Bottom stresses of static packing of granular chains

TL;DR

This study experimentally investigates the static bottom stress in granular chain packings, revealing a transition in saturation mass related to chain length and entanglements, consistent with Janssen model predictions.

Contribution

It provides new experimental evidence on how chain length and entanglements influence stress saturation in granular chains, extending the Janssen model.

Findings

Saturation mass exhibits a nonmonotonic dependence on chain length.

The transition point aligns with the persistence length of chains.

Entanglements significantly affect bottom stress behavior.

Abstract

We experimentally measure the static stress at the bottom of a granular chains column with a precise and reproducible method. The relation, between the filling mass and the apparent mass converted from the bottom stress, is investigated on various chain lengths. Our measurements reconfirm that the scaling behavior of the stress saturation curves is in accord with the theoretical expectation of the Janssen model. Additionally, the saturation mass is displayed as a nonmonotonic function of the chain length, where a distinguishing transition of the saturation mass is found at the persistence length of the granular chain. We repeat the measurement with another measuring methodology and a silo with different size, respectively, the position of the peak maintains robust. In order to understand the transition of the saturation mass, the friction coefficient and the volume fraction of granular chains are also measured, from which Janssen parameter can be calculated. Finally, we preliminarily measure the bottom stress for two distinct packing structures of long chains, find the effect of the entanglements on the bottom stress, and argue that the entanglements might be responsible for the transition of the saturation mass.