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颗粒物质广泛存在于自然界与工业生产当中, 研究颗粒堆积结构对理解其物理性质具有重要意义. 近年来, 颗粒形状对堆积结构的影响备受关注. 非球形颗粒因形状复杂, 易相互嵌合形成稳定结构, 从而具有显著的几何内聚力, 对颗粒堆积的稳定性和孔隙率等特性产生重要影响. 为探索凹形颗粒体系的微观堆积构型, 本研究使用由3个相互正交球棍组成的“六足体”形状颗粒, 基于X射线断层扫描技术研究其在外部振动驱动下致密化过程中堆积结构的演化. 结果显示, “六足体”颗粒堆积体积分数低于硬球体系. 同时, 与硬球体系结果类似, 其在不同振动加速度下的致密化曲线可用Kohlrausch-Williams-Watt函数拟合, 且稳态堆积的体积分数与平均接触数随振动强度的减小而增大. 针对接触点统计分析的结果表明, “六足体”颗粒压实过程由接触形式调整主导, 使颗粒相互锁定程度增加. 本研究揭示了非球形颗粒堆积在压实过程中的结构演化特征, 为理解凹形颗粒堆积的独特力学与动力学性质提供了重要的实验支持.
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关键词:
- “六足”凹体颗粒堆积 /
- 压实过程 /
- 接触结构 /
- X射线断层扫描技术
Granular materials are ubiquitous in nature and industrial production. Investigating the structure of packing is crucial for understanding the physical properties of granular materials. Owing to their symmetry and simple geometry, spherical particles have long served as an ideal model for studying granular packing, yielding numerous research outcomes. In recent years, the influence of particle shape on packing structures has drawn considerable attention. Non-spherical particles, characterized by complex shapes, tend to interlock and form stable structures. Their significant geometric cohesion notably affects the stability and porosity of granular packing. To investigate the structural evolution and compaction mechanisms of three-dimensional concave particles (hexapod-shaped) under external tapping, focusing on the role of geometric cohesion in enhancing mechanical stability, we employ hexapod-shaped particles that are composed of three mutually orthogonal spherocylinders in this study. The granular system subjected to consecutive tapping can reach a stationary state. In the densifying process of the system, packing structures with different volume fractions will be formed. Meanwhile, by combining with X-ray tomography, we can obtain the microstructure. The findings reveal that the volume fraction of “hexapod” particle packing is significantly lower than that of hard-sphere systems. The compaction curves of “hexapod” particles across varying tapping intensities are accurately described by the Kohlrausch-Williams-Watt (KWW) law, which is consistent with hard-sphere system, suggesting a relaxation process governed by heterogeneous modes. Furthermore, both the volume fraction of the steady-state granular packing and the average contact number exhibit an inverse relationship with tapping intensity, increasing as the intensity decreases. A detailed statistical analysis of contact points indicates that the compaction process of “hexapod” particles is predominantly influenced by two factors: the augmentation in the number of neighboring contacting particles and the modification of contact forms. These factors collectively enhance the degree of interlocking among hexapods within the system. Specifically, the compaction process is primarily propelled by the escalation in neighboring contacts and the refinement of contact types, particularly the increase in cylinder-cylinder (cc) contact. This rise in cc contact significantly enhances mechanical stability through strengthening geometric interlocking. This study reveals the structural evolution characteristics of non-spherical particles in the compaction process and provide important experimental support for understanding the unique mechanical and dynamic properties of concave particle packing. This research not only enriches the experimental data of granular packing structures but also offers a new perspective for exploring the universal laws of packing for particles of different shapes. This study is to lay a more solid foundation for the theoretical research and industrial applications of granular materials, thereby promoting technological progress and innovation in related fields. 
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Keywords:
- packing of “hexapod” concave particles /
- compaction process /
- contact structure /
- X-ray tomography technology
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