During the last few decades, magnetorheological (MR) elastomers have attracted a significant amount of attention for their enormous potential in engineering applications. Because they are a solid counterpart to MR fluids, MR elastomers exhibit a unique field-dependent material property when exposed to a magnetic field, and they overcome major issues faced in magnetorheological fluids, e.g. the deposition of iron particles, sealing problems and environmental contamination. Such advantages offer great potential for designing intelligent devices to be used in various engineering fields, especially in fields that involve vibration reduction and isolation. This paper presents a state of the art review on the recent progress of MR elastomer technology, with special emphasis on the research and development of MR elastomer devices and their applications. To keep the integrity of the knowledge, this review includes a brief introduction of MR elastomer materials and follows with a discussion of critical issues involved in designing magnetorheological elastomer devices, i.e. operation modes, coil placements and principle fundamentals. A comprehensive review has been presented on the research and development of MR elastomer devices, including vibration absorbers, vibration isolators, base isolators, sensing devices, and so on. A summary of the research on the modeling mechanical behavior for both the material and the devices is presented. Finally, the challenges and the potential facing magnetorheological elastomer technology are discussed, and suggestions have been made based on the authors’ knowledge and experience.

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A state-of-the-art review on magnetorheological elastomer devices

The need for building robots with soft materials emerged recently from considerations of the limitations of service robots in negotiating natural environments, from observation of the role of compliance in animals and plants [1], and even from the role attributed to the physical body in movement control and intelligence, in the so-called embodied intelligence or morphological computation paradigm [2]-[4]. The wide spread of soft robotics relies on numerous investigations of diverse materials and technologies for actuation and sensing, and on research of control techniques, all of which can serve the purpose of building robots with high deformability and compliance. But the core challenge of soft robotics research is, in fact, the variability and controllability of such deformability and compliance.

Stiffening in Soft Robotics: A Review of the State of the Art

Variable stiffness material and structural concepts for morphing applications

In this study, a magnetorheological elastomer (MRE) was manufactured and tested, and a MRE sandwich beam was also fabricated from a MRE between two thin aluminum layers An experimental test rig was set up to investigate the vibration response of the MRE sandwich beam under a non-homogeneous magnetic field The experimental results show that the first natural frequency of the MRE sandwich beam decreased as the magnetic field applied to the beam was moved from the clamped end of the beam to the free end of the beam It is also noted that the MRE sandwich beam had the capability to left shift the first natural frequency when the magnetic field was increased in the activated regions

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Experimental investigation of the vibration characteristics of a magnetorheological elastomer sandwich beam under non-homogeneous small magnetic fields

In this work the dynamic stability of a rotating three layered symmetric sandwich beam with magnetorheological elastomer (MRE) core and conductive skins subjected to axial periodic loads has been investigated using finite element method (FEM). The derived governing equation of motion is in the form of a multi-degree of freedom Mathieu–Hill's equation with complex coefficients. The instability regions of the sandwich beam for the principal parametric resonance case have been determined by using the harmonic balance method. Effects of applied magnetic field, rotating speed, setting angle, hub radius, static load and dynamic load on the dynamic characteristics and instability regions of the sandwich beam are investigated. This work will find application in the passive and active vibration reduction of rotating sandwich structure using magnetorheological elastomer core, magnetic field and periodic axial load.

Dynamic stability of a rotating sandwich beam with magnetorheological elastomer core

The concept of vibration controllability with smart fluids within flexible structures has been of significant interest in the past two decades. Although much research has been done on structures with embedded electrorheological (ER) fluids, there has been little investigation of magnetorheological (MR) fluid adaptive structures. In particular, a body of research on the experimental work of cantilever MR beams is still lacking. This experimental study investigates the controllability of vibration characteristics of magnetorheological cantilever sandwich beams. These adaptive structures are produced by embedding an MR fluid core between two elastic layers. The structural behaviour of the MR beams can be varied by applying an external magnetic field to activate the MR fluid. The stiffness and damping structural characteristics are controlled, demonstrating vibration suppression capabilities of MR fluids as structural elements. MR beams were fabricated with two different materials for comparison purposes. Diverse excitation methods were considered as well as a range of magnetic field intensities and configurations. Moreover, the cantilever MR beams were tested in horizontal and vertical configurations. The effects of partial and full activation of the MR beams were outlined based on the results obtained. The controllability of the beam's vibration response was observed in the form of variations in vibration amplitudes and shifts in magnitudes of the resonant natural frequency.

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Zbigniew Kęsy

Papers

Vibration characteristics of MR cantilever sandwich beams: experimental study