Gas-Mediated Impact Dynamics in Fine-Grained Granular Materials

TL;DR

This study explores how interstitial gas influences impact dynamics in fine granular materials, revealing a transition from fluid-like to compressible, dissipative behavior as gas is evacuated, with implications for understanding granular drag forces.

Contribution

It demonstrates the critical role of interstitial gas in mediating impact responses in fine granular media, highlighting a crossover in behavior based on gas presence.

Findings

At atmospheric pressure, granular media behave fluid-like.

Evacuating gas makes the material highly compressible.

Gas presence significantly alters impact dissipation mechanisms.

Abstract

Non-cohesive granular media exhibit complex responses to sudden impact that often differ from those of ordinary solids and liquids. We investigate how this response is mediated by the presence of interstitial gas between the grains. Using high-speed x-ray radiography we track the motion of a steel sphere through the interior of a bed of fine, loose granular material. We find a crossover from nearly incompressible, fluid-like behavior at atmospheric pressure to a highly compressible, dissipative response once most of the gas is evacuated. We discuss these results in light of recent proposals for the drag force in granular media.