Capillary suction predictions in granular materials subjected to 1D compression and triaxial loading with emphasis on projectile penetration

Mohmad Mohsin Thakur,Dayakar Penumadu

doi:10.1063/5.0072195

Abstract

The role of partial saturation in penetration resistance of projectiles in granular materials is not clear due to experimental constraints imposed by high cost and special considerations in equipment design. In this work, granular material near the tip and far-field of the projectile is numerically simulated based on 1D compression and triaxial stress paths, respectively, using the finite discrete element method. The crushing of grains in 1D compression simulations is implemented by pre-inserting cohesive interface elements in regular finite element mesh. The capillary suction is numerically predicted by extracting the deformed granular assembly microstructure at different loading steps as an input to the pore morphology method. The results demonstrate the development of high capillary suction in 1D compression loading due to the significant crushing of grains. The evolution of capillary suction is negligible during triaxial loading compared to the 1D compression loading. This suggests that future simulations related to projectile penetration in partially saturated granular materials should account for coupled hydromechanical effects near the tip whereas the far-field can be approximated as a dry material. Finally, the capillary suction corresponding to extreme comminution near the projectile tip is estimated from a 3D assembly of spherical grains with a mean grain size of 1 µm.

Highlights

Granular materials are multiphase materials with widespread occurrence in nature
The state of partial saturation in granular materials subjected to quasi-static loading conditions increases effective stress, as postulated and demonstrated in several studies in the past
The continued evidence suggests that complex hydromechanical interactions exist during the dynamic loading of granular materials and, necessitates an improved understanding of physics across different lengths and time scales

Summary

Introduction

Granular materials are multiphase materials with widespread occurrence in nature. The presence of multiphase components, e.g., soil solids, water, and air phase, results in complex hydromechanical interactions. The state of partial saturation in granular materials subjected to quasi-static loading conditions increases effective stress, as postulated and demonstrated in several studies in the past.. Does not always increase effective stress under dynamic loading conditions, as observed in splitHopkinson pressure bar experiments.. The continued evidence suggests that complex hydromechanical interactions exist during the dynamic loading of granular materials and, necessitates an improved understanding of physics across different lengths and time scales. Omidvar et al (2016) investigated in situ kinematics of a granular assembly during low-velocity penetration by utilizing transparent soils and a high-speed camera. Borg et al (2013) combined projectile penetration experiments with particle image velocimetry to capture bulk and grain-scale response and compared the results with a simple continuum model. The crushing of the grains stiffens the response of sands to external loading and represents an important energy dissipation mechanism near the tip region of the projectile

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