• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.557-560
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• 2003

Magnetorheological finishing(MRF) is a newly developed and recently commercialized for finishing optical components. The magnetorheological fluid consists of a water based suspension of carbonyl iron, nonmagnetic polishing abrasives, and small amounts of stabilizer. This magnetorheological fluid is pumped from conditioner on the rotating wheel and suctioned back to the conditioner, where it cooled to setpoint temperature and evaporative losses are replaced. This method could produce some problems in suction. So newly designed MRF tools is proposed in which MR fluid is not circulated and conditioned by the slurry. The new polishing mechanism is experimented. Measured surface roughness supports the validity of this mechanism.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.775-778
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• 2000

Magnetorheological Finishing(MRF) is a newly developed and recently commercialized for finishing optical components. The magnetorheological fluid consists of a water based suspension of carbonyl iron, nonmagnetic polishing abrasives, and small amounts of stabilizer. Theoretical analysis of MRF, based on Bingham lubrication theory, is illustrated and a correlation between surface shear stress on the workpiece and material removal is obtained.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1840-1843
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• 2003

The Magnetorheological fluid has the properties that its viscosity has drastic changed under some magnetic fields therefore, Magnetorheological fluids has been used for micro polishing of the micro part( for example, a aspherical surface in a micro lens). The polishing process may appears as follows. A part rotating on the spindle is brought into contact with an Magnetorheological finishing(MRF) fluids which is set in motion by the moving wall. In the region where the part and the MRF fluid ate brought into contact, the applied magnetic field creates the conditions necessary for the material removal from the part surface. The material removal takes place in a certain region contacting the surface of the part which can be called the polishing spot or zone. The polishing mechanism of the material removal in the contact zone is considered as a process governed by the particularities of the Bingham flow in the contact zone. Resonable calculated and experimental magnitudes of the material removal rate for glass polishing lends support the validity of the approach.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.46-52
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• 2004

The Magnetorheological fluid has the properties that its viscosity has drastic changed under some magnetic fields therefore, Magnetorheological fluids has been used fur micro polishing of the micro part(for example, a spherical surface in a micro lens). The polishing process may appears as follows. A part rotating on the spindle is brought into contact with an Magnetorheological finishing(MRF) fluids which is set in motion by the moving wall. In the region where the part and the MRF fluid are brought into contact, the applied magnetic field creates the conditions necessary for the material removal from the part surface. The material removal takes place in a certain region contacting the surface of the part which can be called the polishing spot or zone. The polishing mechanism of the material removal in the contact zone is considered as a process governed by the particularities of the Bingham flow in the contact zone. Resonable calculated and experimental magnitudes of the material removal rate for glass polishing lends support the validity of the approach.

• Journal of Magnetics
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• v.21 no.2
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• pp.229-234
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• 2016

Aiming to prepare high performance magnetorheological fluid, firstly, oleic acid and sodium dodecyl benzene sulfonate are chosen as surfactants. And then, the mechanical stirring process including stirring time, stirring temperature and stirring speed are optimized by measuring sedimentation ratio and zero-field viscosity. Finally, the properties of prepared magnetorheological fluid are elaborated. The results indicate that the compounding of oleic acid and sodium dodecyl benzene sulfonate can improve the properties of magnetorheological fluid distinctively, and the optimistic compounding content is 4g:4g or 5g:5g. The surfactants adding orders and the second stirring time have little effect on the properties of magnetorheological fluid, while obviously of the first stirring time, temperature and speed. Moreover, the sedimentation ratio of prepared magnetorheological fluid is less than 5.2% in two weeks, the zero-field viscosity is smaller than $0.6Pa{\cdot}s$ at $20^{\circ}C$, and the maximum yield stress is higher than 50 kPa.

• Smart Structures and Systems
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• v.11 no.3
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• pp.315-329
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• 2013

The construction of an experimental nonlinear structural model with little cost and unlimited repeatability for vibration control study represents a challenging task, especially for material nonlinearity. This paper reports the design, analysis and vibration control of a nonlinear structural experiment platform with adjustable hinges. In our approach, magnetorheological rotary brakes are substituted for the joints of a frame structure to simulate the nonlinear material behaviors of plastic hinges. For vibration control, a separate magnetorheological damper was employed to provide semi-active damping force to the nonlinear structure. A dynamic neural network was designed as a state observer to enable the feedback based semi-active vibration control. Based on the dynamic neural network observer, an adaptive fuzzy sliding mode based output control was developed for the magnetorheological damper to suppress the vibrations of the structure. The performance of the intelligent control algorithm was studied by subjecting the structure to shake table experiments. Experimental results show that the magnetorheological rotary brake can simulate the nonlinearity of the structural model with good repeatability. Moreover, different nonlinear behaviors can be achieved by controlling the input voltage of magnetorheological rotary damper. Different levels of nonlinearity in the vibration response of the structure can be achieved with the above adaptive fuzzy sliding mode control algorithm using a dynamic neural network observer.

• Journal of Magnetics
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• v.22 no.2
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• pp.281-285
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• 2017

To suppress the wall slip effect and improve the yield stress measurement precision of magnetorheological fluid, measurement disks with different grooves are first manufactured. Then, the influence of groove characteristics on the yield stress of magnetorheological fluid is investigated by the method of experiments. Finally, the optimization wall grooves of measurement disks are obtained, and the yield stress of a self-prepared magnetorheological fluid is measured. Results indicate that the groove type and groove width have a slight influence on the shear yield stress, whereas the measured yield stress increases with enhanced groove density, and the optimized groove depth is 0.3 mm. The measured shear yield stress of self-prepared MR fluid can be improved by 18 % according to the optimized grooved disks, and the maximum yield stress can reach up to 65 kPa as the magnetic flux density is 0.5 T.

• Smart Structures and Systems
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• v.25 no.3
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• pp.279-284
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• 2020

Electrical current is usually used to change the damping force of Magnetorheological Dampers (MRDs). However, changing the electrical current could shift the stiffness of the system, the phenomenon that was not considered carefully. This study aims to evaluate this shift. A typical MRD was designed, optimized, and fabricated to do some accurate and detailed experimental tests to examine the stiffness variation. The damper is equipped with a circulating system to prevent the deposition of particles when it is at rest. Besides that, a vibration setup was developed for the experimental study. It is capable of generating vibration with either constant frequency or frequency sweep and measure the amplitude of vibration. The damper was tested by the vibrating setup, and it was concluded that with a change in electrical current from 0 to 1.4 A, resonant frequency would change from 13.8 Hz to 16 Hz. Considering the unchanging mass of 85.1 kg, the change in resonant frequency translates as a shift in stiffness, which changes from 640 kN/m to 860 kN/m.

• Smart Structures and Systems
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• v.29 no.5
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• pp.705-714
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• 2022

In this paper, the effect of magnetic field on the vibration behavior of a Magnetorheological elastomer (MRE) sandwich MEMS actuated by electrostatic actuation with conductive skins are examined within the multiple scales (MMS) perturbation method. Magnetorheological smart materials have been widely used in vibration control of various systems due to their mechanical properties change under the influence of different magnetic fields. To investigate the vibrational behavior of the movable electrode, the Euler-Bernoulli beam theory, as well as Hamilton's principle is used to derive the equations and the related boundary conditions governing the dynamic behavior of the system are applied. The results of this study show that by placing the Magnetorheological elastomer core in the movable electrode and applying different magnetic fields on it, its natural vibrational frequency can be affected so that by increasing the applied magnetic field, the system's natural frequency increases. Also, the effect of various factors such as the electric potential difference between two electrodes, changes in the thickness of the core and the skins, electrode length, the distance between two electrodes and also change in vibration modes of the system on natural frequencies have been investigated.

• Journal of Magnetics
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• v.21 no.2
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• pp.244-248
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• 2016

Aiming to improve the shear yield stress of magnetorheological fluid, magnetorheological fluids with different particle characteristics are prepared, and the influence rules of particle mass fraction, particle size, nanoparticles content and application temperature on shear yield stress are investigated. Experimental results indicate that shear yield stress increases approximate linearly with the enhancement of particle mass fraction. Particle size and the nanoparticles within 10% mass fraction can improve the shear yield stress effectively. When the application temperature is higher than $100^{\circ}C$, the shear yield stress decreases rapidly because of thermal expansion and thermal magnetization effect.