Yangguang Xu

A high-performance magnetorheological material: preparation, characterization and magnetic-mechanic coupling properties

A novel high-performance magnetorheological material, named as magnetorheological plastomer (MRP), was developed by dispersing iron particles into a plastic polyurethane (PU) matrix. The dynamic properties (including storage modulus and loss factor) of the MRP material were systematically tested and the influences of the iron particle content and magnetic field were analyzed. It is found that the anisotropic MRP product with 80% iron particle weight fraction (A-MRP-80), shows a high dynamic property: the maximum magneto-induced storage modulus is 6.54 MPa; the relative MR effect reaches as high as 532%; the loss factor can be reduced to 0.03 by adjusting magnetic field. This kind of MRP shows a much higher magnetorheological performance than the previously reported magnetorhelogical elastomer (MRE). The mechanism for its high MR performance was proposed and the influence of the iron particle distribution and temperature on the dynamic properties were discussed.

Soft magnetorheological polymer gels with controllable rheological properties

A series of magnetorheological (MR) gels consisting of plastic polyurethane matrix swollen by nonvolatile solvent in different weight fractions and carbonyl iron particles were prepared. Their magnetorheological properties, both under oscillatory and rotational shear rheometry, were systematically tested. The results demonstrate that except for the significant influence on the magnetorheological performance, the state of these MR gels can also be easily switched from solid-like (the solvent content is less than 10 wt%) to liquid-like (the solvent content exceeds 25 wt%) by adjusting the solvent content. The huge differences in magnetorheological properties of different MR gels (for example, the G 0 of MR gels without solvent is three orders of magnitude larger than that of MR gels with 45 wt% of solvent in the absence of a magnetic field) and movements of iron particles in the presence of a magnetic field were analyzed, which are helpful in thoroughly understanding the mechanical‐magnetic coupling mechanism between the magnetic particles and the polymer matrix and promoting the application of MR polymer gels. In addition, the stability of MR gels was also investigated. A gravity yield parameter was introduced to quantitatively describe the relationship between particle sedimentation and material characteristics. When the solvent content is lower than 25 wt% or the gravity yield parameter is larger than 0.865, the particle settling phenomenon can be effectively avoided. (Some figures may appear in colour only in the online journal)

The investigation on the nonlinearity of plasticine-like magnetorheological material under oscillatory shear rheometry

To fully understand the structure dependent mechanical property, the harmonic strain loadings were applied to the magnetorheological plastomer (MRP) to study their dynamic properties. Under different test conditions, nonlinearity which was induced by strain amplitude and driving frequency was generated. In order to investigate the mechanism of nonlinearity, a facile and effective strategy by analyzing the response stress and actuating strain within an oscillatory cycle was introduced. In addition, the microstructures of isotropic and anisotropic MRP were observed and the time dependence of dynamic properties for MRP (from isotropic to anisotropic) under an 800 mT magnetic field was also investigated, which were helpful to further understand the structure dependent dynamic properties depending on actuating strain amplitude.

Creep and recovery behaviors of magnetorheological plastomer and its magnetic-dependent properties

The creep and recovery behaviors of magnetorheological plastomer (MRP) were systematically investigated to further understand its deformation mechanism under constant stress. The experimental results suggested that the time-dependent mechanical properties of MRP were highly dependent on the magnetic field and the magnetic-controllable mechanism was discussed. The influences of iron particle distribution and temperature on the creep and recovery behaviors in the absence and presence of a magnetic field were investigated, respectively. A great discrepancy was presented in creep curves for the isotropic and anisotropic MRP under an external magnetic field, which must be induced by the different particle assemblies. In addition, the creep strain of MRP tended to decrease with increasing temperature under a 930 mT magnetic field and this phenomenon was opposite to the results obtained without a magnetic field. Finally, a hypothesis was proposed to explain the temperature effect on the creep behaviors of MRP.

Simulation of magneto-induced rearrangeable microstructures of magnetorheological plastomers

Magneto-induced microscopic particulate structures of magnetorheological plastomers (MRP) are investigated using particle-level dynamics simulation, as this is a basis for studying the macroscopic physical or mechanical properties of MRP. In the simulation, a modified magnetic dipolar interaction force model is proposed to describe the magnetic interaction of two close magnetized iron particles. Other microscopic analytical models of particle–particle and particle–matrix interactions are also constructed. The simulation results show that chain-like and column-like particulate structures are formed when MRP is placed into a steady uniform magnetic field. When MRP is subjected to a stepwise in-plane rotating magnetic field, the microstructure rearranges to form a layered structure parallel to the rotation plane. Moreover, some other patterns or complex magneto-induced rearrangeable microstructures can be achieved by spatially changing the external magnetic field. With the evolution of the microscopic particulate structure in every changing step of the external magnetic field, the microstructure dependent magnetic potential energy and stress state vary sharply at the beginning and then approach respective stable values gradually.

Magneto-induced microstructure characterization of magnetorheological plastomers using impedance spectroscopy

An impedance spectroscopy (IS) method is employed to investigate the magneto-induced microstructure mechanism of magnetorheological plastomers (MRP). The IS of MRP with two typical particle distributions (isotropic and anisotropic) are compared and an equivalent circuit model is proposed to analyze the different impedance responses. It is found that the IS of anisotropic MRP is quite sensitive to the magnetic field and the electron diffusion effect will be restricted in the presence of a magnetic field. Furthermore, the conduction behavior of MRP in the presence of a magnetic field reveals the existence of elasticity in the polymer matrix. The influence of particle chain direction on the conductivity of anisotropic MRP with different particle contents is also investigated. Based on the experimental results, an equivalent method is developed to quantitatively characterize the anisotropy of MRP. With this method, the microstructure-dependent conduction mechanism of MRP can be presented more clearly.

Magneto-induced normal stress of magnetorheological plastomer

An abrupt drop phenomenon of magneto-induced normal stress of magnetorheological plastomer is reported and a microstructure dependent slipping hypothesis is proposed to interpret this interesting behavior. For polyurethane based magnetorheological plastomer sample with 70 wt.% carbonyl iron powder, the magneto-induced normal stress can reach to as high as 60.2 kPa when a 930 mT magnetic field is suddenly applied. Meanwhile, the normal stress shows unpredicted abrupt drop. Particle dynamics is used to investigate the physical generating mechanism of normal stress. The simulation result agrees well with the experimental result, indicating that the interior microstructure of iron particle aggregation plays a crucial role to the normal stress.

Magneto-induced large deformation and high-damping performance of a magnetorheological plastomer

A magnetorheological plastomer (MRP) is a new kind of soft magneto-sensitive polymeric composite. This work reports on the large magneto-deforming effect and high magneto-damping performance of MRPs under a quasi-statical shearing condition. We demonstrate that an MRP possesses a magnetically sensitive malleability, and its magneto-mechanical behavior can be analytically described by the magneto-enhanced Bingham fluid-like model. The magneto-induced axial stress, which drives the deformation of the MRP with 70 wt % carbonyl iron powder, can be tuned in a large range from nearly 0.0 kPa to 55.4 kPa by an external 662.6 kA m−1 magnetic field. The damping performance of an MRP has a significant correlation with the magnetic strength, shear rate, carbonyl iron content and shear strain amplitude. For an MRP with 60 wt % carbonyl iron powder, the relative magneto-enhanced damping effect can reach as high as 716.2% under a quasi-statically shearing condition. Furthermore, the related physical mechanism is proposed, and we reveal that the magneto-induced, particle-assembled microstructure directs the magneto-mechanical behavior of the MRP.

Investigation on the phase-based fuzzy logic controller for magnetorheological elastomer vibration absorber:

This article presents a phase-based fuzzy logic controller for magnetorheological elastomer vibration absorber to trace the excitation frequency rapidly. The phase difference between the relative acceleration of the vibration absorber mass and the absolute acceleration of the primary system is used as the input signal of the fuzzy logic controller to calculate the desired magnetic current. Compared with the traditional stiffness control strategy, the proposed controller does not rely on the accurate relationship between the magnetic current and the resonant frequency of the magnetorheological elastomer vibration absorber. Simulation and experiment results demonstrate that the proposed stiffness controller is efficient to make the magnetorheological elastomer vibration absorber trace the excitation frequency rapidly. When the excitation frequency varies, the magnetorheological elastomer vibration absorber can be tuned properly within several seconds.

Recent progress on the magnetorheological plastomers

Different from the traditional magnetorheological (MR) fluids and elastomers, the magnetic particles in the plastic MR materials are not ‘deadly’ trapped in the polymer matrix; thus, the MR plastomers exhibit higher MR effects and lower sedimentation. The plastic MR materials have attracted increasing attention, and the relevant fundamental mechanisms and practical applications have been intensively studied due to their unique physical and mechanical properties. In this highlight, we have mainly reviewed the preparation and the rheological properties of the MR plastomers. The formation mechanism of the MR plastomers has also been briefly summarized.