Magnetorheological Characteristics Research Articles

Synthesis of rGO/CoFe2O4 Composite and Its Magnetorheological Characteristics.

In this study, composite particles of rGO/CoFe2O4 were synthesized using a solvothermal method to fabricate a low-density magnetorheological (MR) material with enhanced sedimentation stability. The morphology and crystallographic features of rGO/CoFe2O4 were characterized via SEM, TEM, and XRD, and its magnetic properties were tested using VSM. The MR fluid was formulated by blending rGO/CoFe2O4 particles into silicone oil. Under different magnet strengths (H), a rotational rheometer was used to test its MR properties. Typical MR properties were observed, including shear stress, viscosity, storage/loss modulus, and dynamic yield stress (τdy) following the Herschel-Bulkley model reaching 200 Pa when H is 342 kA/m. Furthermore, the yield stress of the MR fluid follows a power law relation as H increases and the index changes from 2.0 (in the low H region) to 1.5 (in the high H region). Finally, its MR efficiency was calculated to be about 104% at H of 342 kA/m.

Magnetorheological fluids: A comprehensive review

The magnetorheological (MR) fluids contain magnetic micro-sized iron particles, non-magnetic-based fluid, and some additives in order to mitigate sedimentation and agglomeration. The various carrier fluids used in the preparation of MR fluids are mineral oil, silicon oil, castor oil, soybean oil, kerosene, synthetic oils, honge oil, organic oil, water-based oils, etc. However, for obtaining better vibration control, silicone oil is the most preferred one due to its higher viscosity index, lower friction characteristics, higher flash point, and higher shear strength. The MR fluids have various application areas such as dampers, prosthetic knees, valves, brakes, clutches, finishing processes etc. The dampers containing MR fluids are used in automobile cushioning for enhancing passenger comfort and MR suspensions significantly improve steering stability in vehicles. In case of MR brakes, the braking torque on the rotating disks is controlled using the generated shear stress. The carbonyl iron (CI) particles exhibit better rheological characteristics as compared to electrolytic iron (EI) particles. The use of MR fluids produces stable and natural limb movement in orthoses, lower limb prostheses, and exoskeletons. The MR fluids also prove to be very significant in polishing applications. There are various issues with preparation methods and difficulties in the storage of MR fluids. The problems encountered in the synthesis of MR fluids include sedimentation, agglomeration, in-use thickening, corrosion, erosion, etc. The impact of particle proportion, particle shapes, and size has been influential in evaluating MR characteristics. The viscosity and shear stress of MR fluid have been mitigated at higher values of temperature and even CI particles get oxidized at higher temperatures. The CI particles as compared to EI particles are the majority favourable particles used for dispersing state within the MR fluids due to their higher value of saturation magnetization, more availability, and lesser cost. The small-sized particles led to lower wettability, whereas larger-sized particles accounted for an increased sedimentation rate. The currently available MR fluids cost is still on the higher side and the preparation of economical MR fluid is still a big challenge for the researchers. The MR fluids storage is also a big concern. The future scope of MR fluid may be in heavy industries such as nuclear, shipbuilding, oil and gas, space and aviation, etc. to achieve the desired damping response.

Magnetorheological study of core−shell structured carbonyl iron/2-D graphene oxide microparticles suspensions with improved sedimentation stability

This study aims to assess the rheological and stabilization characteristics of magnetorheological (MR) suspension by dispersing core–shell particles (graphene oxide (GO) as a shell and carbonyl iron (CI) as a core). A simple wet stirring technique was utilized to achieve the grafting of bare carbonyl particles (CIPs) with para-aminobenzoic acid (g-CIPs), and graphene oxide with concentrations of 1 and 2 wt%. The morphological, magnetization and elemental characteristics of prepared core–shell particles were analyzed by Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), powder X-Ray diffraction (XRD), Raman Spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). The encapsulation of grafted carbonyl iron particles with graphene oxide enhanced the surface roughness, while the structure of carbonyl iron particles retained its spherical shape. The presence of core–shell particles increased the affinity between the suspended particles and carrier oil, leading to better stability against sedimentation. The stability of prepared MR suspensions was examined by the visualization technique in which graphene oxide encapsulated carbonyl iron particles (GO@g-CIPs) showed remarkable improvement in sedimentation stability. The MR suspension is based on 1 wt% graphene oxide coated carbonyl iron particles (GO@g-CIPs-1) exhibits a sedimentation ratio of 44%, which is higher than that of the MR suspension based on 2 wt% graphene oxide coated carbonyl iron particles (GO@g-CIPs-2) (32%) and the MR suspension containing bare CIPs (20%). Finally, the magnetorheological study was carried out using a rotational rheometer. GO@g-CI based MR suspensions demonstrated a promising magnetorheological performance and identical MR characteristics, with varying yield stress.

Characterization of Magnetorheological Brake in Shear Mode Using High-Strength MWCNTs and Fumed Silica-Based Magnetorheological Fluids at Low Magnetic Fields

Abstract The performance of magnetorheological (MR) brakes is dependent on the MR characteristics of the braking fluid, working parameters, and magnetic fields. Due to the size limitations, it is quite difficult to use large-sized electromagnet for a high magnetic field inside an MR brake and thus working parameters indirectly affect the MR properties of MR fluid. Again, MR fluids show thermal thinning with working temperature. Therefore, in the present study, MR fluids that have stable MR properties at high temperatures and can provide better braking torque at low magnetic fields are prepared. To improve the MR properties at high temperature, multi-walled carbon nanotubes (MWCNTs) which have high thermal conductivity are used as additives, and initially, three MR fluids are synthesized by varying MWCNT fractions. The MR properties of these fluids are examined and plotted using magnetorheometer. The effective fraction of MWCNTs at which MR fluid has stable MR properties with temperature is identified. It is found that MR fluid which consists of 0.25% fractions of MWCNTs has large yield strength but only at high magnetic fields. To improve its MR properties at a lower magnetic field, 0.5% fraction of fumed silica is mixed with 0.25% fractions of MWCNTs. Then, a fabricated MR disc brake is characterized using those prepared magnetorheological fluids (MRFs). The braking torque of MRFs at different speeds is presented and compared. It is found that approximately 26% more braking torque is offered by fumed silica + MWCNTs-based MR fluid in comparison to other MRFs at 1200 RPM.

Tunable rheological behaviour of magnetized complex plasma

The shear viscosity (η) of a 3D liquid dusty plasma has been estimated as a function of magnetic field (B) and normalized ion flow velocity (M) from the simulation data using Green–Kubo formalism with the help of Langevin dynamics simulation. It has been shown that in the strongly correlated liquid state, complex plasma may exhibit sharp changes in viscosity with magnetic field and ion drift velocity. In presence of ion drift, an oscillatory and attractive wake potential develops among charged dust particles immersed in a plasma. The amplitude of this wake potential can be modulated by applying an external magnetic field. In this work, we explore how an external magnetic field influences the rheological properties of complex plasma via anisotropic wake potential. It is observed that the rheological property of such plasma depends on the dominant interaction operating among the particles and can be controlled by applying an external magnetic field. A novel regime of magnetic field is observed in which strongly correlated complex plasma liquid exhibits a sharp response to an external magnetic field. Due to this unique property, complex plasma may be used as a platform to study magneto-rheological characteristics of soft matter and there is a possibility of using dusty plasma as a magneto-rheological material in near future.

Fabrication and Magnetorheological Characteristics of Core–Shell-Typed Poly(2-Methylaniline)/Carbonyl Iron Microspheres

Core–shell particles of the poly-2-methylaniline (PMAN)/carbonyl iron (CI) composite material were prepared by dispersion polymerization. Dopamine was used as a chemical grafting agent to modify the surface of CI particles to enhance the affinity between PMAN particles and pure CI particles. The morphology and crystalline structure of the prepared core–shell PMAN/CI microspheres were tested by TEM and X-ray diffraction, respectively. Their magnetic behaviors were analyzed using a vibrating-sample magnetometer. The sedimentation stability of the particles was further analyzed using a Turbiscan analyzer. The analysis results revealed that the dispersion stability of the particles was better than that of the pure CI particles. The characteristics of the PMAN/CI particle-based magnetorheological fluid with a yield stress of 4800 Pa at 342 kA/m were measured using a rheometer.

Numerical Modeling of the Mechanical Characteristics of the Magnetorheological Elastomers

The paper presents the work results associated with the implementation of the developed mathematical model describing the magnetorheological elastomers mechanical characteristics under compressive stress. The employed mathematical instrument constitutes the classic viscoelastic model development, accounting in its structure for the effect of the strain amplitude together with the magnetic field induction on the measured stress values progressive characteristic. The necessity to introduce such changes was demonstrated as a result of earlier studies. Within the this work scope, the structure of the developed numerical model is presented. Further provided are the results of carried out simulations, which are finally juxtaposed and compared with the earlier experiments results. This gives ground to evaluating the proposed model accuracy.

Production, deformation and magnetorheological characteristics of the alginate/chitosan hydrogel magnetic microspheres

To improve dispersion stability and magnetorheological (MR) characteristics of carbonyl iron (CI) particles, we proposed novel hydrogel magnetic microspheres (MPs) dual-coated with alginate (AL) and chitosan (CTS) for the first time. The double-network structures formed by biological crosslinking and chelation reactions are capable to enhance its own structural stability and mechanical properties. The structural characterization, MR properties, and dispersion stability for different MPs were investigated. Additionally, the swelling behaviors were studied by swelling the dried MPs in the deionized water and sodium chloride solution, respectively. The results showed that the AL/CTS hydrogel core/shell MPs displayed the advantages of simple manufacturing, superior MR properties and deformability compared to pure micron-sized CI particles, indicating the improved dispersion stability of the MR fluids compared to that of the pure CI particles-based MR fluids. The introduction of double network structures with natural biopolymers will provide a new thought for the development of MR materials.

Elucidation of the relationship between aggregate structures and magnetorheological properties of a magnetic cubic particle suspension by means of Brownian dynamics simulations

We have developed a Brownian dynamics simulation technique for a cubic magnetic particle suspension in a simple shear flow in order to elucidate the relationship between the particle aggregates and the magnetorheological characteristics. A magnetic field is applied in the direction normal to the shearing plane. In a weak applied magnetic field, if the magnetic particle–particle interaction strength is sufficiently large, the particles aggregate to form closely-packed clusters even when subject to the influence of the shear flow. As the magnetic field strength is increased, the closely-packed aggregate structures are transformed into chain-like structures. The net viscosity is increased because the chain-like clusters give rise to a larger resistance to the flow field. As the magnetic field strength is further increased, the chain-like clusters grow into wall-like clusters aligned in the direction of the magnetic field. If the wall-like clusters are the predominant clusters, a magnetic force arises due to a characteristic of the particle arrangement in the wall-like clusters that tends to accelerate the flow field and, as a consequence, decrease the net viscosity. From these results, it may be suggested that under certain conditions a magnetic cubic particle suspension may exhibit a negative contribution to the magnetorheological characteristic. Highlights of the present study We have developed a Brownian dynamics (BD) simulation technique for a magnetic cubic particle suspension. BD simulations have been performed in order to investigate the relationship between particle aggregates and magnetorheological properties. The net viscosity exhibits a complex dependence on the regime of particle aggregates. It is suggested that under certain conditions a magnetic cubic particle suspension may exhibit a negative contribution to the magnetorheological characteristics. An increase in the shear rate causes instability in the face-to-face configuration and leads to the collapse of closely-packed clusters.

Synthesis of reduced graphene oxide/cobalt ferrite composite particles and their magnetorheological characteristics

The reduced graphene oxide/cobalt ferrite (rGO/Co-Fe) magnetic composite particle was synthesized via a solvothermal process and employed as the magnetorheological (MR) material. The morphology of rGO/Co-Fe was observed by SEM, the chemical structure was confirmed by FT-IR, and the rheological properties of rGO/Co-Fe when suspended in silicone oil were studied by a rotational rheometer under different magnetic field strengths. Along with shear stress curves of rGO/Co-Fe based MR fluid tested in a controlled shear rate mode, their magnetic field strength-dependent yield stresses were observed to fit the universal yield stress function well.

Enhanced magnetorheological characteristics of hollow magnetite nanoparticle-carbonyl iron microsphere suspension

Highly magnetic Fe3O4 nanoparticles with a hollow spherical shape were fabricated via a solvothermal technique and were introduced into soft-magnetic carbonyl iron (CI)-based magnetorheological (MR) fluid to enhance the stability and its MR properties. The structural behaviors and magnetic characteristics of hollow Fe3O4, pure CI, and the hollow Fe3O4/CI mixture were demonstrated by scanning electron microscope, transmission electron microscope, and vibrating sample magnetometry. The MR properties of the systems with and without the hollow Fe3O4 additive were examined by controlled shear rate and oscillatory tests using a rotation-rheometer. The Herschel–Bulkley equation provided an adequate fit for the flow curve, and all of the yield stresses followed the universal scaling equation. The suspension characteristics of the two MR systems were further examined using a Turbiscan device. The CI-based MR fluid with hollow Fe3O4 additive was observed to exhibit higher yield stress as well as improved dispersion than does the pristine CI-based MR fluid, demonstrating that the performance of CI-based MR fluids can be further optimized by using additives.

Novel ring-type measurement system of shear yield stress for magnetorheological fluid under high temperature

In order to investigate the shear yield stress of magnetorheological (MR) fluid at different temperatures, shear gaps, and shear rates, a ring measurement system is designed based on the MR characteristics. The magnetic field and temperature field of the system are simulated and analyzed, which proves that the design of the measurement system is reasonable. On this basis, the measurement system is manufactured and experiments are carried out to verify its performance. The results show that the system can provide a uniform and strong enough magnetic field to make MR effects occur. Meanwhile, the temperature of the shear gap can reach 100 °C in 610 s, and it can increase up to 240 °C when heating continues, which can provide stable measurement conditions at different temperatures, especially at high temperatures. All the results of the experiments show that the measurement system meets the requirements of measuring the shear yield stress of MR fluid. To test the accuracy of the measurement system, repeated experiments are carried out as well. The shear yield stress by the system is almost the same as that provided by the manufacturer, showing excellent measuring precision. The repeatability error of the measurement system is less than 4.02%, indicating that the measurement system is of high accuracy.

Laser-induced fragmentation of carbonyl iron as a clean method to enhance magnetorheological effect

Magnetic nanoparticles (NPs) are widely used as additives in magnetorheological (MR) suspensions to enhance their magnetic performance and kinetic stability. The synthesis of NPs is often resolved via chemical routes or complex manufacturing procedures, which require hazardous chemicals and generate waste products. In this study, a clean, laser-mediated strategy known as laser fragmentation in liquids (LFL) is proposed that enables the synthesis of NP-based additives directly from the given MR suspension, with the added advantage of limiting the production of waste during the fabrication process. The carbonyl iron (CI) microparticles dispersed in ethylene glycol were used as both the MR suspension and precursor agent in the production of the nanoscale additive. The size and crystalline structure of the NPs were investigated via TEM and XRD, respectively. The mixture of the MR suspension and laser-synthesized additive notably facilitated the magnetisation of the CI particles, incrementing the MR characteristics and dynamic yield stress values by up to 31% in a low-to-moderate field region, which are important aspects in various field-controlled robotic, damping and torque systems. The concept presented appears to be an effective and clean alternative for fabricating bidispersed MR suspensions through the nanoscale additive approach.

Nanoparticles Functionalized by Conducting Polymers and Their Electrorheological and Magnetorheological Applications.

Conducting polymer-coated nanoparticles used in electrorheological (ER) and magnetorheological (MR) fluids are reviewed along with their fabrication methods, morphologies, thermal properties, sedimentation stabilities, dielectric properties, and ER and MR characteristics under applied electric or magnetic fields. After functionalization of the conducting polymers, the nanoparticles exhibited properties suitable for use as ER materials, and materials in which magnetic particles are used as a core could also be applied as MR materials. The conducting polymers covered in this study included polyaniline and its derivatives, poly(3,4-ethylenedioxythiophene), poly(3-octylthiophene), polypyrrole, and poly(diphenylamine). The modified nanoparticles included polystyrene, poly(methyl methacrylate), silica, titanium dioxide, maghemite, magnetite, and nanoclay. This article reviews many core-shell structured conducting polymer-coated nanoparticles used in ER and MR fluids and is expected to contribute to the understanding and development of ER and MR materials.

The elucidation of the magnetorheological characteristics of a suspension composed of cubic magnetic particles by means of Brownian dynamics simulations

The elucidation of the magnetorheological characteristics of a suspension composed of cubic magnetic particles by means of Brownian dynamics simulations

Fe–Ga alloy based magnetorheological fluid and its viscoelastic characteristics

Flake-like Galfenol particles were fabricated by a conventional rolling and texture annealing process and adopted as the magnetorheological (MR) particle. The flake morphology and crystalline structure were scrutinized using scanning electron microscope and X-ray diffraction, respectively. The Galfenol particles had a high saturation magnetization value of 174emu/g and a Galfenol particle-based MR suspension exhibited typical MR characteristics under input magnetic field strengths. While its shear stress curves are fitted well using the Bingham model, its storage moduli showed a stable plateau area for whole angular frequencies, suggesting distinguished solid-like behavior of the MR fluid.

Facile Synthesis of Solvent Cast Arabic Gum Coated Carbonyl Iron Microspheres and Their Magnetorheological Characteristics.

Biopolymeric Arabic gum (AG) coated carbonyl iron (CI) particles were synthesized using a solvent casting process, and then their coating was confirmed using scanning electron microscopy analysis. Thermal property and chemical structure of the produced AG coated CI particles were investigated by thermalgravimetric analysis and Fourier transform infrared spectroscopy. In addition, from the measurement using vibration sample magnetometer, magnetic properties including saturation magnetization were also observed. The magnetorheological (MR) fluid was prepared by dispersing CI/AG particles in silicone oil and then its typical MR behaviors of shear stress and shear viscosity were compared to those of the pure CI suspension. Sedimentation stability of the CI/AG based MR suspension was observed to be improved compared to that of the pure CI suspension according to the Turbiscan test.

Magnetorheological characteristics of carbonyl iron microparticles with different shapes

Two different shapes of spherical- and flake-like soft-magnetic carbonyl iron (CI) microparticles were dispersed in silicone oil to prepare magnetorheological (MR) fluids. The magnetic-field dependent rheological behaviors of the MR fluids were scrutinized focusing on their shape effect. Saturation magnetization of the flake-shaped CI was obtained to be slightly lower than that of spherical-shaped CI. However, rheological properties of shear stress, shear viscosity, and storage modulus of the flake-shaped CI MR fluid surpassed those of the spherical-shaped CI MR suspension under applied magnetic field strengths. The flake-shaped CI based MR fluid also demonstrated superior sedimentation stability compared with the spherical-shaped CI. This was due to large surface area, suggesting that the anisotropy of CI particles plays an important role in their MR performance.

Magnetostrictive and viscoelastic characteristics of polyurethane-based magnetorheological elastomer

We fabricated magnetorheological (MR) elastomers using polyurethane and carbonyl iron based MR suspensions. Using dipolar approximation and linear elasticity theory for small deformations, we determined their components of deformations and tensions, showing that their elasticity state depends not only on magnetic field intensity but also on volume fraction. MR characteristics of elastomers’ dynamic properties and creep-recovery values were also measured using a rotational rheometer equipped with a magnetic field supplier. Experimental results from both plane capacitors and viscoelastic tests showed similarities between static and dynamic elasticity states regarding their dependence on magnetic field intensity and volume fraction of magnetizable phase.

Magnetorheology of Core–Shell Structured Mesoporous Fe3O4@mSiO2 Nanoparticles in Carbonyl Iron Dispersion

Core–shell structured magnetic mesoporous Fe3O4@mSiO2 nanoparticles were successfully synthesized using a surfactant-based sol–gel approach and utilized as an additive in a carbonyl iron (CI)-based magnetorheological (MR) fluid to inhibit particle aggregation and to improve the stability and MR characteristics of the dispersion. The magnetic stimuli response of the MR fluids with and without the Fe3O4@mSiO2additive was investigated using the controlled shear rate method, controlled shear stress method, and a dynamic oscillation test using a rotational rheometer. The dispersion characteristics of the MR fluids were measured using a Turbiscan apparatus. Compared to the pure CI-based MR fluid, the CI-based MR fluid with the Fe3O4@mSiO2 additive showed significantly higher yield stresses as well as the enhanced MR characteristics and improved dispersion stability.