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Rôle des contacts adhésifs et frottants dans la rhéologie des suspensions non-browniennes

Abstract : The rheology of suspensions is an area that underwent a small revolution ten years ago. The demonstration of solid contacts between the particles has paved the way for numerous studies combining rheology and tribology in particular. The presence of shear-thinning in concentrated non-Brownian suspensions is a phenomenon that is often observed. The origin of this phenomenon can be twofold, either it comes from the friction between the particles which varies with the stress, or it comes from the presence of adhesion. To date, no study has demonstrated the impact of particle elasticity on the shear-thinning of these systems. In this context, I propose in this thesis an experimental study of the impact of elasticity and particle shape on the shear-thinning of non-Brownian frictional and frictional-adhesive suspensions. I thus show that soft particles suspension behaviour in the absence of adhesion is comparable to frictional hard-sphere suspension behaviour in the limit where the deformation of the particles cannot contribute to the flow. If so, it seems that the behaviour is driven by the modulus of elasticity and the volume fraction. For suspensions of non-adhesive cubic particles, I show that the rheology is very different from that of spheres suspensions. Particularly with the appearance at low volume fraction of a strong contribution from contacts. In addition, the jamming volume fractions are much lower than those of hard spheres suspensions. Secondly, I study the impact of elasticity on adhesive suspensions of soft particles. I experimentally find a characteristic adhesion constraint that seems consistent with JKR's theory. In addition, it appears that once the adhesive regime has passed, the suspensions show frictional behaviour. Finally, for each of the previous systems, I perform shear inversion protocols to dissociate the contribution of contact forces from the contribution of hydrodynamic forces. I thus confirm the observations made in stationary. I finish this manuscript by presenting the first experimental observation of the relaxation of the elastic contact forces between particles upon shear reversal. This contribution is positive from the point of view of flow and the viscosity shows a relaxation at very short time following the shear reversal. This gives us access to certain material quantities such as the modulus of elastic particles.
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Submitted on : Monday, November 22, 2021 - 9:33:11 AM
Last modification on : Tuesday, January 4, 2022 - 6:35:38 AM

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Duncan Gilbert. Rôle des contacts adhésifs et frottants dans la rhéologie des suspensions non-browniennes. Mécanique [physics]. Université Côte d'Azur, 2021. Français. ⟨NNT : 2021COAZ4078⟩. ⟨tel-03438938⟩

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