Dynamic damping property of magnetorheological elastomer

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

Effects of iron particles’ volume fraction on compression mode properties of magnetorheological elastomers

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.

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%.

The magneto-rheological elastomer is mostly used in vibration isolation, for which higher modulus and lower Payne effect factors are crucial parameters. Strain amplitudes and frequencies influence many applications under dynamic modes. In this work, the dynamic viscoelastic properties of MRE, fabricated using electrolyte iron (EI) particles, were measured for varying strain amplitude, magnetic field and frequency. A fractional Kelvin-Voigt (KV) model is used in a frequency region from 0.01 to 40 Hz to predict the rheological behaviour. However, the available models failed to explain the observed behaviour at low frequencies and high magnetic fields and increasing strain amplitude (i.e. in the non-viscoelastic region). Therefore, a new modified KV model is proposed in this work to incorporate the drawbacks and hence can validate for varying frequency, magnetic field and strain amplitudes. The added terms can also be used in the fractional derivative Maxwell model to explain the effect of strain amplitude and magnetic field at various frequencies. The proposed model significantly improves the quality of experimental prediction in the low-frequency range, corresponding to a slow dissipative process at different strain amplitudes.

In this study, anisotropic magnetorheological elastomers with 0% and 15% weight fractions of silicone oil were fabricated under a magnetic field that was rotated with a 45° angle so that the iron particle alignment inside the magnetorheological elastomer was 45° to the direction of flat magnetorheological elastomer. Scanning electron microscopic images confirmed the aligned structure of iron particles and showed that the sample with 15% silicone oil contribution resulted in a less volume fraction of iron particles. The magnetorheological elastomers were then tested in an oscillatory pure shear mode at different shear strain amplitudes under different magnetic flux densities to measure their dynamic viscoelastic properties. The testing results showed that the magnetorheological elastomer with 15% silicone oil had lower zero-field storage and loss moduli and also had higher maximum magnetorheological effect than the magnetorheological elastomer with 0% silicone oil. Because of the 45° iron particle alignment, the storage modulus of the magnetorheological elastomers had a higher value in a particular direction than its contrary direction. These unique properties made the magnetorheological elastomers with 45° iron particle alignment to be potentially used in industry where extra support is needed in a particular direction.

The field-dependent rheological properties of plate-like carbonyl iron particle-based magnetorheological elastomers

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.

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, magnetorheological elastomers (MREs) were synthesized by incorporating various amounts of sucrose acetate isobutyrate (SAIB) ester plasticizer dopped in the epoxidized natural rubber (ENR-50) matrix with constant carbonyl iron particles (CIPs) of 60 weight percent. The effect of SAIB insertion on curing characteristics has been observed using a moving die rheometer. The microstructures appearance of the samples were observed using a field emission scanning electron microscope (FESEM). Finally, the magneto-induced storage modulus was measured by using a rheometer 302. The experimental results have demonstrated that the addition of SAIB ester decreased the cure rate index (CRI) by 63% and increased the MR effect by 37%. Observation of microstructure shows that the CIPs embedded well in the matrix and produced the isotropic structure of the MREs. Meanwhile, the fabricated MREs samples were frequencies dependent, where all MREs samples exhibit the incremental trend when increasing the frequencies. The introduction of SAIB has proven to influence the properties of the MREs.

Determination of the thermal characteristics and temperature-dependent rheological properties of the magnetorheological elastomers (MREs) is of paramount importance particularly with regards to MRE applications. Hitherto, a paucity of temperature dependent analysis has been conducted by MRE researchers. In this study, an investigation on the thermal and rheological properties of epoxidized natural rubber (ENR)-based MREs was performed. Various percentages of carbonyl iron particles (CIPs) were blended with the ENR compound using a two roll-mill for the preparation of the ENR-based MRE samples. The morphological, elemental, and thermal analyses were performed before the rheological test. Several characterizations, as well as the effects of the strain amplitude, temperature, and magnetic field on the rheological properties of ENR-based MRE samples, were evaluated. The micrographs and elemental results were well-correlated regarding the CIP and Fe contents, and a uniform distribution of CIPs was achieved. The results of the thermal test indicated that the incorporation of CIPs enhanced the thermal stability of the ENR-based MREs. Based on the rheological analysis, the storage modulus and loss factor were dependent on the CIP content and strain amplitude. The effect of temperature on the rheological properties revealed that the stiffness of the ENR-based MREs was considered stable, and they were appropriate to be employed in the MRE devices exposed to high temperatures above 45 °C.

The rheological properties of magnetorheological elastomers are influenced by magnetically sensitive fillers and the elastomer matrix. The ability to respond to an external magnetic field is imparted by the fillers, while the load-bearing capability is determined by the matrix type. In this paper, the effect of matrix material on the properties of magnetorhological elastomer is explored experimentally. Carbonyl iron particle content is varied by 0%, 15% and 25% by volume to produce magnetorheological elastomer samples using natural rubber, silicone rubber and nitrile butadiene rubber matrices. Forced transmissibility test approach was employed to evaluate the field induced variations in the dynamic stiffness and loss factor of magnetorheological elastomers. The dynamic stiffness of nitrile butadiene rubber is the highest, while that of silicone rubber is the lowest. Addition of carbonyl iron particles significantly improves stiffness, although these gains depend on the properties of unfilled matrix. The addition of 25% by volume of carbonyl iron particle increased the dynamic stiffness of a silicone rubber matrix based magnetorheological elastomer by 67.78%, while the similar change in magnetorheological elastomer with nitrile butadiene rubber matrix was 38.58%. The field dependent response of magnetorheological elastomers is governed by the matrix and ferromagnetic filler concentration. These qualities are higher in magnetorheological elastomer with a low initial dynamic stiffness matrix and lower in magnetorheological elastomers with a stiffer matrix.

Influence of composition of carbonyl iron particles on dynamic mechanical properties of magnetorheological elastomers

Artificial and synthetic skins are widely used in the medical field; used in applications ranging from skin grafts to suture training pads. There is a growing need for artificial skins with tunable properties. However, current artificial skins do not take into account the variability of mechanical properties between individual humans as well as the age-dependent properties of human skin. Furthermore, there has been little development in artificial skins based on these properties. Thus, the primary purpose of this research is to develop variable stiffness artificial skin samples using magnetorheological elastomers (MREs) whose properties that can be controlled using external magnetic fields. In this study, multiple MRE skin samples were fabricated with varying filler particle volume contents. Using a precision dynamic mechanical analyzer, a series of indenting experiments were performed on the samples to characterize their mechanical properties. The samples were tested using a spherical indenter that indented a total depth of 1 mm with a speed of 0.01 mm/s and unloaded at the same rate. The results show that the modulus or stiffness increases significantly as the iron percent (w/w) in the sample increases. Additionally, the stiffness of the sample increases proportional to the intensity of the applied external magnetic field. To assess the MRE samples’ variability of properties, the testing results were compared with in vivo human skin testing data. The results show the MRE samples are feasible to represent the age-dependent stiffness demonstrated in in vivo human skin testing. The MRE materials studied will be further studied as a variable-stiffness skin model in medical devices, such as radial pulse simulators.

Magnetorheological elastomers (MREs) are smart materials that consist of an elastomer matrix filled with iron particles. The distinguished functionality of this type of material is its response to a magnetic field by changing its mechanical properties. This reliable functionality makes MREs suitable for various applications. In this study, Isotopic MRE samples were fabricated using Liquid silicon rubber (LSR) and Iron particles. Then, the Magneto-hyper-viscoelastic parameters of MRE were identified by fitting the data of static and dynamic uniaxial compression tests. The viscoelastic model is approximated by a generalized Maxwell model and fitted using Prony-series in the frequency domain. In contrast, the modified hyperelastic model was used to match the magnetostatic and hyperelastic properties. Moreover, a Finite element (FE) simulation is performed for the static and dynamic tests using experimentally identified parameters. The results showed that using the Prony-series with the modified hyperelastic model can predict the behavior of MRE with reasonable accuracy and the magnetic field decreasing inside the sample with deformation, especially at the sample center.