Abstract

The study of stress transmission and particles’ mobility in powder beds constitutes a challenging issue to improve processes such as milling, agglomeration and kneading. In this paper the ability to promote particle mobilities by means of an intruder is investigated. An experimental setup was developed to characterize the particles’ mobility at the voxel scale. A particle image velocimetry (PIV) algorithm was employed to determine the velocity fields in the vicinity of an intruder in ascendant vertical motion. A discrete element method model was developed to simulate the same system at the particle scale. Velocity maps were determined relying on a coarse-graining procedure and compared to PIV results. During the rise of the intruder the experimental and simulated drag forces are in good agreement. Spatio-temporal correlation between the granular mobility and the state of the force network are analyzed as a function of the height of the intruder. The drag force profile exhibits a relaxation trend, noised by fluctuations whose origin are in successive loading/rupture events. An interpretation of these fluctuations is proposed with regard to the development of preferential paths in the normal force network, and to the localization of sliding at the contacts scale. Finally, we show that global strains are a consequence of the ejection of particles directly in contact with the ends of the intruder.

Graphic abstract

中文翻译：

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移动入侵者在粒状填料中产生的力和流量：粗粒度和DEM模拟与实验

摘要

对粉末床中应力传递和颗粒迁移率的研究是改善诸如研磨，团聚和捏合等过程的挑战性问题。在本文中，研究了通过入侵者促进粒子迁移的能力。开发了实验装置以表征在体素尺度上粒子的迁移率。粒子图像测速（PIV）算法用于确定上升垂直运动中入侵者附近的速度场。开发了离散元素方法模型以在粒子尺度上模拟相同的系统。根据粗粒度过程确定速度图，并将其与PIV结果进行比较。在入侵者上升期间，实验阻力和模拟阻力是一致的。分析了颗粒迁移率和力网络状态之间的时空相关性，作为入侵者高度的函数。阻力曲线表现出松弛趋势，其波动受到起伏的影响，其起因是在连续的加载/断裂事件中。提出了关于这些波动的解释，涉及法向力网络中优先路径的发展以及在接触尺度上滑动的局部化。最后，我们表明整体应变是直接与入侵者端部接触的粒子弹出的结果。提出了关于这些波动的解释，涉及法向力网络中优先路径的发展以及在接触尺度上的滑动定位。最后，我们表明整体应变是直接与入侵者端部接触的粒子弹出的结果。提出了关于这些波动的解释，涉及法向力网络中优先路径的发展以及在接触尺度上的滑动定位。最后，我们表明整体应变是直接与入侵者端部接触的粒子弹出的结果。

图形摘要