CHAPTER 6: Thin-film Rheology and Tribology of Magnetorheological Fluids

This chapter is concerned with an investigation of the tribological performance of magnetic suspensions. We begin with a state-of-the-art review of related research available in the literature. Then we show that magnetic nanoparticles can both reduce friction and control starvation in lubricated contacts under the presence of non-uniform magnetic fields. Next, we move to the case of pure sliding soft-elastohydrodynamic (EHL) point contacts were friction is not as severe as the case in hard contacts. We show that at low speeds iron particles employed in the formulation of MR fluids are entrapped in the contacts and plow the soft surfaces resulting in a constant friction. This low speed (boundary) regime is dominated by the carbonyl iron grade employed in the formulation. However, at large sliding speeds, well in the full film lubrication regime, the friction coefficient is found to strongly depend on the viscosity of the lubricant oil.