Magnetorheological polymeric gels (MRPG) have been developed for use in semi-active magnetorheological fluid (MRF) dampers and other magnetorheological (MR) devices. The novel MRPGs are prepared by suspending iron particles in polymeric gels. Off-state (i.e, no applied magnetic field) viscosity and settling behavior can be controlled through the selection of polymeric gels. In this study, tunable rheological properties were investigated with a piston-driven flow type rheometer with a shear rate varying from 20 s Ϫ1 to 6,000 s Ϫ1. Silicone MRPG (with 84.5 wt % iron particles) has controllable viscosity and a high shear yield stress over a wide range of shear rates. Silicone MRPG (79.5 wt % iron particles) has the lowest viscosity of those studied. Polyurethane MRPG has the lowest settling rate. The order of addition of magnetic particles and polymer during the polymerization process affects the MRPG final off-state apparent viscosity (80% increase in apparent viscosity for silicone MRPG polymerized after adding iron particles). This indicates that polymer gels modify the surface properties of the magnetic particles, causing interaction among particles. The dynamic shear yield stress is higher for fluids with better dispersion stability. Polyurethane MRPG, which has the lowest settling rate, has a high dynamic yield stress (23 kPa at 350 mT). Both dynamic and static shear stress values of the MRPGs were found to be similar in magnitude (5-8 kPa at 120 mT for silicone MRPG with 84.5 wt % iron particles and polyurethane MRPG), indicating that MRPGs can provide consistent performance in devices.

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This study presents theoretical and experimental investigations of a novel external bypass, fail-safe, magnetorheological fluid (MRF) damper. A fail-safe MRF damper is referred to as a device that retains a minimum required damping capacity in the event of a power supply or electronic system failure. The new MRF device has a simple design, is compact, is capable of generating a considerable dynamic force range, and can be sized for specific vibration control applications. The theoretical formulation is developed based on the Herschel–Bulkley constitutive model for an annular flow. Experimental results are obtained to demonstrate the validity of the theoretical analysis.

Control Strategies Figure 1. Scaled Bridge Model.