On the sensing of magnetorheological elastomers

This work is focused on the study of the dynamic behavior of thick magnetorheological elastomers at high frequencies. Experimental and theoretical studies are conducted to investigate the dynamic shear properties of magnetorheological elastomers which are affected by increasing the thickness, as well as the percentage of iron particles contained in magnetorheological elastomers. A double-shear test setup is designed and built to test the magnetorheological elastomer samples over a range of frequencies from 200 to 800 Hz. The results demonstrate that the thickness of magnetorheological elastomer significantly affects the material properties in the off-state, that is, when no magnetic field is applied. However, for the on-state, when the material is activated by a magnetic field, the thickness of the sample does not show a significant effect on the change in storage modulus induced by a magnetic field. The theoretical analysis includes a macro-mechanical model for the storage modulus and loss modulus of magnetorheological elastomer as a function of thickness, percentage of iron particles, and applied magnetic field. Comparisons between the theoretical and experimental results show that the model reasonably predicts the dynamic behavior of thick magnetorheological elastomers.

Modified silane-coated carbonyl iron/natural rubber composite elastomer and its magnetorheological performance

The linear viscoelastic behaviour of magnetorheological elastomers is analysed in this work according to their formulation and working conditions. This study comprised both the synthesis of different magnetorheological elastomers and the strain and frequency sweep characterization under different magnetic fields and temperatures. The characterization was performed by a Physica MCR 501 rheometer from Anton Paar, equipped with a magnetorheologic cell 70/1T MRD. In the synthesis with a given elastomeric matrix, samples with different magnetic particle content are studied with two types of curing conditions: under the action of a magnetic field (anisotropic magnetorheological elastomers) and without a magnetic field (isotropic magnetorheological elastomers). The working conditions are excitation frequency, temperature and the applied external magnetic field. In this work, a new procedure to determine the linear viscoelastic behaviour is proposed; the loss factor is analysed in addition to analysing the storage modulus to determine the linear viscoelastic region of each sample. The results show that high temperatures and magnetorheological elastomers with higher volume fraction of magnetic particles restrict the linear viscoelastic behaviour of magnetorheological elastomers.

A Magnetorheological Elastomer (MRE) can be categorized as a smart material as it can respond when it is subjected to a magnetic field against itself. Shrinking and changing shape in MRE is due to the displacement of magnetic particle in the MRE matrix. However, the lack of understanding of the magnetic flow through magnetic particle in the elastomer matrix causes difficulties to improve the best MRE matrix type and a magnetic circuit for use in MRE devices. In this paper, a finite element magnetic method (FEMM) software has been used to investigate and to study the effect of the magnetic flow when the angle of the magnetic particle in the MRE changed. The analysis was conducted in two-dimensional cross-section (axisymmetric type) with two magnetic particles in the elastomer matrix and the magnetic core. The result shows by changing the angle of the magnetic particle, the value of the magnetic flow and magnetic flux density also change. As a conclusion, the magnetic particle arrangement in the elastomer matrix plays a vital role in designing the MRE matrix layer and MRE device. By understanding the magnetic flow through the magnetic particle, one can improve the method in the preparation of MRE matrix and MRE magnetics circuit.

Soft hybrid magnetorheological elastomer: Gap bridging between MR fluid and MR elastomer

Semiactive vibration absorbers are tunable vibration absorbers whose natural frequencies can change controllably to minimize vibration better than their passive counterparts, which can be used to reduce occupant vibration in cars. The variable natural frequency is achieved by using a dynamically tunable spring. In order to use a material as a dynamically tunable spring, its transient parameters must be understood and controlled, so as not to lead to instability. This work characterizes the behavior of magnetorheological elastomers (MREs), which are a type of ferromagnetic-elastomer composites whose tensile/compressional stiffness increases as an applied magnetic field is increased. If the transition from one stiffness state to another is too slow, the MRE can have a detrimental effect on vibration control. Transient behavior of MREs with different concentrations of ferromagnetic material and different geometric shapes was recorded empirically, and the MRE stiffness change in response to a change in magnetic field was modeled as a function of ferromagnetic content, MRE geometric shape, and the change in magnetic field strength. MREs in this configuration exhibited natural frequencies in the 30–65-Hz range, where MREs were able to change their natural frequency by up to 17%.

In this study, the vibration analysis of sandwich rectangular plates with magnetorheological (MR) elastomer damping treatment is presented. The rectangular plate is combined with a magnetorheological elastomer core layer and a constraining layer to improve the vibration behaviors of the sandwich system. The MR material shows variations in the rheological properties when subjected to varying magnetic fields. Additionally, the MR material exhibits a rapid time response and is applicable to structures or devices when a tunable system is required. The magnetorheological elastomer is found to have a significant effect on the vibration characteristics of the sandwich rectangular plate. The modal damper and the natural frequencies for the sandwich plate system are calculated for various magnetic fields and some designed parameters by utilizing the finite element method. The damping effects of the sandwich plate system can be controlled and changed when different magnetic field strengths are applied.

The primary goal of this work is to test and model the magnetorheological (MR) properties of the isotropic magnetorheological elastomers (MREs) under the coupled static–dynamic compressive loads. Isotropic MREs with different contents of magnetic particles were fabricated based on the silicone elastomer. In order to apply the controllable magnetic field to the MREs and directly measure the viscoelastic force of the deformed MREs during the dynamic tests, an electromagnet with a magnetic flux density of up to 0.9 T was developed and integrated into an electric dynamic test system. The stress–strain hysteresis loops of the produced MREs were experimentally characterized under the dynamic compressive loads coupled with different static pre-strains. Effects of particle content, strain amplitude, static pre-strain and load frequency on the MR properties of the MREs were examined in terms of the characteristics of the hysteresis loops, as well as the MR effects in the storage modulus, loss modulus and pre-stress. The results revealed that irrespective of the applied magnetic field, the deformation behavior of the produced MREs was in an approximate linear viscoelastic state when the strain amplitude was less than 7.5%. Both the absolute and relative MR effects increase with the increasing particle content, and decrease with the increasing strain amplitude. Only the absolute MR effect increases with the increasing pre-strain. While varying the load frequency has almost no effect on the MR effect of the MREs. Furthermore, two empirical models were proposed respectively for predicting the storage modulus and loss modulus of the MREs as functions of the magnetic flux density, particle content, strain amplitude, pre-strain and load frequency. The graphical comparison and quantitative evaluation show that the proposed models can give effective predictions of the storage and loss moduli of the produced MREs under the applied load conditions in this work.

In this study, 3D printed magnetorheological (MR) elastomer has been characterized through a force vibration testing. The 3D printed MR elastomer is a composite consisting three different materials, magnetic particles and two different elastomers. The MR elastomers were printed layer-by-layer by encapsulating MR fluid within the polymeric elastomer and then allowed to cure at room temperature. The 3D printing allowed to print various patterns of magnetic particles within the elastomeric matrix. In the presence of an external magnetic field, both elastic and damping properties of the 3D printed MR elastomers were changed. Natural frequency, stiffness, damping ratio, damping coefficient, and shear modulus were increased with increasing magnetic field. For the single degree-of-freedoms system, shear mode MR elastomers suppressed the transmitted vibration amplitude up to 31.4% when the magnetic field was 550 mT. The results showed that the 3D printed MR elastomer could be used as a tunable spring element for vibration absorption or isolation applications. However, further optimization of the magnetic particles’ configurations should be performed to obtain the higher MR effect.

The magneto-thermo-elastic steady shear behaviors of isotropic smart composites of silicon rubber matrix randomly filled with ferromagnetic particles, commonly referred to as magnetorheological (MR) elastomers, are investigated experimentally and theoretically in the present study. The strip specimens of the MR elastomer composite with different ferromagnetic particle concentrations are fabricated and implemented for lap-shear tests under both magnetic and thermal fields. It is illustrated that the magneto-thermo-elastic shear modulus of the MR elastomer is markedly enhanced with the volume fraction of ferromagnetic particles and the applied external magnetic field, while the shear modulus is decreased with the environment temperature. To qualitatively elucidate the magneto-thermo-elastic shear performance of this kind of magnetic smart composites, a modified constitutive of hyperelasticity is suggested taking into account the influence of magnetic field and temperature on the magnetic potential energy and strain energy. The theoretical modeling predictions on the stress–strain behaviors for different applied magnetic fields and environment temperatures are compared to experimental observations to demonstrate a good agreement.

Magnetorheological elastomer (MRE) is a novel kind of magnetorheological materials and has been successfully used to control the structure vibration due to its property of variable stiffness under different magnetic field. In order to improve the properties of MRE, it urgently needs to investigate the preparation methods of MRE and build a corresponding test system to evaluate the performance of MRE in different operating modes. In this paper, different magnetic devices for preparing MRE were studied and designed, and the material was fabricated by the permanent magnets with additional permeability equipment at last. Then, according to the SDOF principle, a novel test system was built in order to investigate the mechanical properties of MRE, and exact close-form expressions of the stiffness, loss factor and other mechanical parameters of MRE, under different magnetic field, have been calculated to analyze the properties of MRE.

Magnetorheological elastomers (MREs) have excellent magnetic-control mechanical properties, which ensures its great engineering application value in the field of vibration control. In this paper, the iron–nickel foam (INF) reinforced MREs with excellent magnetorheological (MR) properties were developed. The soft magnetic properties and three-dimensional (3D) foam structure of INF ensure an effective enhancement on the magnetic-control mechanical properties of MRE. The static and dynamic mechanical properties of the MRE were tested based on a parallel plate rheometer. Among them, static compression tests were carried out to study the static mechanical properties of MREs. The test results showed that INF reinforced MREs have excellent magneto-induced compression modulus. The effects of magnetic field, shear strain, and frequency on the dynamic mechanical properties of MREs have studied by the dynamic oscillatory shear tests. The test results revealed that the MRE has excellent MR properties under small strain. In addition, several successive tests were conducted to evaluate the response behavior under transient magnetic field and hysteresis properties of MREs under periodic magnetic field, and no obvious hysteresis in the repeated test curves have been observed. The INF reinforced MRE studied in this paper has potential application prospects in the field of micro-vibration control.

Magnetorheological elastomer (MRE) is an intelligent composite material and has been widely used in various fields such as vibration reduction and sensing. MRE has an excellent magnetorheological effect through the chaining of its internal magnetic particles. Current studies on MREs mainly focus on the preparation of materials and characterization of mechanical properties. However, very few studies have been conducted on the mechanism of magnetic particle motion during MRE curing. Based on the silicone rubber‐based MRE, the motion mechanism of magnetic particles during curing was explored through numerical simulation. First, we analyzed the magnetic force and viscous force of magnetic particles in MRE and discussed the equations of motion of magnetic particles under applied magnetic field. Further, we established a uniform magnetic field model through the finite element method and simulated the motion of two magnetic particles under the magnetic field. Finally, we discussed the effects of particle distribution angles, particle radii, applied magnetic field strength, and distance between particles on particle velocity and displacement. The results show that the distance between particles has the greatest influence on the motion of magnetic particles, and the size of the distance between particles will affect the contact time of the particles, thus affecting the chain formation of magnetic particles in the MRE.

The effect of a uniform magnetic field on the permittivity of magnetorheological elastomers (MREs) is studied. MREs were synthesized on the basis of silicone rubber and magnetic fillers of various chemical nature (Fe, NdFeB and Fe3O4) and particle sizes. The value of permittivity was obtained from the measurements of the capacity of a plane capacitor with MRE samples. A strong increase of the permittivity (magnetodielectric effect) was observed when the applied field was perpendicular to the capacitor plates. The value of the magnetodielectric effect was found to be strongly dependent on the type of magnetic filler as well as on the size and concentration of magnetic particles within MRE composites. The highest magnetic response reaching 150% was observed for the MRE based on a magnetically hard NdFeB filler. A simple model explaining physical reasons for the magnetodielectric effect in a MRE is proposed. The developed MRE with a strong magnetodielectric effect is very promising for a wide range of applications, in particular, as magnetic field sensors and actuators.

This study presents the dynamic numerical model of magneto-rheological elastomers (MREs) along with the dynamic testing of the material under various loading conditions. Primarily the loading in shear mode is considered in this study because many civil engineering structures are subjected to shear loading. Experimental tests were carried out in order to characterize the dynamic behavior of MREs. A test setup was designed and fabricated to load the MRE samples in shear mode with varying magnetic fields. A series of shear tests of MRE samples were performed under various magnetic field values, amplitudes and frequencies of loading. The test results show that the material stiffness is increased with increasing magnetic field and loading frequency within the ranges of the magnetic field and exciting frequency considered in this work. Based on the experimental results, a dynamic model was developed to capture the dynamic behavior of the MRE.