梯度纳米晶体材料的多尺度力学行为研究
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摘要
建立晶粒尺寸梯度分布的表面纳米晶材料本构模型。运用分子动力学模拟软件,得到了梯度单晶铜试样的拉伸应力-应变曲线以及原子构型图。结果表明:计算得到的应力-应变曲线与实验数据大体一致。这种梯度结构使得材料的整体流变应力增加了10%以上。随着应变的增大,曲线会有一段隆起的部分,这与位错的形核以及晶界的限制紧密相关。当应变增加到3%、7%时,小晶粒区域先有位错运动,然后产生堆积缠绕,起到了强化作用。并且,大晶粒使得位错更易从小晶粒向大晶粒区域运动,从而抑制了小晶粒区域裂纹的形成,提高了材料的延展性。
The constitutive model of surface nanocrystalline material with grain size gradient distribution was established.Through molecular dynamics simulation software, the tensile stress-strain curve and the atomic configuration of gradient single crystal copper specimen were obtained. The results show that the stress-strain curves obtained by the calculation are in good agreement with experimental data. The gradient structure makes the flow stress increase by more than 10%. With the strain increasing, there is a part of bulge in the curve, which is closely related to the nucleation of dislocations and the limit of grain boundaries. When the strain increases to 3% and 7%, the dislocation motion appears in the small grain region firstly and then accumulates, which can strengthen the material. In addition, the large grains make the dislocations move more easily from the small grains to the large grain regions, which can inhibit the formation of cracks in the small grain regions, and then, the ductility of the material improves.
The constitutive model of surface nanocrystalline material with grain size gradient distribution was established.Through molecular dynamics simulation software, the tensile stress-strain curve and the atomic configuration of gradient single crystal copper specimen were obtained. The results show that the stress-strain curves obtained by the calculation are in good agreement with experimental data. The gradient structure makes the flow stress increase by more than 10%. With the strain increasing, there is a part of bulge in the curve, which is closely related to the nucleation of dislocations and the limit of grain boundaries. When the strain increases to 3% and 7%, the dislocation motion appears in the small grain region firstly and then accumulates, which can strengthen the material. In addition, the large grains make the dislocations move more easily from the small grains to the large grain regions, which can inhibit the formation of cracks in the small grain regions, and then, the ductility of the material improves.
引文
[1]何柏林,余皇皇.超声冲击表面纳米化研究的发展[J].热加工工艺,2010,39(18):112-115.
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[2]Brooks I,Palumbo G,Hibbard G,et al.On the intrinsic ductility of electrodeposited nanocrystalline metals[J].Mater.Sci.,2011,46:1-12.
[3]Fang T,Li W,Tao N,et al.Revealing extraordinary intrinsic tensile plasticity in gradient nano-grained copper[J].Science,2011,331:1587-1590.
[4]Hirth J P,Lothe J.Theory of Dislocations,2nd edn[M].New York:Wiley,1982.
[5]Chakravarthy S,Curtin W A.Origin of plasticity length scale effects in fracture[J].Phys Rev Lett,2010,105:115502.
[6]Li Jianjun,Soh A K.Enhanced ductility of surface nano-crystallized materials by modulating grain size gradient[J].Modelling Simul.Mater.Sci.Eng.,2012,20:085002.
[7]Hall E O.Variation of hardness of metals with grain size[J].Nature,1954,173:948-949.
[8]Petch N J.The cleavage strength of polycrstals[J].Iron Steel Inst,1953,174:25-28.
[9]Schiφtz J,Vegge T,Tolla F D,et al.Atomic-scale simulations of the mechanical deformation of nanocrystalline metals[J].Physical Review B Condensed Matter,1999,60(17):11971-11983.
[10]Wang Y M,Wang K,Lu K,et al.Microsample tensile testing of nanocrystalline copper[J].Scripta Mater,2003,48:1581-1586.