Towards Modeling Projectile Penetration in Dry and Multiphase Granular Materials

The present work aims at developing and validating numerical modeling strategies in granular materials impacted by a projectile. The focus is on two regions: (a) near-field: region near the tip and along the path of a projectile where comminution of grains is significant, (b) intermediate-field: region far from the projectile where grain-scale interactions are important but stresses are not high enough to cause crushing of the grains.

A novel framework has been introduced and validated wherein particle shape captured using X-ray CT imaging was incorporated in FEM simulations using shell elements for simulating triaxial boundary value problems. The results indicate an increase in computational efficiency and usefulness of the approach in modeling sands in the intermediate field of impacting projectiles. The role of grain morphology and inter-granular friction in the shearing of the granular materials was explored since both these parameters significantly affect the mechanical response. It was observed that the influence of particle angularity is less pronounced as the inter-granular friction decreases. Furthermore, the near tip region of the granular material was investigated based on a 1D compression stress path with modeling of grain fragmentation based on damage mechanics. These approaches when applied together represent multiple physical scales associated with multi-physics phenomena.

The latter part of this dissertation focuses on exploring the effect of partial saturation on the strength of granular materials. Direct pore-scale modeling and experiments have been used to predict and validate the Soil Water Retention Curves (SWRC) in the round and angular sands. It was observed that the angular sand exhibited higher capillary suction and a higher void ratio compared to the rounded sand at the same relative density. Furthermore, the spatial distribution of the fluids and pore space was quantified out using a mathematical framework known as persistent homology. FEM and pore-scale modeling approaches were then used concurrently to estimate capillary pressures at different axial strains in a 1D compression loading. These predictions suggest that the effect of partial saturation should be considered in the near field region and can be ignored in the far-field region for simulating penetration in partially saturated sands.