# Stagnant Zone Formation in a 2D Bed of Circular and Elongated Grains under Penetration

## TL;DR

This study investigates the formation and properties of stagnant zones in a 2D granular bed during penetration, revealing structural anisotropies and shape effects, especially for elongated particles, with implications for understanding granular force responses.

## Contribution

It provides a detailed experimental analysis of stagnant zones in a 2D granular system, including the effects of particle shape and structural anisotropies, which advances understanding of granular penetration mechanics.

## Key findings

- Stagnant zones exhibit structural anisotropies inside and outside the zone.
- Elongated particle shapes influence local structural relationships and fragility.
- A linear force law for large depths is observed, consistent with real granular systems.

## Abstract

When a large blunt object penetrates into a granular material, the force response exhibits an initial nonlinear relationship with depth that is widely attributed to the formation of a shear jammed stagnant zone. We present an experimental study of a model 2D granular system that preserves common aspects of slow granular penetration, such as a linear force law for large depths, while also allowing for direct and precise measurement of a stagnant zone. We also probe structural anisotropies throughout the bed and examine their characteristics inside and outside the stagnant zone. Finally, we simultaneously consider effects of concave elongated particle shapes (dimers) and find that while most results are not affected, the relationship between local structure and strain suggests a distinct fragility in the stagnant zone.