Magnetorheological elastomers (MREs) are smart viscoelastic materials in which their physical properties can be altered when subjected to a varying magnetic field strength. MREs consist of an elastomeric matrix mixed with magnetic particles, typically carbonyl iron particles (CIPs). The magnetic field-responsive property of MREs have led to their wide exposure in research. The potential development and commercialization of MRE-based devices requires extensive investigation to identify the essential factors that can affect their properties. For this reason, this research aims to investigate the impact of CIPs’ type, concentration and coating on the rheological and mechanical properties of MREs. Isotropic MREs are fabricated with four different CIP compositions differing between hard or soft, and coated or uncoated samples. Each MRE composition have three different concentrations, which is 5%, 10%, and 20% by volume. The dynamic properties of the fabricated samples are tested by compression oscillations on a dynamic mechanical analyzer (DMA). Frequency and strain dependent measurements are performed to obtain the storage and loss modulus under different excitation frequencies and strain amplitudes. The emphasis is on the magnetorheological (MR) effect and the Payne effect which are an intrinsic characteristics of MREs. The effect of the CIPs’ type, coating, and concentration on the MR and Payne effect of MREs are elucidated. Overall, it is observed that, the storage and loss modulus exhibit a strong dependence on both the frequency excitations and the strain amplitudes. Samples with hard and coated CIPs tend to have a higher MR effect than other samples. A decrease in the storage modulus and non-monotonous behavior of the loss modulus with increasing strain amplitude are observed, indicating the Payne effect. The results of this study can aid in the characterization of MREs and the proper selection of CIPs grades based on the application.

Walking behaviour in amputees with lower-limb loss is absent from shock-absorbing properties. A damper can be used to reduce the impact of ground reaction force (GRF) during heel strikes. Magnetorheological fluid (MRF) damper is deemed the best option for this application as it includes the advantages of both passive and active dampers. An enhanced MRF damper is essential in supplying the appropriate current and damping force levels. Therefore, an energy-efficient design is required to prolong the battery life used by MRF dampers in prosthetic limbs. This paper investigates two fluids of different properties and magnetic particle volume content. A bypass damper was used to observe the response of both fluids. The findings highlighted that an MRF with a higher percentage of solid weight could produce a more significant damping force with a lesser amount of applied current. This work presents a simulation study on implementing the energy-efficient MRF damper utilizing a Fuzzy-PID controller in a prosthetic limb.

Magnetorheological elastomers (MREs) are a class of emerging smart materials in which their mechanical and rheological properties can be immediately and reversibly altered upon the application of a magnetic field. The change in the MRE properties under the magnetic field is widely known as the magnetorheological (MR) effect. Despite their inherent viscoelastic property-change characteristics, there are disadvantages incorporated with MREs, such as slow response time and the suspension of the magnetic particles in the elastomer matrix, which depress their MR effect. This study investigates the feasibility of a hybrid magnetorheological elastomer-fluid (MRE-F) for longitudinal vibration isolation. The hybrid MRE-F is fabricated by encapsulating MR fluid inside the elastomer matrix. The inclusion of the MR fluid can enhance the MR effect of the elastomer by providing a better response to the magnetic field and, hence, can improve the vibration isolation capabilities. For this purpose, an MRE-based coupling is developed, and isolation performance is investigated in terms of the linear transmissibility factor. The performance of the hybrid MRE-F was compared against two different MRE samples. The results show that further enhancement of MR-effect in MREs is possible by including MR fluid inside the elastomer. The hybrid MRE-F exhibited better stiffness change with the current increase and recorded the highest value of $55.911 \mathrm{N}/\mathrm{mm}$. The transmissivity curves revealed that the MRE-F contributed to a broader shift in the natural frequency with a $7.2 \mathrm{Hz}$ overall shift at $8.9 \mathrm{mT}$. The damping characteristics are higher in MRE-F, recording the highest percentage increase in damping with $33.04\%$. Overall, the results reveal the promising potential of hybrid MRE-F in developing MRE-based coupling for longitudinal vibration isolation.

Longitudinal vibrations due to different external excitations are omnipresent in almost every machine, eventually leading to unplanned downtime, and in some cases, catastrophic failures. The passive approach to isolate such vibration has some limitations. Magnetorheological elastomers (MREs) typically consist of micron-sized magnetic particles dispersed in an elastomeric matrix. Their mechanical and rheological properties can be altered under the influence of magnetic field. Thus, the distinctive behavior of magnetorheological elastomers paved the way for successful employment in vibration isolation. In this study, an MRE-based metamaterial coupler is designed for broadband vibration attenuation with distinctive characteristics unattainable by conventional couplers in longitudinal vibration. The vibration control performance of the proposed model is investigated in terms of its transmissibility factor. Sweep vibration test is conducted to examine the transmissibility factor for single, double, and triple-layer MRE metamaterial couplers accompanied by different activation scenarios. The results reveal that the stiffness of the MRE layers increases with the strength of the applied magnetic field. Utilizing more than one layer of MRE increases the ability to isolate longitudinal vibration at different frequency bands. The maximum reduction curves achieved by single, double, and triple-layer MREs are approximately 84.5%, 97%, and 99.6%, respectively. The findings of this study demonstrate that the proposed MRE-based metamaterial couplers can attenuate vibrations at broadband frequencies.

This research aims to analyze the vibration response of damaged rolling element bearings experimentally and to assess their degree of degradation by examining parameters extracted from the time domain. This task was accomplished in three phases. In the first phase, a test rig was carefully designed and precisely manufactured. In particular, an innovative solution for rapidly mounting and dismounting bearings on the supporting shaft was tested and used successfully. In the second phase, a specific technique of seeding defects inside the ball bearings was developed. In the last phase, damaged bearings (and healthy ones serving as a reference) were installed on the test rig, and different vibration measurements were taken. The results obtained from this work show that different parameters could be extracted from the time domain. In addition to the six common indicators (peak, root mean square, crest factor, kurtosis value, impulse factor, and shape factor), four hybrid new ones have been proposed (Talaf, Thikat, Siana and, Inthar). The experimental results confirm the well-known efficiency of kurtosis in the detection of bearing defects. However, the newly proposed parameters were found to be more responsive to defect growth.

Magnetorheological elastomers (MREs) are smart viscoelastic materials with tunable dynamic properties, typically consisting of an elastomeric matrix with suspended carbonyl iron particles (CIPs). When exposed to an external magnetic field, interactions between the magnetic particles cause deformations in the MRE structure, altering dynamic characteristics. These properties have spurred interest in MRE-based devices requiring tunable dynamics. This research examines the influence of frequency and temperature on isotropic MREs in shear mode with varying CIP compositions. Homogenously dispersed CIPs with concentrations of 5%, 10%, and 20% (hard or soft) are used. The frequency and temperature dependence are analyzed on a dynamic mechanical analyzer (DMA) in shear mode. The results show strong storage and loss moduli dependence on frequency. Increased external magnetic field intensity enhances MRE dynamic properties, with optimal effects at 10% volume fractions, especially for hard CIPs. Temperature effects are negligible, demonstrating strong thermal stability. These findings offer insights into the dynamic properties of MREs, aiding the development of MRE-based devices operating in shear mode.