Magnetorheological Grease Research Articles

High dynamic range and high dispersion stability of a magnetorheological grease damper for semi-active vibration suppression

In this study, the dynamic range and dispersion stability of a shear-type magnetorheological (MR) grease damper were experimentally investigated as important characteristics affecting the performance of semi-active vibration suppression. Furthermore, the damper was applied to the semi-active vibration suppression of a small single-degree-of-freedom model structure subjected to seismic excitation. The performance test results of the damper indicated that it has a dynamic range of 157 times, which is much higher than that of conventional MR dampers. Also, because of the high dispersion stability of MR grease, the results showed that its performance can be kept for 9 days longer in comparison with a similar damper using MR fluid. Moreover, the structural vibration suppression test results demonstrated that the damper can suppress vibration response over a wide frequency range by applying skyhook-based control, which can take full advantage of the damper’s high dynamic range.

Thermorheological properties of magnetorheological grease and its thermomagnetic coupling mechanism

A heating phenomenon exists in the service process of magneto-rheological devices. For magnetorheological devices using magnetorheological grease (MRG) as the working medium, changes in the medium’s rheological behaviors caused by temperature increase will generate challenges in the reliable service of the devices. With laboratory-prepared MRG as the research object, MRG rheological property laws under different temperatures and magnetic field intensities are investigated, and the magnetic properties of carbonyl iron (CI) powder under different temperatures are analyzed. The relationship between the evolution of the MRG structural system and changes in rheological properties under the action of thermomagnetic coupling is discussed. The results show that the MRG structural system is composed of base carrier liquid soap fibers and magnetic chains under the action of a magnetic field, and the soap fibers can strengthen the structural intensity of the MRG. A decrease in the entanglement degree of the soap fiber structure caused by temperature increase will obviously weaken the intensity of the entire MRG system and narrow the regulation and control scope of the MRG rheological properties. The structural evolution of soap fibers under thermomagnetic coupling will affect the chain formation of magnetic particles and ultimately their rheological properties. At low temperature and magnetic field intensity, the entanglement degree of soap fibers is relatively high, and the magnetic force on magnetic particles is weak, which cannot completely overcome the binding of soap fibers. The influence of soap fibers is the dominant factor affecting the MRG rheological properties. As temperature and magnetic field intensity increase, the entanglement degree of soap fibers decreases, magnetic particles gradually disperse from the soap fibers under the action of a large magnetic field force, and the magnetic chain structure gradually becomes the dominant factor affecting the MRG rheological properties. Moreover, the weakening degree of the temperature increase effect on the MRG rheological properties decreases, and the rheological law changes gradually.

Field–Frequency-Dependent Non-linear Rheological Behavior of Magnetorheological Grease Under Large Amplitude Oscillatory Shear

This article investigates the influence of frequency on the field-dependent non-linear rheology of magnetorheological (MR) grease under large amplitude oscillatory shear (LAOS). First, the LAOS tests with different driving frequencies were conducted on MR grease at four magnetic fields, and the storage and loss moduli under the frequency of 0.1, 0.5, 1, and 5 Hz were compared to obtain an overall understanding of the frequency-dependent viscoelastic behavior of MR grease. Based on this, the three-dimensional (3D) Lissajous curves and decomposed stress curves under two typical frequencies were depicted to provide the non-linear elastic and viscous behavior. Finally, the elastic and viscous measures containing higher harmonics from Fourier transform (FT)-Chebyshev analysis were used to quantitatively interpret the influence of the frequency on the non-linear rheology of MR grease, namely, strain stiffening (softening) and shear thickening (thinning), under LAOS with different magnetic fields. It was found that, under the application of the magnetic field, the onset of the non-linear behavior of MR grease was frequency-dependent. However, when the shear strain amplitude increased in the post-yield region, the non-linear rheology of MRG-70 was not affected by the oscillatory frequency.

Analysis of magnetorheological grease normal force characteristics in static and dynamic shear modes

In this paper, the normal stress behavior of magnetorheological grease (MRG) in a quiescent state and its dynamic shear modes were systematically studied. Three types of magnetorheological greases were prepared, MRG-30, MRG-50, and MRG-70 with 30%, 50%, and 70% carbonyl iron(CI) powder mass, respectively. Furthermore, static and dynamic shear tests were carried out using a rheometer, the effects of time, magnetic field strength, shear rate and temperature on normal stress were studied and analyzed under both static and dynamic conditions. In the static mode, the research results show that the normal force is related to the magnetic field strength and the content of magnetic particles in the MR grease, but has nothing to do with historical time. the static normal stress generates the evident fluctuation with changing the temperature when magnetic field strengths of 96 kA m−1 and 194 kA m−1. The fluctuation is very small when the magnetic field strengths are 0kA m−1, 391 kA m−1 and 740kA m−1. Similar to the static normal stress, the dynamic normal stress at the degaussing is greater than the normal stress during magnetic field loading. The dynamic normal stress are almost invariant with prolonging the time below 100 s−1 shear rate under the medium magnetic field strength of 194 kA m−1 whereas the stress is increased at the shear rate of 100 s−1. Besides, the dynamic normal stress is basically independent from the time above the shear rate 0f 1 s-1 at the high magnetic field of 740 kA m−1. Under other conditions, the normal force basically presents a stable value. At the absence of the magnetic field, there are quietly weak effects of temperature on the static and dynamic normal stress. Finally, when a magnetic field strength higher than 96 kA m−1 is applied to the material, the value of dynamic normal stress increases with temperature.

Incorporation of cobalt ferrite on the field dependent performances of magnetorheological grease

Magnetorheological grease (MRG) is one of the smart materials that experiences a high off-state viscosity, which hassles the operation of devices at the beginning and causes more energy consumption upon operation. Therefore, this paper investigates the off-state viscosity of MR lithium-based grease with various percentages of cobalt ferrite (CoFe2O4), as these particles are believed to potentially enhance the field-dependent stress of MRG by reducing the off-state viscosity and increasing mobility of the magnetic particles as the magnetic field applied. The MRG with various concentrations of CoFe2O4 at a ratio of 1–5 wt.% were investigated via Field-Emission Scanning Electron Microscopy (FESEM) and Vibrating Sample Magnetometer (VSM) to analyze their morphology and magnetic properties, respectively. The rheological test of MRG samples in terms of viscosity, shear stress and yield stress were investigated upon shear rate, using rheometer. The results demonstrated that with the incorporation of 5wt.% CoFe2O4 particles, the initial off-state viscosity was reduced by 86% as compared to the pure MRG. The presence of CoFe2O4 particles triggered more chaotic motion thus restricted the formation of agglomeration of particles during shearing process. Meanwhile, the initial viscosity of MRG increased as a 0.64 T of magnetic field was applied along with the increased of CoFe2O4 particles. In fact, there was an enhancement of shear stress and yield stress on the CoFe2O4 incorporated MRG samples as compared with pure MRG. This study underlined the influence of CoFe2O4 particles, which could reduce the initial viscosity of MRG and improve the rheological properties upon the application of magnetic field.

Characterization of nonlinear viscoelasticity of magnetorheological grease under large oscillatory shear by using Fourier transform-Chebyshev analysis

Magnetorheological (MR) grease, which is a type of magneto-sensitive smart material, exhibits complex viscoelastic behavior under different magnetic fields. Storage and loss moduli from oscillatory test are commonly used to characterize such field-dependent viscoelastic behavior. However, they are not able to represent the higher harmonic nonlinearity appeared in oscillatory responses under large amplitude oscillatory (LAOS) shear. In this paper, an investigation is conducted on the characterization of the filed-dependent nonlinearity of MR grease under LAOS by utilizing of Fourier transform (FT)-Chebyshev analysis. To capture the higher harmonic nonlinearity for the modeling and analysis, a comprehensive test program has been conducted. Firstly, MR grease with 70% weight percentage of carbonyl iron particles (MRG-70) is prepared and the stress response of MRG-70 under the oscillatory shear from small to large strain amplitudes with different magnetic field are measured. Then the higher harmonics in stress response signal are used to detect the intercycle nonlinearity of MRG-70 and compare with the traditional analysis method of dynamic modulus. Further, the elastic and viscous measures from FT-Chebyshev analysis are obtained to capture the inter-/intracycle nonlinear behaviors, that is, strain stiffening/softening, shear thickening/thinning, of MRG-70 under LAOS. It is found that, in the presence of magnetic fields, the onset of the intercycle nonlinearities of MRG-70 is originated from shear thickening of MR grease. With the further increase of the shear strain, MRG-70 exhibits the nonlinearities with different combinations of strain stiffening/softening and shear thickening/thinning.

Yield dimensionless magnetic effect and shear thinning for magnetorheological grease

The effects of silicone oil viscosity (SOV), carbonyl iron particles (CIPs) weight fraction and size on the yield dimensionless magnetic effect (DME) and shear-thinning behavior for magnetorheological (MR) grease were experimentally investigated in this study. Nine MR greases were prepared using Taguchi L9 orthogonal array based on an unconventional synthesis technique. The yield DME, namely the controllability of magnetic effect relative to viscous effect under the on-state magnetic fields and zero shear rate, was observed to be closely related to CIPs fraction based upon significance assessment and percent contribution (PC) comparison, whereas the shear-thinning behavior of suspension was dependent on the CIPs fraction and SOV. According to the analysis of discrepancy direction at the presence of magnetic fields, there was a negative linear correlation between yield DME and CIPs fraction, but the shear thinning had positive linear correlation with the CIPs fraction and SOV. Furthermore, the PC and the corresponding actual contribution values (ACV) of SOV and CIPs fraction towards the shear thinning showed distinct characteristics which were relevant to the critical magnetic fields. This study presented a hypothesis in which the difference of relative evolution rate between fiber structures and magnetic constructions under shearing and different magnetic fields caused the differences of PC and ACV of SOV and CIPs fraction to suspensions-viscosity attenuation.

Design and development of a wedge shaped magnetorheological clutch

This paper presents a novel drum magnetorheological clutch design having a wedge shaped boundary. The converging film formed due to the direction of motion of the magnetorheological clutch and the inclination of the wedge planes helps to produce the pressure generating mechanism in the magnetorheological grease film. The resistance force developed due to this mechanism in the proposed case exceeds that of the conventional drum clutch. The proposed wedge shaped drum magnetorheological clutch consists of bimetallic discs made up of aluminium and mild steel. Mild steel disc has a certain number of inclined sliders shaped like a wedge at its boundary, which is immersed in the magnetorheological grease. The yield stress of the magnetorheological grease varies as a function of the magnetic field created by electric current passing through the electromagnet. Bingham model has been employed in the present study to analyse theoretically the torque generated by wedge-shaped drum magnetorheological clutch. The proposed magnetorheological drum clutch with wedge shaped boundary and conventional drum clutch have been designed and fabricated with similar material parameters and magnetic circuits. The experiment has been performed for the different current values (0 A, 0.25 A and 0.52 A). Torque results are plotted and compared for both cases. Experimental results suggest that the proposed wedge shaped drum magnetorheological clutch produces more torque than the conventional drum magnetorheological clutch, and thus it has better performance.

Quasi-Static Rheological Properties of Lithium-Based Magnetorheological Grease under Large Deformation.

This paper investigates the quasi-static rheological properties of lithium-based magnetorheological (MR) grease under large deformation. Three types of lithium-based MR grease comprising different mass ratios of carbonyl iron (CI) particles and lithium-based grease were prepared. The dependence of the magneto-induced stress–strain curves for MR grease on CI particles content, shear rate, and shear deformation under quasi-static monotonic shear conditions were tested and discussed. The results demonstrate that the shear rate dependence of the maximum yield stress is significantly weakened by the magnetic field, and this weakening is further enhanced as the CI particles content of MR grease increases. In addition, to evaluate and characterize the behavior of the cyclic shear–stress curves of MR grease under quasi-static condition, cyclic shear tests under different controlled conditions, i.e., CI particles content, shear rate, shear strain amplitude, and magnetic field strength, were conduct and analyzed. The magneto-induced shear stress of MR grease with higher CI particles content shows a sharp decrease during the transition from loading to unloading. Moreover, the experiment results also show that the damping characteristics of MR grease are highly correlated with CI particles content, shear strain, and magnetic field strength.

Effects of Silicone Oil Viscosity and Carbonyl Iron Particle Weight Fraction and Size on Yield Stress for Magnetorheological Grease Based on a New Preparation Technique.

This paper investigated the effects of silicone oil viscosity (SOV) and carbonyl iron particle (CIP) weight fraction and size on dynamic yield stress for magnetorheological (MR) grease. The MR grease samples were prepared using orthogonal array L9 on the basis of a new preparation technology. The shear rheological tests were undertaken using a rotational shear rheometer and yield stress was obtained based on the Bingham fluid model. It was found that CIP fractions ranging from 65 wt% to 75 wt% and SOV varying from 50 m2·s−1 to 1000 m2·s−1 significantly affect the magnetic field-dependent yield stress of MR grease, but the CIPs with sizes of 3.2–3.9 μm hardly had any influence based on the analysis of variance (ANOVA). In addition, the yield stress of MR grease mainly depended on the CIP fraction and SOV by comparing their percent contribution (PC). It was further confirmed that there were positive effects of CIP fraction and SOV on yield stress through response surface analysis (RSA). The results showed a high dynamic yield stress. It indicated that MR grease is an intelligent material candidate which can be applied to many different areas requiring high field-induced rheological capabilities without flow for suspension. Moreover, based upon the multivariate regression equation, a constitutive model was developed to express the function of the yield stress as the SOV and fraction of CIPs under the application of magnetic fields.

Prediction of field-dependent rheological properties of magnetorheological grease using extreme learning machine method

Magnetorheological grease is seen as a promising material for replacing the magnetorheological fluid owing to its higher stability and the lesser production of leakage. As such, it is important tha...

The Effect of Particle Shapes on the Field-Dependent Rheological Properties of Magnetorheological Greases.

The transient response of magnetorheological (MR) materials, in general, is very important for design consideration in MR-based devices. Better response to magnetic fields is beneficial for a better response rate to the electrical current applied in the electromagnetic coil. As a result, MR-based devices would have a high response to external stimuli. In this work, the principal characteristics of magnetorheological greases (MRGs) which have two different particle shapes are experimentally investigated. One type of particle distributed in the grease medium is conventional spherical-shaped carbonyl iron (CI) particles, while the other is plate-like CI particles made using a high-energy rotary ball mill from spherical CI particles. A set of bidisperse MRG samples are firstly prepared by adjusting the weight percentage of the plate-like CI particles and mixing with the spherical CI particles. Subsequently, three important properties of MRGs in terms of their practical application are measured and compared between the two different particle shapes. The field-dependent apparent viscoelastic properties of the prepared MRG samples are measured, followed by the field-dependent storage and loss moduli using an oscillatory shear rheometer. In addition, the transient response time, which indicates the speed in the actuating period of MRGs, is measured by changing the strain amplitude. Then, a comparative assessment on the three properties are undertaken between two different particle shapes by presenting the corresponding results in the same plot. It is shown that the bidisperse MRG with plate-like CI particles exhibits an increase in the initial apparent viscosity as well as stiffness property compared to the MRG with spherical particles only.

The field-dependent viscoelastic and transient responses of plate-like carbonyl iron particle based magnetorheological greases

The field-dependent viscoelastic and transient behaviours of plate-like-carbonyl-iron-particle-based magnetorheological greases are experimentally investigated in this study. The plate-like carbonyl-iron particles are made from spherical carbonyl-iron particles through a milling process using a rotary ball mill. Several samples of magnetorheological greases consisting of different weight percentages of plate-like carbonyl-iron particles are prepared. The surface microstructures and distributions of the plate-like carbonyl-iron particles in the grease are observed using various types of microscopic investigations. Subsequently, the viscoelastic and transient (dynamic) rheological properties of the plate-like carbonyl-iron particles are investigated using a commercial rheometer. The spherical carbonyl-iron particles are transformed into the flattened plate-like carbonyl-iron particles with a larger surface diameter. It is shown that the viscoelastic properties such as storage modulus and response time of the plate-like carbonyl-iron particles significantly depend on the shape and particle weight fraction. The findings reveal that the shape of the carbonyl-iron particles has a significant effect on the field-dependent behaviours. Thus, the results presented in this work provide very useful scientific contributions for devising appropriate applications utilizing the plate-like-carbonyl-iron-particle-based magnetorheological greases.

Effect of temperature on rheological properties of lithium-based magnetorheological grease

This paper investigates the impact of temperature on the rheological properties of magnetorheological (MR) grease containing carbonyl iron suspended in lithium-based grease Lithium-based MR grease with 70% weight fraction of carbonyl iron is firstly prepared by mechanical mixing. The apparent viscosity and shear stress as a function of shear rate under different temperatures and magnetic field strengths are measured and discussed. It is found that the influence of temperature on apparent viscosity reduces with the increase of magnetic field strength. The dynamic properties of MR grease are obtained under oscillatory shear test. The influences of strain amplitude, driving frequency and magnetic field on the dynamic properties of MR grease at different temperature are discussed. The results demonstrate that the enhancement of temperature leads to the increase of storage modulus and the reduction of the loss factor. Microstructural variation of grease matrix at different temperature is proposed as an explanation of the rheological changes of MR grease.

Normal force of lithium-based magnetorheological grease under quasi-static shear with large deformation.

An experimental study was conducted to explore the normal force of lithium-based magnetorheological (MR) grease under quasi-static shear. Firstly, MR grease with various carbonyl iron (CI) particles content was prepared. Then the influence of magnetic field strength, CI particles content, shear rate and temperature on the normal force–strain curves for MR grease under a quasi-static monotonic shear condition were investigated. The results exhibit that the normal force of MR grease under quasi-static monotonic shear decreases first and then maintains constant along with the increase of shear strain, and the critical strain is affected by the magnetic field strength and CI particles content. Finally, the normal force versus shear strain curves under different magnetic fields and shear strains were obtained by using quasi-static cyclic shear. It was found that the normal force of MRG-70 under quasi-static monotonic shear exhibits peak phenomenon at the beginning of the unloading stage, and the peak value increases with the enlargement of shear strain. Furthermore, when the strain amplitude is higher than 40%, normal force exhibits an abrupt change during the transition from the loading stage to the unloading stage.

Feasibility study of a miniaturized magnetorhological grease timing trigger as safety and arming device for spinning projectile

A safety and arming (S&A) device keeps the fuze of a projectile unarmed during shipping, handling and storage, while arming the firing section at a proper time by sensing external conditions such as pressure, position, etc. With the increasing need for smaller S&A devices, a miniature design with a compact configuration and high reliability is in demand. This paper proposes a miniaturized timing trigger as the S&A device for a spinning projectile by utilizing the ‘locking’ and ‘unlocking’ properties of magnetorheological (MR) grease with/without the presence of a magnetic field. First, the design and arming mechanism of the timing trigger are introduced, in which the MR grease is locked by a magnetic field generated by two permanent magnets (PMs). Under sufficient firing acceleration, the PMs disengage to unlock the contraction flow of the MR grease, which enables its triggering function. A theoretical analysis was conducted to interpolate the delay time against the geometry of the device, the shear/extensional characteristics of MR grease and the spinning rate of a projectile. A series of tests have been conducted to measure the delay times by tuning the physical parameters, including particle concentration, spinning rate and orifice diameter etc. The experimental results showed that this theoretical model is capable of calculating well the delay time of a MR grease timing trigger.

A Model of Magnetorheological Grease using Machine Learning Method

Magnetorheological (MR) grease is a promising material to replace MR fluid because the advantage in term of stability and less possibility to leaking. To improve the material properties, an accurate model can be critical for reducing the time and cost of the development process. A model has been developed to predict MR fluid material properties by including the composition. However, the model may need adjustment and cannot predict other essential rheology parameters, such as viscosity, apparent viscosity, shear rate, and shear stress. Therefore, the technical novelty of this paper is to propose a model with composition as one of the inputs using extreme learning machine method. A scoring system is also introduced to quantify the significance of the composition effect toward the MR grease performance. Then, the model is simulated and compared with experimental data. The performance shows high accuracy estimation with normalized root mean square error about 1.25%.

Investigation of the relationship among the microstructure, rheological properties of MR grease and the speed reduction performance of a rotary micro-brake

Abstract A magnetorheological (MR) grease-based micro-brake is proposed for providing a damping torque for a miniature turbine generator when working at high wind speeds. MR greases with a magnetic particle volume fraction from 10% to 90% are prepared for the MR grease-based micro-brake. Flow curves show that the shear thinning behaviour of MR grease is enhanced by the increased volume fraction. The zero magnetic rheological behaviour of MR grease is studied with a Herschel-Bulkley model. Then, the speed reduction effect of the MR grease-based micro-brake is experimentally studied. A rotational speed difference Δn as high as 6750 r/min is achieved by applying a current of 1.01 A to the micro-brake. MR grease with lower volume fraction demonstrates a more significant speed reduction effect under low applied currents, since the chain forming behaviour is enhanced by the decreased volume fraction. Finally, a comprehensive model for the MR grease-based micro-brake is developed to reveal the relationship among the microstructure, rheological properties of the MR grease and the speed reduction performance of the MR grease-based micro-brake.

Rheological properties of plate-like shape carbonyl iron particles compositions based magnetorheological grease in oscillatory mode

This paper investigates dynamic viscoelastic properties of magnetorheological (MR) grease with different fractions of plate-like Carbonyl Iron (CI) particles (MRGP). The plate-like CI particles were prepared through milling process. Subsequently, three types of MRGP was developed by dispersing 30 to 70 wt% of plate-like CI particles into grease using mechanical stirrer. The rheological test was performed using oscillatory shear rheometer under flux density influence of 0 to 0.7T and strain amplitude ranging from 0.001 to 10% at constant temperature of 25°C. The experimental results show that the storage and loss moduli of the MRGP is dependent on the fractions of the plate-like CI particles. The enhancement in the MR effect in the plate-like CI particles based MR grease is observed due to the anisotropy shape which leads to the strong inter-particle configuration and chain formations.

Improvement of magnetorheological greases with superparamagnetic nanoparticles

Magnetorheological greases (MRGs) is a viscoelastic suspension comprised of carbonyl iron (CI) particles in a thixotropic medium; grease, which able to solve the instability problem that occurs in oil medium like MRFs. The primary purpose introduction of superparamagnetic nanoparticles γ-Fe2O3 in MRGs suspension is to investigate the effect of additives toward MRGs characteristics. Two types of MRGs suspension with and without nanoparticles γ-Fe2O3 were prepared in the same CI particles concentration for comparison purpose. It was observed that MRGs with incorporated of 1 wt% nanoparticles γ-Fe2O3 showed an increment regarding magnetic properties. In the meantime, the off-state viscosity of MRGs containing nanoparticles γ-Fe2O3 was reduced, however, increased during on-state condition. This fact indicates that the interspaces between CI particles are filled by the nanoparticles γ-Fe2O3. Therefore, the introduction of the nanoparticles indirectly improved the MRGs properties.