Seminar "Deciphering geomaterial degradation instability with the help of dynamic radiography"

Speaker: Dr.François Guillard, Particles and Grains Laboratory, School of Civil Engineering, The University of Sydney

Title: Deciphering geomaterial degradation instability with the help of dynamic radiography

Abstract:
Brittle porous materials are common in nature and industry, encompassing for example bones, metallic foams, and breakfast cereals. In the geotechnical field, most materials belong to this class, such as sand, rocks, or ice. Under specific loading conditions, these materials may exhibit compaction instabilities, leading to sudden stress drops within the material as grains rearrange or break. This is a particularly prominent effect when degradation mechanisms are at play, where the grains themselves get dissolved from chemical reaction, melting, or dissolution. We will discuss the origin of such instabilities, and the conditions for their emergence.

Such compaction dynamic can be difficult to efficiently observe experimentally though, due to the opaque nature of geomaterials, which limits their observation via visible imaging to boundaries or free surfaces. The second part of this talk will discuss the opportunities offered by multi-angle dynamic x-ray imaging for the study of divided materials such as granular materials, geomaterials, and foams. These materials have internal density variations, which encode information on the shape and size of the particles, and their tracking over time is a signature of the velocities within the material. We will showcase the unique insights X-ray radiography can provide on several granular and geomechanical systems.