Magnetorheological (MR) fluids are a class of controllable fluid whose rheological properties may be rapidly varied by the application of a magnetic field. MR fluids are the magnetic analogs of electrorheological (ER) fluids whose properties are controlled by electric fields. Such controllable fluids whose rheology may be varied by the application of an external input have long been seen as offering the possibility of simple, quiet, rapid response interfaces between electronic controls and mechanical systems. In particular, such controllable fluids have long been envisioned as providing the means for rapid acting valves for use in the active control of mechanical vibrations. Stable, robust, high-= strength MR fluids have recently been developed that provide the enabling technology to finally realize the benefits of controllable fluids in many practical, real world applications. This talk examines some of the fundamental design principles for devices that use MR fluids and compares the ability of typical ER and MR fluids to meet the needs of practical devices. The various modes in which MR fluids may be used are described and specific examples of a variety of MR fluid devices now or soon to be in commercial production are presented. Examples include small, linear dampers for real-time, semi-active vibration control in vehicles, rotary brakes for aerobic exercise equipment, large linear dampers for semi-active control of seismic motions in buildings and bridges, and special purpose devices for medical rehabilitation.
[S22.02] Dynamic-Light-Scattering Study of Chain Dynamics in a Dilute Magnetorheological Fluid
Martin Hagenbuechle (CSULB)
The application of a constant magnetic field to a ferrofluid emulsion induces a magnetic dipole moment in each of the emulsion droplets. Due to the induced dipole-dipole interaction the droplets align themselves into chains. In dilute emulsions, dynamic light scattering is used to study the formation (Smoluchowski aggregation) and dynamics of these chains. As the chains grow, the measured correlation function shows pronounced oscillations. We ascribe these oscillations to the internal motion of the chains, i.e. thermal fluctuations. The dependence of the chain fluctuations on various parameters like the magnetic field strength, the scattering vector and the viscosity of the solvent will be reported. The effect of AC magnetic fields on the chain dynamics will also be discussed.
[S22.03] Simulation of Magnetic-Field-Induced Chain Dynamics In a Dilute Magnetorheological Fluid
Xuelei Zeng (), Yun Zhu, Jing Liu (Department of Physics & Astronomy, California State University at Long Beach, Long Beach, CA 90840)
A computer simulation is used to investigate the dynamics of a chain formed by dipoles in a dilute magnetorheological fluid in an externally applied magnetic field. The simulation results will be comparied with the experimental data obtained by dynamic light scattering. Different internal vibration modes will be discussed.
[S22.04] Electro- and Magneto-Rheological Fluid: A New Smart Fluid
R. Tao (Southern Illinois University at Carbondale)
Electro- and magneto-rheological (EMR) fluids are liquid suspensions of particles which can be polarized by both electric field and magnetic field. Examples of such EMR fluids include titanium-coated iron particles in oil or high T_c superconducting particles in liquid nitrogen. EMR fluids have their effective viscosity continuously and rapidly controllable by either electric field or magnetic field. In addition, EMR fluids show very interesting properties when the applied electric field E (in the z direction) is perpendicular to the magnetic field H (in the x direction). In such a case, there is a structure transition as the ratio between the electric field and magnetic field changes. In the case of dominate electric field or dominate magnetic field, EMR fluids form thick columns in the dominate field direction. These columns have a body-centered tetragonal lattice as the ideal structure. However, when E and H are compatible, EMR fluids have a layer-structure. The layers are parallel to the x-z plane. Within one layer particles form a hexagonal lattice. From special relativity, this structure transition may also occur when an EMR fluid flows in a constant electric field E with an increasing speed at a direction perpendicular to E.
[S22.05] Magnetic Properties of Magnetorheological Fluids
J.M. Ginder (Ford Motor Company), M. Parthasarathy (University of Wisconsin)
Magnetorheological (MR) fluids, which are dense suspensions of micrometer-sized magnetizable particles in liquids, can be rapidly and reversibly solidified by the application of a magnetic field. While these field-induced rheological changes are central to the operation of MR-fluid-based controllable devices, the magnetic properties of these materials are also relevant: they are not only critical to the design of MR-fluid-based components, but they are also useful to test models of the magnetorheological effect. We will report measurements of the quasistatic field-dependent magnetization of a series of MR fluids containing various volume fractions of carbonyl iron particles. These data reflect both field-induced structure formation \-- particle chaining \-- and saturation of the particle magnetization. They will be compared with numerical (J.M. Ginder and L.C. Davis, Appl. Phys. Lett. \bf65), 3410 (1994) and analytical (J.M. Ginder, L.C. Davis, and L.D. Elie, Int. J. Mod. Phys. B \bf10), 3293 (1996) models of magnetorheology and the magnetization process in these materials. We will also discuss the results of magnetic permeability measurements under low ac fields, which are sensitive to the linear magnetic properties of these materials.
[S22.06] Column Formation in Magnetorheological Fluids
Mark Gross (California State University, Long Beach)
In 1990, Halsey and Toor identified a long-range attractive interaction between \underbarinfinite chains of thermally fluctuating dipoles associated with Peierl's instability. It was suggested that this explained the formation of columns from single chains in dilute electrorheological fluids where the chains are effectively infinite due to image dipoles. In the approximation of Halsey and Toor, this attractive interaction term was independent of external field.
In magnetorheological (MR) fluids there are no image dipoles and as a result, finite size corrections must be included. We show that these corrections give rise to a repulsive term which is also long ranged, and in addition grows roughly as the external field squared. The net effect of this term and the Halsey-Toor term is that the range of attraction between two MR chains (i) is typically only a couple of particle diameters and (ii) decreases as the external field increases. (i) and (ii) appear to be in gross contradiction with experiments on MR fluids.
Analytical and numerical results will be presented in an attempt to solve this paradox.
[S22.07] The effect of structure on Rheology in a Model Magnetorheological Fluid
Yun Zhu (), Jing Liu (Dept. of Phys., Calf. State Univ., Long Beach, CA 90840)
An externally applied magnetic field can induce two types of structures in a magnetorheological (MR) fluid where magnetizable particles are suspended in a liquid: separated columns and "bent walls" of particles. The first is formed by slowly increasing the applied field and the second with a top view of "worm" pattern is formed by fast ramping the magnetic field. The rheological measurement with a controlled-strain-rate rheometer has revealed differences in yield stress and apparent viscosity between the two induced structures. This result is consistent with the fact that the columnar structure corresponds to lower energy than the "bent wall" structure.
[S22.08] Nonlinear viscoelastic response of ER/MR suspensions
M. Parthasarathy, D. J. Klingenberg (University 0f Wisconsin-Madison)
Electrorheological (ER) and magnetorheological (MR) suspensions are fascinating materials that show dramatic changes (solidify) upon the application of electric and magnetic fields, respectively. Due to their stress/torque transfer capabilities, these fluids have many potential applications. Most proposed devices will subject the fluids to finite, transient deformations, eliciting a nonlinear visco-elastic/plastic response. Surprisingly, such responses have received little attention.
This talk will focus on mapping the nonlinear rheological response of ER/MR fluids using a molecular dynamics-like simulation method and a simple model that has been shown to qualitatively reproduce the rheological behavior of these fluids. We show that there is a vast region of operating parameters where the rheological response is quite complex and is not described by existing analytic models. Predictions will be compared to experimental data.
[S22.09] Frequency Dependent Electrorheological Properties: Origin and Bounds
Hongru Ma (Department of Physics, Jiaotung University, Shanghai, People's Republic of China), Weijia Wen, Wing Yim Tam, Ping Sheng (Physics Department, The Hong Kong University of Science and Technology)
We present a unified framework for the first-principles calculation of the frequency dependent shear modulus, static yield stress, and structures of dielectric electrorheological systems. It is shown that a strong (applied field) frequency dependence of the static yield stress, in good quantitative agreement with those measured experimentally, can arise from Debye relaxation effects that are typical of poor insulators. Physical upper bounds on the yield stress and the shear modulus, as well as frequency-induced structural soft modes, are predicted.
[S22.10] Unsedimentation ferro-magnetic-electric microsphere: a new material leads to the application of ER fluids in industry and engineering
Weijia Wen, Ning Wang, Hongru Ma, Wing Yim Tam, Xiao Yan, Ping Sheng (Department of Physics, Hong Kong University of Science and Technology, Hong Kong)
A new kind of material named as ``unsedimentation particle" and its ER and MR properties are investigated in this paper. This material can be made as so-called ferro-magnetic-electric microspheres by adding a ferromagnetic component to the ferroelectric sol-gel solution during gel-making process and finally fabricated as spherical with a high temperature spouting device. If the spheres are ferromagnetic, the application of a very small magnetic field, such as that from a small permanent magnet , can permanently suspend the spheres in liquid, thereby solving the traditional problem of particle sedimentation. It is found that this material has very strong ER effect in a low electric field strength up to 3 KPa of static yield stress at field strngth of 1 KV, and it also displays significant MR effect. In addition, both the dielectric and magnetic properties are measured and discussed in this paper. Our experimental results can be explained by the DER theoretical model proposed recently.