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The magnetic permeability of three kinds of inclusions (Carbonyl iron, Ferroferric oxide, NiFe-alloy) filled polymer (Polydimethylsiloxane) is investigated at room temperature by using a Buck circuit for the dynamic test and vibrating sample magnetometer (VSM) for the static test. Unlike the traditional measurement method using an impedance analyzer, the self-built circuit can generate a maximum test current of ampere amplitude over high frequencies to simulate the transformer's operation status. The present work considers the effects of inclusion content (from 0 VOL.% to 33 VOL.%) and testing frequencies(100 kHz-1MHz). The experimental results of permeability are compared with the theoretical predictions in the previous works. Three main conclusions can be drawn: First, the magnetic permeability increases with the inclusion addition; Second, as the testing frequency increases, the permeability of the composite material maintains constant, showing no evident dependence on the testing frequency; Third, type of magnetic inclusion will gently affect the permeability of the composite material. This work systematically investigated the permeability of polymer-based magnetic materials, and the results are helpful for the soft-core transformer application of magnetoactive elastomers.

Fatigue life prediction is of great significance in ensuring magnetorheological elastomer (MRE) based rubber components exhibit reliability and do not compromise safety under complex loading, and this necessitates the development of plausible fatigue life predictors for MREs. In this research, silicone rubber based MREs were fabricated by incorporating soft carbonyl iron magnetic particles. Equi-biaxial fatigue behaviour of the fabricated MREs was investigated by using the bubble inflation method. The relationship between fatigue life and maximum engineering stress, maximum strain and strain energy density were studied. The results showed that maximum engineering stress and stored energy density can be used as reliable fatigue life predictors for SR based MREs when they are subjected to dynamic equi-biaxial loading. General equations based on maximum engineering stress and strain energy density were developed for fatigue life prediction of MREs.

A magnetorheological elastomer based on silicone rubber with carbonyl iron micro-particles was developed. The influence of the different amount of iron particles was experimentally studied by means of XRD, SEM, FTIR, EDS, XPS, uniaxial tension and rheological and cyclic tests. Different contents of carbonyl iron particles (10–40 wt%) were used to obtain the ratio of magnetic particles/silicone rubber that could provide the best mechanical properties on the MRE material. It was found that the composite material can have an increase of about 95% in its tensile strength when adding 20% of carbonyl iron particles to the raw rubber material. SEM analysis indicates a good dispersion of the magnetic particles on the rubber matrix, and the FTIR and XPS techniques confirm, as expected, that there is no chemical interaction between the iron from the carbonyl iron particles and the silicone rubber matrix due to a proper coating of the particles with silicone oil used as coupling agent. The TGA results evidenced that the addition of coated carbonyl iron particles had an impact on the thermal stability of the MRE and on the formation of cross-linked structures. The viscoelastic behavior of the magnetorheological elastomer is described by running experimental test on a rheometer device. Furthermore, cyclic testing were performed on the material sample to characterize the Mullin's effect.

Magnetosensitive elastomers (MSE) are innovative high-tech materials that exhibit changed dynamic properties when an external magnetic field is applied. In this work, the influence of particle content, frequency, temperature and magnetic field on the maximum attenuation of isotropic MSEs was studied. Six particle content types were synthesised using carbonyl iron powder particles embedded in a room-temperature vulcanizing silicone rubber matrix. The characterization of the MSE samples was performed with a Physica MCR 501 rheometer from the Anton Paar Company that is equipped with a magnetorheological cell. All samples were characterized using frequency sweep tests within the lineal viscoelastic region. In addition, a four-parameter fractional derivative model was used and extended over a wide frequency range. The influence of temperature was modelled using the Arrhenius model, coupled with the fractional derivative model. The maximum attenuation is increased with frequency and magnetic field and is independent of temperature.

Magneto-rheological fluids (MRF) are known as a category of smart materials because they exhibit sudden viscosity changes upon application of magnetic field. In contrast to normal fluids, MRFs can sustain shear up to a yield stress. Stability and resistance against movement are important factors which determine the extent of application of a MRF. In this work, new MRFs are developed using engine oil as carrier liquid, carbonyl iron powder as magnetic particle, stearic acid and CHRYSO® Optima100 as additives. Stability of the samples is measured over time. The samples are exposed to magneto-rheological tests with combined liquid and Peltier temperature control. Samples A, B and C are prepared with low, medium and high particle fractions respectively and tested at different temperatures (−10 °C, 5 °C, 60 °C) but for samples D, E, F and G the rheology tests are conducted in room temperature (25 °C) but at variable magnetic field and shear rate. Inherent assumption of the existing constitutive models is that the flow curve of MRF is shifted by a field-dependent yield stress. In this paper the effect of magnetic field is formulated and based on the physical properties of MRFs, a new method is introduced for identification of material parameters. This method predicts the yield stress by comparing the storage and shear moduli. Obtained results are compared with those obtained from fitting the experimental flow curves and also with those obtained from Bingham model. It is shown that, results of the proposed model are in good agreement with the experimental data. Moreover, the calculated sedimentation ratio shows that simultaneous use of stearic acid and Optima100 significantly improves stability of MRFs.

The paper presents experimental research and numerical modeling of dynamic properties of magnetorheological elastomers (MREs). Isotropic and anisotropic MREs have been prepared based on silicone matrix filled by micro-sized carbonyl iron particles. Dynamic properties of the isotropic and anisotropic MREs were determined using double-lap shear test under harmonic loading in the displacement control mode. Effects of excitation frequency, strain amplitude, and magnetic field intensity on the dynamic properties of the MREs were examined. Dynamic moduli of the MREs decreased with increasing the strain amplitude of applied harmonic load. The dynamic moduli and damping properties of the MREs increased with increasing the frequency and magnetic flux density. The anisotropic MREs showed higher dynamic moduli and magnetorheological (MR) effect than those of the isotropic ones. The MR effect of the MREs increased with the rise of the magnetic flux density. The dependence of dynamic moduli and loss factor on the frequency and magnetic flux density was numerically studied using four-parameter fractional derivative viscoelastic model. The model was fitted well to experimental data for both isotropic and anisotropic MREs. The fitting of dynamic moduli and loss factor for the isotropic and anisotropic MREs is in good agreement with experimental results.

Isotropic and anisotropic thermoplastic magnetorheological elastomer (MRE) composites were prepared by melt blending carbonyl iron (CI) particles with poly(styrene- b -ethylene-co-butylene- b -styrene) (SEBS) matrix in the absence and presence of a magnetic field. Effects of CI concentration and processing conditions on the microstructure, thermal stability, mechanical properties, viscoelastic properties and magnetorheological properties of these MRE composites based on SEBS were investigated. Adding magnetic CI particles significantly improves the thermal stability and mechanical strength of SEBS matrix, but does not sacrifice the elasticity and toughness. The CI/SEBS composites, prepared with greater CI concentration at higher temperature, longer time and stronger magnetic field for pre-structuring, exhibit higher field induced modulus change and greater magnetorheological effect, due to the strengthening of mutual particle interactions and the formation of longer and more ordered chain structures.

In this paper, core-shell structured poly methyl methacrylate (PMMA) coated carbonyl iron (CI) particles were prepared to study the influence of particle coating on the dynamic properties of magnetorheological elastomers (MREs). The CI-PMMA composite particles were encapsulated via an emulsion polymerization method. Two MRE samples were prepared with CI-PMMA composite particles and CI particles, respectively. Their microstructure was observed by using a scanning electron microscope (SEM). Dynamic properties of these two samples under various strain and magnetic fields were measured with a dynamic mechanical analyzer (DMA). The experimental results indicate that the MRE sample with CI-PMMA composite particles has larger storage modulus, smaller loss factor and smaller Payne effect than that of the sample with only CI particles. The analysis indicates that the use of CI-PMMA particles would increase the bond strength between particles and matrix. These experimental results were also verified by the SEM images.

In this paper, we prepared MR elastomers containing carbonyl iron particles based on silicon rubber without using a magnetic field during curing by γ-ray radiation. The effects of interactions between iron particles and the matrix on the performance of MR elastomers based on silicon rubber, including MR effect and mechanical properties, were investigated. The rubber/magnetic particle interactions were controlled by the modification of the iron surface using different kinds of silane coupling agents and characterized by SEM and DSC. The results showed that tensile strength increased with the increased interaction. However, the MR effect had a certain relationship with the structure of silane coupling agents and this is discussed in detail in relation to the mechanism of the MR effect.

This paper presents a new method to fabricate isotropic magnetorheological (MR) elastomers under natural conditions. In the absence of a magnetic field, a variety of MR elastomer samples made of carbonyl iron particles, silicon rubber and silicone oil, were fabricated. Their dynamic viscoelastic properties were characterized by a measurement system developed by our group. Also, the microstructure of the samples was observed by a scanning electron microscope. The effects of iron particles and additives on the MR effect and the relationship between microstructure and mechanical properties were investigated. Furthermore, a simple self-assembled microstructure was proposed to explain the inherent magnetoviscoelasticity of MR elastomers prepared in the absence of a magnetic field. The analytical results of the model are in agreement with experimental data. The study is also expected to provide a good guide for designing and preparing new MR elastomers.

In this research work, compression behavior of magnetostrictive silicone gels under the influence of an external magnetic field was investigated. Magnetostrictive gel specimens were made of silicon gel with 80% weight fraction of 3.8 μm embedded carbonyl iron particles. Compression tests were performed on cylindrical samples of these materials in the absence and in the presence of a magnetic field. It was found that the presence of a magnetic field would increase both the stiffness and the load-bearing capacity, but would reduce the maximum strain of the material. At 30% strain, a 50% increase in maximum stress in the presence of 0.32 T and 100% in stress in the presence of 0.44 T magnetic field inductions were observed. The induced magnetic force on the samples was also measured. The induced force decreased nonlinearly with the distance of the electromagnet from the sample and increased nonlinearly with the magnetic induction. This research was oriented towards certain applications. These types of material characterization may provide useful information for potential applications of soft magnetostrictive elastomers in muscle type actuators and tunable stiffness elements.

Magnetorheological (MR) rubber materials are the solid analog of magnetorheological fluids; hence, their rheological properties can be controlled by an applied magnetic field. If the particles embedded in the matrix are carbonyl iron, they have to be aligned by a magnetic field before the curing of the rubber, in order to achieve a substantial MR effect. However, the use of a crosslinked matrix allows larger particles to be used. We show that MR rubber materials with large irregular particles have a large MR effect although the particles are not aligned within the material. This is explained by the low critical particle volume concentration of such particles. A similar effect can be obtained for materials with carbonyl iron, if the particles are badly dispersed and thereby behaving like larger irregular particles. Besides the achieved level of dispersion, the rheological properties of the matrix material do not influence the MR effect.