Magnetorheological Fluid Samples Research Articles

The study of magnetorheological fluids sedimentation behaviors based on volume fraction of magnetic particles and the mass fraction of surfactants

Magnetorheological fluids (MRFs) is composed of carbonyl iron (CI) powder distributed in carrier fluid. This paper studied the sedimentation behavior of MRFs in a cylindrical column by using direct visual observation (VO). In order to obtain the settlement law of MRFs with respect to particle concentration and surfactant contents, MRF samples with different particles volume fractions (i.e., 4, 10, 20 and 28 vol%) and with different surfactant mass fractions (i.e., none, 2, 4 and 5 wt%) were prepared, separately. And the commercial MRFs with the same magnetic particles volume fraction was used as the control group. In addition, the morphology of bare CI and surface modified CI particles samples were measured, experimentally, by light microscope. At last, three different settling velocity models (Vesilind model, Dick model, and Richardson and Zaki model) were considered to acquire the sedimentation velocity of magnetic particle concentration of MRF samples. Results present Dick model is more suited to the sedimentation rule of MRF sample in our study. The propagation velocity formula of the volumetric concentration of particles was also established on the basis of sedimentation velocity of particles and the particle setting velocity equation with the variational surfactant contents was also obtained.

Capillary breakup extensional magnetorheometry

This work introduces a novel design of a fixture to be adapted to the commercial version of the capillary breakup extensional rheometer (CaBER), here termed as an extensional magneto-rheological fixture (ExMRFx), that allows the characterization of magnetic fluids under uniaxial extensional flow. The fixture consists of four solenoids that generate a homogeneous magnetic field with a tunable intensity on the fluid sample, while characterized in the CaBER under uniaxial extensional flow. The ExMRFx is designed in two configurations, one to impose a magnetic field parallel, while the other to impose a magnetic field perpendicular to the deformation axis. As an example of possible application, the ExMRFx has been tested with a magnetorheological fluid (MRF) consisting of a suspension of carbonyl iron particles dispersed in glycerine. The experimental results show that the filament thinning process of the MRF sample is influenced by the concentration of carbonyl iron particles used, the orientation of the magnetic field (parallel or perpendicular), the intensity of the magnetic field applied, and finally the Hencky strain imposed. Depending on the combination of these latter parameters, the MRF sample may result in a very stable filament bridging the two measuring plates, which will remain stable, as long as none of the experimental parameters change.This work introduces a novel design of a fixture to be adapted to the commercial version of the capillary breakup extensional rheometer (CaBER), here termed as an extensional magneto-rheological fixture (ExMRFx), that allows the characterization of magnetic fluids under uniaxial extensional flow. The fixture consists of four solenoids that generate a homogeneous magnetic field with a tunable intensity on the fluid sample, while characterized in the CaBER under uniaxial extensional flow. The ExMRFx is designed in two configurations, one to impose a magnetic field parallel, while the other to impose a magnetic field perpendicular to the deformation axis. As an example of possible application, the ExMRFx has been tested with a magnetorheological fluid (MRF) consisting of a suspension of carbonyl iron particles dispersed in glycerine. The experimental results show that the filament thinning process of the MRF sample is influenced by the concentration of carbonyl iron particles used, the orientation of the mag...

Determination of optimal magnetorheological fluid particle loading and size for shear mode monotube damper

Magnetorheological (MR) fluids belong to a class of controllable fluids, and the composition and concentration of its components govern its magnetorheological properties. In this study, an optimum particle loading (or mass fraction) and size of iron particles in MR fluid for use in a shear mode monotube MR damper were determined based on the damping force and off-state viscosity of synthesized MR fluid samples. Initially, the morphological and magnetic properties of carbonyl iron particles were characterized. Six MR fluid samples were prepared composed of combination of three different particle loadings and two sizes of iron particles. Magnetorheological tests were conducted on these samples to determine the flow curves at off-state and on-state magnetic field conditions. Herschel–Bulkley model was used for mathematical representation of flow curves at different magnetic fields and to determine their dynamic yield stress. Further, a shear mode monotube MR damper with accumulator was designed by using optimization technique for desired dynamic range and damping force. Magnetostatic analysis was performed to determine the magnetic field strength generated in the shear gap at different currents. The damping force was calculated for synthesized MR fluids based on their dynamic yield stress corresponding to the magnetic field strength in the shear gap. Analysis of variance was performed to analyse the significance of independent factors on the damping force and off-state viscosity of MRF. The optimal particle loading and size which yielded maximum damping force with minimum off-state viscosity were determined using a multi-objective genetic algorithm.

Monitoring sedimentation of magnetorheological fluids using a vertical axis monitoring system with a low aspect ratio sensor coil**This research was conducted at the University of Maryland while the first author was a visiting student.

Adaptive energy absorbers (EAs) utilizing magnetorheological fluids (MRFs) are currently being investigated for severe impact or shock mitigation problems because magnetorheological energy absorbers can adjust stroking load to account for severity of impact and payload mass. Utilizing MRFs in such EAs requires a highly stable suspension that maintains a uniform concentration. Suspension stability of MRFs can be studied using a MRF column and an automated vertical axis inductance monitoring system (AVAIMS), where an inductance sensor is translated up and down the vertical MRF column to track the mud-line, defined as the boundary between the clarified fluid at the top of the column and the MRF below. The rate of descent of the mud-line is typically referred to as the sedimentation rate of the MRF. In this paper, a refined inductance sensor is developed that features a low aspect ratio coil to better localize rapid changes in concentration or sedimentation zone boundaries, as well as to improve symmetry of the applied magnetic field in the MRF sample enclosed by the sensor. This low aspect ratio solenoid (LARS) sensor was developed to measure the vertical distribution of the concentration of carbonyl iron particles in the MRF column. Compared with the high aspect ratio solenoid sensor used in our prior work, the results of FEM simulation and sedimentation experiments demonstrate that the LARS sensor was better able to localize rapid changes in concentration or density. Using the AVAIMS with the refined LARS sensor, a method was developed, based on the measured concentration gradient profile, to identify sedimentation zone boundaries in an MRF column, and these results were compared to our prior work using the measured concentration profile only. Sedimentation zone boundaries that are consistent with Kynch’s sedimentation theory were obtained using the concentration gradient profile method, such as monotonically descending mud-line, linearly ascending gel-line, and linearly ascending cake-line. Key metrics to characterize the time histories of the sedimentation zone boundaries are measured including mud-line descent rate, gel-line ascent rate, and cake-line ascent rate. Identification of sedimentation zone boundaries using the LARS sensor in conjunction with the concentration gradient profile method exhibited two main advantages including the direct measurement and improved localization of the large concentration change that occurs at a sedimentation zone boundary, and the elimination of sensor bias.

Improving sedimentation stability of magnetorheological fluids using an organic molecular particle coating

A key goal for implementation of magnetorheological fluids (MRFs) is to minimize sedimentation or to increase suspension stability. In this study, a series of MRF samples were synthesized by suspending carbonyl iron particles (CIPs), which had different organic molecules and auxiliaries grafted onto their surface, in silicone oil. The magnetorheology of these MRF samples was measured using a magneto-rheometer, and their sedimentation behaviors were quantitatively evaluated using a thermal conductivity sedimentation measurement method. The effect of these coatings on the stability of the MRFs was analyzed. Results show that all of the MRFs exhibit good MR effects and that the surface modification does not greatly weaken the MR effect. Suspension stability was substantially improved by grafting organic molecular structures onto the surface of the CIPs, and the sedimentation rate was influenced by the organic molecule structure. Compared to the uncoated CIPs, when the organic molecule was changed from octyl acyl ethylenediamine triacetate (C7H15COED3A) to lauryl acyl ethylenediamine triacetate (C11H23COED3A) and stearyl acyl ethylenediamine triacetate (C17H35COED3A), the sedimentation rate decreased by 53.9% to 64.2% and 75.1%, respectively. The mechanisms of how organic molecular structure affects the stability of MRFs are discussed.

Thermal conductivity enhancement and sedimentation reduction of magnetorheological fluids with nano-sized Cu and Al additives

This work presents enhanced material characteristics of smart magnetorheological (MR) fluids by utilizing nano-sized metal particles. Especially, enhancement of thermal conductivity and reduction of sedimentation rate of MR fluids those are crucial properties for applications of MR fluids are focussed. In order to achieve this goal, a series of MR fluid samples are prepared using carbonyl iron particles (CIP) and hydraulic oil, and adding nano-sized particles of copper (Cu), aluminium (Al), and fumed silica (SiO2). Subsequently, the thermal conductivity is measured by the thermal property analyser and the sedimentation of MR fluids is measured using glass tubes without any excitation for a long time. The measured thermal conductivity is then compared with theoretical models such as Maxwell model at various CIP concentrations. In addition, in order to show the effectiveness of MR fluids synthesized in this work, the thermal conductivity of MRF-132DG which is commercially available is measured and compared with those of the prepared samples. It is observed that the thermal conductivity of the samples is much better than MRF-132DG showing the 148% increment with 40 vol% of the magnetic particles. It is also observed that the sedimentation rate of the prepared MR fluid samples is less than that of MRF-132DG showing 9% reduction with 40 vol% of the magnetic particles. The mixture optimized sample with high conductivity and low sedimentation was also obtained. The magnetization of the sample recorded an enhancement of 70.5% when compared to MRF-132DG. Furthermore, the shear yield stress of the sample were also increased with and without the influence of magnetic field.

Effects of Nano Copper Additive on Thermal Conductivity of Magnetorheological Fluid at Different Environment Temperature

Low thermal conductivity of magnetorheological (MR) fluid limits its potential to be applied in high temperature environment. Recently, enhancing thermal conductivity of similar fluids through addition of nanocopper has attracted to address the problem. This paper presents the effects of nanocopper addition on thermal conductivity properties of MR fluid at different environment temperatures. The nanocopper added MR fluid samples were synthesized with carbonyl iron powder in hydraulic oil. The samples were then stabilized with addition of fumed silica and were homogenized using ultrasonic bath. Thermal conductivity of the samples and references material was measured using thermal property analyser. The environment temperature of the samples was controlled by waterbath incubation method. The results showed that enhancement of thermal conductivity with the presence of copper nanoparticles was higher at 40 vol% of CIP compared to 20 vol% of CIP and a slight variation in thermal conductivity of MR fluid was observed in environment temperatures of 30–70°C. This finding leads to development of new class of magnetorheological fluid with enhanced thermal properties.

Investigation and Simulation on Magnetic Hysteresis Properties of Magnetorheological Fluid

Magnetorheological fluid (MRF) materials are used in many devices as smart materials. However, the application of this material is limited to damper or vibration absorber because of the lack of understanding of its magnetic hysteresis properties. This paper systematically presents our recent investigation and simulation on the magnetic hysteresis properties of MRF materials. The measurement of its magnetic hysteresis property was accomplished by using a two-dimensional single sheet tester with an MRF sample container. An extended large-scale atomic/molecular massive parallel simulator, which is combined with the Stoner–Wohlfarth hysteresis model, was employed for simulating the magnetic hysteresis properties of MRF material. The measurement and simulation results are compared, analyzed, and discussed. The results will be useful for modeling of magnetic hysteresis properties of MRF materials.

Vertical Axis Inductance Monitoring System to Measure Stratification in a Column of Magnetorheological Fluid

This paper addresses an automated method and experimental apparatus to measure the sedimentation of magnetorheological fluids (MRFs) in a vertical column. The automated vertical axis inductance system (AVAIMS) developed at the University of Maryland monitored the particle concentration (i.e., particle volume fraction) of an MRF as a function of column height and standing time through an automatic process of scanning with an inductance sensor driven by a stepper motor. With the acquired data, the extent and the concentration gradients of four distinct sedimentation zones were monitored and automatically determined without human decision-based post-processing of data: supernatant zone, original concentration zone, variable concentration zone, and sediment zone. The evolution of these sedimentation zones provides a characterization of an MRF’s sedimentation behavior. Insights gained from these studies enable a better understanding of the dynamics of hindered settling of MRFs in closed systems, such as in rotary or linear stroke magnetorheological energy absorbers. An MRF sample consisting of carbonyl iron powder in a silicone carrier fluid with an initially uniform 21% particle volume fraction (hereinafter 21 vol%) was synthesized to demonstrate the method and the automated analysis of the AVAIMS. The 130 mm fluid column was scanned from top to bottom in 0.5 mm increments every 3 h for a total sedimentation period of six days (144 h). The results proved to be comparable to the characterizations obtained from our previous study with a manually operated VAIMS.

Research on chain-model transition identification of magnetic dipole theory for magneto-rheological fluid

Chain formation model is very useful to characterize the magneto-rheological phenomenon and prepare good magneto-rheological fluids. The single-chain model is common to explain the process of chain formation for ferromagnetic particles under magnetic field. With the increment of magnetic field and ferromagnetic particle content, the chain will transit from the single chain to multi-chains. However, there are few literatures involved in this phenomenon. This study investigates the effect of magnetic field and ferromagnetic particles content on the transition. The static yield stresses at different magnetic fields were measured under quasi-static mode for different magneto-rheological fluid samples. The results show that the transition of chain model can be identified on two parameters including the amplitude of static yield angle, [Formula: see text], and the inclined angles distribution, [Formula: see text]. The single-chain model is only effective under low magnetic field and ferromagnetic particles below content of 30% volume. With the increment of magnetic field and ferromagnetic particles content, the transition from single chain to multiple chains will be observed, which validates that there is a transition from the single chain to multi-chains.

Long term stability of magnetorheological fluids using high viscosity linear polysiloxane carrier fluids

Stability of magnetorheological fluids (MRFs) or suspensions has been a key issue in the development of various practical applications. In our prior work, it was experimentally confirmed that a high viscosity linear polysiloxane carrier fluid based MRF (hereinafter HVLP MRF) with 26% particle volume fraction (hereinafter 26 vol%) showed high sedimentation stability for 96 days because HVLP carrier fluids have remarkable shear thinning behavior, that is, very high viscosity at low shear rate but low viscosity at high shear rate. In addition, the effects of HVLP carrier fluid viscosity and carbonyl iron (CI) particle concentration on suspension stability were investigated with the objective of synthesizing highly stable HVLP MRFs for practical applications. The HVLP MRFs were synthesized by suspending nominally 32 vol% of CI particles in carrier fluids with different viscosities (i.e., 140, 440, and 800 Pa s). To illustrate the effect of particle concentration on suspension stability, because it is well known that suspension stability increases as particle concentration increases, two low concentrations, 5 and 10 vol%, and two high concentrations, 20 and 32 vol%, were prepared to demonstrate MRFs with relatively severe sedimentation, and stable suspensions, respectively. A vertical axis inductance monitoring system was employed to evaluate the suspension stability of the HVLP MRFs for 365 days by scanning the inductance of the MRF samples in a vertical fluid column, and logging this data with respect to height and time. In addition, the suspension stability of a commercially available MRF (i.e., Lord MRF-132DG) was also measured and compared with similar measurements for HVLP MRFs.

Measuring the sedimentation rate in a magnetorheological fluid column via thermal conductivity monitoring

Measuring sedimentation rate of magnetorheological fluids (MRFs) is of great importance when designing and synthesizing MRFs for engineering applications. A method of characterizing sedimentation rate in an MRF column is proposed utilizing thermal conductivity correlated with particle concentration. A series of MRF samples composed of carbonyl iron particles suspended in silicone oil were prepared, and their concentrations (measured as volume fraction, ∅) and thermal conductivities, k, were tested. A calibration curve was developed to relate particle concentration, ∅, to thermal conductivity, k, using this set of MRF samples with known concentration. The particle concentration, ∅, in the MRF column was then monitored by measuring thermal conductivities (k) at a fixed location and using this calibration relationship. Finally, sedimentation rate in the MRF column was determined by examining how particle concentration varied with time. The sedimentation rate measured in the MRF column was validated using visual observation of mudline (boundary between the topmost clarified fluid zone and MRF below).

Testing and analysis of magnetorheological fluid sedimentation in a column using a vertical axis inductance monitoring system

This study investigates the sedimentation of magnetorheological fluids (MRFs) in a vertical column using a vertical axis inductance monitoring system (VAIMS). The particle concentration (i.e., particle volume fraction) of MRF samples consisting of carbonyl iron powder in a silicone carrier fluid was monitored as a function of column height for 156 h with a measurement nominally every 12 h. In addition, the extent and concentration gradients in four distinct sedimentation zones were monitored: supernatant zone, original concentration zone, variable concentration zone, and sediment zone. In order to obtain the settling velocity of the MRF with respect to particle concentration, MRF samples with different volume fractions (i.e., 15, 19, 26, 30 and 40 vol%) were synthesized, and mudline (i.e., the boundary between clarified supernatant fluid zone and the original concentration zone below) descent of each sample was measured using both the VAIMS and visual observation. In this study, three different settling velocity models (i.e., Vesilind, Richardson and Zaki, and Dick models) were considered in order to capture settling velocity as a function of concentration. Vesilind’s settling velocity model was found to be most suitable for the MRF sample in our study, and the setting velocity distribution in the vertical column could be measured for each MRF sample. Based on Kynch’s sedimentation analysis, the mass balance equation was obtained and integrated with Vesilind’s settling velocity model to obtain the concentration propagation velocity. In addition, the solids flux within the fluid column was obtained to provide insight in sedimentation stability as a function of particle concentration.

Rheological measurement of redispersibility and settling to analyze the effect of surfactants on MR particles

The smart materials such as magnetorheological (MR) fluids are gaining wide popularity due to their superior control abilities. These abilities are strongly dependent about the stability of the MR fluid which needs to be sustained for the useful life of the system. In the present research work, experimental studies focusing on aggregation, redispersibility and settling of carbonyl iron-based MR fluids have been conducted to analyze the effect of surfactants on controlling settling and redispersibility. The experimental investigations were conducted by preparation of nine MR fluids samples using three types of surfactants (oleic acid, citric acid and tetramethylammonium hydroxide) and three different carrier fluids (water, silicone oil and DTE light mineral oil). The samples were prepared by mixing on rotational machine for 24 h and the homogeneity of the samples was visually inspected. The shear stress and viscosity variation of the homogenous mixture with respect to shear rate was obtained using magnetic rheometer. A new method is presented for measuring the settling of homogenous mixtures by measurement of the change in the magnetic field strength due to settlement of particles. The effect of surfactant type and its quantity on the stability of MR fluid is explored and the results of settling and redispersibility have been presented.

Effect of Particle Size on the Wear Property of Magnetorheological Fluid

Aiming to study the effect of particle size on the wear property of magnetorheological fluid (MRF), experiment materials, preparation process, and test methods are elaborated, and three different MRF samples consisting of particles of different size are prepared. Test experiments are carried out and the effect of particle size on the wear property of MRF is discussed. Moreover, the microstructures of particles extracted from MRF obtained before and after the wear experiments are observed by scanning electron microscope (SEM). Experimental results show that the particle size has a significant effect on wear property of MRF. Furthermore, the MRF with particles of 1.5–2.8 μm diameter on average is good for the requirement of engineering applications.

A comprehensive viscosity model for micro magnetic particle dispersed in silicone oil

Magnetorheological behavior of micro magnetic particle dispersed in silicone oil has been characterized by a multiplied form of phenomenological models taking the effect of shear rate, powder volume fraction, temperature and magnetic flux density. Magnetorheological fluid samples with seven different particle volume fraction were prepared by adding ferrite particles in silicone base oil and their shear viscosity of fluid samples were measured under three different temperatures (40°C, 70°C, and 110°C) and ten different magnetic flux density (0–100mT). The fluid had an upper limit to the increase of viscosity under the effect of external magnetic field and the saturation values were dependent on the operating temperature, shear rate and volume fraction of magnetic powder. The rheological behaviors have been characterized by our developed model which can be very useful for the precise control of the magnetorheological fluid.

Measurement of temperature-dependent mechanical properties of magnetorheological fluids using a parallel disk shear stress testing device

Mechanical properties are critical to the working performance of magnetorheological fluids (MRFs), especially in high temperature situations. This paper presents an experimental investigation to analyze the effects of temperature on mechanical properties of MRFs. First, a parallel disk method was implemented for the shear stress measurement of MRFs and the measurement principle was theoretically illustrated. Then, a detailed introduction to the MRF sample preparation and the testing device development was performed as well. In the study, five kinds of MRF samples with different material parameters were prepared and a shear stress testing device which possesses the temperature control function was developed and evaluated. After these, a series of measurements were conducted on the viscosity–temperature characteristic, shear stress–temperature characteristic and thermal stability of MRF samples. Measuring results indicated that the mechanical properties of MRFs were obviously dependent on temperature. The phenomenon mainly embodied in the reduction of off-field viscosity and shear stress with increasing temperature, as well as the performance degradation after undergoing a low–high–low temperature cycle or a high temperature treatment of more than 150 ℃.

The effect of the volume fraction and viscosity on the compression and tension behavior of the cobalt-ferrite magneto-rheological fluids

The purpose of this work is to investigate the effects of the volume fraction and bimodal distribution of solid particles on the compression and tension behavior of the Co-ferrite-based magneto-rheological fluids (MRFs) containing silicon oil as a carrier. Hence, Co-ferrite particles (CoFe2O4) with two various sizes were synthesized by the chemical co-precipitation method and mixed so as to prepare the bimodal MRF. The X-Ray Diffraction (XRD) analysis, Fourier Transform Infrared Spectroscopy (FTIR), Laser Particle Size Analysis (LPSA) and Vibrating Sample Magnetometer (VSM) were conducted to examine the structural and magnetic properties, respectively. The results indicated that the increase of the volume fraction has a direct increasing influence on the values of the compression and tension strengths of fluids. In addition, the compression and tension strengths of the mixed MRF sample (1.274 and 0.647 MPa) containing 60 and 550 nm samples were higher than those of the MRF sample with the same volume fraction and uniform particle size of 550 nm.

Heterocoagulation in Bidisperse Magnetorheological Fluids Containing Like-Charged Nanosized and Micron Particles Without a Magnetic Field

Based on extended Derjaguin–Landau–Verwey–Overbeek theory, a heterocoagulation model is proposed for magnetorheological (MR) fluids containing like-charged nanosized and micron particles without a magnetic field. This model considers three major interactions, namely van der Waals attraction, electrical double layer (EDL) interaction, and steric repulsion. The EDL interaction has been identified as the most important factor. The surface potential ratio β (ψ2/ψ1) between two dissimilar particles with like charge plays an important role in controlling the change of EDL interaction. At higher β ratios, the EDL interaction becomes attractive when the surface separation falls within a certain range. Two groups of MR fluid samples have been used in experimental studies based on electroacoustic measurements. In the first group, the ratio and the sum of the zeta potentials between carbonyl iron particles and ceria were 4 and −734.57 mV, respectively. In the second group, these parameters were 1.38 and −108.17 mV, respectively. The experimental results suggested that the second group did not undergo heterocoagulation, whereas the first group showed extensive heterocoagulation. The difference in surface potentials between particles of two different phases has been found to be critical for determining the state of dispersion or heterocoagulation in concentrated MR fluid systems.

Rheological characterization of a magnetorheological ferrofluid using iron nitride nanoparticles

Magnetorheology of a magnetorheological ferrofluid (MRFF) was investigated to study the role of a ferromagnetic nanoparticle (NP) additive in magnetorheological fluids (MRFs). Iron nitride (Fe16N2) NPs, nominally within the diameter range of ∼16–45 nm (spherical NPs) and ∼30–66 nm (cubic NPs), were coated with carboxy-polyethylene glycol (carboxy-PEG) and dispersed in silicone oil in order to produce a magnetic carrier fluid or ferrofluid for two solids loadings: 2 vol. % and 5 vol. %. Conventional spherical carbonyl iron (CI) particles, varying in diameter from 6 to 10 μm, were suspended in the ferrofluid at 25 vol. % solids loading. Rheological properties of the MRFF synthesized with the carboxy-PEG-based ferromagnetic carrier fluid were compared to the MRF synthesized with silicone oil to determine how ferrofluid can influence dynamic viscosity and yield stress. Rheological measurements of both MRF and MRFF samples were carried out using a Paar Physica 300 rheometer to estimate the field-off viscosity and to measure flow curves (i.e., shear stress vs. shear rate) as a function of magnetic field. A Bingham-plastic model was used to characterize the flow curves, and results show that there is an increase in the dynamic viscosity of the MRFF over the MRF. The ferromagnetic carrier fluid greatly increases yield stress as only 2 vol. % of added carboxy-PEG NPs improves the yield stress performance by almost 5%. A second MRFF sample synthesized with 5 vol. % of added carboxy-PEG NPs contained in the ferrofluid significantly enhanced the yield stress performance by 13% over the MRF at the same CI solids loading (25 vol. %).