Analysis of magnetorheological grease normal force characteristics in static and dynamic shear modes

In this paper, the normal stress behavior of magnetorheological grease (MRG) in a quiescent state and its dynamic shear modes were systematically studied. Three types of magnetorheological greases were prepared, MRG-30, MRG-50, and MRG-70 with 30%, 50%, and 70% carbonyl iron(CI) powder mass, respectively. Furthermore, static and dynamic shear tests were carried out using a rheometer, the effects of time, magnetic field strength, shear rate and temperature on normal stress were studied and analyzed under both static and dynamic conditions. In the static mode, the research results show that the normal force is related to the magnetic field strength and the content of magnetic particles in the MR grease, but has nothing to do with historical time. the static normal stress generates the evident fluctuation with changing the temperature when magnetic field strengths of 96 kA m ^−1 and 194 kA m ^−1 . The fluctuation is very small when the magnetic field strengths are 0kA m ^−1 , 391 kA m ^−1 and 740kA m ^−1 . Similar to the static normal stress, the dynamic normal stress at the degaussing is greater than the normal stress during magnetic field loading. The dynamic normal stress are almost invariant with prolonging the time below 100 s ^−1 shear rate under the medium magnetic field strength of 194 kA m ^−1 whereas the stress is increased at the shear rate of 100 s ^−1 . Besides, the dynamic normal stress is basically independent from the time above the shear rate 0f 1 s-1 at the high magnetic field of 740 kA m ^−1 . Under other conditions, the normal force basically presents a stable value. At the absence of the magnetic field, there are quietly weak effects of temperature on the static and dynamic normal stress. Finally, when a magnetic field strength higher than 96 kA m ^−1 is applied to the material, the value of dynamic normal stress increases with temperature

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