Cohesive Granulates

My first research interest concerns the mechanical properties of cohesive granular materials, where solid but deformable bonds ensure rigidity. This part of the project involves within the group Alexander Schmeink, who is working for his Master thesis on the fracture properties of this class of materials.

I am also interested in linking macroscopic properties of cohesive aggregates to microscopic modes of deformation. We developed to this end a stress-strain experiment combined with X-ray micro-tomography, allowing tracking of individual grains during compression and access to their relative motion.

Understanding the mechanical properties of such a model system for cohesive granular media where particular properties can be systematically varied could be relevant for various problems such as fracturing of rocks, fluid invasion, or seismology.

My other current research interest is the study of microbial growth in model porous media. Although this topic may seem far from the previous one at first glance, the simple example of porous sandstone weakened by a biofilm growing on its surface shows how these two subjects can be related. Keeping this example, it appears that most of the studies on biodeterioration have been on its chemical aspects, while mechanical contributions have been neglected. However, it is reasonable to think that a colony of microbes growing in a constrained environment such as the porous matrix of a stone will eventually fill all the available space and apply a mechanical pressure on the inner structure.

Using soft-lithography techniques, we investigate at which conditions a colony of micro-organisms jams in a model 2D porous medium with tunable pores and throats size, and the resulting pressure on the PDMS matrix. We also study the microbial growth in the (3D) cohesive granular material described previously. Using information obtained from the 2D system we try to optimize its design in terms of size of beads and strength of the bonds, to observe mechanical damages induced by the pressure of the growing colony. Within the group, I collaborate with Benjamin Dimond on this specific topic, who is currently focusing on the soft-lithography experiments.

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