Jalali Payman, Zhao Yuchen, Socolar Joshua E S
School of Energy Systems, 53851 Lappeenranta-Lahti University of Technology, Lappeenranta, Finland.
Department of Physics, Duke University, Durham, NC 27708, USA.
Soft Matter. 2021 Mar 18;17(10):2832-2839. doi: 10.1039/d0sm01914c.
A spherical intruder embedded in a confined granular column is extracted by pulling it upward by an attached string. As the tension of the string gradually increases, a failure event occurs at a certain pulling force, leading to rapid upward acceleration of the intruder. The threshold force and the dynamics of the failure event are experimentally investigated for different filling heights and column diameters, using Ottawa sand and glass beads. For the Ottawa sand, we find that the failure force can be fit by a model describing the weight of the granular material in a cone with the vertex at the bottom of the intruder and a vertex angle of 72°. The agreement between the model and experiments is good for heights less than the column (tube) diameter, but measured values deviate from the model for larger heights. We also report on experiments with glass beads that reveal unexpected effects for relatively small ratios of tube diameters to grain size. The dynamics of the intruder during the failure event is studied using high-speed video analysis. The granular drag force monotonically decays during the pullout for sufficiently large tube diameters. In narrow columns, a monotonic decay of drag force after failure is observed for low heights, whereas a secondary peak can be seen in sufficiently deep and narrow columns, indicating the existence of different mechanisms of failure. The normalized drag force declines with intruder displacement closely for all tube diameters within small displacements.
通过系在嵌入受限颗粒柱中的球形侵入体上的绳子向上拉，将其取出。随着绳子张力逐渐增加，在一定拉力下会发生失效事件，导致侵入体迅速向上加速。使用渥太华砂和玻璃珠，针对不同的填充高度和柱直径，对失效事件的阈值力和动力学进行了实验研究。对于渥太华砂，我们发现失效力可以用一个模型来拟合，该模型描述了以侵入体底部为顶点、顶角为72°的圆锥内颗粒材料的重量。对于高度小于柱（管）直径的情况，模型与实验结果吻合良好，但对于较大高度，测量值与模型存在偏差。我们还报告了用玻璃珠进行的实验，这些实验揭示了对于相对较小的管径与颗粒尺寸比的意外影响。使用高速视频分析研究了失效事件期间侵入体的动力学。对于足够大的管径，在拔出过程中颗粒阻力单调衰减。在狭窄的柱体中，对于低高度，失效后阻力单调衰减，而在足够深且窄的柱体中可以看到二次峰值，这表明存在不同的失效机制。在小位移范围内，对于所有管径，归一化阻力随侵入体位移密切下降。
