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

Most devices for single-site or natural orifice transluminal surgery are very application specific and, hence, capable of effectively carrying out specific surgical tasks only. However, most of these instruments are rigid, lack a sufficient number of degrees of freedom (DOFs), and/or are incapable of modifying their mechanical properties based on the tasks to be performed. The current philosophy in commercial instrument design is mainly focused on creating minimally invasive surgical systems using rigid tools equipped with dexterous tips. Only few research efforts are aimed at developing flexible surgical systems, with many DOFs or even continuum kinematics. The authors propose a radical change in surgical instrument design: away from rigid tools toward a new concept of soft and stiffness-controllable instruments. Inspired by biology, we envision creating such soft and stiffnesscontrollable medical devices using the octopus as a model. The octopus presents all the capabilities requested and can be viewed as a precious source of inspiration. Several soft technologies are suitable for meeting the aforementioned capabilities, and in this article a brief review of the most promising ones is presented. Then we illustrate how specific technologies can be applied in the design of a novel manipulator for flexible surgery by discussing its potential and by presenting feasibility tests of a prototype responding to this new design philosophy. Our aim is to investigate the feasibility of applying these technologies in the field of minimally invasive surgery and at the same time to stimulate the creativeness of others who could take the proposed concepts further to achieve novel solutions and generate specific application scenarios for the devised technologies.

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Soft Robotics Technologies to Address Shortcomings in Today's Minimally Invasive Surgery: The STIFF-FLOP Approach

The remarkable advances of robotics in the last fifty years, which represent an incredible wealth of knowledge, are based on the fundamental assumption that robots are chains of rigid links. The use of soft materials in robotics, driven not only by new scientific paradigms (biomimetics, morphological computation, and others), but also by many applications (biomedical, service, rescue robots, and many more), is going to overcome these basic assumptions and makes the well-known theories and techniques poorly applicable, opening new perspectives for robot design and control.The current examples of soft robots represent a variety of solutions for actuation, and control. Though very first steps, they have the potential for a radical technological change. Soft robotics is not just a new direction of technological development, but a novel approach to robotics, unhinging its fundamentals, with the potential to produce a new generation of robots, in the support of humans in our natural environments.

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Soft Robotics: New Perspectives for Robot Bodyware and Control

Smart materials are kinds of designed materials whose properties are controllable with the application of external stimuli such as the magnetic field, electric field, stress, and heat. Smart materials whose rheological properties are controlled by externally applied magnetic field are known as magneto-rheological materials. Magneto-rheological materials actively used for engineering applications include fluids, foams, grease, elastomers, and plastomers. In the last two decades, magneto-rheological materials have gained great attention of researchers significantly because of their salient controllable properties and potential applications to various fields such as automotive industry, civil environment, and military sector. This article offers a recent progressive review on the magneto-rheological materials technology, especially focusing on numerous application devices and systems utilizing magneto-rheological materials. Conceivable limitations, challenges, and comparable advantages of applying these magn...

A state of art on magneto-rheological materials and their potential applications:

Magnet filler-polymer matrix composites (Magpol) are an emerging class of morphing materials. Applications of Magpol can include artificial muscles, drug delivery, adaptive optics and self healing structures. Advantages of Magpol include remote contactless actuation, several actuation modes, high actuation strain and strain rate, self-sensing and quick response. The actuation modes of Magpol, its dynamic properties, work output and transduction characteristics are described. Analogies between Magpol actuation and phase transformations are presented. As an illustration of Magpol actuation, a proof of concept artificial muscle is presented. Current applications and future prospects are described.

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Morphing Soft Magnetic Composites

Magnetorheological (MR) and electrorheological (ER) materials show variations in their rheological properties when subjected to varying magnetic and electric fields, respectively. They have quick time response, in the order of milliseconds, and thus are potentially applicable to structures and devices when a tunable system response is required. When incorporated into an adaptive structural system, they can yield higher variations in the dynamic response of the structure. This study presents a detailed analysis of vibration control capabilities of adaptive structures based on MR and ER materials, and compares their vibration minimization rates, time responses and energy consumption rates. Homogeneous one-dimensional MR and ER adaptive beam configurations were considered. A structural dynamic modeling approach was discussed and vibration characteristics of MR and ER adaptive beams were predicted for different magnetic and electric field levels. In addition to the model predictions, actual MR and ER adaptive beams were fabricated and tested. Both studies illustrated the vibration minimization capabilities of the MR and ER adaptive beams at different rates and environmental conditions. The relative performances of both MR and ER adaptive beams were discussed in detail and their advantages and disadvantages were listed.

https://iopscience.iop.org/article/10.1088/0964-1726/8/5/306/pdf

Magnetorheological and electrorheological materials in adaptive structures and their performance comparison

This paper discusses the investigation of vibration suppression capabilities of magnetorheological (MR) materials in adaptive structures. Homogeneous three-layered adaptive beams with MR materials sandwiched between two elastic layers were considered. By varying the externally applied magnetic field level over the MR layer, the stiffness and damping properties of the adaptive beam can be varied. These variations in the damping and stiffness properties can be used to tune the vibration characteristics of the adaptive beams such as natural frequencies, vibration amplitudes, mode shapes and loss factors. In this study, theoretical investigation of the MR adaptive beams vibration behavior based on the energy approach is accomplished. Experiments were performed to observe the theoretically predicted vibration responses in real time. From both studies, vibration suppression capabilities of MR adaptive beams were observed in the forms of shifts in natural frequency values, variations in loss factors, and vibration amplitudes.

https://iopscience.iop.org/article/10.1088/0964-1726/13/1/001/pdf

Vibration suppression capabilities of magnetorheological materials based adaptive structures

In this study, the semi-active vibration control capabilities of electrorheological (ER) material based axially non-homogeneous adaptive beams were investigated. The adaptive nature of such beams was achieved by controlling the pre-yield rheology of ER material in response to varying applied electric field levels. The beams focused on were designed in a way that can allow for independent control of the electric field levels applied to four sections of the beam. The cross-sectional configuration was based on sandwiching of the ER material between the elastic faceplates. Controllability of the four sections was achieved by selectively coating electrically non-conductive elastic faceplates with a conductive material. Narrow insulated regions were left between adjacent adaptive sections. A vibration model was developed based on thin-plate theory, and the transverse continuous vibration response of the non-homogeneous ER adaptive beam was studied. The developed model was applied to each region of the axially non-homogeneous beam separately. Continuity in the response of the overall structure was achieved by appropriate coupling of the adjacent regions. The resulting analytical model was able to predict the structural vibration response in the forms of natural frequencies, mode shapes, loss factors and the transverse vibration response at any location on the beam surface as functions of excitation frequency and applied electric field levels. Vibration control capacity of the ER adaptive beam was illustrated by emphasizing mode shape control. The structure was subjected to on and off position electric field configurations at each section. The `on' state was defined as an applied electric field of 3.5 kV and the `off' state was actually 0.5 kV . Based on the on/off conditions at each section, various electric configurations were selected for the overall adaptive beam. Variations in the mode shape amplitude and geometry were studied for the selected electric field configurations. Natural frequencies and loss factors of the structure were predicted for each configuration. Controllability of the non-homogeneous ER adaptive beam was observed.

https://iopscience.iop.org/article/10.1088/0964-1726/7/1/015/pdf

Electrorheological material based non-homogeneous adaptive beams

Composite materials, with their high stiffness, high strength, and low weight properties, are attractive materials for industries with advanced needs such as the space, defense, naval systems, and transportation industries. However, due to the complex mechanism of fiber-matrix bonding, the mechanical properties of composite materials may be severely degraded by the presence of a defect. This limitation restricts engineering design from taking full advantage of the benefits of composite materials. While recent studies are continuing to develop composite materials having damage tolerant qualities (less brittle fibers and higher fracture toughness), this study aims to identify methods to measure the health condition of composite structures, fatigue, and its remaining life by identifying defects. As damage occurs and/or propagates, most composite material physical parameters show variations. The changing physical parameters, also called characteristic damage parameters, are listed as stiffness reduction, strength reduction, changes in dynamic properties (such as natural frequencies and damping properties), ultrasonic and acoustic emission properties, thermal and electrical properties. Various non-destructive testing (NDT) methods have been developed to measure characteristic damage parameters. In this study, up to date identified NDT methods are reviewed and their feasibility in health monitoring and damage detection of composite materials are evaluated. Integration of intelligent sensing and signal analysis processes for health monitoring of composite structures is emphasized.

Melek Yalcintas

Papers

Magnetorheological and electrorheological materials in adaptive structures and their performance comparison

Vibration suppression capabilities of magnetorheological materials based adaptive structures

Electrorheological material based non-homogeneous adaptive beams

Composite structures health monitoring