Magnetorheological Effect Research Articles

Study on the Magnetorheological Effect of MR Elastomer under Shear-compression Mode

Magnetorheological elastomers are a new kind of MR materials, which consist of magnetizable particles and elastomers. Because of the controllable orheological properties, the materials show a widely prospect in engineering application. In this paper, the magnetic-induced modulus under shear-compression mode was studied. Based on the modulus, the relative MR effect and its influence factor were systematically analyzed. The results show that the relative MR effect will increase with the increasing volume fraction of magnetizable particles, the exterior magnetic field strength and compression strain, and decrease with the increasing shear strain and modulus of matrix. For the study of the relative MR effect, it will give useful advices for the design of MR materials and MR devices.

Physically crosslinked poly(vinyl alcohol) hydrogels with magnetic field controlled modulus

Physically cross-linked isotropic and anisotropic poly(vinyl alcohol) (PVA) hydrogels containing micron-sized carbonyl iron particles were prepared through a cyclic freezing–thawing process. The PVA hydrogel can respond to a magnetic field and shows a magnetorheological (MR) effect, i.e., the modulus of the PVA hydrogel can be adjusted under a magnetic field. The chain-like structures of carbonyl iron are formed in the PVA hydrogel after orientation under a magnetic field of 1.5 T. Also some magnetic field induced oriented pores with a tunable diameter are observed in the dried PVA gel. The MR effect can be adjusted by changing the carbonyl iron content, the initial concentration of PVA solution and test frequency. The formation of aligned chain-like structures of carbonyl iron in the anisotropic PVA MR hydrogel improves the compression properties and the MR effect. At a carbonyl iron content of 70 wt%, the maximum absolute and relative MR effect of anisotropic PVA MR hydrogels are ∼1.24 MPa and ∼230%, respectively. The PVA hydrogels with good MR effects and moderate mechanical strength have potential applications in artificial muscle, soft actuators and drug release.

Negative Magneto-Rheological Effect of a Dispersion Composed of Spindle-Like Hematite Particles

We have investigated the negative magneto-rheological effect of a dispersion composed of spindle-like hematite (α-Fe2O3) particles by means of the experimental method. The spindle-like hematite particles were synthesized by aging a solution of FeCl3 and KH2PO4 for 72 hours at 373K. The particle size distribution was determined by a digital image analysis method from the electronic microscope observation of the particles. In the present study we have considered a glycerol-water-based dispersion in order to clarify the influences of the shear rate and the magnetic field strength on the negative magneto-rheological effect. The measurement of the viscosity was carried out using the rotational-type rheometer in an external magnetic field generated by the Helmholtz coils. The main results obtained here are summarized as follows. The viscosity of hematite/glycerol-water dispersions relative to that for no applied magnetic field case decreases with increasing magnetic field strength: that is, the negative viscosity certainly occurs, as theoretically predicted. Moreover, this negative magneto-rheological effect tends to decrease with increasing shear rate, which also qualitatively agrees with the theoretical prediction.

Performance of Magnetorheological Fluids Flowing Through Metal Foams

If magnetorheological (MR) fluids are stored in porous materials, when excited by the external magnetic field, MR fluid will be drawn out and produce MR effect, which could be used to solve the following problems of the MR damper, such as the seal, volume and the cost of MR fluid damper. In this paper, the effect of structure of metal foams on the performance of MR fluid is investigated; the relationship between the penetrability and the porosity of the metal foams is measured, the change of MR fluid performance flowing though the metal foams is obtained. It shows that, after flowing through metal foams, the change of performance of MR fluid is about 2.5%. Compared to the sponge, the porous metal foams have the obvious advantages in high porosity and rigidity, which provide a convenient and low-cost way to design the MR damper.

Macroscopic and microscopic structural integrity in magnetic colloids—cationic micellar solution: Rheology, SANS and magneto-optical study

A stable mixture of two colloid system composed of double surfactant coated aqueous nanomagnetic fluid and aqueous micellar solution of cationic micelles of cetyletrymethyl ammonium bromide (CTABr) is prepared as a function of nanomagnetic fluid concentration. This mixed system is analyzed using three techniques such as zero field and field induced viscosity measurements, Small Angle Neutron Scattering technique and magneto-optical birefringence measurements. In field induced viscosity measurement it is observed that even 20% magnetic fluid concentration in CTABr aqueous solution shows 75% increase in viscosity compared to pure magnetic fluid. This suggests that in presence of CTABr micelles, a novel magneto rheological effect for low concentration of magnetic fluid is observed. From SANS measurements it is observed that aggregation number and a/b ratio increases with magnetic fluid concentration and magnetic birefringence reveals non-superimpose behavior of normalized field induced retardation. Results of these experiments are compared and indicate zero fields and field induced structural integrity between magnetic particles and soft micelles.

High-Performance Hybrid Magnetorheological Materials: Preparation and Mechanical Properties

To improve mechanical performance of magnetorheological elastomers (MREs), two novel hybrid magnetorheological elastomers that were embedded with magnetorheological fluids (MRFs) and magnetorheological gels (MRGs) were fabricated. In this work, MRFs and MRGs were injected into different numbers of holes that were punched on MRE specimens regularly. The nonlinear mechanical properties of the as-prepared magnetorheological fluid-elastomers (MRFEs) and magnetorheological gel-elastomers (MRGEs) were investigated in the presence of external homogeneous magnetic fields. The modulus, loss factor, and hysteresis were evaluated with a modified dynamic mechanical analyzer (DMA) and vibrating sample magnetometer (VSM). Dependence of the rheological response on the volume fraction was also investigated. As the experimental results show, not only were the initial moduli of the two novel hybrid magnetorheological materials higher than those of both the MRFs and MRGs, but also their magnetorheological (MR) effects were better than those of MREs. The loss factors of the two new hybrids were different from those of traditional MREs. Moreover, their dynamic properties changed according to the different volume ratios of MRFs and MRGs injected into the MRE specimens. These results suggest that the two novel hybrid magnetorheological elastomers are improved systems with volume-fraction-dependent rheological responses and the mechanical properties of MREs can be improved by embedding them with MRFs and MRGs.

Ultra Smooth Planarization Polishing Technique Based on the Cluster Magnetorheological Effect

A new planarization polishing method based on the cluster magnetorheological (MR) effect is presented to polish optical glass in this paper. Some process experiments were conducted to reveal the influence of the content of carbonyl iron and the abrasive materials in the MR fluid on the machining effect, and the machining characteristic of polished surface was studied. The results indicate that the surface roughness of the polished workpiece can be reduced rapidly when the strong magnetic field is applied, and ultra smooth surface with Ra 1.4 nm can be achieved while the CeO2 abrasives are used in the MR fluid. The content of carbonyl iron obviously influences the machining effect of this planarization polishing method based on cluster MR-effect. With the increase of the content of carbonyl iron in the MR fluid, the material removal rate improves and the surface roughness reduces rapidly. However, the difference of abrasive material results in various machining effects. As for the K9 optical glass, the CeO2 abrasive is better polishing abrasive than the SiC abrasive in the planarization polishing technique based on the cluster MR-effect.

A Non-Linear Flow Channel Implementation Method in Magnetic Gap Space of Magneto-Rheological Valve

A non-linear flow channel implementation method in magnetic gap space of magneto-rheological valve is proposed in this paper. The involved magneto-rheological valve in the method has a non-line flow channel which is formed by magnetic gap space between oil inlet disc and oil distribution disc, the concentric annular trapezoidal concave of the surface of the oil inlet disc, the concentric annular trapezoidal convex of the surface of the oil distribution disc, the corresponding convex and concave trapezium between the inlet oil disc and the oil distribution disc, the surface of oil distribution disc and oil inlet disc. The method is beneficial, because the maximum magneto-rheological effect is produced by placing the magneto-rheological fluid in the magnetic field whose intensity is maximum and not more than magneto-rheological fluid saturation intensity, and the magneto-rheological fluid channel length is lengthen in the limited space of the magnetic gap, we can further poly-magnetic by using of separated magnetic sheeting under condition of taking full advantage a limited poly-magnetic cross-section of the magnetic field. The method can significantly enhance the magneto-rheological fluid pressure difference under the same magneto-rheological fluid and flow requirements, size requirements, response time requirements and energy requirements.

Influence of Magnetic Field Strength on Polishing Effect of the Tiny-Grinding Wheel Cluster Based on the Magnetorheological Effect

A new tiny-grinding wheel cluster polishing method based on the Magnetorheological (MR) effect is presented to polish optical glass in this paper and some process experiments were conducted to reveal the influence of magnetic field strength, the content of carbonyl iron in the MR fluid and the speed of polishing disc on the material removal rate and the surface roughness of the glass workpiece. The results indicate that when the external magnetic field is applied, the material removal rate of the workpiece improves rapidly but the surface roughness increases slightly. When the Magnetic field strength is 100 Gs and the content of carbonyl iron is 3.5%, the material removal rate improves by a factor of 16.8% compared with that of the conventional polishing methods with dissociative abrasive particles, while the surface roughness of the workpiece increases unobviously.

Stiffness and Damping in Fe, Co, and Ni Nanowire-Based Magnetorheological Elastomeric Composites

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The stiffness and damping properties of the aligned magnetorheological (MR) elastomer composites filled with 10 wt% Fe, Co, and Ni nanowires were investigated under normalized strain amplitude of 1, 2, and 3%, cyclic deformation frequency of 1 Hz, and magnetic flux density of 0, 0.1, and 0.2 T. The highest values of the dynamic stiffness are observed for the Ni- and the lowest for the Fe-based composites within the whole range of strain amplitude and magnetic flux density. The MR effect on the dynamic stiffness is the most significant for 1% strain amplitude and it almost completely disappears for 3% amplitude for all composites. The equivalent damping coefficient values have maxima for 1% strain amplitude for all composites. These values abruptly drop with an increase of strain amplitude to 2% and only slightly change as strain amplitude is further increased to 3%. The MR effect on the equivalent damping coefficient is high for all composites and strain amplitudes. </para>

The composite MRE embedded with a copper coil

A new composite magnetorheological elastomer (MRE) embedded with a copper coil wasdesigned to induce a magnetic field inside and improve the field-dependent properties of theMRE. The composite MRE can avoid flux leakage, increase the utilization ratioof the magnetic field, and make magnetorheological equipment lightweight. Ashearing stress–strain experiment for the composite MRE was carried out and theresult showed that the composite MRE has a good magnetorheological effect.

Effect of Cyclic Deformation on Magnetorheological Elastomers

Fatigue properties of magnetorheological elastomer (MRE) samples were investigated based on cis-polybutadiene rubber by using a fatigue test machine. Three MRE samples with iron particles mass fraction of 60%, 70%, and 80% were fabricated, and their properties dependence of three strain amplitudes (50%, 75%, and 100%) were measured. The absolute magnetorheological (MR) effect, storage modulus, and loss modulus of MRE samples after fatigue were evaluated by a modified dynamic mechanical analyzer. The results revealed that MR effect, storage modulus, and loss modulus of MREs containing 80% iron particles depended strongly on the strain amplitudes and the number of cycles, while storage modulus and loss modulus of MREs containing 70% iron particles also depended on the strain amplitudes and the number of cycles but not as strongly as sample which contains 80% iron particles, but the properties of MREs containing 60% iron particles after cyclic deformation were almost independent of the fatigued conditions. In order to investigate the fatigue mechanism of MREs, the sample was carried out with a quasi-static tensile testing and its surface morphology during testing was observed in situ by scanning electron microscopy.

A study of the magnetorheological effect of bimodal particle based magnetorheologicalelastomers

This paper presents theoretical and experimental studies of the mechanical performanceand magnetorheological effects of magnetorheological elastomers (MREs) fabricated withmixtures of large and small particles. First of all, an effective permeability model wasdeveloped to theoretically analyze the MR effect of bimodal particle based MR elastomers.From the theoretical analysis, an optimum volume fraction was derived which resulted inenhanced MR effects. Two categories of iron products with different particle sizes of 50 and 5 µm were used to fabricate a series of bimodal MRE samples. Their mechanical performanceswere characterized by using an MR rheometer. Experimental results agreed fairly well withtheoretical analysis. The theoretical prediction of the optimum mixture ratio between largeand small size particles was experimentally verified.

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.

Influence of polyurethane properties on mechanical performances of magnetorheological elastomers

AbstractMagnetorheological elastomers (MREs) are mainly composed of magnetizable particles and elastic polymer. The polymer matrix plays an important role in mechanical performances of MREs. In this study, the polyurethane (PU), which is synthesized by using toluene diisocyanate (TDI) and poly (propylene glycol) (PPG‐220), is selected as a matrix because it has better degradation stability than natural rubber and higher mechanical stability than silicone rubber. Four different MRE samples were fabricated by adjusting the reaction molar ratio of TDI to PPG to change the property of PU matrix. Structural characterization of the PU matrix was described by Fourier transform infrared analysis. The microstructures of samples were observed by using an environmental scanning electron microscope. The mechanical performances of samples, including shear modulus, magnetorheological effect (MR) effect, loss factor, and glass transition temperature (Tg), were characterized with dynamic mechanical analyzer. The results show that the shear modulus, the relative magnetic residual shear modulus and glass transition temperatures of samples increase with the increment of toluene diisocyanate, while the relative MR effects and loss factors decrease steadily. The experimental results indicate that optimal molar ratio (TDI : PPG) is 3 : 1. The field‐induced shear modulus of sample with molar ratio 3 : 1 is 4.9 MPa, and the relative MR effect is 121% under an external magnetic field of 800 mT at room temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

A simple route to synthesize ZnFe2O4 hollow spheres and their magnetorheological characteristics

In this paper, a simple route to synthesize hollow spheres ofZnFe2O4 without the assistance of a template is reported. The crystal structure and morphology ofthese particles were characterized by x-ray diffraction (XRD), transmission electronmicroscopy (TEM), and field emission scanning electron microscopy (FE-SEM). It wasfound that the final products were hollow spheres with perfect morphology, andtheir size and the thickness of their shells decreased with the increase of ureaprecursor. Ferromagnetism was observed from the magnetic hysteresis loops of theZnFe2O4 hollowspheres at room temperature. The possible formation mechanism of the hollow spheres is discussed. Inaddition, ZnFe2O4 magnetorheological (MR) fluids were prepared and then their MR effect was investigatedon a rotational rheometer equipped with a magnetic field generator.

Radiation Vulcanization of Magnetorheological Elastomers Based on Silicone Rubber

The fabrication of magnetorheological (MR) elastomers was studied by two vulcanization methods, including heat vulcanization (HV) and radiation vulcanization (RV), were employed to fabricate MRE samples. The dynamical mechanical properties were characterized by using a dynamic mechanic analyzer. In particular, both the MR effect and its durability were investigated. The experimental results showed that RV samples have large magneto-induced modulus, large zero-field modulus, and good durability property of MR effect. To explain these results, cubic deformation and plasticizer migration were analyzed. Large magneto-induced modulus of RV sample results from cubic deformation during vulcanization process. And the plasticizer migration results in better durability of MR effect.

Preparation and characterization of isotropic polyurethane magnetorheological elastomer through in situ polymerization

AbstractThe highly filled isotropic polyurethane (PU) elastomer with a magnetorheological (MR) effect was prepared through an in situ polycondensation method. The carbonyl iron particles were treated by coupling agents and then the dispersions of polyol/carbonyl iron particles was prepared by a ball milling process. The dispersion problem of magnetizable particles at a high content in PU matrix was tried to overcome by the combination of surface modification, ball milling, and in situ polymerization. The microstructure and properties of the composite were examined in detail. With increasing the content of carbonyl iron particles, the degree of phase separation of PU increased and the glass transition temperature (Tg) of PU soft segment decreased. Highly filled carbonyl iron particles led to the decrease in the thermal stability of PU matrix, especially in the heating air atmosphere. The MR effect appeared when the content of carbonyl iron particles was higher than 50 wt %, and became relatively pronounced at a 70 wt % of carbonyl iron content. The mechanical properties of PU MR elastomers were deteriorated significantly at a high content of carbonyl iron. Surface modification of carbonyl iron particles can improve the mechanical properties to some extent; however, it was also found that surface modification led to a decrease in the MR effect because of the improved interfacial adhesion. The MR test showed that the maximum absolute MR effect and relative MR effect of PU composite were ∼ 0.31 MPa and ∼ 8.1% at 1 Hz and 400 mT with 70 wt % of carbonyl iron, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Influence of Abrasive on Planarization Polishing with the Tiny-Grinding Wheel Cluster Based on the Magnetorheological Effect

Experiments were conducted to polish optical glass with the magnetorheological (MR) effect-based tiny-grinding wheel cluster, and the influences of abrasive material, particle size and content on the material removal rate and surface roughness are investigated. The experimental results indicate that: the higher the hardness of abrasives, the higher the material removal rate, but the abrasives with lower hardness can obtain lower surface roughness. The better polishing quality of the workpiece can be obtained when the particle size of abrasives is similar to the particle size of magnetic particles. Moreover, the content of abrasives has an optimum value, and the material removal rate and the surface quality can not be improved further when the content of abrasives exceeds the optimum value. On the basis of above, the material removal model of the new planarization polishing technique is presented.

Effect of polar interactions on the magnetorheology of silica-coated magnetite suspensions in oil media

This work deals with the role of nonmagnetic interactions on the magnetorheological (MR) response of suspensions of magnetic particles in nonaqueous carriers (MR fluids). Although electrostatic interactions between particles are negligible, van der Waals and, eventually, polar forces might be present. Nevertheless, they are typically neglected when compared to magnetic or hydrodynamic ones. In order to perform a comparative evaluation of the contributions of these interactions, we carried out an MR investigation on two samples of silica-coated magnetite: one (MagSilica 50-H8) is hydrophobic and the other (MagSilica 50-85) is hydrophilic. We describe a careful surface thermodynamic characterization of the two kinds of silicas, confirming their very different hydrophobicities. MR measurements show that only the suspensions of 50-85 particles change from Newtonian to pseudoplastic when a magnetic field is applied, with a yield stress increasing with field strength H, and saturating when H ≅ 100 kA/m. The experimental values of yield stress are compared to theoretical predictions based on the chain model, and it is found that the theory overestimates the experimental values. It is suggested that the nonnegligible interfacial interactions are responsible for both the absence of MR effect in 50-H8 samples and the low yield stress in 50-85 suspensions.