Theoretical and experimental studies of magnetorheological (MR) fluids and MR greases/gels: From rheology to system application

This work investigates magneto-rheological (MR) grease/gel and MR fluid performance under different applied conditions. Research incorporates the following four particular applications: (1) developing a model for MR grease/gel yield stress, (2) a study of MR valve and MR fluid pressure response time, (3) two-dimensional computational study of MR flow through a complex valving geometry, and (4) a design of MR fluid bypass damper for preventing vehicle rollover. (1) A new constitutive model considering behavior of shear yield stress of MR greases/gels under combined effects of applied magnetic field and temperature has been developed. MR greases/gels are a class of field-responsive materials which consist of micron-size ferrous particles suspended in a grease-like material. The main advantage of MR grease over MR fluid is that in MR grease ferrous particles do not settle. However, the rheological properties of grease carrier materials are very sensitive to changes in temperature. Therefore, the temperature effect on the yield stress of MR greases may be one of the key parameters in developing these materials. In this study, the steady-shear magneto-rheological response of MR grease subject to various temperatures was investigated. Experimental data was obtained for magnetic fields ranging from 0.14T to 0.53T and temperatures ranging from 10°C to 70°C. It was observed that temperature has a pronounced effect on the field induced yield stress of MR greases. A new model for MR grease/gel yield stress as a function of magnetic field and temperature was obtained based on the Herschel-Bulkley constitutive equation. Excellent agreement between the model predictions and experimental data was obtained. (2) Dynamic response times of MR fluid and MR fluid valves have been studied. Two types of MR valves were designed: annular MR flow, and radial MR flow. Dynamic response times of MR fluid valves under pulses with constant cycles generated by a current driver and a voltage driver were compared. Rising and falling response times of MR valves under constant volume flow rate were experimentally investigated. The system time constant was determined for both rising pressure regime and falling pressure regime for annular, as well as, radial valve geometries. Furthermore, dynamic response time of MR fluid was theoretically and experimentally investigated. It was observed that pressure response times of MR fluid valves and MR fluids are highly dependent on flow geometry. It was also demonstrated that radial flow MR valve have faster pressure response time compared to annular flow MR valve. (3) Two-dimensional computational fluid dynamics (CFD) simulations of MR flow through a complex valving geometry were performed in order to predict the pressure drop across MR valve. The simulation model was constructed based on a designed MR valve, which have circular, radial and annular flow regions. The non-Newtonian constitutive models available in a CFD package have been used for modeling the radial MR flow regions where the magnetic field is activated. Pressure drops across the MR valve have been studied employing analytical, computational, and experimental approaches. (4) A unique MR fluid bypass damper for heavy vehicle controllable suspension systems was designed, fabricated, and tested. Relatively, high dynamic force range was obtained in order to prevent vehicle rollover under certain crucial circumstances. The rollover performance of a heavy vehicle incorporated with four MR fluid dampers was carried out using a vehicle dynamic software (TruckSIM). Emergency maneuver and rollover scenarios were simulated. The results show that the MR fluid dampers can achieve satisfactory performance for protection against vehicle rollover. It was estimated that the roll angle can be reduced by 45% compared to the regular original equipment manufacturer (OEM) passive dampers.