Dynamics of oblique impact in a photoelastic granular medium

TL;DR

This study investigates how oblique impacts affect force dynamics in a photoelastic granular medium, revealing weaker horizontal force chains and a decrease in inertial drag with increasing impact angle.

Contribution

It extends previous normal impact studies to oblique impacts, providing new insights into force propagation and drag force behavior at various impact angles.

Findings

Horizontal force chain propagation is weaker during oblique impacts.

Inertial drag force decreases as impact angle increases.

High-resolution imaging captures detailed force and trajectory data.

Abstract

When a solid projectile impacts a granular target, it experiences a drag force and abruptly comes to rest as its momentum transfers to the grains. An empirical drag force law successfully describes the force experienced by the projectile, and the corresponding grain-scale mechanisms have been deciphered for normal impacts. However, there is little work exploring non-normal impacts. Accordingly, we extend studies to explore oblique impact, in which a significant horizontal component of the drag force is present. In our experiments, a projectile impacts a quasi-two-dimensional bed of bidisperse photoelastic grains. We use high-speed imaging to measure high-resolution position data of the projectile trajectory and simultaneously visualize particle-scale force propagation in the granular medium. When the impact angle becomes important, the spatial structure of the stress response reveals relatively weak force chain propagation in the horizontal direction. Based on these observations, we describe the decrease of the inertial drag force with impact angle.