Intrusion into granular media beyond the quasi-static regime

TL;DR

This paper investigates how drag force on an object intruding into granular media depends on velocity and depth, revealing a crossover behavior at a characteristic time that challenges existing models.

Contribution

It provides experimental and simulation evidence of a velocity-to-depth crossover in drag force, extending understanding beyond the quasi-static regime.

Findings

Velocity dependence crosses over to depth dependence after a characteristic time.

Crossover time depends on speed, depth, gravity, and geometry.

Current models assuming additive contributions are challenged.

Abstract

The drag force exerted on an object intruding into granular media can depend on the object's velocity as well as the depth penetrated. We report on intrusion experiments at constant speed over four orders in magnitude together with systematic molecular dynamics simulations well beyond the quasi-static regime. We find that velocity dependence crosses over to depth dependence at a characteristic time after initial impact. This crossover time scale, which depends on penetration speed, depth, gravity and intruder geometry, challenges current models that assume additive contributions to the drag.