Preparation of a novel MR fluid for squeeze-shear mode by compositing micron-scale and nano-scale particles

The magnetorheological (MR) fluid under the squeeze-shear mode has an enhanced structure by reducing the distance between particles, significantly increasing the yield stress compared to the single shear mode. The existing research on preparing MR fluid is all based on single shear mode. This work mixes micron-scale carbonyl iron powders and micron-scale soft magnetic particles to prepare the specialized MR fluid for the devices working under squeeze-shear mode. Several kinds of micron-scale carbonyl iron powders and micron-scale soft magnetic particles are selected, of which the magnetic properties are tested to obtain the suitable soft magnetic particles for MR fluid. Then, the optimal combination of micron-scale carbonyl iron powders and micron-scale soft magnetic particles is obtained when the orthogonal test is used to compare the yield stress of different combinations. At the same time, the appropriate surfactants and base carrier fluid were selected, according to the previous work. On this basis, the novel MR fluid is prepared by the base fluid displacement method, and its performances are tested. The results show that the sedimentation rate is 0.8 % after standing for 20 days, which can keep the MR device in a stable state. The viscosity of the novel MR fluid is 8.0 Pa·s at room temperature, exhibiting good liquidity, which allows it to be injected into MR devices. The shear yield stress of the novel MR fluid is 60.28 kPa at the squeeze pressure of 600 kPa, which is 1.5 times higher than that under single shear mode, significantly enhancing the mechanical performance of MR fluid. The novel MR fluid with good sedimentation stability, appropriate viscosity, and better mechanical performance can be applied to more MR devices, especially the MR devices under squeeze-shear mode.