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Sedimentations and hard cakes formation of magnetic particles restrict magnetorheological fluid response to magnetic field and can cause the MR fluid containing device to collapse. Therefore, researches on MR fluids sedimentation reduction procedures and its effective factors are in great deal of interest to improve magnetorheological applications. In this study, the effects of some parameters on typical MRF stability were investigated. For this purpose, at first, MRF samples were constructed and the effects of various factors including carrier fluid type, particles concentrations and MRF mixing methods on its stability were investigated and the importance of each factor were determined by Taguchi algorithm and the stable MRF sample for application of magnetorheological dampers was chosen. Next, by investigation of the most stable MRF sample, based on the combination of stability and off- state viscosity factors, the relation for yield stress in various magnetic fields was presented. This relation was derived based on fitting the Herschel- Bulkley model with experimental data in conjunction with the existing relations of yield stress. As the results shown, after 168 hours, sedimentation for the most stable sample is 7%. This sample consists of silicon oil and 70%wt iron powder which prepared with mechanical stirrer. Adding 3%wt stearic acid to carrier fluid for increasing the stability, results to increasing the viscosity of carrier fluid up to 39 times. In spite of this, an acceptable MR effect is presented so that, in magnetic field of 146KA/m the sample yield stress is 15KPa.

Keywords: stability, Magnetorheological fluid, sedimentation, off-state viscosity, Rheology

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