一定的理论指导。The study on damage and fracture of superconducting Nb_(3)Sn under cyclic loading is an indispensable part of understanding the origin of the irreversible strain limit in Nb_(3)Sn.This paper uses molecular dynamics simulation to investigate the fracture and deformation damage behavior of polycrystalline and single crystal Nb_(3)Sn/Nb composite materials under cyclic loading at extremely low temperatures.The effects of strain rate on crack initiation and growth were carefully analyzed in both polycrystalline and single crystal Nb_(3)Sn/Nb composite materials.The results indicate that slip occurs in single crystal Nb_(3)Sn/Nb composite materials after cyclic loading.When the local stress at the slip band intersection exceeds the material strength,microcracks initiate at the slip band intersection,leading to fracture failure of the composite material.In contrast,the failure of polycrystalline Nb_(3)Sn/Nb composite materials is due to the inability of stress at grain boundaries to relax under cyclic loading,which leads to the initiation of microcracks at the grain boundaries and intergranular fracture of the composite material.The analysis of the different damage,fracture,and failure mechanisms of polycrystalline and single crystal Nb_(3)Sn/Nb composite materials at different strain rates shows that the fracture is brittle at low strain rates.As the strain rate rises,the number of slip bands in the single crystal Nb_(3)Sn layer increases,enhancing the toughness of the single crystal Nb_(3)Sn/Nb composite material.Conversely,the influence of grain boundaries on material strength decreases in polycrystalline materials as the strain rate increases.Moreover,polycrystalline Nb_(3)Sn/Nb composite materials exhibit significant residual strength after local fracture of Nb_(3)Sn at high strain rates.The research results will contribute to a better understanding of the damage evolution process of Nb_(3)Sn/Nb composite materials under cyclic loading and offer theoretical guidance for optimizing material performance.

关 键 词：Nb_(3)Sn/Nb复合材料 分子动力学模拟 循环载荷 变形损伤 应变率效应 

分 类 号：O347[理学—固体力学]