Understanding the particle-scale dynamics of granular materials during rapid compaction and flow is of fundamental importance for manufacturing, planetary science, geology, and defense applications. Time-resolved 2D radiography and static 3D x-ray tomography are powerful in situ tools for studying particle-scale dynamics but provide detail only in 2D or with significant time-scale limitations, respectively. Here, we introduce a new method that uses 2D in situ x-ray imaging for determining time-resolved 3D particle-scale dynamics in rapidly compressed granular materials. The method employs initial particle packing structures obtained from x-ray tomography, a 2D x-ray image generation algorithm, and an optimization algorithm. We first describe and validate the method using finite element simulations. We then apply the technique to x-ray phase-contrast images obtained during rapid compaction of granular materials with varying particle morphology and sample thickness. The depth-resolved particle-scale dynamics reveal complex velocity and porosity fields evolving heterogeneously along and perpendicular to the compaction direction. We characterize these features, their fluctuations near the compaction front, and the compaction front thickness. Our technique can be applied to understanding granular dynamics during rapid compaction events, and rearrangements during slower, but non-quasi-static, flows.

中文翻译：

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从时间分辨的原位 2D X 射线图像在快速压实过程中量化粒子尺度 3D 颗粒动力学

了解颗粒材料在快速压实和流动过程中的颗粒尺度动力学对于制造、行星科学、地质学和国防应用至关重要。时间分辨 2D 射线照相术和静态 3D X 射线断层扫描术是用于研究粒子尺度动力学的强大原位工具，但分别仅提供 2D 或具有显着时间尺度限制的细节。在这里，我们介绍一种使用 2D原位的新方法用于确定快速压缩颗粒材料中时间分辨 3D 粒子尺度动力学的 X 射线成像。该方法采用从 X 射线断层扫描获得的初始粒子堆积结构、2D X 射线图像生成算法和优化算法。我们首先使用有限元模拟来描述和验证该方法。然后，我们将该技术应用于在具有不同颗粒形态和样品厚度的颗粒材料的快速压实过程中获得的 X 射线相衬图像。深度解析的粒子尺度动力学揭示了复杂的速度和孔隙度场，它们沿着和垂直于压实方向不均匀地演化。我们描述了这些特征，它们在压实前沿附近的波动，以及压实前沿的厚度。