The Effect of Particle Shapes on the Field-Dependent Rheological Properties of Magnetorheological Greases

Abstract

The transient response of magnetorheological (MR) materials, in general, is very important for design consideration in MR-based devices. Better response to magnetic fields is beneficial for a better response rate to the electrical current applied in the electromagnetic coil. As a result, MR-based devices would have a high response to external stimuli. In this work, the principal characteristics of magnetorheological greases (MRGs) which have two different particle shapes are experimentally investigated. One type of particle distributed in the grease medium is conventional spherical-shaped carbonyl iron (CI) particles, while the other is plate-like CI particles made using a high-energy rotary ball mill from spherical CI particles. A set of bidisperse MRG samples are firstly prepared by adjusting the weight percentage of the plate-like CI particles and mixing with the spherical CI particles. Subsequently, three important properties of MRGs in terms of their practical application are measured and compared between the two different particle shapes. The field-dependent apparent viscoelastic properties of the prepared MRG samples are measured, followed by the field-dependent storage and loss moduli using an oscillatory shear rheometer. In addition, the transient response time, which indicates the speed in the actuating period of MRGs, is measured by changing the strain amplitude. Then, a comparative assessment on the three properties are undertaken between two different particle shapes by presenting the corresponding results in the same plot. It is shown that the bidisperse MRG with plate-like CI particles exhibits an increase in the initial apparent viscosity as well as stiffness property compared to the MRG with spherical particles only.

Rheological Analysis on Hardening of Magnetorheological Grease with Kerosene

“…The facilitated movement was theorized to result in stronger CIP chains, which increased resistance. The results obtained in this part of the study were validated by comparing it with previous studies [13], [14]. After 1 year, the storage modulus obtained is shown in Figure 6.…”

“…The breaking down of MRG, as stated in the previous studies [12]- [14], was a strong indication of grease degradation. Several studies have established the degradation of grease in various conditions, including high temperature [9], repeated shear [15], and even decomposition due to electrical discharge [16].…”

“…However, it was observed that excess dilution oils caused oil separation as the grease thickener could not structurally hold on to the amount of liquid in the MRG. Different dilution oils seemed to have different effects on the initial viscosity and oil separation as studies reported that the use of hydraulic fluid, which has a higher viscosity than kerosene, would hold a higher weight percentage of dilution oil without separation [13], [14]. The sample with kerosene started to separate at around 15 wt% kerosene in the MRG, while the hydraulic fluid sample stayed intact throughout the study.…”

A machine learning approach to estimate magnetorheological suspension composition based on magnetic field dependent-rheological properties

“…The first and second additional data were taken from [15] of the spherical and plate-like data, respectively, with total data points of about 90. In terms of training accuracy, the R 2 value of 1 has shown almost the same result with data 2 [47]. In terms of testing accuracy, the prediction based on additional data can produce better accuracy than the model based on data 2.…”

Study on the rheological and polishing properties of electromagnetic two-phase composite particles with abrasive characteristics

“…Pan et al [20] showed that the non-magnetic material on the surface increased the spacing between the magnetic particles, so the magnetic properties of the composite particles will be weaker than before the coating. Therefore, it can be seen from figure 7 that the magnetorheological shear stress of the CDS type EMRF is smaller than that of the CI type in the range [0, 1.8]A and significantly smaller than that of the Fe 3 O 4 type in [0, 1]A. Mohamad et al [23] showed that a MRF prepared with complex-shaped magnetic particles has greater magneto-rheological shear stress than that prepared with smooth spherical magnetic particles. The irregular shape increases the friction between the magnetic particles, which can improve the structural strength of the magnetic chain.…”