Soutenance mémoire
Propriétés diélectriques des fluides ER
Diatomite Particles
The ETSERF is a new mixture in which diatomite particles are immersed into silicon oil with a surfactant TWEEN 80 (Polyethylene glycol sorbitan monooleate). The diatomite powder was selected because of its honeycomb structure, and due to the fact that it has certain useful characteristics, such as a high absorptive capacity, a large surface area, a high chemical stability, and a low bulky density. The density of the diatomite powder is 2.1 g/cm3 [29].
The diatomite particles selected were divided into two categories, according to their mean sizes. One batch, called crunched, was crunched, while the other, called uncrunched, was kept as received; the particle sizes were inspected using an optical microscope, and the uncrunched batch, called ETSERF40, had an average diameter of 40 μm, while the crunched batch, called ETSERF20, had an average diameter of 20 μm. The particle geometry of the ETSERF20 changes because some honeycomb structures break down as the particle size is reduced.
Relation between the ageing of ETSERF and dielectric loss
The ER and dielectric properties of an ETSERF40 suspension, with a concentration of 23% of dry particles, were observed for more than 72 hours in order to study the effect of fluid ageing. Figure 3.12 shows the rheograms of the ETSERF at various electric fields.However, this effect becomes significant after ageing when the electric field is applied, especially with a relatively high electric field (2 kV/mm). For example, the shear stress decreases from 394Pa to 193Pa at a 462 (1/s) shear rate under a 2 kV/mm electric field strength during ageing.
If we define this phenomenon as the ageing of ER fluids, then the ER properties and the dielectric properties (mainly the dielectric loss) are strongly dependent on the duration of ageing. This ageing phenomenon may be due to the fact that the particles agglomerate into bigger particles. It can be seen in Figure 3.13 that there are significant variations in the dielectric constant, particularly in the relaxation frequency range. The relaxation frequency decreases from 30 Hz to 0.2 Hz for ageing taking place over 72 hours. In theory, the smaller the relaxation frequency, the slower the response for establishing a polarization, thus indicating that the ER system needs a longer time to form particle chains. In shear mode, there will not be enough time to form particle chains at a relative high shear rate, and therefore, the ER efficiency will be reduced.
Control strategies
As expected for a two D.O.F. system, two natural frequencies are observed accordingly with the variation of the electric field. While an ordinary dynamic absorber only works into a very narrow-band frequency range, it can be seen from Figure 5.15 that the frequency range of SERDA is enlarged when the electric field is applied, and that the FRF amplitudes of the primary system show minimum values under a large frequency range, thus allowing the operating speed range to be widened. The maximum values of the FRF amplitudes of the primary system have been investigated and the results show that they decrease as the electric field increases. Optimal values are obtained as the electric field varies between 1250 V/mm and 2000 V/mm, which represents an improvement (100 x (Max amplitude-Min amplitude/Min amplitude) greater than 150 % in terms of controlling the vibrations.
Because of the saturation of damping at very high electric fields, the improvement is attenuated somewhat when the electric field varies between 2500V/mm and 3500V/mm. The experimental results are described in Figure 5.17 and are compared with the simulation results. Using equations (5.26) and (5.30), the maximum amplitudes of the primary system are computed at each electric field. It can be seen in Figure 5.17 that the results are comparable, with the greatest differences appearing at low electric fields (500EV≤), since the absorber works like a Houdaille damper (Inman, 1994), due to its low stiffness.
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Table des matières
CHAPITRE 1 INTRODUCTION
1.1 Problématique de la recherche
1.2 Objectifs de la recherche, originalité et méthodologie
CHAPITRE 2 REVUE DE LA LITTÉRATURE
2.1 Principe des fluides électrorhéologique (ER)
2.1.1 Définitions d’un fluide électrorhéologique
2.1.2 Composition des fluides électrorhéologiques
2.1.2.1 Les particules
2.1.2.2 Le liquide support
2.1.2.3 L’activateur polaire
2.1.2.4 Effet des surfactants
2.1.3 Comportement des fluides ER
2.1.4 Propriétés diélectriques des fluides ER
2.1.5 Types des fluides ER
2.1.6 Mélanges usuels
2.2 Les modèles rhéologiques du fluides ER
2.2.1 Nombre de Mason Mn
2.2.2 Modèle de Bingham
2.2.3 Modèle de Casson
2.2.4 Modèle de Cross
CHAPITRE 3 ARTICLE #1 «A QUASI-BINGHAM MODEL FOR PREDICTING ELECTRORHEOLOGICAL FLUID BEHAVIOUR»
3.1 Introduction
3.2 Rheological Behaviour of ETSERF
3.2.1 Rheological Behaviour of Various ER Fluids
3.2.2 Preparation of ETSERF Fluids
3.2.2.1 Diatomite Particles
3.2.2.2 Optical observation of chain formation
3.2.3 Measurement of dielectric and dynamic properties of ETSERF
3.2.3.1 Electrorheological response under AC electric field in ER fluid 36 3.2.3.2 Transient response of ER fluids
3.2.3.3 Dielectric proprieties of ETSERF fluids
3.2.3.4 Relation between the ageing of ETSERF and dielectric loss
3.3 Experimental Design and Procedure
3.3.1 Design of Experiment
3.3.2 Statistical Results Analysis
3.3.2.1 Shear stress induced by particle sizes and surfactant under different concentrations (CDE)
3.3.2.2 Shear stress effect induced by shear rate, particle concentration and size (ACE)
3.3.2.3 Shear stress induced by electric field strength, the surfactant and particle size (BDE)
3.3.2.4 Shear stress effect induced by the size and electric field strength under different concentrations (BCE)
3.3.2.5 Shear stress effect induced by the electric field strength and the shear rate under different sizes (ABE)
3.3.2.6 Shear stress induced by electric field strength and the surfactant under different concentrations (BCD)
3.3.2.7 Shear stress effect induced by the electric field strength, the shear rate and surfactant (ABD)
3.3.2.8 Shear stress effect induced by the electric field and shear rate under different concentrations (ABC)
3.4 Empirical Model for Shear Stress
3.4.1 Quantitative relationship between the dynamic shear stress and the independent variables
3.4.2 A new Quasi-Bingham Model
3.5 Conclusion
Acknowledgment
3.7 References
CHAPITRE 4 ARTICLE #2 «EXPERIMENTAL INVESTIGATION OF DIELECTRIC PROPERTIES ON ELECTRORHEOLOGICAL FLUIDS»
4.1 Introduction .
4.2 Experimentation
4.3 Basic concepts
4.3.1 Polarization mechanism of heterogeneous dielectrics
4.3.2 Theories of the slow polarization
4.3.3 The dependence on Relaxation of the ER effect
4.4 Results and discussions
4.4.1 ER effect
4.4.2 The dielectric properties of ER suspensions
4.4.2.1 Influence of particle sizes, particle concentrations and surfactant on dielectric properties of ER suspension
4.4.2.2 Influence of humidity on dielectric properties of ER suspension
79 4.4.3 Polarization mechanisms in ER suspensions (Interfacial polarization)
4.4.4 The relation between the ageing of ETSERF and dielectric loss
4.5 Conclusion
4.6 Acknowledgements
4.7 References
CHAPITRE 5 ARTICLE #3 «CONTROL OF ROTOR TORSIONAL VIBRATIONS BY USING AN ELECTRORHEOLOGICAL FLUID DYNAMIC ABSORBER»
5.1 Introduction
5.2 Modeling of the ER fluids in shear mode
5.2.1 Steady-state modeling of the ER fluids in shear mode (Quasi-Bingham model)
5.2.2 Rheological Behaviors of ER fluids
5.2.3 Oscillatory dynamic model in shear mode (General Quasi-Bingham model in shear mode)
5.2.3.1 Introducing visco-elasticity in the pre-yield region
5.2.3.2 Torsional damping and stiffness of ER Dynamic absorber
5.3 Smart ER Dynamic Absorber (SERDA)
5.4 Simulation and experimental results
5.4.1 Simulation of yield stress, strain and shear modulus
5.4.2 Experimental identification of ERF dynamic parameters in shear mode (S.D.O.F. system
5.4.3 Design of Smart ER Dynamic Absorber (SERDA)
5.4.4 Control strategies
5.5 Conclusions
5.6 Acknowledgment
5.7 References
CHAPITRE 6 SYNTHÈSE, CONCLUSIONS ET RECOMMANDATIONS
6.1 Synthèse
6.2 Conclusions
6.3 Recommandations
ANNEXE I ARTICLES DE CONFÉRENCE
ANNEXE II DIMENSIONNEMENT DES PIÈCES DE COUETTE VISCOSIMÈTRE
BIBLIOGRAPHIE
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