School of Materials Science and Engineering, Northeastern University, Shenyang 110004, P. R. China.
Soft Matter. 2019 Mar 6;15(10):2260-2268. doi: 10.1039/c8sm02166j.
The formation and growth of local order clusters in a tetrahedral granular assembly driven by 3D mechanical vibration were captured in DEM (discrete element method) dynamic simulation using a multi-sphere model. Two important kinds of clusters, dimer and wagon wheel structures, were observed based on which the growth behavior and mechanism of each local cluster with different orientations/structures were investigated. The results show that during vibration, dimer clusters are formed first and then most of them grow into linear trimers and tetramers. Wagon wheel clusters are also frequently observed that grow into hexamers and, further, octamer and nonamer local clusters. Coordination number (CN) evolution indicates that the decrease of local mean CN can be regarded as the signal for the formation of local clusters in the tetrahedral particle packing system. Nematic order metric analysis shows that although the two basic structures (dimer and wagon wheel structures) grow into complex local clusters during packing densification, these local clusters are randomly distributed in the tetrahedral particle packing system. Stress analysis indicates that the dimer-based local clusters are mostly formed in the compaction state of the tetrahedral particle packing system during the vibrated packing densification process. In comparison, the wagon wheel-based local clusters need much stronger interaction forces from tetrahedral particles during vibrated packing densification.
采用多球体模型，通过 DEM（离散单元法）动态模拟，捕捉到 3D 机械振动驱动下四面体颗粒组装体中局部有序簇的形成和生长。观察到两种重要的簇，二聚体和轮辐结构，基于此，研究了具有不同取向/结构的每个局部簇的生长行为和机制。结果表明，在振动过程中，首先形成二聚体簇，然后它们中的大多数生长成线性三聚体和四聚体。还经常观察到轮辐结构的簇生长成六聚体，进一步生长成八聚体和非九聚体的局部簇。配位数（CN）演化表明，局部平均 CN 的降低可以看作是四面体颗粒堆积系统中局部簇形成的信号。向列有序度度量分析表明，尽管这两种基本结构（二聚体和轮辐结构）在堆积密实化过程中生长成复杂的局部簇，但这些局部簇在四面体颗粒堆积系统中是随机分布的。应力分析表明，在振动填充密实化过程中，四面体颗粒堆积系统的压实状态下主要形成基于二聚体的局部簇。相比之下，基于轮辐结构的局部簇在振动填充密实化过程中需要来自四面体颗粒的更强相互作用力。
