Penetration into granular materials such as carbonate sand is of fundamental importance to granular physics, and impact and civil engineering, but research along this line suffers considerably from the lack of direct experimental observations. Here we investigate such penetration dynamics of carbonate sand using a vertical gas gun implemented with in situ, high-speed, synchrotron-based X-ray phase contrast imaging. The experiments yield the first direct observation on the penetration dynamics (projectile trajectory/velocity) and particle-scale deformation in real or natural granular materials during sphere penetration, at high temporal and spatial resolutions. The particle displacement fields around the projectile are obtained via X-ray digital image correlation, and the ejecta velocity fields, with particle image velocimetry. Effects of the moisture content and container size on the penetration process are discussed. The enhanced cohesion between wet particles results in particle clustering during splash and a smaller amount of ejecta. Therefore, the particle rearrangement is limited and the projectile penetration depth is smaller. A small container size confines the lateral movement of particles and yields a much more pronounced compaction of particles beneath the projectile, which results in a smaller penetration depth as well.

渗透到碳酸盐砂之类的颗粒材料中对颗粒物理，撞击和土木工程至关重要，但是沿这方面的研究由于缺乏直接的实验观察而遭受了很大的困扰。在这里，我们使用现场实施的立式气枪研究碳酸盐砂的这种渗透动力学，基于同步加速器的高速X射线相衬成像。实验首次以高的时间和空间分辨率，对球体穿透过程中真实或天然颗粒材料中的穿透动力学（弹丸轨迹/速度）和粒子尺度变形进行了首次直接观察。射弹周围的粒子位移场是通过X射线数字图像相关性获得的，而射流速度场是通过粒子图像测速法获得的。讨论了水分含量和容器尺寸对渗透过程的影响。湿颗粒之间的内聚力增强会导致飞溅期间的颗粒聚集和少量的喷射。因此，颗粒重排受到限制并且弹丸穿透深度更小。