Soft solids meet hard flow: pressure-driven fluid flow through deformable porous materials

Soft filters in fluidic systems, the cartilage in your joints, boluses of digested material in the small intestine, and (more appetisingly) compacted 'pucks' of coffee grounds are all examples of porous, deformable, materials that are subjected to potentially high pressure differences that drive flow through their pores. Unlike traditional "hard" porous media, we can't just use the standard linear relationship between flow rate and pressure gradient since stresses applied by the fluid will compact and deform the solid scaffold itself. Furthermore, these flows may even modify the elastic and transport properties of the medium by squeezing pores tighter (lowering the permeability) and shear-stiffening.

In this talk, I'll give an overview of how to model these competing effects and feedback mechanisms, taking inspiration from the last decade's developments in models for granular and poroelastic material beds. I will show how some of these compaction effects can be exploited for beneficial new applications, but also how the compacted steady states of many such solids are unstable under high pressure differences. I will outline my recent work that illustrates two different ways in which flow can break down soft solids, giving rise to wormhole-like channels or horizontal banding dependent on the material's microstructure, before eventually fracture takes over. These mechanisms allow us to properly understand for the first time the effect of scaffold cross-linking on the integrity of compacted poroelastic beds.