Cohesion in Particulate media

Introduction

How do grains flow? Can we predict the behavior of sand, snow, powders, and more generally, a collection of particles? In many situations, both in nature and industry, this question is important for predicting avalanches, landslides, or designing silos and industrial processes.

Challenges in Predicting Granular Flow

While for simple fluids the measure of viscosity is sufficient to compute and predict flow, for granular materials, the question remains open. The challenge of understanding the physics of granular flows has motivated many researchers, and constitutive laws have been developed for grains interacting by friction and collision.

Cohesive Granular Materials

However, in many applications, grains present cohesion, making it much more challenging to predict their behavior. Sticky or humid grains, powders, snow, and fibers are examples of granular media that have difficulties flowing, often leading to clogging, agglomeration, and intermittency.

Project Goals

The CohPa project aims to achieve a fundamental understanding of the behavior of cohesive granular materials by combining experimental, numerical, and theoretical approaches. The ultimate goal is to develop constitutive laws capable of predicting their behavior in any configuration.

Work Packages

The project is divided into two work packages corresponding to two types of cohesive materials:

1. WP1: I will study cohesion resulting from the presence of adhesive forces between particles. This work will focus on the development of model materials made of sticky grains with tailored surface properties, as well as on real powders. By developing innovative rheological techniques coupled with numerical simulations, we hope to gain a new understanding of the rheology.

2. WP2: I will study the cohesion arising from entanglement between frictional particles, as observed in an assembly of fibers (such as in a bird's nest or a cotton ball) or when mixing fibers and grains (typically roots in soils). These materials constitute a new class of disordered materials, where the tensile strength results from a subtle coupling between geometry, elasticity, and friction, which is not yet understood.