The rheological properties of magnetorheological (MR) materials, such as their viscosity and dynamic modulus, can be tuned or controlled by changing the intensity of the magnetic field using appropriate control schemes. Thanks to their robustness, performance and smart properties, numerous studies have been undertaken on the development of new MR materials, and microscopic and macroscopic modelling approaches. Novel applications include engine mounts and clutch systems in the automotive industry, shock absorbing safety devices for cockpit seats in aerospace, and shock absorption from movement in semi-active human prosthetic legs. This book introduces magnetorheological fluids and elastomers, and explores their material properties, related modelling techniques and applications in turn. The book offers insights into the relationships between the properties and characterisation of MR materials and their current and future applications, making it useful reading for researchers, engineers and graduate students who work in the field of smart materials and structures.
Inspec keywords: magnetic materials; elastomers; intelligent materials; magnetorheology; non-Newtonian fluids
Other keywords: MRFs; MRPs; MREs; magnetorheological materials; magnetorheological plastomers; magnetorheological fluids; magnetorheological elastomers; application devices
Subjects: Intelligent materials; General electrical engineering topics; Monographs, and collections; Engineering materials; Engineering mechanics; Intelligent materials (engineering materials science); Magnetic materials; Electrorheological and magnetorheological fluids; Magnetic liquids; Mechanical components, systems and devices
In the literature about magnetorheological fluids (MRFs), with both theoretical and experimental results of physical models to explain the magnetorheological (MR) effect, often the MRF is prepared with only two components, a magnetic dispersed phase and a carrier liquid, while attempting to keep the MRF formulation as simple as possible. On the other hand, many patents of MRF include three, four or more components, such as some surfactant and thixotropic additives. In order to formulate a good and reliable MRF for different applications such as MR shock absorbers, clutches and brakes, the MRF redispersibility is a challenge, but necessary key property for out-of-lab real-world applications. In this chapter, we show how to measure and evaluate the MRF redispersibility.
Modeling MR fluids is a challenging task that has been undertaken from different points of view and using different computational methods. In particular, the use of microscopic approaches is of outstanding interest today. Among the different microscopic approaches reported in the literature, DEM simulations have proved to be strong candidates to model MR fluids because they are able to gather the most basic features under static and flow conditions. DEM simulations are shown here to appropriately capture the aggregation kinetics of dilute MR fluids as well. On the other hand, FEM simulations are a complementary tool to accurately ascertain magnetostatic interparticle forces. Although this type of simulation is hard to implement in dynamic systems with a large number of particles due to its high computational cost, it is demonstrated here that it is still very useful in the precise determination of the yield stress in concentrated MR fluids.
This study presents a new hybrid optimal controller to enhance the robustness and stability of dynamic systems subjected to uncertainties and external disturbances. In the formulation of the proposed control system, the Bolza-Meyer (BM) criterion of the optimal controller is modified to meet the system variation, and the sliding-mode controller is modified to obtain the classical control property with the prescribed performance. The proposed controller also includes the H-infinity technique as a bridge for connecting the sub-controls and improving the robust performance of the system. Fuzzy neural networks are used as filters to choose the optimal values for the next calculation. Hence, many advantages of fuzzy neural networks are acquired, related to optimal control, sliding mode control, prescribed performance, and H-infinity techniques. To demonstrate these advantages, the proposed hybrid controller is applied to a vehicle seat suspension for vibration control. Simulation results show that the proposed control obtains good performances than the compared controllers.
A mathematical model of an object or a physical process is always a crucial component of the model development process. Given a set of requirements and objectives, the model is usually required to copy the object/process behavior with a realistic accuracy and reasonable computational effort. It is then important that all the necessary features and characteristics of the examined object/process are incorporated in the modeling process. With the multi-physics objects such as magnetorheological (MR) actuators, the process becomes even more complicated as they require coupling the expertise from various and sometimes distant fields of engineering and science. The multi-physics nature of MR actuators (also known as MR dampers) calls for the expertise in solid body mechanics, fluid mechanics, heat transfer, electromagnetics, power electronics, chemistry, control theory, etc. It requires the use of appropriate tools and methodologies for specific tasks. Therefore, a need to outline various methodologies and models applied in R&D studies on MR dampers/actuators has arisen. Briefly, in the chapter the author discusses how the models and methods can be used in solving engineering and research problems.
This book chapter presents comprehensive investigations on the use of magnetorheological (MR) shock absorber to mitigate the effect of impact loading, with emphasis on the recoil system. A physical model of the field gun is established and a long-stroke MR recoil absorber with four-stage parallel electromagnetic coils is designed to apply separate current respectively and generate variable magnetic field distributions in the annular flow channel. The response time and the compensation method are investigated to facilitate the application. Based on the dynamic analysis and firing stability condition during the process of shock, the ideal recoil force-stroke profiles of MR absorber at different limiting firing angles are obtained. The experimental studies are carried out on the impact test rig under different combinations of current loading: conventional unified control mode, separate control mode and timing control mode.
In order to ensure the driving safety (the anti-roll performance) of vehicles when steering and the ride comfort when passing through uneven roads, this chapter proposes the principle and configuration of a novel reciprocating rotary damper based on a smart material-magnetorheological (MR) fluid with a large controllable torque range and a semi-active stabilizer bar system based on the MR damper. The dynamic model of the MR semi-active stabilizer bar system is established. The mathematical model of the proposed MR damper is derived, and the corresponding controllable torque characteristics are obtained and evaluated using the finite element analysis results via software ANSYS. A piecewise control strategy with respect to vehicle body roll angular velocity is proposed, and a preliminary control of MR stabilizer bar is conducted and compared with the passive-on stabilizer bars on the vehicle anti-roll performance.
In this chapter, a hybrid active and semi-active seat suspension for heavy-duty vehicles is experimentally investigated to fill the performance gap between the two kinds of seat suspensions. An active actuator with low continuous force output, which is insufficient for an active seat suspension system, is applied together with a semi-active MRF damper. It has several advantages. First, the energy consumption will be less than a merely active seat suspension. Second, the benefits of active and semi-active seat suspension in vibration control will be integrated. The MRF damper can assist the active actuator to suppress the high resonance vibration with low energy consumption, and at the higher frequency (2-4 Hz) vibration, the semiactive seat suspension cannot further improve the seat suspension performance, but the active actuator further reduces the vibration with small force output. Third, it is a fail-safe system because of the semi-active actuator; the failure of the active actuator will have less influence on the system security. Additionally, the low-power active actuator has a small size and a low current requirement which can benefit the installation and application of the hybrid system in an existing semiactive seat suspension. In this study, the proposed hybrid controller only applies measurable variables in practical application.
This chapter focuses on new development of MRB with magnetic coils placed on side housings (side-coil MRB). First, an overview of configurations of MRB is introduced; from this, the reason for development of side-coil MRB is figured out. Then, the chapter focuses on modeling, optimal design and evaluation of different configurations of side-coil MRB such as single side-coil, double side-coil and triple side-coil MR brakes. In addition, experimental works are conducted to validate performance of the proposed multiple side-coil MRB. The chapter is closed by a summary on the advantages and potential development of the side-coil MRBs.
As a viscoelastic smart material with magnetic-control properties, a magnetorheological (MR) elastomer (MRE) is prepared by solidifying the magnetic particles (hardness) into the viscoelastic polymer matrix (softness). MRE is a magnetic-sensing smart material whose mechanical property can be controlled by external magnetic field. MRE possesses advantages of both MR material and elastomer, such as rapid response, good reversibility, excellent polymer properties and strong controllable capacity. It overcomes the disadvantages of sedimentation, poor stability and sealing problems of MR fluid (MRF). These advantages result in MRE having broad application prospects in the fields of noise reduction, vibration attenuation and smart sensing. Consequently, it has become a hotspot of MR materials in recent years. In this chapter, the MRE materials' preparation, characterization and application research are introduced. Finally, the future development of MREs is also prospected.
We have investigated the tensile modulus of structured magnetorheological elastomers (MREs) to understand their anisotropic properties in terms of spatial configuration of particles, particle volume fraction and magnetization density. A micromechanical model incorporated into the macroscopic constitutive laws was derived from the equivalent effective medium theory by considering the anisotropy of structured MREs. A three-parameter microscopic representative volume element was constructed to describe the microstructure of MREs in which the magnetic particles were arranged in the matrix forming layer or chain structure. By considering the transverse isotropic of the pure tensile modulus, we established a relationship between tensile modulus of magnetic-induced stress and mechanical strain, which can derive the tensile modulus of structured MRE in two directions under uniform magnetic field. The theoretical analysis showed that the field-response effect of the tensile modulus of MRE was dependent on the magneto-induced stress, magneto-induced spatial structure and far-field strain. Considering the particle interaction force in the presence of a magnetic field under tensile stress, we found that when the magneto-induced stress decreases with mechanic strain, the positive MR effect is generated, while the magneto-induced stress increases with mechanical strain, the negative MR effect is generated. Simulation results show that there is an optimal particles' volume fraction for structured MRE, in which the changing rate of tensile modulus is the largest in one direction. We evaluated the anisotropy of MREs by showing the ratio of Ez/Ex for both chain and layer structures as a function of magnetic field strength and particle fractions. The anisotropy of MRE with chain structure is most evident with the particles loading of 17.04%, in the absence of magnetic field and the anisotropy of MRE with layer structure reaches peak with the particles loading of 23.3%. When the magnetic field is applied, the anisotropy of MRE with chain structure is weakened and that with layer structure is enhanced with the particles loading lower than 10.1%. When the particles' volume fraction is higher than 10.1%, the anisotropy of both layer structure and chain structure of MRE is reinforced.
In this chapter, a kind of new magnetorheological elastomer (MRE) is developed with the brominated isoprene isobutylene rubber matrix, a high damping property rubber. In order to investigate the performance of the new kind of MRE and find out the difference with the MRE based on a natural rubber matrix, the physical and dynamic mechanical properties of these samples are tested. In addition, the proposed magnetoviscoelasticity parametric model is introduced, and the parameters are identified for this kind of MRE, then the force-displacement curves obtained from model simulation and experimental data are compared with the numerical simulation.
This chapter explores the existing application of magnetorheological elastomer (MRE)-based devices which have been proposed in several field applications. It covers the design parameter and general performances of the devices. Some applications which have been published through patents as well as scientific articles were highlighted in the last two decades. The working principle and prototype performances are also delivered. We classify practical applications into three areas of semi-active, active, and sensory systems. However, the discussion is limited to the basic working principle of the device without further elaboration of their control strategies. This is because control systems in MRE-based devices have broad coverage. Besides, the fundamental technique in controlling MRE-based devices is similar to that of controlling MR-fluid-based equipment.
This study proposes to incorporate magnetic nonlinearity into the linear magnetorheological elastomer (MRE) absorber, aiming at further broadening its operating bandwidth under each constant current. The test results under different amplitudes show that the absorber performs nonlinearity and its effective frequency bandwidth will be enlarged when it works on nonlinear mode. Then the adaptability for the linear case and the nonlinear case were both verified and evaluated. Afterwards, the absorption effectiveness of this nonlinear MRE absorber on vibration control was experimentally carried out. The vibration absorption evaluation also demonstrates that the nonlinear working mode absorber has larger effective bandwidth. And finally a short-time Fourier transform was used to control the nonlinear MRE absorber to track the excitation frequency variation. The test result demonstrates that the hybrid MRE absorber can also tune its stiffness to trace the excitation frequency and performs better than passive absorbers.
This chapter details the development of a smart base isolation system for seismic protection of civil structures utilising magnetorheological (MR) elastomer (MRE). Critical components of the development of the system, i.e. adaptive base isolator, control design and shake table testing, are described. Finally, shake table testing is conducted to verify the effectiveness of the proposed smart-base isolation system.
Magnetorheological (MR) plastomer (MRP) is a class of magneto-sensitive smart material that incorporates magnetic particles into a soft polymer matrix. The low cross-linking density matrix allows the magnetic particles to be entrapped without sedimentation. Moreover, the magnetic particles can be moved under the induction of the magnetic field, so the MRP shows well stability and exhibits high MR effect. This chapter provides a detailed introduction to MRPs, including preparation, mechanical and electrical properties, formation mechanism, and applications.