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08 Novembre 2017 Brice SAINT MICHEL

« Dynamics of a shear-thickening suspension under imposed stress "

Brice Saint Michel de l’ Ecole Normale Supérieure de Lyon

Mercredi 08 Novembre 2017 de 11h à 12h, « Salle des conférences » RDC bâtiment NANOBIO DCM 570 rue de la Chimie (en face du bâtiment E) badge pour entrer

Résumé :Discontinuous shear-thickening (DST) fluid are highly concentrated suspensions of particles which, for increasing applied shear stresses, exhibit – on average – a shear rate plateau. The flowing properties of such materials are of critical importance, e.g. for concrete pumping and placement in the construction industry.

For fifty years, no model or simulation could successfully reproduce the strong thickening observed until the recent emergence of frictional suspension dynamics models [1-3]. Such models state that rough particles may experience solid friction with each other under sufficient compression, which decreases the maximum particle packing fraction [3], and results in a global increase of the fluid viscosity [4]. In real life applications, however shear-thickening is also associated with particle
migration when stresses are slightly non-uniform, because it induces a strong shear localization and a sharp viscosity increase [5], which may shadow the microscopic frictional transition previously described.

We decide to investigate the relevance of such scenarii for cornstarch suspensions stirred in a small-gap (2mm) Couette rheometer. We investigate the global dynamics of the suspension under an imposed shear stress using standard rheology measurements. In addition, we probe the local response of our suspensions using an original ultrasound apparatus, which allows us to measure critical quantities such
as instantaneous wall slip and shear profiles. We will try to confront our data with the models previously described.

[1] M. Wyart and M. Cates,Phys. Rev. Lett.(2014).
[2] F.Boyer, É. Guazzelli and O. Pouliquen,Phys. Rev. Lett.(2011).
[3] R. Seto, R. Mari, J. Morris and M. Denn,Phys. Rev. Lett.(2013).
[4] I. Krieger and T. Dougherty,Trans Soc. Rheol.(1959).
[5] A. Fall, F. Bertrand, D. Hautemayou, C. Mezière, P. Moucheront, A. Lemaître and G. Ovarlez,
Phys. Rev. Lett.(2015).

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