Magnetorheological Behavior Research Articles

Magnetorheology of colloidal dispersion containing Fe nanoparticles synthesized by the arc-plasma method

Spherical crystalline Fe nanoparticles, ∼100 nm in diameter, were synthesized under Ar–50% H 2 arc-plasma. These nanoparticles were dispersed in silicone oil after silane treatment on as-grown thin oxide layer (∼2 nm) to make their surfaces hydrophobic. The resulting Fe nanoparticles exhibited a high saturation magnetization of ∼190 emu/g at room temperature. The static magnetorheological behavior was measured for the colloidal dispersion (solid concentration: 15 vol%) at room temperature under magnetic flux densities of 0–0.3 T, using a parallel-plate-type commercial rheometer. The yield stress continuously increased with magnetic flux density, demonstrating the Bingham plastic behavior. Moreover, subjecting the sample to a magnetic flux density of 0.3 T increased the yield stress by ∼10 2. Additionally, the colloidal dispersion exhibited good stability against sedimentation.

Magnetorheological Behavior of Polyethyene Glycol-Coated Fe3O4 Ferrofluids

Polyethyene glycol (PEG)-coated Fe3O4 ferrofluids were prepared by suspending the PEG-coated Fe3O4 nanoparticles in an oligomeric PEG-400 carrier liquid, and their magnetorheological steady flow behavior was investigated. The PEG modification did not change the crystalline structure of Fe3O4, and the PEG-coated Fe3O4 nanoparticles were of nearly spherical shape and had a narrow size distribution (4±1 nm in diameter). These nanoparticles exhibited no significant aggregation in the absence of the magnetic field. Under the magnetic field, the nanoparticles aggregated into string-like clusters oriented in the direction of the field. Correspondingly, the ferrofluids behaved essentially as the Newtonian fluids in the absence of the magnetic field but exhibited, under the magnetic field, a magnetorheological effect, i.e., the increase of the shear stress/viscosity associated with a pseudo-plastic and thinning character with no real yield stress. This lack of the real yield stress, possibly reflecting the absence of huge clusters connecting the measuring parts (plates) in the rheometer, suggested that the magnetorheological effect of the ferrofluids were related to deformation/disruption of the magnetically formed clusters of finite sizes under the shear. Interestingly, this effect was most significant for the Fe3O4 nanoparticles having an intermediate amount of PEG coating. This result suggested a possibility that the relaxation of PEG chains in the coating layers of nanoparticles in the clusters contributed to the magnetorheological effect.

Magneto-rheological fluid behavior in squeeze mode

Little published data exists on the behavior of MR fluids in squeeze mode. Many of thebasic properties of MR fluids in squeeze mode are still unknown. In squeeze mode, MRfluids can generate a large range of force associated with a small displacement.As a result, squeeze mode has recently received more attention. This researchfocuses on modeling and testing MR fluids in squeeze mode. A novel squeezemode rheometer is designed and built. MR fluid is tested in squeeze mode toevaluate its performance and behavior. The rheometer can test MR fluid underdifferent conditions (gap size, magnetic field density, speed, etc). It utilizes a Gaussmeter for direct measurement of the magnetic field density. MR fluid squeeze testresults show that MR fluid can deliver a large range of force that is comparable inmagnitude to the force in shear mode. The tests also indicate a clumping effectof the fluid when tested in repeated cycles that does not appear to have beendocumented previously. This paper describes, in detail, the clumping effect and providespossible reasons for this phenomenon. A non-dimensional mathematical model isdeveloped and validated experimentally. The non-dimensional model directlycompares the squeeze mode force to the shear mode force. The results indicate thatMR fluid in squeeze mode can be used in many applications requiring a largerange of controllable force in envelopes that can only accommodate small strokes.

Synthesis and Magnetorheological Characterization of Magnetite Nanoparticle and Poly(Vinyl Butyral) Composite

Iron oxide nanoparticle of magnetite, one of well-known soft magnetic materials, has been investigated due to their various potential applications. In order to apply it as a magnetorheological (MR) material, composite of poly(vinyl butyral) and magnetite nanoparticles was prepared via solvent evaporation method using synthesized magnetite nanoparticles because of their proper magnetic characteristics and dispersion stability in a viscous medium. The magnetite nanoparticle was prepared via a co-precipitation method using ferrous and ferric ionic aqueous solutions. Surface and internal morphology of the composite particles were observed via scanning electron microscope and transmittance electron microscope. The MR fluid was prepared by suspending the composite particles in mineral oil. Its MR characteristics were examined via a rotational rheometer in a parallel plate geometry equipped with a magnetic field supplier. MR properties of the composite based MR fluid exhibit typical MR behavior with maximum yield stress of 800 Pa when 343 kA/m of magnetic field was applied.

Magnetorheological Characteristics of Polymer Coated Magnetite Particle Composites With Carbon Nanotube Nanohybrid

This study demonstrates physical adsorption of polymer coated nano-sized magnetite (Fe3O4) onto multiwalled carbon nanotube (MWNT) surface. A new hybrid material was made following four consecutive procedures of co-precipitation, polymer coating, functionalized MWNT, and ultrasonication method. Polymer coated magnetite particle (MaPAm) composites with MWNT nanohybrid (MaPAmNT) were acquired. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have been used to investigate their nanostructure and morphology, thus verifying that polyacrylamide coated magnetite particles were well adsorbed onto surface of the MWNT. From thermogravimetric analysis (TGA) data, we also confirmed compositions of the MaPAmNT. Magnetorheological (MR) properties of the MaPAmNT under an external magnetic field were investigated, exhibiting typical MR behavior of yield stress and shear stress.

Study of the magnetorheology of aqueous suspensions of extremely bimodal magnetite particles

In this paper we describe the magnetorheological behavior of aqueous suspensions consisting of magnetite particles of two size populations, in the micrometer and nanometer scale, respectively. Previous works on the magnetorheology of oil-based fluids demonstrated that the addition of nanoparticles has a very significant effect on the intensity of the magnetorheological effect. The present contribution confirms such results in the case of aqueous fluids, based on the dependence of the yield stress and the viscosity of the bimodal suspensions on both the composition of the mixtures and the magnetic field strength. It is demonstrated that for a given concentration of micrometer particles, increasing the amount of nanometer magnetite provokes a clear enhancement in the yield stress for all the magnetic fields applied. This is proposed to be due to the formation of heterogeneous aggregates that improve the stability of the suspensions and ease the building of well-arranged field-induced structures. The behavior of both the yield stress and the post-yield viscosity agrees better with the predictions of standard chain models when the relative proportion of both types of particles confers optimum stability to the bimodal dispersions.

Temperature effect on the magneto-rheological behavior of magnetite particles dispersed in an ionic liquid

The magneto-rheological properties of iron(II, III) oxide particles dispersed in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate were investigated in the temperature range from 25 °C to 76 °C. The experimental results have revealed that the apparent viscosity of the dispersion slightly changes with the temperature when a constant magnetic field is applied and its value mainly depends on the shear rate and the strength of the magnetic field. The viscosity of the dispersion remains practically unmodified with both the temperature and the magnetic field intensity as the magnetic saturation of the material is reached; in this regime the viscosity will only depend on the applied shear rate. In contrast, the yield stress values of the dispersion as well as the corresponding shear stress vs. shear rate curves have shown and inversely proportional behavior with temperature for a constant magnetic field. Moreover, a power law model was utilized to predict the temperature dependence of the yield stress under the presence of a constant magnetic field.

Experiments and Models of the Magneto Rheological Behavior of High Weight Percent Suspensions of Carbonyl Iron Particles in Silicone Oil

Flow properties of magnetorheological (MR) fluids are greatly altered by the application of a magnetic field. The design, optimization, and control of novel devices that exploit MR fluid behavior in multidegree of freedom applications require three dimensional models characterizing the coupling of magnetic behavior to mechanical behavior in MR fluids. The authors have derived 3D MR fluid models based on multiscale kinetic theory. The underlying bases of the models are summarized, with phenomenological empiricism distinguished from multiscale first principles, and the models’ ability to capture the experimentally measured mechanical response of a MR fluid-based damper to specified magnetic fields is assessed. The results of this comparison are that the kinetic theory-based models both relate macroscale MR fluid behavior to a first-principles description of magnetomechanical coupling at the microscale and possess the flexibility to best match the measured behavior of a particular MR fluid device observed in our experiments.

Effect of particle aggregation on the magnetic and magnetorheological properties of magnetic suspensions

In this work, the magnetorheological behavior of concentrated (10% solid volume fraction) iron-based magnetorheological fluids was studied. Two different compounds were added to stabilize the suspensions against aggregation and settling processes: A surfactant (aluminum stearate, AlSt), and a gel-forming agent (silica nanoparticles). The shear stress vs. shear rate flow curves of the suspensions were obtained in a wide range of applied magnetic fields with the aim of determining the intensity of the field-induced yield stress, that is, the strength of the so-called magnetorheological (MR) effect. The suspension stabilized against particle aggregation by surfactant addition reached the strongest MR response, while the opposite behavior (the weakest MR response) was found in the suspension that contained silica nanoparticles added as anti-settling agent. The scaling between the yield stress and the magnetic field strength (σy∼Hn) was calculated and compared with the predictions of theoretical structural models. The results demonstrated that such scaling depends on both the aggregation degree of iron particles in the suspensions and the ratio H∕MS0 (MS0, saturation magnetization of the iron powder), showing a continuous decrease in the exponent n for high enough magnetic fields.

Study of the magnetorheological response of aqueous magnetite suspensions stabilized by acrylic acid polymers

In this paper we describe the magnetorheological (MR) behavior of aqueous suspensions consisting of magnetite particles stabilized by poly(acrylic acid) polymers (PAA). A previous work on the colloidal stability of the same systems for different pH values and polymer concentrations demonstrated that the addition of PAA polymers has a very significant effect on the stability. In the present contribution, we study the MR effect of the suspensions stabilized by two different commercial polymers, as a function of pH, magnetic field strength and magnetite volume fraction. All the results are discussed in terms of the interfacial properties of the systems. It is demonstrated that for a given concentration of micrometer particles, the rheological response strongly depends on pH, on the volume fraction of magnetite particles, on the type of polymer added for increasing the stability and on the magnetic field strength. Changing the polymer used provokes clear rheological differences for the same sample conditions (field strength, volume fraction and pH). This is suggested to be due to the hydrophobic/hydrophilic balance of the polymer affecting the magnetic field ability to form magnetic structures by aggregation of the magnetized particles. The results are compared to the predictions of the so-called standard chain model, based on the assumption that the MR effect is the result of the balance between the magnetic interactions (tending to establish some degree of order in the suspension by formation of particle chains in the direction of the field) and hydrodynamic ones (tending to destroy the formed structures by viscous stress on the chains). It is found that the behavior of the yield stress does not agree well with the predictions of the model when the relative proportion of both particle and polymer confers optimum stability to the dispersions. This is likely due to the fact that the presence of the stabilizing polyelectrolyte provokes that the magnetic field is not as effective in structuring the suspension as deduced from the chain model.

CFD analysis of journal bearing hydrodynamic lubrication by Bingham lubricant

Design of smart journal-bearing systems is an important issue that opens up the possibility for semi-active dynamic control of bearing behavior. Recent studies show that there is an increasing interest in designing hydrodynamically lubricated bearings using electro-rheological fluids (ERFs) or magneto-rheological fluids (MRFs). Both smart fluids behave like Bingham fluids, and thus the Bingham plastic model is used to describe the grease and the electro-rheological (ER) and magneto-rheological (MR) fluids behavior of the non-Newtonian fluid flow. The performance characteristics of a hydrodynamic journal bearing lubricated with a Bingham fluid are derived by means of three-dimensional computational fluid dynamics (3-D CFD) analysis. The FLUENT software package is used to calculate the hydrodynamic balance of the journal using the so-called “dynamic mesh” technique. The results obtained from the developed 3-D CFD model are found to be in very good agreement with experimental and analytical data from previous investigations on Bingham fluids. Journal-bearing performance characteristics, such as relative eccentricity, attitude angle, pressure distribution, friction coefficient, lubricant flow rate, and the angle of maximum pressure, are derived and presented for several length over diameter ( L/ D) bearing ratios and dimensionless shear numbers T 0 of the Bingham fluid. The above diagrams are presented in the form of Raimondi and Boyd charts, and can easily be used in the design and analysis of journal bearings lubricated with Bingham fluids. The core profile formed in the bearing is also calculated and presented for various bearing eccentricities, L/ D ratios, and shear numbers T 0, and found to be in very good agreement with previous experimental and theoretical investigations. The analysis presented here leads to charts that could be used by the designer engineer to design smart journal bearings.

Polymeric nanobead coated carbonyl iron particles and their magnetic property

AbstractMagnetic carbonyl iron (CI) particles have attracted great attention due to their high saturation magnetization and appropriate particle size for magnetorheological (MR) materials. However, hydrodynamic instability of the CI particle suspension which was attributed to the large density mismatch between the dispersed CI particles and the medium has affected its predominant role for MR applications. A novel magnetic CI/polystyrene (PS) composite with nano‐scaled PS spheres sprinkled on the surface of the CI particles was fabricated via a normal dispersion polymerization in this work. Physical properties, MR behaviors as well as the improvement in sedimentation problem were investigated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

MAGNETORHEOLOGY OF CARBONYL-IRON SUSPENSION WITH IRON/MCM-41 ADDITIVE

Iron containg hexagonal mesoporous silica particle ( Fe - MCM -41) was prepared and adopted into carbonyl-iron ( CI ) based magnetorheological (MR) suspension as an additive to improve the sedimentation problem of the CI based MR fluid. Structural properties and morphology of the synthesized Fe - MCM -41 particles were observed using SEM. Their MR properties such as oscillation characteristics and flow response (shear stress and shear viscosity) were examined via a rotational rheometer in parallel plate geometry equipped with a magnetic field supplier under external magnetic field strengths ranging from 0 to 257 kA/m. The addition of Fe -containing mesoporous particles into CI suspension was found to improve not only MR behaviors but also sedimentation problem of the CI based MR fluid.

Analysis of the magnetomechanical behavior of MRFs based on micromechanicsincorporating a statistical approach

A micro–macro model is formulated for the magnetomechanical behavior ofmagnetorheological fluids (MRFs) based on micromechanics and a statisticalapproach. It includes two stages: (1) the analysis of the aggregation of the particles inan MRF into chains of dipoles aligning in the direction of the applied magneticfield and its contribution to resistance against shear deformation, and (2) theattainment of solid-like mechanical properties of the MRF by assuming numerouschains inclining with the angles arranged in a normal distribution. This modeltakes into account the effect of each of the main influencing factors, such as theintensity of magnetic induction, the size and the volume fraction of particles,shear strain rate and saturation magnetization, etc, on the critical shear stressof MRFs. The effect of typical governing parameters on the behavior of MRFsis investigated individually, which shows the capability of the proposed modelin the description of the magnetorheological behavior of MRFs. The commonBingham’s model of viscoplasticity and the dual-viscosity model can be obtained fromthe proposed model as special cases. The model is comprehensive, simple, andcan easily be used for the initial design and optimization of high-performanceMRFs.

A Unifying Perspective on the Quasi-steady Analysis of Magnetorheological Dampers

A magnetorheological (MR) fluid, modeled as a Bingham plastic (BP) material, is characterized by a field dependent yield stress, and a (nearly constant) postyield plastic viscosity. Based on viscometric measurements, such a BP model is an idealization to physical MR behavior, albeit a useful one. A better approximation involves modifying both the preyield and postyield constitutive behavior as follows: (1) assume a high viscosity preyield behavior when the shear stress is less than the transition stress, and (2) assume a power law fluid (i.e., strain rate dependent viscosity) when the shear stress is greater than the transition stress. Assuming a power law fluid in postyield allows the model to account for shear thinning behavior exhibited by MR fluids at higher strain rates. Such an idealization for MR fluid constitutive behavior is called an viscous-power law model, or a Herschel—Bulkley (HB) model with preyield viscosity. This study develops a quasi-steady analysis for such a constitutive MR fluid behavior applied to an MR flow mode damper. Closed form solutions are developed for the fluid velocity, as well as key performance metrics, such as damping capacity and dynamic range (ratio of field-on to field-off force). For the given fluid properties and flow mode damper geometry, the fluid velocity profile and gradient, and the relationship of the damper force and piston velocity are analyzed. In addition, specializations to existing models, such as the HB, biviscous, and BP models, are shown to be easily captured by this model when physical constraints (idealizations) are placed on the rheological behavior of the MR fluid.

High Precision Positioning with Ferrofluids as an Active Medium

Ferrofluids are magnetically controllable fluids which can be used as an active medium in high precision positioning systems. The capability of ferrofluids for being fixed with an applied external magnetic field and their magnetorheological behavior are main properties for technical applications. Beside that, amplifying the magnetic force acting on the surface of a paramagnetic actor which levitates in a ferrofluid can be used for the high precision positioning of objects. In this paper different types of magnetofluidic positioning systems are described and the influences on the velocity of positioning and on the accuracy of positioning are discussed.

Magnetorheology of Carbonyl-Iron Suspensions With Submicron-Sized Filler

We added novel submicron-sized particles into carbonyl-iron (CI) suspension to improve the sedimentation problem. The added string-like graphite nano-fiber enhanced the resistance to sedimentation and improved flocculation stability without macroscopically noticeable change in the magnetorheological behaviors. This gap-filling submicron-sized particle between /spl mu/m-sized CI spheres reduced the physical contact of CI particles, and reduced the caking behavior. These systems with and without additives were investigated and compared via a rotational rheometer by accurately controlling the magnetic field strengths.

Features of magnetorheology of suspension with the Cowin polar carrier fluid

The rheological constitutive equations for dilute suspension of rigid axisymmetric particles immersed in the Cowin polar fluid are obtained within the framework of structure-phenomenological approach. As a hydrodynamic model of suspended particles possessing constant magnetic moment and zero buoyancy a symmetric triaxial dumbbell is used. The effect of couple stresses and rotational viscosity of the polar suspension carrier fluid is investigated on pseudoplastic and elasticoviscous rheological properties of suspension in stationary simple shear flow in combination with stationary transverse magnetic field. Obtained results are used for magnetorheological behavior investigation of dilute suspension of rigid particles in blood.

RHEOLOGICAL AND MAGNETORHEOLOGICAL BEHAVIOUR OF SOME MAGNETIC FLUIDS ON POLAR AND NONPOLAR CARRIER LIQUIDS

Rheological and magnetorheological behaviour of monolayer and double layer sterically stabilized magnetic fluids, with transformer oil (UTR), diloctilsebacate (DOS), heptanol (Hept), pentanol (Pent) and water (W) as carrier liquids, were investigated. The data for volumic concentration dependence of dynamic viscosity of high colloidal stability UTR, DOS, Hept and Pent samples are particularly well fitted by the formulas given by Vand (1948) and Chow (1994). The Chow type dependence proved its universal character as the viscosity data for dilution series of various magnetic fluids are well fitted by the same curve, regardless the nonpolar or polar charcater of the sample. The magnetorheological effect measured for low and medium concentration water based magnetic fluids is much higher, due to agglomerate formation process, than the corresponding values obtained for the well stabilized UTR, DOS, Hept and Pent samples, even at very high volumic fraction of magnetic nanoparticles.

Description of magnetorheological behavior with internal variables

The macroscopic theory of magnetorheological (MR) fluids is investigated by the use of the tensorial and vectorial internal variables. After both variables are defined, the balance equations, entropy inequality and evolution equations can be obtained. Under the consideration of physical phenomena of MR fluids (the existence of yield stress and the elasticity of MR solids), some parameters in the evolution equations are suitably chosen. The discussion is focused on the expression of stress tensor and the mechanism of energy dissipation. Comparisons among the vectorial internal variable, the tensorial internal variable, and the Cauchy's deformation tensor are made to explicate the connection among the different approaches. Finally, taking account of the effect of the gradient of the vectorial internal variable, modified expressions for entropy inequality and rotational invariant are also discussed.