Magneto-induced rheological properties of magnetorheological gel under quasi-static shear with large deformation

Micromechanism of interparticle normal magnetic attraction effect in magnetorheological suspensions based on magnetic-dipole theory

In order to reveal adsorption-regulation micromechanism and debonding micromechanism between wall surface and magnetorheological (MR) wall-climbing robot legs, an interparticle normal magnetic attraction (NMA) mechanics model was constructed based upon the magnetic-dipole theory. According to analysis of NMA mechanics, it was confirmed that the interparticle NMA could be intensified with enhancing magnetic-particle diameter but was weakened with ratio of adjacent magnetic-particles distance to magnetic-particle radius. It means that the adhesive capacity between MR wall-climbing robot legs and wall surface could be strengthened by increasing magnetic-particle size and decreasing interparticle distance. Furthermore, it was found that the NMA of the first particle in the magnetic chain was positively related to magnetic-particles number until the magnetic-particles number reached a critical value. Consequently, the adsorption ability between MR wall-climbing robot legs and wall surface could be effectively controlled by changing magnetic-particles number. Besides, the strongest NMA appeared at the middle of the magnetic chain. However, the weakest NMA locates at both ends of the magnetic chain. Thus, it could be concluded that the end of the magnetic chain would be separated from wall surface rather than fracture occurred in the middle of the magnetic chain when the MR wall-climbing robot legs divorced from wall surface.

Influence of Magnetic Field and Temperature on Rheological Behavior of Magnetorheological Gel

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.

Experimental investigation on the influence of temperature on the hysteresis behavior of magnetorheological gel by employing a large-amplitude-oscillation-shear test method

It is of great significance to explore the mechanism of temperature influence on magnetorheological gel before employing materials for device design. Because of the temperature of the materials rising by the coil during the working process, the wall sliding effect, the interaction between the particles and the interaction between the particles and the polymer chain occur inevitably, which further affects the mechanical properties of the material. This study investigated the effect of temperature on magnetorheological hysteresis properties and its mechanism by employing a large-amplitude-oscillation-shear test method at different temperatures (i.e., 10 °C, 30 °C, 50 °C, 70 °C, 90 °C). The temperature behavior of the MR gel-70 is experimentally evaluated under various loading conditions, including five levels of current inputs of 0 A, 0.5 A, 1 A, 2 A and 4 A, and three excitation frequencies of 5 Hz, 10 Hz and 15 Hz, respectively. The microstructure and the magnetic performance of the sample are probed by employing a scanning electron microscope and vibrating sample magnetometer. It is indicated from the result that magnetorheological gel as a magnetized-induced material and its mechanical properties are greatly influenced by temperature, current and frequency.