Norzilawati Mohamad

The Field-Dependent Rheological Properties of Magnetorheological Grease Based on Carbonyl-Iron-Particles

This paper presents dynamic viscoelastic properties of magnetorheological (MR) grease under variation of magnetic fields and magnetic particle fractions. The tests to discern the field-dependent properties are undertaken using both rotational and oscillatory shear rheometers. As a first step, the MR grease is developed by dispersing the carbonyl iron (CI) particles into grease medium with a mechanical stirrer. Experimental data are obtained by changing the magnetic field from 0 to 0.7 T at room temperature of 25 °C. It is found that a strong Payne effect limits the linear viscoelastic region of MR grease at strains above 0.1%. The results exhibit a high dynamic yield stress which is equivalent to Bingham plastic rheological model, and show relatively good MR effect at high shear rate of 2000 s-1. In addition, high dispersion of the magnetic particles and good thermal properties are proven. The results presented in this work directly indicate that MR grease is a smart material candidate that could be widely applicable to various fields including vibration control.

Effect of carbonyl iron particles composition on the physical characteristics of MR grease

Magnetorheological (MR) grease is an extension of the study of magnetorheological materials. The MR grease can help to reduce the particles sedimentation problem occurred in the MR fluids. Within this study, an effort has been taken to investigate the effect of different weight compositions of carbonyl iron particles on the physical and chemical characteristics of the MR grease under off-state condition (no magnetic field). The MR grease is prepared by mixing carbonyl iron particles having a size range of 1 to 10 µm with commercial NPC Highrex HD-3 grease. Characterizations of MR grease are investigated using Vibrating Sample Magnetometer (VSM), Environmental Scanning Electron Microscopy (ESEM), Differential Scanning Calorimeter (DSC) and rheometer. The dependency of carbonyl iron particles weight towards the magnetic properties of MR grease and other characterizations are investigated.

An overview of nanoparticles utilization in magnetorheological materials

Magnetorheological (MR) materials belong to smart materials family where the rheological properties can be altered continuously, rapidly and reversibly through the external magnetic field. The tuneable properties depend on the magnitude of the external magnetic field. The micron-sized magnetizable particles having high saturation magnetization within matrix carrier react to the magnetic field resulting in alteration of MR effect. The classic problem of smart materials is particles sedimentation and aggregation issues due to the high concentration and large size of magnetic particles. Many researchers have attempted to solve this issues by introducing nano-sized particles into these materials. Based on the previous researches, the nanoparticles incorporation in MR materials is reported to improve the stability of the MR materials and at the same time enhance the MR performance. This paper presents an overview of nanoparticles incorporation in different types of MR materials which are MR fluids, MR grease, and MR elastomer including the stability and performance achievement regarding rheological properties.

A comparative work on the magnetic field-dependent properties of plate-like and spherical iron particle-based magnetorheological grease

In this study, a new magnetorheological (MR) grease was made featuring plate-like carbonyl iron (CI) particles, and its magnetic field-dependent rheological properties were experimentally characterized. The plate-like CI particles were prepared through high-energy ball milling of spherical CI particles. Then, three different ratios of the CI particles in the MR grease, varying from 30 to 70 wt% were mixed by dispersing the plate-like CI particles into the grease medium with a mechanical stirrer. The magnetic field-dependent rheological properties of the plate-like CI particle-based MR grease were then investigated using a rheometer by changing the magnetic field intensity from 0 to 0.7 T at room temperature. The measurement was undertaken at two different modes, namely, a continuous shear mode and oscillation mode. It was shown that both the apparent viscosity and storage modulus of the MR grease were heavily dependent on the magnetic field intensity as well as the CI particle fraction. In addition, the differences in the yield stress and the MR effect between the proposed MR grease featuring the plate-like CI particles and the existing MR grease with the spherical CI particles were investigated and discussed in detail.

Improvement of magnetorheological greases with superparamagnetic nanoparticles

Magnetorheological greases (MRGs) is a viscoelastic suspension comprised of carbonyl iron (CI) particles in a thixotropic medium; grease, which able to solve the instability problem that occurs in oil medium like MRFs. The primary purpose introduction of superparamagnetic nanoparticles γ-Fe2O3 in MRGs suspension is to investigate the effect of additives toward MRGs characteristics. Two types of MRGs suspension with and without nanoparticles γ-Fe2O3 were prepared in the same CI particles concentration for comparison purpose. It was observed that MRGs with incorporated of 1 wt% nanoparticles γFe2O3 showed an increment regarding magnetic properties. In the meantime, the off-state viscosity of MRGs containing nanoparticles γFe2O3 was reduced, however, increased during on-state condition. This fact indicates that the interspaces between CI particles are filled by the nanoparticles γ-Fe2O3. Therefore, the introduction of the nanoparticles indirectly improved the MRGs properties.

The Damping Properties of Plate-Like Magnetorheological Elastomer

This paper aims to investigate the damping properties of plate-like carbonyl iron particle (CIP) magnetorheological elastomer (MRE). The damping properties of MRE is mainly dependent on the strength of magnetic field. Anisotropic MRE was fabricated under various magnetic fields strength (70, 210, 345, and 482 mT) and its damping property prior to frequency-dependent was measured using a rheometer. Firstly, the plate-like CIP was first synthesized from spherical CIP using a ball-milling method. The microstructure of plate-like CIP was observed using low vacuum scanning electron microscope. Subsequently, two types of MREs which are isotropic and anisotropic were fabricated using 70 weight percent (wt.%) of plate-like CIP. The experimental results showed that the anisotropic MRE has lower damping factor than isotropic MRE. Meanwhile, the damping factor increases with the increase of frequency.

A Model of Magnetorheological Grease using Machine Learning Method

Magnetorheological (MR) grease is a promising material to replace MR fluid because the advantage in term of stability and less possibility to leaking. To improve the material properties, an accurate model can be critical for reducing the time and cost of the development process. A model has been developed to predict MR fluid material properties by including the composition. However, the model may need adjustment and cannot predict other essential rheology parameters, such as viscosity, apparent viscosity, shear rate, and shear stress. Therefore, the technical novelty of this paper is to propose a model with composition as one of the inputs using extreme learning machine method. A scoring system is also introduced to quantify the significance of the composition effect toward the MR grease performance. Then, the model is simulated and compared with experimental data. The performance shows high accuracy estimation with normalized root mean square error about 1.25%.

Physicochemical and Viscoelastic Properties of Magnetorheological Solids

A broad view of solid state magnetorheological (MR) materials is discussed in this book chapter. The MR solids are divided into several classes i.e. magnetorheological elastomers, magnetorheological plastomers, and magnetorheological grease/gels. The states of integration into functional devices are described. The status of materials and fabrication methods are explained based on the existing research. The knowledge on physicochemical and viscoelastic characterization of the MR solids is delivered to figure out the possible behaviors that can be revealed from such materials. The quantitative achievements in physicochemical and viscoelastic properties are presented to ease readers in establishing mind maps considering the raw materials, fabrication, and viscoelastic testing procedures.