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Magnetorheological elastomers (MREs) are well-known for their ability to self-adjust their mechanical properties in response to magnetic field influence. This ability, however, diminishes under high-strain conditions, a phenomenon known as the stress-softening effect. Similar phenomena have been observed in other filled elastomers; hence, the current study demonstrates the role of fillers in reducing the effect and thus maintaining performance. Anisotropic, silicone-based MREs with various carbonyl iron particle (CIP) concentrations were prepared and subjected to uniaxial tensile load to evaluate high-strain conditions with and without magnetic influence. The current study demonstrated that non-linear stress–strain behavior was observed in all types of samples, which supported the experimental findings. CIP concentration has a significant impact on the stress–strain behavior of MREs, with about 350% increased elastic modulus with increasing CIP content. Microstructural observations using field emission scanning electron microscopy (FESEM) yielded novel micro-mechanisms of the high-strain failure process of MREs. The magnetic force applied during tension loading was important in the behavior and characteristics of the MRE failure mechanism, and the discovery of microcracks and microplasticity, which was never reported in the MRE quasi-static tensile, received special attention in this study. The relationships between these microstructural phenomena, magnetic influence, and MRE mechanical properties were defined and discussed thoroughly. Overall, the process of microcracks and microplasticity in the MRE under tensile mode was primarily formed in the matrix, and the formation varies with CIP concentrations. [ABSTRACT FROM AUTHOR]

Temperature is one of the most influential factors affecting the performance of elastomer matrix in magnetorheological elastomer (MRE). Previous studies have utilized silica as a reinforcing filler in polymer composite and as a coating material in MRE to improve the thermal stability of the base material. However, the usage of silica as an additive in the thermal stability of MRE has not been explored. Thus, in this study, the effect of silica as an additive on the temperature-dependent mechanical and rheological properties of ethylene propylene diene monomer (EPDM)-based MREs was investigated by using 30 wt.% carbonyl iron particles (CIPs) as the main filler, with different contents of silica nanoparticles (0 to 11 wt.%). The microstructure analysis was examined by using field-emission scanning electron microscopy (FESEM), while the thermal characterizations were studied by using a thermogravimetric analyzer and differential scanning calorimetry. The tensile properties were conducted by using Instron Universal Testing Machine in the absence of magnetic field at various temperatures. Meanwhile, the rheological properties were analyzed under oscillatory loadings in the influence of magnetic field, using a rotational rheometer at 25 to 65 °C. The results revealed that the temperature has diminished the interfacial interactions between filler and matrix, thus affecting the properties of MRE, where the tensile properties and MR effect decrease with increasing temperature. However, the presence of silica capable improved the thermal stability of EPDM-based MRE by enhancing the interactions between filler and matrix, thus reducing the interfacial defects when under the influence of temperature. Consequently, the incorporation of silica nanoparticles as an additive in EPDM-based MRE requires more exploration, since it has the potential to sustain the properties of MRE devices in a variety of temperature conditions. Thus, the study on the temperature-dependent mechanical and rheological properties of MRE is necessary, particularly regarding its practical applications. [ABSTRACT FROM AUTHOR]

Magnetorheological elastomers (MREs) are a kind of emerged smart material, where its responsive moduli in terms of mechanical and rheological properties are largely influenced by the presence of an external magnetic field. However, the incompatibility on the surface properties of its raw materials (fillers and matrix) may deteriorate the required properties of MREs. Therefore, in this study, the innovation of MRE by embedding silica nanoparticles as an additive has been experimentally investigated to strengthen the interactions between filler and matrix, thus resulted in enhancement of mechanical and rheological properties of MRE. The ethylene propylene diene monomer (EPDM)-based MREs were fabricated by mixing the EPDM with carbonyl iron particles (CIPs) as the main filler and different contents of silica nanoparticles (0 wt%–11 wt%) as an additive. The microstructures, magnetic properties and tensile properties of isotropic EPDM-based MREs were observed by using field emission scanning electron microscopy, vibrating sample magnetometer and Instron Universal Testing Machine, respectively. Meanwhile, the rheological properties were examined under oscillatory loadings in the absence and presence of magnetic field using rotational rheometer. The experimental results showed that the silica nanoparticles play a significant role in improving the properties of EPDM-based MREs. The adhesiveness of silica into CIPs has amended the interfacial interactions between CIPs and matrix by occupying the gaps between distributed CIPs within the MRE. Consequently, the addition of 11 wt% silica has not only improved the tensile properties (tensile strength and elongation at break), but also enhanced the MR effect compared to EPDM-based MREs without silica. Thus, incorporation of silica nanoparticles as an additive in EPDM-based MRE has the potential to be further explored and compromised to bring new innovation in real engineering applications. [ABSTRACT FROM AUTHOR]

The widespread use of magnetorheological elastomer (MRE) materials in various applications has yet to be limited due to the fact that there are substantial deficiencies in current experimental and theoretical research on its microstructural durability behavior. In this study, MRE composed of silicon rubber (SR) and 70 wt% of micron-sized carbonyl iron particles (CIP) was prepared and subjected to stress relaxation evaluation by torsional shear load. The microstructure and particle distribution of the obtained MRE was evaluated by a field emission scanning electron microscopy (FESEM). The influence of constant low strain at 0.01% is the continuing concern within the linear viscoelastic (LVE) region of MRE. Stress relaxation plays a significant role in the life cycle of MRE and revealed that storage modulus was reduced by 8.7%, normal force has weakened by 27%, and stress performance was reduced by 6.88% along approximately 84,000 s test duration time. This time scale was the longest ever reported being undertaken in the MRE stress relaxation study. Novel micro-mechanisms that responsible for the depleted performance of MRE was obtained by microstructurally observation using FESEM and in-phase mode of atomic force microscope (AFM). Attempts have been made to correlate strain localization produced by stress relaxation, with molecular deformation in MRE amorphous matrix. Exceptional attention was focused on the development of molecular slippage, disentanglement, microplasticity, microphase separation, and shear bands. The relation between these microstructural phenomena and the viscoelastic properties of MRE was diffusely defined and discussed. The presented MRE is homogeneous with uniform distribution of CIP. The most significant recent developments of systematic correlation between the effects of microstructural deformation and durability performance of MRE under stress relaxation has been observed and evaluated. [ABSTRACT FROM AUTHOR]

The characteristics and behaviors of magnetorheological elastomer (MRE) within the elastic region are significantly important to demonstrate potentiality toward infinitesimal deformation in various applications. As MRE dynamically shears within an elastic region at constant small deformation, its significant consequence has long been a pending topic, hampered partly by the lack of empirical evidence. Therefore, this paper aimed to investigate the onset microscopically transformation of the MRE sample precipitated to storage modulus behavior under stress relaxation conditions. To achieve the aim, MRE with 70 wt% carbonyl iron particles was dynamically sheared at 1 Hz frequency and 0.01% strain for a designated period of test duration. The morphology evaluation of the sheared sample disclosed the development of permanent microplasticity in a very narrow region of shear bands. The deformation adequately reduced the storing energy ability of the MRE at a dominantly elastic behavior. The results revealed that the ability of MRE to store deformation energy slightly reduced by 0.3%–0.5% for the 2000 s test interval. This interesting onset phenomenon was successfully achieved, and the establishment of this early-stage deformation was undeniably important as preliminary data for catastrophic investigation at a longer duration. [ABSTRACT FROM AUTHOR]

Carbonyl iron particles (CIPs) embedded in magnetorheological elastomers (MREs) as magnetic filler play a dominant candidate that can affect resultant properties of MREs including the field-dependent viscoelasticity. In this work, the effects of corrosion rate on the rheological properties of MREs are experimentally investigated. The CIPs undergo an accelerated corrosion test in diluted hydrochloric (HCl) acid at various concentrations, particularly at 0.5, 1.0 and 1.5 vol.% for 30 min immersion time, individually. Four samples of CIPs, including the non-corroded one are prepared, and their morphological characterization are observed via field emission scanning electron microscope (FESEM), that equipped with energy dispersive x-ray spectroscopy (EDS) for elemental compositions. In addition, x-ray diffraction (XRD) is used to identify the crystalline phase structure of the samples. In order to examine the corrosion rate of each sample, weight-loss method is used by pressing the CIPs into pellet shape and being immersed in the respective concentrations of HCl. It is shown that the corrosion rate of CIPs is increased with the increasing of HCl concentration in which higher weight loss of the measured pallet CIPs is observed. Meanwhile, the field-dependent rheological properties of MREs are investigated via rheometer to analyze the change in dynamic modulus of MREs such as storage modulus, loss factor and absolute MR effect. These experimental results indicate that MRE samples with higher corrosion rate of CIP exhibit lower storage modulus, loss factor and MR effect, as this subsequently would deteriorate the performance of MRE. Therefore, it is identified that the purity of CIP plays the most important contribution towards the field-dependent viscoelastic properties of MRE for a long period use of the material. [ABSTRACT FROM AUTHOR]

Micro mechanism consideration is critical for gaining a thorough understanding of amorphous shear band behavior in magnetorheological (MR) solids, particularly those with viscoelastic matrices. Heretofore, the characteristics of shear bands in terms of formation, physical evolution, and response to stress distribution at the localized region have gone largely unnoticed and unexplored. Notwithstanding these limitations, atomic force microscopy (AFM) has been used to explore the nature of shear band deformation in MR materials during stress relaxation. Stress relaxation at a constant low strain of 0.01% and an oscillatory shear of defined test duration played a major role in the creation of the shear band. In this analysis, the localized area of the study defined shear bands as varying in size and dominantly deformed in the matrix with no evidence of inhibition by embedded carbonyl iron particles (CIPs). The association between the shear band and the adjacent zone was further studied using in-phase imaging of AFM tapping mode and demonstrated the presence of localized affected zone around the shear band. Taken together, the results provide important insights into the proposed shear band deformation zone (SBDZ). This study sheds a contemporary light on the contentious issue of amorphous shear band deformation behavior and makes several contributions to the current literature. [ABSTRACT FROM AUTHOR]

This paper presents the effect of the micro-sized particles on the storage modulus and durability characteristics of magnetorheological elastomers (MREs). The initial phase of the investigation is to determine any associations among the microparticles' weight percent fraction (wt%), structure arrangement, and the storage modulus of MRE samples. In order to carry out this, both isotropic and anisotropic types of MRE samples consisting of the silicone rubber matrix and 50, 60, 70, 75, and 80 wt% microparticles of carbonyl iron fractions are prepared. It is identified from the magneto-rheometer that the increase in storage modulus and decrease in linear viscoelastic region limit are observed in varying consistency depending on wt% and particle arrangement. The consistency of this dependency feature is highlighted by superimposing all of the graphs plotted to create the proposed the samples' behavior model. In response to increasing magnetic stimulation, a sample of 70 wt% microparticles with an isotropic arrangement is found to be significant and stable. The experimentally defined fraction is then used for the durability test as the second phase of the investigation. During this phase, the durability evaluation is subjected to stress relaxation for an extended period of time. After undergoing durability testing, storage modulus performance is decreased by 0.7–13% at various magnetic stimulation levels. This result directly indicates that the storage modulus characteristics of different forms of MRE are sensitive to the different iron particle fractions' and microparticles' alignment. Therefore, important treatments to alter the storage modulus can be undertaken before the practical implementation to accommodate any desired performance of MRE itself and MRE application systems. [ABSTRACT FROM AUTHOR]