Description
Year: L3/M1/M2
Laboratory : IRPHE
Contact : Marie-Julie Dalbe marie-julie.dalbe@univ-amu.fr et Nicolas Vandenberghe nicolas.vandenberghe@univ-amu.fr
A granular medium, such as sand, is a collection of rigid particles that interact through contact. These media have both fluid properties (they can flow) and solid properties (a pile can retain its shape despite gravity). Adding a small amount of liquid significantly alters the mechanical properties of these media. Capillary bridges form between the grains, inducing a cohesive force that holds the grains together, thereby strengthening the medium's ability to withstand stress without significant deformation. However, when a sufficiently high stress is applied, the wet granular medium flows like a liquid, but can also, under certain conditions, crack like a solid medium. To date, it is not possible to predict the conditions under which cracks will appear, and there is no model available to describe their progression dynamics.
To better understand this phenomenon, we propose an experiment involving the observation of a crack opening in a wet granular medium, measuring the displacement of the grains using a camera. The objective is to determine the energy required to propagate a crack based on measurements of forces and grain displacements, and to characterize the variations in this energy with different physical parameters (grain size, surface tension of the liquid). The role of the geometry of the grain stacking, and in particular its density, will also be studied. A better understanding of the physical basis of fracture energy in cohesive granular media will improve the models used, for example, to predict risks in geophysics (landslides or avalanches) or for powder flow in an industrial context.
The proposed study is experimental in nature. The intern recruited will conduct experiments on an existing device, which he or she will help to improve, and will analyze the results to identify the physical parameters relevant to the failure of wet granular media.
