Granular Dynamics during Impact

TL;DR

This study investigates how prestrain affects impact dynamics in granular beds, revealing that internal pressure influences stopping force and that static friction contributes to energy dissipation during impact.

Contribution

It demonstrates that prestrain modifies the pressure-dependent component of the stopping force and highlights the role of static friction in energy dissipation during granular impact.

Findings

Prestrain affects the prefactor of the linear depth-dependent stopping force.

We visualize and track individual grain trajectories during impact.

We find that weaker force chains lead to more irreversible grain rearrangements.

Abstract

We study the impact of a projectile onto a bed of 3 mm grains immersed in an index-matched fluid. Specifically, we vary the amount of prestrain on the sample, strengthening the force chains within the system. We find this affects only the prefactor of linear depth-dependent term in the stopping force. We therefore attribute this term to pressure within the material, and not the grain-intruder friction as is sometimes suggested. Using a laser sheet scanning technique to visualize internal grain motion, a high-speed camera, and particle tracking, we can measure the trajectory of each grain throughout an impact event. Microscopically, our results indicate that weaker initial force chains result in more irreversible, plastic rearrangements during impact, suggesting static friction between grains does play a substantial role in the energy dissipation within the granular material.