The significance of grain morphology and moisture content on the response of silica sand to ballistic penetration

Abstract

The dynamic response of sand is of interest for a wide range of applications, from civil engineering to asteroid impact, in addition to defense and industrial processes. Granular dynamics are controlled by a complex network of inter-grain force chains, yet our understanding of how grain morphology, moisture, rate and loading geometry affect the response to rapid compaction remains limited. Here, we show how just 1% moisture can significantly reduce penetration resistance in silica sand, while smoother-grained material-with similar bulk density, grain size and mineralogy-exhibits markedly improved stopping power. Cylindrical targets are impacted by spherical steel projectiles, with Digital Speckle Radiography employed to determine both penetration depth and sand bed displacement at a series of incremental time steps after impact. The results provide substantial insight into how slight adjustments to grain-grain contact points can affect the bulk dynamic response of brittle granular materials.

Numerical modelling study of a modified sandbag system for ballistic protection

“…Due to the granular structure of sand, it tends compact and densify when it is under a compressive load [1,6,39]. Previous studies have shown a change in the energy absorption behaviour of sand as its density changes, thus implying a shift in its penetration resistance [3,7]. The plate was placed in the sandbag so that it was not impacted by the projectile given the timescale of the simulation.…”

“…The major threat from blast is the propagation of the shockwave through the material [4,5]. Sand resists blast by undergoing densification due to the pressure load from the shockwave [6,7].…”

“…The process of compaction increases the contact between particles, allowing the dissipation of energy from the propagating shockwave [7][8][9]. More recently, sand has found application as a common infill in protective systems such as HESCO.…”

“…The primary advantage of using numerical methods for studying impact is that it is not resource heavy. It also allows the direct visualisation of the behaviour of the impacted sand and to accurately quantify the response of sand under loading [7,20,21]. Furthermore, the use of numerical methods increases the versatility of the study because it allows the user to easily work with a variety of materials and geometries for the same impact problem.…”