The role of initial speed in projectile impacts into light granular media

Abstract

Projectile impact into a light granular material composed of expanded polypropylene (EPP) particles is investigated systematically with various impact velocities. Experimentally, the trajectory of an intruder moving inside the granular material is monitored with a recently developed non-invasive microwave radar system. Numerically, discrete element simulations together with coarse-graining techniques are employed to address both dynamics of the intruder and response of the granular bed. Our experimental and numerical results of the intruder dynamics agree with each other quantitatively and are in congruent with existing phenomenological model on granular drag. Stepping further, we explore the 'microscopic' origin of granular drag through characterizing the response of granular bed, including density, velocity and kinetic stress fields at the mean-field level. In addition, we find that the dynamics of cavity collapse behind the intruder behaves qualitatively different with different impact velocities. Moreover, the kinetic pressure ahead of the intruder decays exponentially in the co-moving system of the intruder. Its scaling gives rise to a characteristic length scale, which is in the order of intruder size. This finding is in perfect agreement with the long-scale inertial dissipation type that we find in all cases. From the perspective of applications, EPS or EPP particles are widely used for construction, packaging, damping, as well as raw materials for molded forms, due to its light yet rigid, and good thermal isolation properties 29 . The drop tower facility in Bremen 30 , for instance, uses EPS particles regularly as damping materials to capture drop capsules that weight typically over 400 kg. As such, a better understanding of granular drag, particularly the physical mechanisms behind the empirical laws, is arXiv:1912.00328v1 [cond-mat.soft] 1 Dec 2019 3/15

Pendulum-based measurements reveal impact dynamics at the scale of a trap-jaw ant

“…For example, impact tests against arthropod exoskeleton may reveal how viscoelastic materials respond to impact, including tuned impact energetic responses across different parts of animals, as has been found in the telson armor used during mantis shrimp ritualized fighting (Taylor and Patek, 2010;Taylor et al, 2019). Likewise, impact tests against loose media, such as sand or soil, may illuminate how impact-based jumps and strikes operate, while also providing a new spatiotemporal lens on the physics of particle jamming (Aguilar and Goldman, 2016;Huang et al, 2020;Umbanhowar and Goldman, 2010).…”

“…rocks, sand and soil; Fig. 1; see Aguilar and Goldman, 2016;Huang et al, 2020;Umbanhowar and Goldman, 2010 for nonlinearity of substrate behavior). However, the impact energetics of trap-jaw ant mandible strikes and other small, high-acceleration impacts have rarely been measured experimentally.…”

Radar for projectile impact on granular media

“…Thus, radar tracking technique can be used here to explore the "microscopic" origin of the drag force induced by granular particles in combination with numerical simulations. Interested readers may refer to [15] for a recent example.…”

Advances in Projectile Penetration Mechanism in Soil Media

“…The error in the prediction of penetration depth for the projectiles of different nose shapes in different soil targets using the proposed analytical models lie within 10% when compared with experimental results. In shallow penetration, the granular medium dissipates much of its energy in the initial phase of penetration, while in deep penetration, the compression and shear of the granular medium result in energy dissipation [50]. The absorption of energy in the shear is primarily due to friction and volume changes as the grains slip, roll, and climb over each other.…”

“…A projectile's infinite penetration into light-weighted "expanded polystyrene particles (EPP)" is detected when the projectile's weight exceeds a critical value. The role of initial velocity with various impact velocities in infinite penetration into a light granular material consist of EPP particles media is investigate by Huang et al [50]. In granular material, pore collapse, grain fracture, and the formation of force chains are some of the significant phenomena regulating sand behavior at grain scale, and dynamic target-projectile interactions on a bulk scale are further challenging.…”