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Effet d'ultrasons de puissance sur les matériaux mous : vers des matériaux "acousto-rhéologiques"

Abstract : Ultrasonic imaging and velocimetry has been proved to be very efficient methods to study various materials. At high intensity, ultrasonic waves are known to exert steady forces in newtonian fluid through nonlinear effects like the acoustic radiation pressure. However those effects have never been used in fundamental studies of the physics of soft materials. This thesis aims at exploiting the interaction between high intensity ultrasound and soft jammed materials to probe actively and even modify their mechanical properties.We first introduce an alternative technique for active microrheology we called « acoustic mesorheology ». By analyzing the motion of an intruder under the acoustic radiation pressure we characterize locally the rheology of the system under study. We test this technique on a simple yield stress fluid, namely a carbopol microgel. We compare the results with those obtained by standard rheology measurements of the behaviour of this gel under its yield stress.Then we describe the fluidization of an immersed granular packing by high intensity focused ultrasound. We compare our observations with the results of molecular dynamics simulations. The obtained fluidization is original as the injection of energy is discontinuous in time. It is hysteretic and intermittent and those properties are well captures by both simulations and a phenomenological model.Finally, we replace the plane of a standard cone-plate rheometer by an ultrasonic transducer. This allows us to characterize the effect of high frequency vibrations on the rheology of a fragile carbon black gel. We observe a significant and eventually irreversible effect of ultrasound on the elastic modulus and on the yielding of the system. Vibrations are shown to favor wall slip but seem to induce changes in the volume of the sample though.
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Submitted on : Saturday, December 17, 2016 - 1:04:57 AM
Last modification on : Wednesday, November 20, 2019 - 3:10:56 AM
Long-term archiving on: : Tuesday, March 21, 2017 - 12:49:00 PM


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  • HAL Id : tel-01418772, version 1


Pierre Lidon. Effet d'ultrasons de puissance sur les matériaux mous : vers des matériaux "acousto-rhéologiques". Matière Molle [cond-mat.soft]. Université de Lyon, 2016. Français. ⟨NNT : 2016LYSEN014⟩. ⟨tel-01418772⟩



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