Squeeze-Strengthening Effect of Silicone Oil-based Magnetorheological Fluid

In order to study the squeeze-strengthening effect of silicone oil-based magnetorheological fluid （MRF）, theoretical basis of disc squeezing brake was presented and a squeezing braking characteristics test-bed for MRF was designed. Moreover, relevant experiments were carded out and the relationship between squeezing pressure and braking torque was proposed. Experiments results showed that the yield stress of MRF improved linearly with the increasing of external squeezing pressure and the braking torque increased three times when external squeezing pressure achieved 2 MPa.

DESIGN METHOD OF MAGNETORHEOLOGICAL FLUID SHOCK ABSORBER FOR CAR SUSPENSION

The Bingham constitutive model, which is previously used in depiction of magnetorheological （MR） fluids rheological behaviors for design devices, exhibits discontinuous characteristics in representation of pre-yield behaviors and post-yield behaviors. A Biviscous constitutive model is presented to depict rheological behaviors of MR fluids and design automotive shock absorber. Quasi-static flow equations of MR fluids in annular channels are set theoretically up based on Navier-Stokes equations and several rational simplifications are made. And both flow boundary conditions and flow compatibilities conditions are established. Meantime, analytical velocity profiles of MR fluids though annular channels are obtained via solution of the quasi-static flow equations using Biviscous constitutive model. The prediction methodology of damping force offered by MR fluid shock absorber is formulated and damping performances are predicated in order to determine design parameters. MR fluid shock absorber for Mazda 323 car suspension is designed and fabricated in Chongqing University, China. Measurements from sinusoidal displacement cycle by Shanchuan Shock Absorber Ltd. of China North Industry Corporation reveal that the analytical methodology and design theory are reasonable.

Optimizing control of a two-span rotor system with magnetorheological fluid dampers

A control system aims at vibration reduction in a two-span rotor system with two shear mode magnetorheological （MRF） dampers is designed. A finite element model of the MRF damper- rotor system is built and used to analyze the rotor vibration characteristics. Based on Hooke and Jeeves algorithm and the numerical simulation analysis, an optimal appropriate controller is proposed and designed. Experimental results show that rotor vibration caused by unbalance is well controlled （ first critical speed region 37% , second critical speed region 42% ）. To reflect advantages of optimi- zing strategy presented and validate the intelligent optimization control technology, detailed experi- ments were developed on a two-span rotor-vibration-control platform. The influence on accuracy, rapidity and stability of optimizing control for rotor vibration are analyzed. It provides a powerful technical support for the extension and application in target and control for shafting vibration.

Optimizing Control for Rotor Vibration with Magnetorheological Fluid Damper

The aim of this work is to analyze and design a control system for vibration reduction in a rotor system using a shear mode magnetorheological fluid(MRF)damper.A dynamic model of the MRF damper-rotor system was built and simulated in Matlab/Simulink to analyze the rotor vibration characteristics and the vibration reduction effect of the MRF damper.Based on the numerical simulation analysis,an optimizing control strategy using pattern search method was proposed and designed.The control system was constructed on a test rotor bench and experiment validations on the effectiveness of the proposed control strategy were conducted.Experimental results show that rotor vibration caused by unbalance can be well controlled whether in resonance region(70%)or in non-resonance region(30%).An irregular vibration amplitude jump can be suppressed with the optimization strategy.Furthermore,it is found that the rapidity of transient response and efficiency of optimizing technique depend on the pattern search step.The presented strategies and control system can be extended to multi-span(more than two or three spans)rotor system.It provides a powerful technical support for the extension and application in target and control for shafting vibration.

A New Theoretical Model about Shear Stress in Magnetorheological Fluids with Small Shear Deformation

Based on the single-chain structure model of magnetorheological fluids, a formu la for the calculation of shear stresses was established. The interaction force of two magnetic particles in an infinite single-chain was deduced using a new theoretical model which is founded on Ampere' molecular curr ent hypothesis, dipole theory and Ampere' law. Furthermore, the resultant force on a particle was then deduced by taking into account of the action caused by al l the other particles in the single-chain. A predictive formula for shear stres ses was made corresponding to the case that MR fluids were sheared by a small an gle and the calculating results fit well on the order with the yield stresses of the commercial MR fluids.

First order sensitivity analysis of magnetorheological fluid damper based on the output damping force

With many features,the magnetorheological fluid( MRF) damper is widely applied in the semiactive vibration control system. And sensitivity analysis is an important method to study the influence weight of various parameters on damping force characteristics. A mathematical model of the output damping force on the MRF damper is established by the mechanism modeling method,a first order output sensitivity equation is deduced and the expression of the first order output sensitivity function is obtained. The first-order sensitivity functions of ten design parameters are solved,and the influence degree of system parameters change on the output force of MRF damper is analyzed by comparing the sensitivity index of the parameters. Two sensitivities of vibration velocity and control current are obtained through experiment to prove the other parameters sensitivity analysis conclusion by analogy verification,which provides guidance for the structure optimization design of MRF damper.

A Novel Dual Helical Magnetorheological Fluid Micro-Robot

To address the problem of flexible drive control of gastrointestinal(GI)tract micro-capsule robot posture,a novel dual helix magnetorheological fluid(MRF)micro-robot(DHMRFMR)is proposed and developed in this paper.Based on the mechanical properties of magnetorheological fluid,the relationship model of magnetic field force is obtained,and the thrust model is established.Double micro DC deceleration motor is used to drive the two ends of the helical actuator to make the DHMRFMR forward and backward,by changing the external magnetic field rotation speed,direction and distance,adjust the attitude direction of the robot.Numerical simulation software ANSYS is used to analyze the motion law of external fluid of DHMRFMR,and the visualization of fluid velocity and pressure distribution is realized.The front-end helix actuator can change the flow path of the fluid,and the middle and tail of the DHMRFMR bear less pressure,which improves the stability and flexibility of the robot.The novel DHMRFMR is suitable for internal drive in bending environment,and has a good application prospect in biomedical engineering field in human intestinal unstructured environment.

Friction Behavior of Magnetorheological Fluids with Different Material Types and Magnetic Field Strength

Magnetorheological （MR） fluid is a type of a smart material that can control its mechanical properties under a magnetic field. Iron particles in MR fluid form chain structures in the direction of an applied magnetic field, which is known as MR effect, resulting in variation of stiffness, shear modulus, damping and tribological characteristics of MR fluid. As MR effect depends on the density of particles in the fluid or the strength of a magnetic field, the experiments are conducted to evaluate the friction property under reciprocating motion by changing the types of MR fluid and the strength of a magnetic field. The material of aluminum, brass, and steel are chosen for specimen as they are the most common material in mechanical applications. The surfaces of specimen are also observed by optical microscope before and after experiments to compare the surfaces with test conditions. The comparing results show that the friction coefficient increases as the strength of a magnetic field increases in regardless of types of MR fluid or the material. Also the density of particle in MR fluid affects the friction characteristic. The results from this research can be used to improve the performance of mechanical applications using MR fluid.

Preparation and characterization of carbonyl iron/strontium hexaferrite magnetorheological fluids

The heat transfer oil-based magnetorheological fluid （MRF） was prepared using oleic acid-modified micron carbonyl iron powder as a magnetic dispersed phase and strontium hexaferrite （SrFe12019） nanoparticles as an additive. The sedimentation stability of MRFs was studied. The results indicated that the stability of MRFs was improved remarkably by adding SrFel2019 nanoparticles and the sedimenta- tion ratio was only 0.88 in 20 days when the content of nanoparticles reached 10wt%. The rheological properties were characterized by a HAAKE rheometer without a magnetic field and a capillary rheometer with and without a magnetic field. The effects of SrFe12019 nanoparticles, the temperature, and magnetic field strength were investigated. In addition, the rheological properties could be predicted well using the improved Herschel-Bulkley model, even under a magnetic field. A theoretical model was also proposed to predict the yield stress based on the microstructure of the MRF under an applied magnetic field.

Lubrication Property of Magnetorheological Fluid With Nano-Silica Additives Under Magnetic Field

Magnetorheological(MR)fluid is colloidal suspension and stiffens into semi-solid when subjected to a magnetic field.In order to investigate the effect of magnetic field on lubrication property of MR fluid with nano-silica additives,a pin-on-disc tribometer is used to carry out friction and wear experiment of steel under the magnetic field.The MR fluids with different additive concentrations are prepared and their theological properties are examined via a rotational rheometer.Different lubrication performance of the MR fluid with nano-silica additives with and without magnetic field is presented.In addition,through observing the morphology and analyzing the elemental composition of the worn surfaces,the effects of additives on the lubrication property are investigated.

Properties and mechanism of ionic liquid/silicone oil based magnetorheological fluids

A magnetorheological fluid(MRF)is a smart composite suspension composed of nonmagnetic liquid and soft magnetic particles.Carrier fluids can considerably influence the performance of MRFs;therefore,to investigate the effect of carrier fluids on MRFs,an SO/IL-MRF was prepared by mixing an ionic liquid(IL)with silicone oil(SO)in this study.Three types of MRF samples were prepared for experiments(pure SO,pure IL,and SO/IL).According to the experi-mental results,the SO/IL-MRF has better sedimentation stability than those based on pure SO and pure IL.Further,three methods were used to determine the shear yield stresses of the MRFs.The SO/IL-MRF achieved a higher shear yield stress than those of the other two because a network structure is formed between the ionic fragments and the molecular chains of the SO in the SO/IL-MRF.This increases the movement resistance of the particles in the carrier fluid,and it is unlike the mechanism of the IL-enhanced MRF.This work provides new ideas for improving the MRF performance.

The influence of aspect ratio on the properties of cobalt nanowire-based magnetorheological fluids

The yield stress of magnetorheological(MR)fluids has been shown to depend on particle morphology,but the exact nature of this contribution is still not fully understood.In this study,MR fluids containing 4 vol.%cobalt particles(spherical particles vs.nano-wires)suspended in silicone oil were investigated.The influence of the aspect ratio on the rheological properties of suspensions that contained cobalt nanowires with aspect ratios ranging from 10 to 101 in increments of~6 is described.The cobalt nanowires were fabricated using alumina template-based electrodeposition,produ-cing wires with 305±66 nm diameters.The shear stress was measured as a function of shear rate for increasing applied mag-netic fields.The apparent yield stress and viscosity as a function of changing aspect ratio of the nanowire suspensions were deter-mined.At a saturated magnetic flux density,the yield stress was found to increase linearly up to an aspect ratio of 23(7.1μm long wires)at which time the yield stress reached a plateau of 3.7 kPa even as the aspect ratio was further increased.As a comparison,suspensions containing 4 vol.%1.6μm spherical cobalt particles only reached a maximum yield stress of 1.6 kPa.

Modelling of Magnetorheological Fluids with Combined Lattice Boltzmann and Discrete Element Approach

A combined lattice Boltzmann and discrete element approach is proposedfor numerical modelling of magnetorheological fluids. In its formulation, the particledynamics is simulated by the discrete element method, while the fluid field is resolvedwith the lattice Boltzmann method. The coupling between the fluid and the particlesare realized through the hydrodynamic interactions. Procedures for computing magnetic, contact and hydrodynamic forces are discussed in detail. The applicability ofthe proposed solution procedure is illustrated via a two-stage simulation of a MR fluidproblem with four different particle volume fractions. At the first stage, simulationsare performed for the particle chain formation upon application of an external magnetic field;and at the second stage, the rheological properties of the MR fluid underdifferent shear loading conditions are investigated with the particle chains establishedat the first stage as the initial configuration.

Effect of nanoparticles on the performance of magnetorheological fluid damper during hard turning process

Magnetorheological(MR)fluid damper which allows the damping characteristics of the damper to be continuously controlled by varying the magnetic field is extensively used in metal cutting to suppress tool vibration.Even though magnetorhelogical fluids have been successful in reducing tool vibration,durability of magnetorhelogical fluids remains a major challenge in engineering sector.Temperature effect on the performance of magnetorhelogical fluids over a prolonged period of time is a major concern.In this paper,an attempt was made to reduce temperature and to improve viscosity of magnetorhelogical fluids by infusing nanoparticles along with MR fluids.Aluminium oxide and titanium oxide nanoparticles of 0.1%and 0.2%concentration by weight were considered and experimental tests were conducted to study the influence of nanoparticles on the performance of magnetorheological fluid.From the experimental results it was observed that the presence of nanoparticles in MR fluid reduces temperature and increases the viscosity of MR fluid thereby increasing the cutting performance during turning of hardened AISI 4340 steel.

Experimental Investigation and Semi-Active Control Design of A Magnetorheological Engine Mount

In this paper;the dynamic characteristics of a semi-active magnetorheological fluid(MRF)engine mount are studied.To do so,the performance of the MRF engine mount is experimentally examined in higher frequencies(50~170 Hz)and the various amplitudes(0.01~0.2 mm).In such an examination,an MRF engine mount along with its magnetically biased is fabricated and successfully measured.In addition,the natural frequencies of the system are obtained by standard hammer modal test.For modelling the behavior of the system,a mass-spring-damper model with tuned PID coefficients based on Pessen integral of absolute error method is used.The parameters of such a model including mass,damping ratio,and stiffness are identified with the help of experimental modal tests and the recursive least square method(RLS).It is shown that using PID controller leads to reducing the vibration transmissibility in the resonance frequency(=93.45 Hz)with respect to the typical passive engine mount by a factor of 58%.The average of the vibration transmissibility decreasing is also 43%within frequency bandwidth(50~170 Hz).

Shear Stress in MR Fluid with Small Shear Deformation in Bctlattic Structure

A theoretical model based on BCT lattice structure was developed. Resultant force in the BCT lattice structure was deduced, following the interaction force of two kinds of magnetic particles. According to empirical FroHlich-Kermelly law, the relationship between the magnetic induction and the magnetic field was discussed, and a predictive formula of shear stresses of the BCT lattice structure model was established for the case of small shear deformation. Compared with the experimental data for different particle volume fractions, the theoretical results of the shear stress indicate the effects of the saturation magnetization and the external magnetic field on the shear stress.

Advanced nonlinear rheology magnetorheological finishing: A review

High-performance devices usually have curved surfaces, requiring high accuracy of shape and low surface roughness. It is a challenge to achieve high accuracies for form and position on a device with low surface roughness. However, due to the unique nonlinear rheology, magnetorheological fluids with hard abrasives are widely applied in ultra-precision surface finishing. Compared with conventional mechanical finishing, magnetorheological finishing displays obviously advantages, such as high precision shape of machined surface, low surface roughness and subsurface damage, and easy control for finishing processes. However, finishing performance depends on various factors, e.g. volume fraction and distribution of magnetic particles, types of hard abrasives and additives, strength of magnetic field, finishing forms. Therefore, a comprehensive review on related works is essential to understand the state-of-the-art of magnetorheological finishing and beneficial to inspire researchers to develop lower cost, higher machining accuracy and efficient approaches and setups, which demonstrates a significant guidance for development of high-performance parts in fields of aerospace, navigation and clinical medicine etc. This review starts from the rheological property of magnetorheological fluids, summarizing dynamically nonlinear rheological properties and stable finishing approaches. Then, the effect of components in magnetorheological fluids is discussed on finishing performance, consisting of magnetic particles, carrier fluid, additives and abrasives. Reasonable configuration of magnetorheological fluids, and different magnetorheological finishing methods are presented for variously curved surfaces. In addition, the current finishing forms and future directions are also addressed in this review.

A novel method of water bath heating assisted small ball-end magnetorheological polishing for hemispherical shell resonators

Hemispherical shell resonator(HSR)is the core component of hemispherical resonator gyro.It is aφ-shaped small-bore complex component with minimum curvature radius less than 3 mm.Thus,traditional polishing methods are difficult to polish it.Small ball-end magnetorheological polishing method can polish the small components with complicated three-dimensional surface and obtain non-destructive surface.Therefore,this method is suitable for polishing HSR.However,the material removal rate of the ordinary small ball-end magnetorheological polishing is low,leading to long polishing time and low output of HSR.To solve this problem,a water bath heating assisted small ball-end magnetorheological polishing method is proposed in this research.The influence rule of processing parameters on the material removal rate is studied experimentally.A set of optimal processing parameters is obtained to maximize the material removal rate.Compared with the ordinary method,the material removal rate of the new method can be improved by 143%.Subsequently,an HSR is polished by the new method.The results show that the polishing time can be reduced by 55%,and the polished surface roughness can reach 7.7 nm.The new method has the great potential to be used in actual production to improve the polishing efficiency of HSR.

Fractional Modeling and Analysis of Coupled MR Damping System

The coupled magnetorheological(MR) damping system addressed in this paper contains rubber spring and magnetorheological damper. The device inherits the damping merits of both the rubber spring and the magnetorheological damper.Here a fractional-order constitutive equation is introduced to study the viscoelasticity of the combined damper. An introduction to the definitions of fractional calculus, and the transfer function representation of a fractional-order system are given. The fractional-order system model of a magnetorheological vibration platform is set up using fractional calculus, and the function of displacement is presented. It is indicated that the fractional-order constitutive equation and the transfer function are feasible and effective means for investigating of magnetorheological vibration device.

Surface Roughness Simulation During Rotational-Magnetorheological Finishing of Poppet Valve Profiles

Surface finishing is essential for various applications in the aerospace industry.One of the applications is the poppet valve,which is used for leak-proof sealing of high-pressure gases in aerospace gas propulsion engines.The combustion engine also typically employs a poppet valve as an intake and exhaust valve.Nano-finishing a poppet valve is difficult because of its complex narrow profile.The precise nano-finished poppet valve perfectly fits on its seat and reduces hydrocarbon emissions.The rotational-magnetorheological fluid-based finishing process can be used effectively for these complicated surfaces.The polishing agent in this process is magnetorheological fluid,and rheological properties are controlled by a permanent magnet.This article presents the uniform finishing of the poppet valve's narrow ridge profile,which is analyzed through finite element analysis(FEA),wherein the outcomes are uniform shear stress,normal stress,and magnetic flux density distributions along the poppet ridge profile.The study of forces exerting on abrasive grains and surface roughness simulation is also conducted using FEA findings.The experiment is subsequently performed to verify the simulation results for poppet profile polishing.The obtained experimental and simulated surface roughness values are comparable.After the finishing process,the maximum percentage improvement of surface roughness is obtained as 93.71%.The rotational-magnetorheological fluid-based finishing process has high accuracy and reliability for specific applications.