Possible Stratification Mechanism in Granular Mixtures

TL;DR

This paper introduces a model explaining how granular mixtures of different sizes and shapes spontaneously form alternating layers during pouring, emphasizing the role of repose angle differences and a kink mechanism.

Contribution

It presents a new model for stratification in granular mixtures that highlights the importance of repose angle differences and introduces a kink mechanism for the dynamics.

Findings

Stratification occurs when grains have different repose angles.

Experimental confirmation supports the model's predictions.

A kink mechanism describes key aspects of stratification dynamics.

Abstract

We propose a mechanism to explain what occurs when a mixture of grains of different sizes and different shapes (i.e. different repose angles) is poured into a quasi-two-dimensional cell. Specifically, we develop a model that displays spontaneous stratification of the large and small grains in alternating layers. We find that the key requirement for stratification is a difference in the repose angles of the two pure species, a prediction confirmed by experimental findings. We also identify a kink mechanism that appears to describe essential aspects of the dynamics of stratification.