Hexapods, consisting of three mutually orthogonal arms, have been utilized as a representative nonconvex shape to demonstrate the impact of interlocking on the strength properties of granular materials. Nevertheless, the microstructural characteristics of hexapod packings, which underlie their strength, have remained insufficiently characterized. We use particle dynamics simulations to build isotropically-packed aggregates of hexapods and we analyze the effects of aspect ratio and interparticle friction on the microstructure and force transmission. We find that the packing fraction is an unmonotonic function of aspect ratio due to competition between steric exclusions and interlocking. Interestingly, the contact coordination number declines considerably with friction coefficient, showing the stronger effect of friction on the stability of hexapod packings as compared with sphere packings. The pair distribution functions show that local ordering due to steric exclusions disappears beyond the aspect ratio 3 and the hexapods touch their second neighbors. Remarkably, hexapods of aspect ratio 3 tend to align with their neighbors and form locally ordered structures, implying a contact coordination number which is highly sensitive to the confining pressure. We also show that the probability density function of forces between hexapods is similar to that of sphere packings but with broadening exponential fall-off of strong forces as aspect ratio increases. Finally, the elastic bulk modulus of the aggregates is found to increase considerably with aspect ratio as a consequence of the rapid increase of contact density and the number of contacts with second neighbors.

中文翻译：

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六足形颗粒聚集体中的接触网络和力传递

由三个相互正交的臂组成的六足体已被用作代表性的非凸形状，以证明互锁对颗粒材料强度性能的影响。然而，六足填料的微观结构特征（其强度的基础）仍然没有得到充分的表征。我们使用粒子动力学模拟来构建各向同性堆积的六足体聚集体，并分析纵横比和颗粒间摩擦对微观结构和力传递的影响。我们发现，由于空间排斥和互锁之间的竞争，堆积分数是长宽比的非单调函数。有趣的是，接触配位数随着摩擦系数的增加而显着下降，这表明与球形填料相比，摩擦对六足填料稳定性的影响更强。对分布函数表明，由于空间排斥而导致的局部排序在长宽比 3 之外消失，并且六足体接触它们的第二个邻居。值得注意的是，纵横比为 3 的六足机构倾向于与其相邻的六足机构对齐并形成局部有序结构，这意味着接触配位数对围压高度敏感。我们还表明，六足体之间的力的概率密度函数与球体堆积的概率密度函数相似，但随着纵横比的增加，强力的指数衰减范围扩大。最后，由于接触密度和与第二邻居接触的数量迅速增加，聚集体的弹性体积模量被发现随着纵横比的增加而显着增加。