基于晶粒旋转的纳晶材料非均匀变形行为研究

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The formation and development of shear band are the main reason for the non-homogeneous deformation, low ductility and premature failure of nanocrystalline materials. In order to study the nature of shear band, based on a grain rotation theory of diffusion-accommodated grain boundary sliding, an evolution model of shear band was established. The effect of grain orientation and grain size on evolution of shear band was investigated. In the model, the grains were divided into soft-grains within shear bands and hard-grains without shear bands according to the differences between grain orientation and shear orientation. Under the grain rotation, more and more grains become soft-grains and the size and overall volume fraction of shear bands were changed with the loading of materials. The results show that as the increasing of plastic strain, the volume fraction of shear bands general increases for all grain clusters with different mean maximum Sehmid factors, the volume fraction of shear bands is inverse ratio to grain size. The larger the grain size, the smaller the volume fraction of the shear zone.纳晶材料中剪切带的形成和发展是导致其非均匀变形、延性降低、材料过早断裂的主要原因。为了研究纳晶材料剪切带的特点，建立了基于扩散驱动晶界滑移引起的晶粒旋转理论的剪切带演化模型，探讨了晶粒取向以及晶粒尺寸对剪切带演化的影响，在该模型中，按照晶粒取向与剪切方向的差异，将晶粒分成剪切带内容易发生滑移的软晶粒和剪切带外只发生扩散蠕变的硬晶粒；随着材料的加载，晶粒发生旋转，并导致越来越多的晶粒成为软晶粒，进而剪切带变宽变长，总的体积比率发生变化。研究结果表明，随着应变的增加，对于拥有不同的最大平均Schmid因子值的晶粒集合，剪切带的体积分数普遍有所增加；晶粒尺寸越大，剪切带的体积分数越小。