Granular Matter Across Scales

Description & aims

Introduction:

Taking a walk on the beach is easy, but understanding the mechanical response of a collection of grains such as sand or gravel is still difficult. Granular materials demand a detailed grasp of the connection between particles and the way they are stacked together, between microscopic ingredients and their macroscale properties. While the last decades have seen significant progress on understanding various physical mechanisms relevant for granular materials, we are still far away from a complete understanding that gives predictive power on all relevant time and length scales.

Challenge:

Currently, there is no generally accepted continuum theory that can be used for granular materials or soils at the large scale. In such an advanced continuum model, macroscopic measures like stress and strain are informed by properties and geometry at the particle scale. Different communities have made much effort towards achieving this goal, yet the field remains fragmented with results that are difficult to connect and correlate in order to arrive at a generic micro-based constitutive model.

Aims:

The aim of our workshop is therefore to bring together a focused group of researchers with a cross-disciplinary overlap to discuss those multi-scale aspects of dense granular matter. Now is an opportune moment to do so, as multiple communities working on granular materials have mostly reached the conclusion that the behavior of granular materials at the largest macro-scale phenomena is intimately related to grain characteristics. Particle material, shape, roughness, kinetic processes at the smallest contact- or particle-scale, fabric and the presence of pore fluids with one or more phases all are necessary to integrate in a micro-based continuum model.

Among the many possible subjects relevant for granular materials, we have identified three areas that already see activity in several disciplines: (I) Modelling approaches to granular statics and dynamics includes many length and time scales, which are approached with different methodologies in different communities. What are the methodological commonalities and differences? (II) The emergence of high throughput sensing and the huge reduction in cost and complexity of three dimensional imaging methods has opened up an array of new opportunities to extract microscopic variables from granular experiments. How can such data induce new modeling and theory across the scales? (III) The emergence of a phase boundary between static and flowing disordered media is still a subject of intense debate among engineers (critical state) and physicists (jamming). Are these phenomena the same? The workshop aims to generate open discussions and find answers to these questions.