Séminaire de Mécanique d'Orsay

Le Jeudi 2 juin 2022 à 14h00 - Salle des séminaires FAST-LPTMS (Bât. 530, salle C.120, 1er)

Rheology of hard concentrated suspensions: the role of solid contacts

Brice Saint-Michel
Laboratoire Navier, Université Gustave Eiffel

Concentrated non-Brownian suspensions are one of the most commonly encountered forms of matter, both in natural (mud, blood, …) and industrial (concrete, moisturizer, …) contexts. Such systems are naturally out-of-equilibrium, crowded, and possess long-range pairwise interactions. As hallmark complex systems, they display unusual and rich physics under flow. In particular, suspensions of hard particles have attracted attention due to the online popularity of shear-thickening. Breakthrough numerical [1], theoretical [2] and experimental [3] works have recently established a new scenario for shear-thickening, in which solid contacts between particles can be activated under stress. Activating solid contacts leads to an increase in local friction and ultimately to an unstable response (the shear rate) of the suspension to an applied shear stress. There is however no consensus regarding what the instability looks like at the meso- and macroscopic scales. Far beyond the shear-thickening regime, models inspired by dry granular flows suggest that concentrated suspensions flow in a quasi-Newtonian, fully frictional fashion [4]. In this presentation, I will introduce two experimental setups allowing us to measure the local velocity and local particle concentration in non-Brownian concentrated suspensions. Local velocity measurements obtained using ultrasound echography suggest that discontinuous shear thickening takes the form of propagative bands in the vorticity direction at the mesoscopic scale [5]. I will also show local concentration maps measured by X-ray absorption during viscous resuspension experiments of a frictional suspension. Our results challenge the established scenario of quasi-Newtonian behavior [6] and highlight the key role of inter-particle contact laws in concentrated hard suspensions. References: [1] R. Seto et al., Phys. Rev. Lett. 111, 218301 (2013) [2] M. Wyart & M. E. Cates, Phys. Rev. Lett. 112, 098302 (2014) [3] C. Clavaud et al., Proc. Natl. Acad. Sci. U.S.A. 114, 5147-5152 (2017) [4] E. Guazzelli & O. Pouliquen, J. Fluid Mech. 852, P1 (2018) [6] B. Saint-Michel et al., Phys. Rev. X 8, 031006 (2018) [7] B. Saint-Michel et al., Phys. Fluids 31, 103301 (2019)

Accès Salle des séminaires FAST-LPTMS (Bât. 530, salle C.120, 1er)