Huaxia Deng

Development of an adaptive tuned vibration absorber with magnetorheological elastomer

In this technical note we develop an adaptive tuned vibration absorber (ATVA) based on the unique characteristics of magnetorheological elastomers (MREs), whose modulus can be controlled by an applied magnetic field. The MRE used in the developed ATVA was prepared by curing a mixture of 704 silicon rubber, carbonyl iron particles and a small amount of silicone oil under a magnetic field. The ATVA works in shear mode and consists of an oscillator, smart spring elements with MREs, a magnet conductor and two coils. Natural frequencies of the ATVA under different magnetic fields were both theoretically analyzed and experimentally evaluated by employing a beam structure with two ends supported. The experimental results demonstrated that the natural frequency of the ATVA can be tuned from 55 to 82 Hz. The relative frequency change is as high as 147%. Furthermore, the absorption capacity of the developed ATVA can achieve as high as 60 dB, which was also experimentally justified.

Adaptive Tuned Vibration Absorber based on Magnetorheological Elastomer

This study presents an adaptive tuned vibration absorber (ATVA) which is based on magnetorheological elastomer (MRE). Traditional dynamic absorber has limited its application and vibration absorption capacity for its narrow working frequency bandwidth. MRE is a kind of smart material whose modulus can be controlled by applied magnetic field. Based on MREs, an ATVA which works on shear mode is proposed in this study. After the vibration mode shapes of the ATVA are analyzed, the mechanical structure of the ATVA is brought forward. Then the magnetic circuit of the ATVA is identified by ANSYS software. By using a modified dipole model, the shift-frequency properties of the ATVA versus magnetic field and strains are theoretically analyzed and simulated. Furthermore, by employing a beam with two ends supported, its shift-frequency property and vibration absorption capacity are experimentally justified. The experimental results demonstrate that the designed ATVA has better performance than traditional passive absorber in terms of frequency-shift property and vibration absorption capacity.

A novel magnetorheological elastomer isolator with negative changing stiffness for vibration reduction

Magneto-rheological elastomers (MREs) have attracted notable credits in the development of smart isolators and absorbers due to their controllable stiffness and damping properties. For the purpose of mitigating unwanted structural and/or machinery vibrations, the traditional MREbased isolators have been generally proven effective because the MR effect can increase the stiffness when the magnetic field is strengthened. This study presents a novel MRE isolator that experienced reduced stiffness when the applied current was increased. This innovative work was accomplished by applying a hybrid magnet (electromagnet and permanent magnets) onto a multilayered MRE structure. To characterise this negative changing stiffness concept, a multilayered MRE isolator with a hybrid magnet was first designed, fabricated and then tested to measure its properties. An obvious reduction of the effective stiffness and natural frequency of the proposed MRE isolator occurred when the current was continuously adjusted. This device could also work as a conventional MRE isolator as its effective stiffness and natural frequency also increased when a negative current was applied. Further testing was carried out on a onedegree-of-freedom system to assess how effectively this device could isolate vibration. In this experiment, two cases were considered; in each case, the vibration of the primary system was obviously attenuated under ON-OFF control logic, thus demonstrating the feasibility of this novel design as an alternative adaptive vibration isolator.

The development of an adaptive tuned magnetorheological elastomer absorber working in squeeze mode

In the past, adaptive tuned vibration absorbers (ATVAs) based on magnetorheological elastomers (MREs) have mainly been developed in a shear working mode. The enhancing effect of MREs in squeeze mode has already been investigated, but ATVAs in squeeze mode have rarely been studied. This paper reports the development of a compact squeeze MRE absorber and its subsequent performance in various magnetic fields characterized under various frequencies by a vibration testing system. The results revealed that the natural frequency of the MRE absorber working in squeeze mode can be tuned from 37 Hz to 67 Hz. Following this, a theoretical model based on magnetic dipole theory was developed to investigate the dynamic performance of the squeeze MRE absorber, and the vibration attenuation of the squeeze MRE absorber was then verified by mounting it on a beam with supports under both ends. The results revealed that the squeeze MRE absorber extended its vibration attenuation range from 37 Hz to 67 Hz while the passive absorber was only effective around 53 Hz.

Investigation on the mechanism of damping behavior of magnetorheological elastomers

Magnetorheological elastomers (MREs) are a group of smart materials which have many applications such as dynamic vibration absorbers, engine mounts, and so on. The damping behavior is important for applications of MREs. However, the mechanism of the damping of MREs has not been investigated thoroughly. In this study, MREs are modeled as special particle reinforced composites with magneto-induced properties and the mechanism of the damping behavior of MREs is investigated theoretically and experimentally. It has been found that there are three types of damping property in MREs: the intrinsic damping, the interface damping and the magneto-mechanical damping. The presented damping model is successfully validated by damping tests on a series of MRE samples. Furthermore, the relationships between the damping properties and formulas of MREs are discussed; this provides guidance for the manufacture of MREs with various damping properties.

An adaptive tuned vibration absorber based on multilayered MR elastomers

Adaptive tuned vibration absorbers (ATVAs) featuring magnetorheological elastomers (MREs) have attracted considerable research interests because of the advantages of fast response, controllable frequency, and broad working range. Generally, the ATVA uses single layer of MRE sheet, which has some issues such as small oscillator stroke and being effective only on high frequency. In this research, an ATVA which incorporates multilayer MRE sheets was designed and prototyped. Its performance under various scan frequencies was tested on a horizontal vibration platform. A theoretical model was proposed to predict the MRE absorber performance. For the clear demonstration of the advantages of multilayered MRE absorber, two kinds of absorbers with only one layer of MRE were prepared as comparison. The experiments compared the vertical support capability and the tuning frequency range of these two ATVAs, which have clearly highlighted the capabilities of multilayered MRE absorber with larger oscillator stroke (as large as 13.6 mm) and lower working frequencies (as low as 3.2 Hz). The vibration absorption evaluation was conducted by mounting the multilayered MRE absorber on a single-degree-of-freedom system. The results identify that the ATVA with multilayered MREs could work lower than 10 Hz, which is very difficult for the one with single layer MRE. Additionally, the performance of the passive and adaptive tuned laminated MRE absorbers on attenuating a swept frequency vibration are presented, respectively. The ATVA was more effective than the passive absorber over a wide frequency range.

Morphology, Thermal and Mechanical Properties of Poly (Styrene-Acrylonitrile) (SAN)/Clay Nanocomposites from Organic-Modified Montmorillonite

Poly (styrene-acrylonitrile) (SAN)/clay nanocomposites have successfully been prepared by melt intercalation method. The hexadecyl triphenyl phosphonium bromide (P16) and cetyl pyridium chloride (CPC) are used to modify the montmorillonite (MMT). The structure and thermal stability property of the organic modified MMT are, respectively characterized by Fourier transfer infrared (FT-IR) spectra, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The results indicate that the cationic surfactants intercalate into the gallery of MMT and the organic-modified MMT by P16 and CPC has higher thermal stability than hexadecyl trimethyl ammonium bromide (C16) modified MMT. The influences of the different organic modified MMT on the structure and properties of the SAN/clay nanocomposites are investigated by XRD, transmission electronic microscopy (TEM), high-resolution electron microscopy (HREM), TGA and dynamic mechanical analysis (DMA), respectively. The results indicate that the SAN cannot intercalate into the interlayers of the pristine MMT and results in microcomposites. However, the dispersion of the organic-modified MMT in the SAN is rather facile and the SAN nanocomposites reveal an intermediate morphology, an intercalated structure with some exfoliation and the presence of small tactoids. The thermal stability and the char residue at 700°C of the SAN/clay nanocomposites have remarkably enhancements compared with pure SAN. DMA measurements show that the silicate clays improve the storage modulus and glass transition temperature (Tg) of the SAN matrix in the nanocomposites.

Improving the critical speeds of high-speed trains using magnetorheological technology

With the rapid development of high-speed railways, vibration control for maintaining stability, passenger comfort, and safety has become an important area of research. In order to investigate the mechanism of train vibration, the critical speeds of various DOFs with respect to suspension stiffness and damping are first calculated and analyzed based on its dynamic equations. Then, the sensitivity of the critical speed is studied by analyzing the influence of different suspension parameters. On the basis of these analyses, a conclusion is drawn that secondary lateral damping is the most sensitive suspension damper. Subsequently, the secondary lateral dampers are replaced with magnetorheological fluid (MRF) dampers. Finally, a high-speed train model with MRF dampers is simulated by a combined ADAMS and MATLAB simulation and tested in a roller rig test platform to investigate the mechanism of how the MRF damper affects the trains stability and critical speed. The results show that the semi-active suspension installed with MRF dampers substantially improves the stability and critical speed of the train.

Performance evaluation and comparison of magnetorheological elastomer absorbers working in shear and squeeze modes

The adaptive tuned vibration absorbers based on magnetorheological elastomers are mainly developed in shear and squeeze working modes. The distinctions between the two kinds of magnetorheological elastomer absorbers are less investigated. In order to investigate the distinctions induced by the working mode, two magnetorheological elastomer absorbers working in different modes are theoretically and experimentally analyzed in this article. Magnetorheological elastomer was first prepared and tested in shear and squeeze modes by parallel-plate rheometer and materials test system, respectively. Then, the fabricated magnetorheological elastomers were used to develop absorbers working in shear and squeeze modes. The performance of these two absorbers at various magnetic fields is characterized under swept excited frequencies by using a vibration testing system. The experimental results illustrate that the natural frequency of the magnetorheological elastomer absorber working in shear mode can be tuned from 32 to 62 Hz, while the variation range of the natural frequency of the magnetorheological elastomer absorber working in squeeze mode is from 62 to 127 Hz, which indicates the squeeze magnetorheological elastomer absorber has larger frequency-shift range than the shear magnetorheological elastomer absorber. Then, two theoretical models are presented to investigate and predict the frequency-shift performance of the two magnetorheological elastomer absorbers. The theoretical analysis results further verify the above conclusion.

Horizontal vibration reduction of a seat suspension using negative changing stiffness magnetorheological elastomer isolators

Magnetorheological elastomers (MREs) are being used more and more for the development of isolators and absorbers to attenuate vibrations. In this study, four innovative multilayer MRE isolators with negative changing stiffness characteristics are prototyped for horizontal vibration reduction of a seat. For each MRE isolator, a magnetic system consisting of two permanent magnets and an electromagnetic coil was designed to realise negative changing stiffness. This performance of the MRE isolators was verified by the experimental results which indicate that the MRE isolators exhibit a controllable negative changing stiffness characteristic; and this was further verified by the measured natural frequency shift of the MRE isolators. An experimental platform was also developed to test the vibration suppression of the MRE isolators for a real truck seat suspension. The test results demonstrate that the ride comfort of the MRE isolator based seat suspension is significantly better than passive seat suspension.