Xue Kun, Han Panpan, Du Kaiyuan, Gan Yixiang, Wang Ziwei, Bai Chunhua
State Key Laboratory of Explosive Science and Technology, Beijing Institute of Technology, Beijing, 100081, China.
Soft Matter. 2020 Feb 12;16(6):1498-1517. doi: 10.1039/c9sm02150g.
In this paper, we investigate the initiation and growth of instability patterns arising from the shock loaded internal surfaces of granular rings confined in a Hele-Shaw cell using both experimental and numerical approaches. A variety of patterns are formed in granular media consisting of grains with varying morphologies. When the particle shape becomes increasingly irregular, and/or the gap in the Hele-Shaw cell becomes narrower, it is increasingly hard for confined particles to fluidize. Consequently the emergent pattern transitions from a smooth circle with trivial undulation which grows in a self-similar manner to an unstable finger-like structure with significant tip-splitting. The distinct growth mode of the well-defined instability pattern is closely associated with its inception phase alongside the transmission of the compaction front. The runaway growth of the incipient perturbations gives rise to the unstable growth of the late-time finger-like instabilities. Conversely the minimal growth of the perturbations in the inception phase guarantees the ensuing self-similar growth of the instability patterns featuring insignificant corrugation. The grain-scale simulations reveal the fundamental role played by the heterogeneous non-linear force network inherent to granular media in the stable-to-unstable transition of the instability pattern. The present work reveals the correlation between the grain-scale physics underpinning the formation of surface instability upon shock loading granular media and the nature of the resulting macro-scale instability patterns. The macroscopic flowability of particles through the confined space is found to be the foremost indicator of the nature of the shock induced granular instability pattern.
在本文中，我们采用实验和数值方法，研究了在赫雷肖盒中受限的颗粒环冲击加载内表面产生的不稳定性模式的起始和生长。在由具有不同形态的颗粒组成的颗粒介质中形成了各种模式。当颗粒形状变得越来越不规则，和/或赫雷肖盒中的间隙变得越来越窄时，受限颗粒越来越难以流化。因此，出现的模式从具有微小波动的光滑圆以自相似方式生长转变为具有明显尖端分裂的不稳定指状结构。明确的不稳定性模式的独特生长模式与其起始阶段以及压实前沿的传播密切相关。初始扰动的失控生长导致后期指状不稳定性的不稳定生长。相反，起始阶段扰动的最小生长保证了随后具有不明显波纹的不稳定性模式的自相似生长。颗粒尺度模拟揭示了颗粒介质固有的非均匀非线性力网络在不稳定性模式从稳定到不稳定转变中所起的基本作用。目前的工作揭示了冲击加载颗粒介质时表面不稳定性形成的颗粒尺度物理与由此产生的宏观尺度不稳定性模式的性质之间的相关性。发现颗粒通过受限空间的宏观流动性是冲击诱导颗粒不稳定性模式性质的首要指标。
