Yield Stress Of Magnetorheological Fluids Research Articles

Constitutive model for shear yield stress of magnetorheological fluid based on the concept of state transition

Magnetorheological fluid (MRF) is a smart material whose rheological properties can be varied by a magnetic field; it has been applied in the development of semiactive dampers for a variety of applications. The material essentially consists of a suspension of magnetic particles in a nonmagnetic carrier fluid. It is important to understand the magnetic response of MRF and its dependence on several parameters for improving and designing MRF devices. The purpose of this work is to develop a constitutive model that describes the behavior of the shear yield stress of the material as function of the magnetic field and composition. Taking into account that the material changes its rheology and apparent viscosity according to magnetic field, a magnetically induced state transition is proposed; by the use of a state transition equation, a constitutive model for shear yield stress is defined, consisting of an expression that relates composition of the material and the stimulus applied, it also associates the volume fraction of particles, magnetic field and the material that composes the particles.

Squeeze strengthening of magnetorheological fluids using mixed mode operation

This research details a novel method of increasing the shear yield stress of magnetorheological fluids by combining shear and squeeze modes of operation to manipulate particle chain structures, so-called squeeze strengthening. Using a custom built Searle cell magnetorheometer, which is a model device emulating a rotary magnetorheological energy absorber (MREA), the contribution of squeeze strengthening to the total controllable yield force is experimentally investigated. Using an eccentric rotating inner cylinder, characterization data from large (1 mm) and small (0.25 mm) nominal gap geometries are compared to investigate the squeeze strengthening effect. Details of the experimental setup and method are presented, and a hybrid model is used to explain experimental trends. This study demonstrates that it is feasible, utilizing squeeze strengthening to increase yield stress, to either (1) design a rotary MREA of a given volume to achieve higher energy absorption density (energy absorbed normalized by active fluid volume), or (2) reduce the volume of a given rotary MREA to achieve the same energy absorption density.

Magneto-Rheological Dynamometer Dynamic Model Research

This article simply introduces a new material magneto-rheological fluid (MRF) and its widely used, and developed a new type of magneto-rheological dynamometer based on the rheological properties of MRF. This dynamometer introduces magneto-rheological fluid as the working medium, and using the shear yield stress of magneto-rheological fluid in a magnetic field to transmit torque. The paper explored the working mechanism of MR dynamometer, established the torque transmission model of MR dynamometer, and analyzed the flow properties of MRF in the dynamometer under steady-state based on Bingham model and fluid momentum equation.

A new resonant based measurement method for squeeze mode yield stress of magnetorheological fluids

A new approach to measure the field-dependent yield stress of magnetorheological (MR) fluids in squeeze mode using the resonance concept is proposed. The measurement system is designed using the piezolaminated cantilever beam coupled with an electromagnetic coil based MR fluid squeezing setup. The cantilever beam is maintained at resonance using simple closed-loop electronics. The magnetic field produced by the coil changes the viscosity of MR fluids and produces an additional stiffness to the resonating cantilever beam. The shift in resonant frequency due to the change in viscosity of the MR fluid is measured, and the shift in frequency is analytically related to the yield stress. Two types of MR fluids based on sphere and plate iron particles are used to demonstrate the effectiveness of the proposed measurement system.

Influence of wall characteristics on transmittable torque of magnetorheological fluid

Magnetorheological fluid is a controllable fluid that exhibits changeable yield stress and attractive rheological properties on the applied magnetic field. In order to enhance the yield stress of magnetorheological fluid and suppress wall slip effect in the case of transmission, the mechanism and corresponding influence factors of the wall slip effect were investigated theoretically and experimentally. Different transmittable disks and a magnetorheological transmission test-bed were built, and the influence of wall characteristics on the transmission capacity of magnetorheological fluids was investigated on the test-bed. The results showed that the material types, surface roughness, and surface textures of transmission wall have distinct influence on the transmission capacity of magnetorheological fluid. The transmission wall with a groove depth of 0.2 mm, higher material magnetic permeability, higher surface roughness, radial grooves at the surface, and higher groove density was determined as the best transmission wall.

Design of magnetorheological damper with a combination of shear and squeeze modes

Magnetorheological (MR) damper is a semi-active suspension device that uses MR fluid to produce controllable damper. The mechanical properties of the suspension can be controlled by adjusting the yield stress of MR fluid. This paper presents the design of a new concept for MR damper with a combination of shear and squeeze working modes. Finite Element Method Magnetics (FEMM) was utilized to simulate the magnetic field generated by electromagnetic coils in MR damper. The MR damper was designed and fabricated according to the simulation results. The experimental tests were performed under quasi-static loading in three different conditions; shear mode, squeeze mode and combination of both modes. The results showed that the mixed mode MR damper has produced a unique damping characteristic where in general, a higher damping force has obtained in mixed mode than single mode.

Design of a squeeze film magnetorheological brake considering compression enhanced shear yield stress of magnetorheological fluid

A magnetorheological brake, consisting of rotating disks immersed in a MR fluid and enclosed in an electromagnet, is proposed to replace the conventional heavy weight low response hydraulic disk brake. The frictional characteristics of the proposed brake can be controlled by regulating the yield stress of the MR fluid as function of magnetic field and normal compressive force. The controllable yield stress retards the surfaces of rotating disks, thus MR fluid can be used as a brake lining material. The present research work attempts designing a squeeze film MR brake by accounting compression enhanced shear yield stress of magnetorheological fluid. Theoretical calculations indicate that the estimated braking torque of the six plate squeeze film MR brake, under compression, is in the order of 600Nm. To validate the theoretical design and its findings, a prototype of single-plate squeeze film MR disk brake has been developed. Experimental test setup helps to illustrate braking torque under different control currents (0.0 to 1.25 A).

Optimal Design of Magneto-Rhological Damper

For the complex nonlinear property and a lot of regulatory parameter, it is difficult to design a reasonable magneto-rheological (MR) damper by simply process or experience. To solve this problem a structural optimization has been presented in this article. Three stages have been discussed in the article. By calculate the flux of MR fluid based on the yield stress of MR fluid, selected common design targets such as maximal output damping force, dynamic range and consult volume of damper has been presented in formula respectively with the parameter according to damper structure. By approximate the magnetic circle, the power of excitation also has been presented as an expression of structure parameter. An optimum method named multi-goal attach has been applied to solve the optimum problem. Finally some confirmation and experiment results have been presented. The experiment results indicated that the method presented in the article was effectively.

Tension and Shearing Characteristics of Magneto Rheological Fluid under Magnetic Fields

The mechanical properties of a magneto rheological (MR) fluid in tension and shearing have been studied in the magnetic field which is generated by a coil carrying different magnitudes of DC electrical current. An experiment setup was designed and fabricated to perform this operation. The magnetic behavior of the equipment was analyzed using software of ANSYS/Multiphysics. The shear yield stress represents the effect of the interaction force along the shear direction (perpendicular to the direction of the magnetic field). The tensile yield stress of MR fluids represents the effect of the interaction force between the polarized particles along the direction of the applied magnetic field. The shearing tests showed that the shear yield stress is proportional to the external magnetic flux density with an exponent of 1.19. The tensile yield stress is about four times of shear yield stress.

Study on the Model of Magnetic Flocculation of Magneto-Rheological Fluid

Magneto-rheological fluid (MRF) is non-colloidal suspension. In this paper, it is introduced that MRF will produce magnetic coagulation at an applied magnetic field by analyzing the interact energy between particles in MRF, and the coagulation is chain-like flocculation. The main reason that MRF produced magnetic coagulation is the direction between chain-like structure and magnetic field is the same. According to the studies above, the formula of yield stress for MRF at an applied magnetic field can be deduced. It can be seen from the formula that there is a square relationship between yield stress of MRF and particle magnetization, and the yield stress of MRF is closely related with volume concentration. The conclusions above match the results of existing experiments very well.

Shear and Squeeze Rheometry of Magnetorheological Fluids

The mechanical properties of a magnetorheological (MR) fluid in shearing, compression and shearing after compression have been studied in the magnetic field which is generated by a coil carrying different magnitudes of DC electrical current on a self-constructed test system. The relations of compression stress versus compression strain, yield stress versus compression stress were studied under different magnetic fields. The compressing tests showed that the MR fluid is very stiff at small compressive strains lower than 0.13. The shear yield stress of MR fluids after compression was much stronger than that of uncompressed MR fluids under the same magnetic field. The enhanced shear yield stress of MR fluids can be utilized to design the MR clutch and brake for new structure and will make MR fluids technology attractive for many applications.

Yield and Rheological Behaviors of Magnetorheological Fluids

Magnetorheological (MR) fluids are materials that respond to an applied magnetic field with the change of their yield and rheological behaviors. In this paper, the yield and rheological behaviors of MR fluids are discussed. Based on the microstructure of magnetic chain a theoretical model is developed to analyze the effect of an applied magnetic field on the yield stress of MR fluids. Bingham model is used to describe the rheological behaviors of MR fluids subject to an applied magnetic field. The results show that altering the strength of an applied field can control the yield stress of MR fluids. The shear stress increases as the strength of an applied magnetic field increases, and it hardly changes with the increase of shear strain rate. MR fluids exhibit Bingham plastic model.

Effect of seven different additives on the properties of MR fluids

Magnetorheological (MR) fluids have been developed for application in semi-active magnetorheological fluid dampers and other magnetorheological fluid devices. In order to prepare special MR fluids to satisfy the demands of tracked vehicle, two different carrier fluids were chose to prepare MR fluids. Preparation of MR fluids, which are based on carriers such as special shock absorption fluid and 45# transformer oil, was finished. And characteristics of these samples were tested and analyzed. Results indicate, Tween-80 and Span-80 can improve sedimentary stability. Using 45# transformer oil instead of special shock absorption fluid as a carrier, the shear yield stress remains nearly invariable but the viscosity and the sedimentary stability are reduced. MR fluids with diameter of 2.73μm show better sedimentary stability than that of the MR fluids with diameter of 2.3μm, or 4.02μm. Stearic acid obviously improves sedimentary stability and off-state viscosity, but don't perform an obvious function on shear yield stress. In magnetic field of 237KA/m, the shear yield stress of MR fluid based on special shock absorption fluid and 45# transformer oil is 18.34KPa, 14.26KPa, respectively.

MR댐퍼를 적용한 6WD 군용차량의 성능평가

This paper proposes a new type of MR(magnetorheological) fluid based suspension system and applies it to military vehicle for vibration control. The suspension system consists of gas spring and MR damper. The nonlinear behavior of spring characteristics is evaluated with respect to the wheel travel and damping force model due to viscosity and yield stress of MR fluid is derived. Subsequently, a military vehicle of 6WD is adopted for the integration of the MR suspension system and its nonlinear dynamic model is established by considering vertical, pitch and roll motion. Then, a sky-hook controller associated with semi-active actuating condition is designed to reduce the imposed vibration. In order to demonstrate the effectiveness of the proposed MR suspension system, computer simulation is undertaken showing vibration control performance such as roll angle and pitch angle evaluated under bump and random road profiles.

The strengthening effect of guar gum on the yield stress of magnetorheologicalfluid

In this paper we present a novel approach for producing obvious strengthening ofthe magnetorheological (MR) effect of MR fluids. Carbonyl iron powders coatedwith guar gum were used as magnetic particles in the MR fluid. Experimentalresults showed that inducing a guar gum coating not only greatly improved thesedimentation stability but also strengthened the yield stress of the MR fluid. Anintermolecular force based model was proposed for explaining the strengthening effect.

Study of magnetorheological fluids at high shear rates

The tunable rheological properties of magnetorheological (MR) materials at high shear rates are studied using a piston-driven flow-mode-type rheometer. The proposed method provides measurement of the apparent viscosity and yield stress of MR fluids for a shear rate range of 50 to 40,000 s−1. The rheological properties of a commercial MR fluid, as well as a newly developed MR polymeric gel, and a ferrofluid-based MR fluid are investigated. The results for apparent viscosity and dynamic and static shear stresses under different applied magnetic fields are reported.

Rheological properties of magnetorheological fluid prepared by gelatin — carbonyl iron composite particles

Gelatin — carbonyl iron composite particle was prepared by micro emulsion method. The analysis of scanning electron microscope(SEM) shows that the ultrafine particles are spheroids coated by gelatin, and the average sizes of particles are 3 – 10 µm. The specific saturation magnetization σs is 130.9 A · m2/kg, coercivity H c is 0.823 A/m, and residual magnetism r is 4.98 Am2/kg for the composite particles. It is shown that the particles possess properties of soft magnetic. The yield stress of magnetorheological fluid (MRF) with composite particle reaches 70 kPa at 0.5 T magnetic induction. Magnetorheological effects are superior in lower magnetic field intensity and the subsidence stability of the MRF is excellent compared with pure carbonyl iron powder.

MAGNETORHEOLOGICAL FLUIDS AND THEIR PROPERTIES

Magnetorheological (MR) fluids are materials that respond to an applied magnetic field with a change in their rheological properties. Upon application of a magnetic field, MR fluids have a variable yield strength. Altering the strength of the applied magnetic field will control the yield stress of these fluids. In this paper, the method for measuring the yield stress of MR fluids is proposed. The curves between the yield stress of the MR fluid and the applied magnetic field are obtained from the experiment. The result indicates that with the increase of the applied magnetic field the yield stress of the MR fluids goes up rapidly.

Structure-enhanced yield stress of magnetorheological fluids

The yield stress of magnetorheological (MR) fluids depends on the induced solid structure. Since thick columns have a yield stress much higher than a single-chain structure, we improve the yield stress of MR fluids by changing the fluid microstructure. Immediately after a magnetic field is applied, we compress the MR fluid along the field direction. Scanning electron microscopy images show that particle chains are pushed together to form thick columns. The shear force measured after the compression shows that the structure-enhanced static yield stress can reach as high as 800 kPa under a moderate magnetic field, while the same MR fluid has a yield stress of 80 kPa without compression. This improved yield stress increases with the magnetic field and compression pressure and has an upper limit well above 800 kPa. The method may also be useful for electrorheological fluids.