Taixiang Liu

Stress pulse attenuation in shear thickening fluid

The stress pulse attenuation of the 62 vol/vol. % dense silica particle-ethylene glycol suspension was investigated by using a modified spilt Hopkinson pressure bar. In comparison to the neat ethylene glycol solution, the transmission pulse of the shear thickening is much weaker under the same impact condition. No energy loss is progressed for the neat ethylene glycol solution, thus it can be concluded that the energy dissipation behavior was happened in the silica particle based shear thickening fluid. In this work, the energy dissipation of the shear thickening fluid was reversible.

Oscillatory normal forces of magnetorheological fluids

The normal forces of magnetorheological fluids were investigated by a commercial magneto-rheometer with plate–plate geometry. Based on the analysis, it was found that the oscillatory normal forces can be achieved both under steady shear and oscillatory shear. The oscillatory normal forces obtained under steady shear developed from the nonparallelism of the testing plates, while the oscillatory normal forces under oscillatory shear mainly arose from the microstructure revolution of magnetorheological fluids. Finally, a dynamic simulation was utilized to analyze this oscillatory shear normal force and the formation mechanism was discussed.

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.

The prestress-dependent mechanical response of magnetorheological elastomers

Magnetorheological elastomers (MREs) are intelligent materials consisting of a rubber matrix filled with magnetizable particles. In many engineering applications, MREs are usually pre-confined and work with constraint-induced prestress. The prestress can significantly change the mechanical properties of MREs. In this work, the influence of prestress on the mechanical response of MREs is studieds both experimentally and theoretically. The storage modulus as well as the magneto-induced modulus change non-linearly with increasing prestress and three regions can be found in the non-linear change. In the non-full contact region, the MREs present poor mechanical properties at small prestress due to the unevenness of the sample surface. In the full contact region, the MREs are under suitable prestress, thus they present good mechanical properties. In the overload region, the pre-configured microstructure of the MREs is destroyed under the large prestress. Moreover, an analytical model is proposed to study the prestress-dependent mechanical properties of MREs. It is revealed that the prestress can change the inter-particle distance, thus further affecting the mechanical response of MREs.

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.