Stiffness Of Magnetorheological Elastomer Research Articles

Design of model-free reinforcement learning control for tunable vibration absorber system based on magnetorheological elastomer

This paper proposes a novel model-free reinforcement learning (RL) for vibration control of a magnetorheological elastomer (MRE)-based application. Because the modeling of the MRE stiffness is nonlinear and time-varying depending on various environmental factors, this paper approached the MRE control issue via a model-free learning based method. In this study, an RL model is designed for the MRE-based tunable vibration absorber (TVA) which can control the optimal stiffness of MRE to maximize the vibration suppression. The designed RL algorithm continuously learns and updates the optimal control input of the MRE stiffness adaptively to the dynamic environment without using any prior knowledge of the MRE modeling. From analyzing the mechanism of MRE TVA, the RL algorithm and parameters are carefully designed for a high vibration performance. Also, this study proposed several ideas to make the RL model simpler and converge at a high rate. The experiments confirmed that the proposed RL model showed a rapid convergence to the optimal policy which could minimize the vibration level with respect to the dynamic excitation disturbance. Results showed that the RL model had a similar performance as the conventional tuning method and suppressed the vibration level as much as 57% compared to the one without the controller. Also, the proposed RL algorithm was able to estimate the actual dynamics of the MRE TVA by learning from the environment. Thus, this study showed the feasibility of implementing a model-free RL model to realize an adaptive controller for applications based on highly nonlinear MRE.

Hysteresis behaviour of different magnetorheological elastomer models: modelling and simulation

Smart materials are materials by which their properties can be altered due to external stimuli such as temperature, pressure, and magnetic field. Magnetorheological Elastomer (MRE) is a type of smart composite material consisting of a polymer matrix embedded with ferromagnetic particles. In the presence of an external magnetic field, its mechanical properties such as stiffness change due to the interaction between the magnetic particles. Vibration isolation has been of interest to researchers for decades. In this work, simulation studies were done by utilizing different MRE models from the literature such Bignham, Bouc-Wen, Modified Bouc-Wen, Dahl and Hysteresis models on a base motion isolation (base excitation) system in order to understand the characteristics of MRE. Results showed that as the magnetic field increases, the stiffness of MRE increases significantly. Shifting in the natural frequency of the system from the transmissibility curve was observed for all models which lead to vibration isolation.

Experimental research and modelling of the response of magnetorheological elastomers to cyclic load

Magnetorheological elastomers (MREs) belong to the new group of functional materials called “smart”. The MR effect is increased by choosing the material of the particles with high permeability. The dependence of dynamic moduli and damping of MREs on the external magnetic field and the applied frequency of cyclic shear deformation was studied. Samples of MRE were made of the silicon rubber matrix filled with micron-sized particles. The dynamic stiffness of MRE depends on magnetic flux density and rises with increasing frequency. The loss factor of MRE samples is controlled by the magnetic flux density and it depends also on the testing frequency. The behaviour of viscoelastic materials under uniaxial loading may be represented using rheological models composed of elastic and viscous elements. The dynamic variables storage and loss moduli and loss tangent were determined on the basis of the fitted parameters of the fractional model.

Effect of Electromagnetic Force on Dynamic Mechanical Properties of the Magnetorheological Elastomer Under Compression Mode

Abstract Under the compression mode, the direction of force on the magnetorheological elastomer (MRE) is parallel to the direction of electromagnetic force, so the effect of electromagnetic force on its dynamic mechanical properties cannot be ignored. Therefore, this paper focuses on the effect of electromagnetic force on the dynamic mechanical properties of MRE under compression mode. A new type of testing device was designed and processed. Under a different loading frequency, strain amplitude and external magnetic field, dynamic mechanical properties of MRE were tested, respectively. The result shows that the stiffness and energy dissipation capacity of MRE increase with the current and loading frequency. The stiffness of MRE decreases with the increase in the strain amplitude, but the energy dissipation capacity increases. Comparing the force-displacement curve of MRE with or without the effect of the electromagnetic force, it shows that the electromagnetic force has a great effect on the stiffness of MRE and little effect on its energy dissipation capacity. When the electromagnetic force is removed, the stiffness of MRE decreases, and the change rate of stiffness increases with current. The maximum change rate of stiffness is 5.65%.

Dynamic blocked transfer stiffness method of characterizing the magnetic field and frequency dependent dynamic viscoelastic properties of MRE

Magneto rheological elastomer (MRE) is a potential resilient element for the semi active vibration isolator. MRE based isolators adapt to different frequency of vibrations arising from the source to isolate the structure over wider frequency range. The performance of MRE isolator depends on the magnetic field and frequency dependent characteristics of MRE. Present study is focused on experimentally evaluating the dynamic stiffness and loss factor of MRE through dynamic blocked transfer stiffness method. The dynamic stiffness variations of MRE exhibit strong magnetic field and mild frequency dependency. Enhancements in dynamic stiffness saturate with the increase in magnetic field and the frequency. The inconsistent variations of loss factor with the magnetic field substantiate the inability of MRE to have independent control over its damping characteristics.

Dynamic Tuning of Torsional Transmissibility Using Magnetorheological Elastomer: Modelling and Experimental Verification

Mechanical systems with rotary machines or rotating elements experience torsional vibration, which may lead to an extreme damage and wear. Conventionally, to isolate these undesirable structural vibrations, passive elastomer or torsional dampers are used. However, these passive vibration isolators are not adaptive to varying oscillation frequencies in real time. Due to the need for a real time adaptability and controllable stiffness, the research and development of a smart material called magnetorheological elastomer (MRE) is of interest. This paper presents the mathematical modelling and development of MRE with its implication in torsional vibration control. Based on the model and through experimental studies, the properties of the MRE such as stiffness and transmissibility factor in regard to varying magnetic fields are investigated. The change in magnetic field is achieved by changing the amount of applied current. It is found out that the stiffness of MRE increases with increasing magnetic field and consequently modifies system’s natural frequency. This allows shift in the transmissibility curve to achieve minimum transmissibility factor in the applications involving varying frequency.

Vibration control of platform structures with magnetorheological elastomer isolators based on an improved SAVS law

This paper presents a study on the vibration control of platform structures with magnetorheological elastomer (MRE) isolators. Firstly, a novel MRE isolator design is put forward based on the mechanical properties of MREs, and subsequently a single-degree-of-freedom (SDOF) dynamic model and a multiple-degree-of-freedom (MDOF) dynamic model for platform systems incorporating such isolators are developed. In order to overcome the shortcomings of the conventional on–off control law, an improved semi-active variable stiffness (SAVS) control law is proposed. The proposed SAVS scheme makes full use of the continuously variable stiffness of MREs, and it takes into account the influence of the sampling interval such that the field-dependent restoring force is made to do negative work during the whole sampling interval as far as possible. The results of numerical simulations demonstrate that the improved SAVS control law can achieve better vibration-control effectiveness than the on–off control law. The comparative results are discussed through examining the mechanisms of these two control laws in light of the power spectral density and the energy input. For an MDOF platform a simplified approach is proposed to combine the local response signals with an equivalent SDOF representation to generate the control parameters for individual isolators, and the effectiveness of such a scheme is also verified through numerical simulation.

Dynamic viscoelastic modeling of magnetorheological elastomers

A micromechanics-based viscoelastic constitutive model is proposed to estimate the zero-magnetic-field- and magnetic-field-dependent dynamic shear stiffness and damping behavior for magnetorheological elastomers (MREs). The effect of imperfect interfacial condition between the ferromagnetic particles and the elastomeric matrix on those properties is incorporated in the proposed model. A concept of effective volume fraction of particles is introduced to take into account the particle agglomeration in MREs. The magnetic dipole interaction is further employed to evaluate the magnetic-field-induced increase in shear stiffness of MREs. Numerical simulations are conducted and compared with experimental data to verify the proposed model.

Research on Hybrid Isolation System for Micro-Nano-Fabrication Platform

In order to obtain better vibration suppression effect, this paper designs a semiactive/fully active hybrid isolator by using magnetorheological elastomer (MRE) and piezoelectric material. Combined with multimode control scheme, full frequency vibration suppression is achieved. Firstly, series type structure is determined for the hybrid isolator, and the structure of hybrid isolator is designed. Next, the dynamic model of hybrid isolator is derived, the dynamic characteristics measurement for MRE isolator and piezoelectric stack actuator (PSA) is established, and parameters such as voltage-displacement coefficient, stiffness and damping constant are identified from the experimental results, respectively. Meanwhile, the switch frequency is determined by experimental results of PSA and MRE isolator. Lastly, influence of the stiffness of MRE, control voltage of PSA, and intermediate mass on hybrid isolator system is analyzed by simulations, and the results show that the hybrid isolator proposed is effective.

Fabrication and Mechanical Properties Study of the Magnetorheological Elastomer

Magnetorheological elastomer (MRE) is a novel kind of magnetorheological materials and has been successfully used to control the structure vibration due to its property of variable stiffness under different magnetic field. In order to improve the properties of MRE, it urgently needs to investigate the preparation methods of MRE and build a corresponding test system to evaluate the performance of MRE in different operating modes. In this paper, different magnetic devices for preparing MRE were studied and designed, and the material was fabricated by the permanent magnets with additional permeability equipment at last. Then, according to the SDOF principle, a novel test system was built in order to investigate the mechanical properties of MRE, and exact close-form expressions of the stiffness, loss factor and other mechanical parameters of MRE, under different magnetic field, have been calculated to analyze the properties of MRE.

Note: Real time control of a tunable vibration absorber based on magnetorheological elastomer for suppressing tonal vibrations

An adaptive tunable vibration absober based on magnetorheological elastomer (MRE) is designed as an intelligent device for auto-tuning itself to the time-varying harmonic disturbance force to reduce the unwanted vibration of the primary system in the steady state. The objectives of this note are to develop and implement a continuous control method for a MRE tunable vibration absorber (TVA) and to evaluate its performance in suppressing time-varying tonal vibrations. In the proposed control, the stiffness of MREs is continuously varied based on a nonlinear tuning function that relates the response of the system to the input magnetic field density. Through experiments, it will be shown that the proposed MRE TVA reduces in real time the transmission of a time-varying excited vibration of 48-55 Hz, which shows the potential applicability of the MRE in reducing unwanted vibration to precision devices.

Mechanical properties of magnetorheological elastomers under shear deformation

In this paper, urethane magnetorheological elastomers (MREs) consisting of carbonyl-iron particles in a polyurethane matrix were studied. The volume fraction of particles was equal to 11.5%. Three types of ferromagnetic particles were used, with average particle size ranging from 1 to 70μm. The elastic (storage) modulus G′ was measured as a function of angular frequency ω and strength of magnetic field. The measured G′ values were approximated with empirical model. The highest magnetorheological effect has been found for samples with 6–9μm carbonyl-iron powder. The highest increase in the yield stress is observed for samples with particles aligned at 30° to the magnetic field lines. It has been found that rheological properties strongly depend on the MRE microstructure, in particular on the size/shape of particles and their arrangement. By optimizing the particles size, shape and alignment, the stiffness of MREs has been increased under applied magnetic field.

A feasibility study on smart base isolation systems using magneto-rheological elastomers

This study proposes a new smart base isolation system that employs Magneto-Rheological Elastomers (MREs), a class of smart materials whose elastic modulus or stiffness can be varied depending on the magnitude of an applied magnetic field. It also evaluates the dynamic performance of the MRE-based isolation system in reducing vibrations in structures subject to various seismic excitations. As controllable stiffness elements, MREs can increase the dynamic control bandwidth of the isolation system, improving its vibration reduction capability. To study the effectiveness of the MRE-based isolation system, this paper compares its dynamic performance in reducing vibration responses of a base-isolated single-story structure (i.e., 2DOF) with that of a conventional base-isolation system. Moreover, two control algorithms (linear quadratic regulator (LQR)-based control and state-switched control) are considered for regulating the stiffness of MREs. The simulation results show that the MRE-based isolation system outperformed the conventional system in suppressing the maximum base drift, acceleration, and displacement of the structure.

Dynamic compression testing of a tunable spring element consisting of a magnetorheologicalelastomer

Magnetorheological elastomers (MRE) are interesting candidates for active vibration control ofstructural systems. In this study, spring elements consisting of magnetorheologicalelastomer were prepared and tested in dynamic compression to study the changes in theirstiffness and vibration damping characteristics under the influence of a magnetic field.Aligned and isotropic magnetorheological elastomer composites were preparedusing room temperature vulcanizing silicone elastomer as the matrix material andcarbonyl iron as the magnetizable filler. Aligned MREs were prepared by curing thematerial under an external magnetic field. Aligned MREs were tested and theresults were compared with isotropic composites with no preferred orientation.The mechanical properties of the MREs were tested in cyclic compression passively andwith increasing magnetic flux density. The influence of the testing frequency and strainamplitude on the dynamic stiffness and damping properties was studied. It was noted thatwhen measured in a magnetic field both the dynamic spring constants and the loss factorvalues of aligned MREs were increased compared to the zero-field values. Thedynamic stiffness of aligned MREs increased with increasing testing frequency and itwas tunable with magnetic flux density in the studied frequency range. The lossfactor of aligned MREs was also tunable with the magnetic flux density but theabsolute values also depend on the testing frequency. The dynamic stiffness of thealigned MREs measured in compression decreased with increasing strain amplitude,but the damping properties were not affected similarly. On the basis of theseresults, MREs are applicable as tunable spring elements for active vibration control.