Magnetorheological gel (MRG) is a kind of magneto-sensitive smart material mainly composed of soft magnetic particles and polyurethane, which can decrease or even avoid the severe sedimentation problem appearing in MR fluids. In this work, the rheological properties of MRG under quasi-statically monotonic and cyclic loading with large deformation were investigated, respectively. The results could provide effective guidance for the design of MR devices that are often subjected to quasi-static loading. Firstly, MRG was fabricated by mixing carbonyl iron particles (CIPs) with the polyurethane matrix. Then, variations of normal force with time and magnetic field for MRG were tested and discussed. Moreover, the influences of CIPs content, shear rate, shear strain amplitude and magnetic field on the energy dissipation density of MRG were analyzed. The results showed the magneto-induced damping performance of MRG is highly relevant to the CIPs content and magnetic field, i.e. the magneto-induced enhancement of energy dissipation density of MRG with 60% CIPs content could reach up to 104 900% when the external magnetic strength increases to 391 kA m⁻¹. Furthermore, the related mechanisms, from the perspective of microstructure, were proposed to qualitatively explain the various mechanical phenomena occurring in shear stress and normal force.

Of all the smart materials that can vary with a change in external excitation, magnetorheological gel (MRG) is one of the most pre-eminent composites, having controllable and reversible responses according to the magnitude of the external magnetic field. Temperature has been identified as another important driver that can alter the dynamic properties of a MRG, and so far this has not been studied systematically. The temperature-dependent dynamic properties of a MRG under different magnetic field strengths were investigated by three kinds of experiments—strain amplitude, frequency and magnetic field sweep tests. The experimental results demonstrate that the storage and loss moduli of MRGs display a temperature-induced stiffening effect with a magnetic field but a temperature-induced softening effect in the absence of a magnetic field. The storage modulus improves with magnetic field strength, whereas the loss modulus first shows rapid growth and then a gradual reduction with increasing magnetic field strength. This temperature dependence of dynamic properties is also interpreted through different mechanisms related to the transformation of the MRG microstructure. Furthermore, a modified magnetic dipole model which could predict the relationship between storage modulus and magnetic field strength is combined with the classical Arrhenius equation expressing the effect of temperature on viscosity to describe the temperature dependence of the storage modulus of a MRG under different magnetic field strengths. This paper may provide some useful guidance for designing a magnetorheological device.

In this paper, the effect of temperature on rheological properties of magnetorheological (MR) gel is investigated under rotational steady shear and oscillatory dynamic shear. A kind of fluid-like MR gel (MRG) was firstly synthesized by mixing carbonyl iron powder (CIP) with polymer matrix. Then, the relationship between yield stress, normal stress of MRG and shear rate under six temperatures and four magnetic field strengths were studied by rotational shear experiments. The results demonstrate that the dependence of shear stress on temperature displays an opposite tendency in comparison with that of normal stress on temperature. Moreover, maximum yield stress, one of the most important parameter of MR materials, decreases with the increment of temperature. Under oscillatory dynamic shear test, storage and loss moduli and normal stress of MRG all increase with temperature when a magnetic field is applied, which presents a contrary trend in the absence of a magnetic field. Related mechanisms about the alternation of microstructures of MRG were proposed to explain the above-mentioned phenomena. This paper is helpful in fabricating semi-active engineering devices using MR materials as a medium.