While fractures are not observed in a dry granular medium (a pile of rigid grains), wet or even immersed granular material (grains + water) can experience fracture, and even fragmentation, when it is sufficiently deformed. This is due to the cohesive forces resulting from the presence of interstitial liquid in the granular medium, either by capillary bridges between grains, or by a transient drop in the interstitial liquid pressure [1].
In this context, we want to understand (i) the mechanisms allowing the existence of fracture in the granular medium and (ii) the dynamics of the fracture in this medium. This complex ‘grain + water under deformation' system calls on many fields of physics: rheology of dense suspensions, elastic properties of a granular stack, fracture mechanics, hydrodynamics in porous media.
We propose to study the different fracture regimes in wet and liquid-saturated granular media, deformed by impact. Thus we will systematically control the cohesion forces in the material and we will measure the deformation field at the fracture tip using ultra-fast imaging [2]. The results obtained will lead to the development of analytical and / or numerical models of crack propagation in dispersed media.
This study could be extended to liquid suspensions, more complex such as cornstarch (grains of corn starch in water), providing new insights into the microscopic interactions between particles and their role on the macroscopic behavior of suspensions [3].
Keywords: suspensions rheology ; dispersed media mechanics ; fracture mechanics
Methods: high-speed imaging ; digital image correlation ; dilation and pressure measurements
This project is a collaboration between the Physics Lab. at ENS Lyon (Elsa Bayart) and the LMFA at Univ. Lyon 1 (Simon Dagois-Bohy and J. John Soundar Jerome). The experimental setup is located at ENS.
Contact: Elsa Bayart ;
elsa.bayart@ens-lyon.fr ; 04 26 23 39 60
Refs:
[1] Unifying impacts on granular matter from quicksand to cornstarch, J.J.S. Jerome et al, Phys. Rev. Lett. 117, 098003 (2016).
[2] Calibrating thermoelastic stress analysis with integrated digital image correlation: Application to fatigue cracks, J. Gamot et al, J Strain Analysis 54, 320-330 (2019)
[3] Dynamic Fracture of Nonglassy Suspensions, M. Roché et al, Phys. Rev. Lett. 110, 148304 (2013).