Magnetorheological (MR) fluids have many attractive features, including high yield strength, low viscosity and stable hysteretic behavior over a broad temperature range. In general, low viscosity MR fluids are widely acceptable to the applications to industrial devices with low energy loss under no magnetic field. While, although high viscosity MR fluids are suitable for some applications such as torque converters, viscous couplings, and damping devices which need fail-safe, there is almost no research to investigate the properties of high viscous MR fluids. In this research, the rheological properties and particle settling rate of high viscous MR fluids have been investigated, focusing on the effects of the MR fluid viscosity on its induced yield stress, flow curves and particle settling rate. The tested MR fluids are suspensions of micron-sized carbonyl iron particles dispersed into high viscosity silicone oils and mineral oil. The rheological properties in constant rpm tests and oscillatory tests have been measured using a HAAKE RSI50 parallel disk rheometer with magnetic circuit. An effective means of producing a stable MR fluid is by the increase of viscosity and the addition of anti-settling agent.
