Behavior Of Magnetorheological Fluid Research Articles

Impact of magnetorheological fluid composition on their behaviour in gradient pinch mode

Magnetorheological (MR) fluids can be utilized in one of the fundamental operating modes of which the gradient pinch mode has been the least explored. In this unique mode non-uniform magnetic field distributions are taken advantage of to develop a so-called Venturi-like contraction in MR fluids. By adequately directing magnetic flux the material can be made solidified in the regions near the flow channel wall, thus creating a passage in the middle of the channel for the fluid to pass through. This leads to unique variations of the slope in the pressure-flow rate characteristics. It can be stated that the effect of the MR fluid composition on the behaviour of the MR fluid in gradient pinch mode has not been thoroughly investigated yet. In this study, the behaviour of MR fluids was assessed with a dedicated pinch mode MR valve that provided a valuable insight into the contraction mechanism using fluorescence microscopy. Briefly, seven MR fluid samples were prepared with different particle concentrations (10%, 22% and 32 vol%) and mean particle sizes (2, 4.5 and 8.2 μm). It was found that the MR fluid sample with the larger particle size exhibits a significantly larger slope change observed in the pressure-flow rate characteristics. Increasing the particle size from 2 μm (base) to 8 μm resulted in the slope increase by a factor of 2.6 compared to the base sample. Increasing the particle concentration has a negligible effect on the pinch mode effect. Finally, these results were analysed using the modified Wuest equation, which is commonly used for characterizing sharp-edged orifices in low Reynolds number flow regimes. The simple equation was determined to describe the behaviour of MR fluids in gradient pinch mode with adequate accuracy.

Development and characterization of a magnetorheological damper with low-velocity sensitivity

Magnetorheological (MR) dampers, utilizing the unique properties of advanced materials, are extensively applied in vibration control systems. However, their performance is often compromised by the structural limitations of conventional designs. The damping force in conventional MR dampers is highly sensitive to velocity variations, primarily due to the interdependence between the piston area and the dimensions of the throttling channels, which are typically inseparable. This inherent coupling restricts the simultaneous optimization of the damping force and adjustable damping ratio, reducing the effectiveness of the magnetorheological dampers in velocity-sensitive environments. Moreover, conventional MR dampers are often characterized by complex structures and large sizes. To overcome these limitations, a novel double-rod bypass magnetorheological damper is proposed. Through the application of fluid mechanics principles and the rheological behavior of MR fluids, the velocity distribution within the throttling channel is thoroughly examined. The Bingham model is employed to establish both the velocity profile and the corresponding mechanical model, and the theoretical results align closely with experimental data, confirming the accuracy of the quasi-static model. Experimental results further demonstrate the proposed damper’s superior sensitivity to low velocities. This approach provides valuable theoretical guidance for the design of advanced MR dampers.

Thermohydrodynamic analysis of magnetorheological conical bearings with conjugated heat transfer

This study presents a comprehensive investigation into a 3D simulation of magnetorheological (MR) conical bearings, focusing on considering viscous dissipation using the conjugated heat transfer approach. The behavior of MR fluids is expressed through the utilization of the Bingham-Papanastasiou constitutive equation. Notably, this study considers variations in viscosity and yield stress as functions of both magnetic field intensity and temperature. The study utilizes a multidisciplinary approach, encompassing fluid dynamics, magnetism, and heat transfer, to model and analyze the behavior of MR fluids within conical bearing geometries. The governing equations containing Cauchy momentum, energy, and Maxwell equations are solved using the finite element method. This research delves into the impacts of viscous dissipation on the functional and characteristic attributes of conical bearings. The energy equations in solid and fluid domains and extended considerations to the plug region within viscous dissipation are specifically addressed. Extensive validation is performed through a comparative analysis involving experimental, numerical, and analytical studies to ensure the validity of results. The results reveal the substantial impact of temperature on both the characteristics and functionality of magnetorheological conical bearings.

Performance Analysis of Textured Spherical Hybrid Journal Bearings Operated With Magnetorheological Fluid

Abstract Recently, textured surfaces have been used to enhance the performance of tribological systems. This paper examines the effect of textured surfaces on hole-entry spherical hybrid journal bearings operated using magnetorheological (MR) fluid. The different geometric shapes of textured surfaces, including spherical, rectangular, and conical, have been selected for numerical analysis. Next-generation design for tribological systems based on MR fluid lubrication emphasizes dynamic performance. MR fluid responds quickly, and its rheological characteristics can be simply adjusted. The present paper also deals with the non-Newtonian behavior of MR fluid on the bearing performance characteristics parameters. The finite element method is used to solve the modified Reynolds equation. The findings of numerical simulation show that the application of textured surfaces and MR fluid improves the values of minimum fluid film thickness and stability of the bearing.

Normalized structure parameter of magnetorheological fluids under unidirectional monotonous squeeze

The evolution of chain structure parameters for magnetorheological (MR) fluids under unidirectional monotonous squeeze were studied. A normalized structure parameter SnT was proposed. The compressive behavior of MR fluids was experimentally researched under compressive speeds v in squeeze flow and the nominal shear yield stress was calculated according to the squeeze flow theory. So SnT can be derived. It showed that SnT rapidly increases with increasing compressive strain under a high magnetic field and low v. As an analogy for friction, the correspondence between τy/B2 and friction coefficient suggests a possible origin of friction in the mechanical behaviors of MR fluids. Moreover, the results at lower v seem to deviate from the predictions of Deborah number De and the Kelvin model. The aggregation of chain structure leading to much longer relaxation times at lower v was thought to result in the high De in squeeze flow.

Magnetorheological fluids subjected to non-uniform magnetic fields: experimental characterization

Magnetorheological (MR) fluids are suspensions of fine, low-coercivity, high-magnetizable particles in a continuous liquid phase. When subjected to magnetic field, the material exhibits a rapid change in the apparent viscosity of several orders of magnitude. This unique capability has been successfully exploited in automotive semi-active suspensions systems or systems for manufacturing high quality optics. In a majority of the existing systems, the rheology of MR fluids is controlled by an external uniform field oriented perpendicularly to the fluid flow direction. In general, it is an inherent feature of MR systems operating in flow, shear or squeeze modes, respectively. There is an experimental evidence that the behavior of MR fluids in the so-called pinch-mode (in which the fluid is subjected to non-uniform magnetic field distributions) clearly stands out against the remaining three operating modes. With the predecessors, the flow through the channel occurs once a pressure across it exceeds the field-dependent threshold pressure. For comparison, in pinch mode valves the magnetic flux energizes mostly the layers of the materials near the channel walls. The outcome is a change in the channel’s effective diameter achieved solely via material means without changing its geometry. To study the fluid’s unique behaviour in the pinch mode, the authors designed a prototype valve assembly and examined several fluid formulations of various particle concentration levels across a wide range of external (velocity, magnetic field density) stimuli in an organized effort to further comprehend the phenomenon. The obtained data indicate that the magnitude of the particular effect does not only depend on the magnitudes of the magnetic stimuli but also on the particle concentration; the smaller the concentration of particles the more pronounced the pinch mode like behavior is. In general, the authors believe that the study may provide guidelines as to the selection of fluid formulations for developing novel valveless actuators utilizing MR fluids operating in pinch mode.

The friction and Wear behavior of Silicon oil-based Magnetorheological fluid with Solid lubricant

Due to its lower energy consumption, higher mechanical properties and easier to control, magnetorheological(MR) fluid has been widely used in the engineering field. However, the friction and wear behavior of it, which may hinder its applicability, needs to be modified. The tribological behavior of silicon oil-based MR fluid with different types and contents of solid lubricant was investigated on a four-ball machine. The worn surfaces of the steel balls were observed by using a scanning electron microscope (SEM). The results showed that the friction and wear property of silicon oil-based MR fluid could be improved by some solid lubricants. Both of molybdenum disulfide and graphite can decrease friction coefficient of silicon oil-based MR fluid significantly, but graphite has the better wear resistance than molybdenum disulfide. Adding polytetrafluoroethylene (PTFE) can enhance the wear resistance of MR fluid obviously, but the friction coefficient is larger than the first two. The friction and wear property of MR fluid hardly changes by adding boron nitride. Increasing the content of graphite can improve the friction and wear resistance of MR fluid, and the wear resistance of MR fluid has an optimal point when the weight percent of graphite is 2%.

The effect of mesocarbon microbeads on magnetorheological fluid behavior

Magnetorheological (MR) fluids are composed of magnetizeable particles suspended in a carrier fluid and change apparent viscosity upon the application of a magnetic field. Previous studies have shown that passive particles, such as hollow glass spheres, can augment the yield stress of MR fluids, but this yield stress augmentation has limited endurance because the hollow glass microspheres are not sufficiently durable. This study evaluates mesocarbon microbeads (MCMBs) as an alternative passive particle with the potential for MR yield force augmentation but with greater durability. The yield properties of six MR fluid concentrations with varying carbonyl iron particle (CIP) and MCMB volume fractions were tested using a shear mode rheometer and flow mode MR damper. MCMBs did not augment yield stress in shear mode, but, in contrast, in flow mode, the yield force increased nonlinearly with MCMB volume fraction. Furthermore, this yield force-enhancing effect did not diminish over 100,000 cycles (or 5 km of piston travel). The theoretical non-dimensional plug thickness which arises from an approximate parallel plate analysis of a fluid element in flow mode is used illustrate to a potential mechanism for the yield force augmentation effect.

Magnetorheological damper modeling based on a refined constitutive model for MR fluids

A systematic modeling study is conducted to predict the dynamic response of magnetorheological (MR) damper based on a refined constitutive model for MR fluids. A particle-level simulation method is first employed to probe the microstructured behavior and rheological properties of MR fluids, based on which the refined constitutive model is developed. The constitutive model is further validated by comparing the predicted results with the data obtained from microscopic simulations and existing experiments. It is revealed that the proposed constitutive model has comparable accuracy and good applicability in representing MR fluids. Subsequently, a computational fluid dynamics (CFD) model is established to explore MR damper’s behavior by using the proposed constitutive model to describe the fluid rheology. For better capturing the dynamic hysteretic behavior of MR damper, a modified parametric model is developed by combing the Bingham plastic model and the proposed constitutive model. The modified model for MR damper shows its validity and superiority over the existing Bingham plastic models.

Introducing the thermal field into multi-physics coupling for the modeling of MR fluid-based micro-brake

Miniaturization of magnetorheological (MR) fluid-based actuator, as an essential building block of miniature electromechanical systems, is of significant importance. Since the feature size of miniature electromechanical systems 1–10 mm, the heat generation and dissipation process in the MR fluid would dramatically affect the speed reduction mechanism of micro-brake. The objective of this manuscript is to propose a model for the MR fluid-based micro-brake with high accuracy by introducing the thermal field into the multi-physics coupling. The temperature- and field-dependent rheological properties of MR fluid are investigated and the data is presented. The rheological behavior of MR fluid under the comprehensive effect of temperature field, magnetic field and flow field is modeled by introducing the Arrhenius equation. A COMSOL Multiphysics-based simulation method, which includes two heat sources, is proposed to calculate the thermal distribution of the miniature turbine generator under the multi-physics coupling. The influence of temperature on the yield stress τy and the influence of shear rate γ˙ on viscosity η are also introduced into the MR fluid-based micro-brake to obtain a torque calculation model with high precision. The miniature turbine generator was driven with an initial rotational speed of 18,200 r/min. The temperature ranged from 41 to 123 °C as a current from 0.3 to 1.5 A was applied to the micro-brake. Results show that the accuracy has been improved more than 12.9% by introducing thermal analysis to the micro-brake model. We believe this work is significant for realizing the high precision control of MR fluid-based micro-brake at high rotational speeds.

Synthesis and characterization of the rheological behavior of MR fluid for polishing silicon wafer using double-disc chemical-assisted magneto-rheological finishing process

Double-disc chemical-assisted magneto-rheological finishing (DDCAMRF) process is a successfully developed precision material removal process that has been applied to the polishing of brittle materials viz. monocrystalline silicon wafer. The mechanism of silicon polishing using the DDCAMRF process depends mainly on the magneto-rheological (MR) fluid, which behaves as a multi-point finishing tool. The MR fluid synthesized in the present work comprised of carbonyl iron powder, alumina abrasives, deionized water, and glycerol as the base fluid. The application of a magnetic field in the prepared MR fluid samples significantly affects its rheological properties, which in turn affects the quality of finished wafer surface. Therefore, the rheological, as well as magnetic properties of prepared MR fluid samples need to be studied in detail. The flow behavior of MR fluid is affected by the applied magnetic field, which therefore exhibits transition from Bingham-fluid like structure to gel-like structure. To characterize MR fluid's magnetic behavior, the M−B curve of the prepared MR fluid samples was plotted to determine the saturation magnetization using the data obtained from vibrating sample magnetometer (VSM). Rheological properties like viscosity and yield stress of the prepared MR fluid were measured by using the parallel-plate rheometer. The obtained rheological data from the rheometer was fitted using the defined constitutive equations of respective fluid models, viz. Bingham-Plastic (BP), Herschel-Bulkley (HB), and Casson’s (CS), respectively. The experimental results were analyzed, and the effect of increase in temperature on viscosity and yield stress was also discussed.

Magneto rheological fluid: Fabrication and characterization of its temperature-dependent properties

The behavior of magneto rheological fluids at different temperature was tested by using oscillatory rheometer. The shear flow, oscillatory shear tests was performed at varying intensities of magnetic flux density, amplitude of stress, strain rate over a different temperature range. The magnetic field density and temperature range effects on the yield stress of MR fluids had been assessed using the measured shear stress and shear strain data, the data obtained beneath harmonic pressure signals were analyzed for storage, loss modulus as the capabilities of the temperature and the strain amplitude. Whenever there is no such magnetic field is applied, the results confirmed that the robust impact of temperature on its rheological properties of the MR fluids; however, the magnetic field became the overriding influence on it. Whenever under the application of the magnetic field the temperature effects can only be seen at low strain rates.

Evaluation of Static and Dynamic Yield Stress for Isotropic and Anisotropic Particle–Based MR Fluids: Modeling and Analysis

Structural deformation in the low shear rate region that is an undeformed state is investigated for the isotropic and anisotropic magnetic particle–based magnetorheological (MR) fluid. Flow curves were obtained for both MR fluids between 0.1 s−1 and 500 s−1 in the absence and in the presence of magnetic fields. A model to describe the flow behavior over the full shear rate study is proposed. The proposed model accounts for the friction contribution coming from particle-particle as well as particle-carrier interactions of anisotropic particles particularly in flake-shaped particles. The parameters derived from the fit have physical meaning, and it correlates with the observed dependency in rheology study. To get a better understanding of particle-particle friction contribution, magnetic nanoparticles were added in the MR fluid and flow behavior is studied. The study clearly demonstrates the contribution of particle-particle friction on the MR properties. The contribution of particle-carrier friction, due to the shape of the particle, is verified by comparing the result with spherical-shaped particle–based MR fluid.

Rheological properties of magnetorheological suspensions stabilized with nanocelluloses

Two kinds of anisotropic cellulosic nanoparticles, cellulose nanocrystal (CNC) and nanofiber (CNF), were used as additives for the aqueous carbonyl iron particles (CIPs) based magnetorheological (MR) fluids, aiming at disclosing effect of nanocelluloses on the magneto-responsive behavior and stability of MR fluids. Both CNC and CNF can stabilize MR fluids, and improve their sensitivity to alterations of magnetic field strengths. Relative to electrostatic repulsion, physical hindrance is more important to the stability improvement. Thus, CNF is the better option because it has higher aspect ratio and surface charge. Moreover, the presence of cellulosic nanoparticles hinders coalescence of CIP chains to stronger columns, and hence the nanoparticles stabilized MR fluids show thixotropy evidently. At the comparative concentration (0.3 wt%), the presence of CNF even enhances the magneto-responsive levels because the percolated CNF network acts as stress amplifier. This work opens up a new door for applications of nanocelluloses in MR fluids.

Magnetorheological valves based on Herschel–Bulkley fluid model: modelling, magnetostatic analysis and geometric optimization

Magnetorheological (MR) fluids find wide application in various engineering applications. At the design stage of any MR devices, choosing a suitable rheological model for describing the flow behaviour is very critical. Since, the Herschel–Bulkley (H–B) is the most suitable model to describe the flow behaviour of MR fluids, the present study models the flow of MR fluid in the annular valve using the H–B model and does geometric optimization of the valve for three different commercially available MR fluids. The work discussed in the paper consist of three broader parts viz. (i) flow modelling, (ii) magnetostatic analysis and (iii) geometric optimization. In flow modelling, MR fluid flow is modelled using the H–B fluid model and validated by computational fluid dynamic analysis in ANSYS environment. Further, in magnetostatic analysis, for calculating the values of objective functions during the optimization process, magnetic flux density in the MR valve has been calculated using a polynomial model for the relative magnetic permeability for three different MR fluids, rather than conventionally choosing a constant value which is valid only for low ranges of current. The magnetostatic analysis has been validated through finite element modelling in ANSYS software package for different valve geometries. After defining the magnetization model for the chosen MR fluids and geometric design of the valve, variation of valve mass and performance indices such as damping force, dynamic range, inductive time constant and control energy, have been shown for all chosen fluids. In geometric optimization, the performance indices of the valve have been kept as objective functions which incorporate H–B fluid model for its definition. Such work has not been reported in the literature. Finally, a single-objective minimization problem has been formulated for the optimization with application-specific weight factors and solved using Genetic Algorithm in MATLAB® environment. The optimal results are then discussed and the best possible MR fluid has been suggested for the chosen applications.

A Simulation Study on the Behavior of Magnetorheological Fluid on Herringbone-Grooved Hybrid Slot-Entry Bearing

In recent years, extensive use of smart lubricants has been made in order to control the tribological performance of fluid film bearings. The grooved surfaces of the journal bearing greatly influence the performance of bearings. In the present work, various geometric shapes of herringbone grooves (rectangular, triangular, and parabolic) with groove angles (30° and 60°) have been considered to numerically simulate the performance of slot-entry bearings. The work reported in this article deals with the numerical simulation of magnetorheological (MR) fluid–lubricated slot-entry herringbone-grooved hybrid journal bearings. Dave equation, a constitutive relation of the Bingham model, was employed to simulate the flow behavior of MR fluid. Using the finite element method (FEM), the governing Reynolds equation for a hybrid slot-entry bearing model was solved. The result shows that the use of a herringbone-grooved surface and application of MR fluid in a slot-entry bearing offers better stability and higher fluid film stiffness and minimizes frictional torque.

Effect of medium viscosity on rheological characteristics of magnetite-based magnetorheological fluids

This study examined the magnetorheological (MR) behavior of magnetite-based MR fluids according to the magnetite concentration, magnetic field strength, and different viscosity of silicone oil as the carrier fluid. To this end, an experimental design was chosen to decrease the experimental error and provide a better rheological interpretation. The flow behavior parameters increased remarkably with increasing medium viscosity and nanoparticles (NPs) concentration, whereas the magnetic field strength had a milder effect, exhibiting a saturation value above which its effect became almost negligible. Moreover, both the Bingham plastic and power law models were found to fit their flow behaviors well. Almost all the critical rheological parameters of the aforementioned models experienced remarkable improvement after increasing the magnetic field strength, NPs concentration and carried fluid viscosity. In addition, mathematical correlations were derived to model each of the rheological parameters such as plastic viscosity and yield stress (for Bingham fluid model) and the consistency and power-law indices (for power-law model).

Comparative experimental study on constitutive mechanical models of magnetorheological fluids

Accurate and feasible mechanical constitutive models of magnetorheological (MR) fluids can facilitate the design of MR devices. Therefore, the purpose of this article is to compare which of the three models can better describe the mechanical behavior of the MR fluids, and the experiments were implemented to measure the shear stress and apparent viscosity of a representative MR fluid under varying shear rates and different applied magnetic field conditions. The obtained rheological properties of the MR fluid are then fitted to the Bingham, Casson, and Herschel–Bulkley models to test the constitutive mechanical performance and accuracy. The results demonstrate that, although the models above appropriately describe the approximate Newtonian fluid properties of the MR fluid in the absence of a magnetic field, the Bingham and Casson models are difficult to describe the nonlinear characteristics of the MR fluid in the pre-yield region under an excited magnetic field. Meanwhile, the Casson are not sensitively responsive to equation forms change and can only be suitable to describe the mechanical behavior of the MR fluids roughly. However, the Herschel–Bulkley model can closely describe the constitutive mechanical behaviors of shear stresses varying nonlinearly with the external excited magnetic field. Especially in the pre-yield region, the model can reflect the peristaltic mechanical behaviors of MR fluids. These findings could provide theoretical guidance for the design of MR devices.

The Changed of Behaviour of MR Fluid in MR Damper after a Long-Term Operation

Magnetorheological (MR) fluid devices are now applied in various applications. Although a lot of studies have been discussed in long-term implementation of MR devices, only few studies have concerned on MR fluid application in valve operation mode, such as at MR valve. The experiments were conducted on a dynamic test machine in a custom MR damper with meandering MR valve. The experiment test was applied at continuous-load in long term-operation with parameters of 20 mm length of stroke, 0.4 Hz of frequency, 0.5 A of applied current and 175,000 cycles. The rheological properties of MR fluid were characterized using rotational and oscillatory shear rheometer. The result showed that the rheological properties of MR fluid changed after applied in long-term operation. The changed of MR fluid also investigated through morphological characteristics using SEM and EDX.

Experimental Evaluation of Magnetorheological Damper Characteristics for Vibration Analysis

Magnetorheological (MR) fluid damper has been designed, fabricated and tested to find the stiffness and damping characteristics. Experimentally the MR damper has been tested to analyse the behaviour of MR fluid as well as to obtain the stiffness for varying magnetic field. MR damper mathematical model has been developed for evaluating dynamic response for experimentally obtained parameters. The experimental results show that the increase of applied electric current in the MR damper, the damping force will increase remarkably up to the saturation value of current. The numerical simulation results that stiffness of the MR damper can be varied with the current value and increase the damping forces with the reduced amplitude of excitation. Experimental and theoretical results of the MR damper characteristics demonstrate that the developed MR damper can be used for vibration isolation and suppression.