Study On The Evaluation Of The Stability Of Magentorheological Fluids

Magnetorheological (MR) fluids are dispersions of fine (～0.05-10μm) magnetically soft, multidomain particles. The apparent yield strength of these fluids can be changed significantly within milliseconds by the application of an external magnetic field. MR fluid devices are being used and developed for shock absorbers, clutches, brakes, and seismic dampers. The major goals of this research were to advance the science of MR fluids.The stability of magnetorheological (MR) fluids used in magnetorheological application remain is a main of factors to hold back the development of magnetorheological technology. And how to character the sedimentation stability of MR fluids is also a key technology. The stability of MR fluids in long time will change with the structure, which can bring the chang of the viscosity. In this article, a new method is discussed: the viscosities were measured by the Rheometric Scientific Advanced Rheometric Expansion System (ARES) dynamic strain rheometer. And a modle was established to predict the stability of the MR fluids.At present, Some methods for characterization of the stability fasten on the sedimentation stability of the MR fluids. The current techniques of improving the subsidence stability in magnetorheological fluids are reviewed in detail. But, there is not a viable method to character the sedimentation stability of the MR fluids, which is expedite and save sample. In this article, a modle. which will save time, was established to predict the stability of the MR fluids.At first, MR fluids were prepared with volume function of 40%. Some samples of MR fluids were transferred to 10 ml graduated test tubes and placed in still storage,at a room temperature. And another were placed at 90℃. The sedimentation ratio can be obtained by observing the phase boundary between the supernatant liquid and the concentrated suspension, until reaching an asymptotic value. Secondly, the rheology properties of the MR sample were tested. The relationship of the viscosity between room temperature and 90℃was discussed.The effection of temperature on the sedimentation stability of MR fluids was discussed. We found that the viscosity and shear stress of MR fluids without magnetic fields was decreased with the increasing of the temperature. As a result, the sedimentation of MR fluids became quickly.