| Magnetorheological fluid (MRF) is one kind of smart material that is sensitive to magnetic field. MRF is a mixture liquid consisting of magnetic granules, base fluid and surfactant. Magnetic field remarkablely effects on rheological behavior of MRF. Without external magnetic field, magnetorheological fluid flows well that shows liquid properties. The apparent viscosity of MRF augments and some solid properties present, becomeing dense even losing its fluidity, if an external magnetic field is applied. It resumes its fluidity rapidly and this change is reversible and continuous when external magnetic field is removed. Furthermore, its performance is independent to temperature.One key performance of magnetorheological fluid is yield stress. When the external stress is less than yield stress, magnetorheological fluid shows the solid properties; While the stress is bigger than yield stress, it begins to flow and shows liquid properties.Because many theoretic issues are still in discussion, there are many questions to be solved about its rheological behavior changing mechanism, its frame variation laws in magnetic field, its manufacture and yield, performance testing, design standard and its element control theory and technology, etc. This technology has not yet been widely used at the present time.This paper introduces the present state and trend of development of MRF, MRF devices and MRF technology at first. Then rheological behavior changing mechanism and its models are discussed. The present state of soft-start and the significance of MRF introducing into transmission engineering field are analysed thirdly. Finally, the goals and contents of this dissertation have been put forward briefly.Through selecting magnetic granules, based liquid and surfactant, good performance magnetorheological fluid is prepared. Four MRF are prepared with carbonyl iron, which volume percent are 57.9%, 36.2%, 26.7% and19.6%, using average diameter 2.5um granules. And 57.9 volume percent MRF with 3.5 um carbonyl iron powder is prepared, either. The magnetic particles can be regarded as dipoles. The influnce factors on stability of MRF is analysed using magnetic dipole theory, which are magnetic force, gravity, Van. Der Waals, exclusive force from dispersant. It illuminates that the key factor causing magnetic granules deposit is gravity field. The exclusive force from dispersant is the key factor that prevents magnetic granules reunites together by magnetic force and Van. Der Waals. It's impossible to preparat never subsideing MRF.A pulling testing instrument measureing yield stress of MRF is manufactured. Different materials, copper, aluminium, steel, and different pulling sheets grooved with 1mm/2mm, rectangular/triangular roughness are maked. The relationship between yield stress and magnetic field strength with these diffent sheets are tested.It observed that wall effect is related to magnetic field strength, surface roughness and coupling material. The coupling material is the most important. Wall effect occurs if the couplings are made in non-magnetoconductivity material and the magnetic field is strong enough. While wall effect doesn't occur if the couplings are made in magnetoconductivity material, whether how smooth the surface is.The response process is tested by measureing the resistance of MRF in magnetic field. It shows that the magnetorheological effect is gradual changing. When it reaches the critical point, magnetorheological effect response within milliseconds, then buildups gradually. It doesn't stop even 1000 milliseconds passed. Different volume percent MRF have similar response process. The experiments prove that MRF is a viscoelastic body.A sheer mode high-power MRF soft-start device was manufactured based on Bingham model and its static performances are measured. The temperature rises when rotate speed difference being 10 rpm and emulated soft-start process are tested. The experiments prove that the device can transfer huge moment, equilibrate the power among motors. But the soft-start process can't exceed 30seconds.
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