Several applications of magnetorheological (MR) fluids are nowadays present in the industrial world, however sometimes system requirements require better material properties. In technical literature an interesting previous work shows that MR fluids exhibit a pressure dependency called squeeze strengthen effect. Since a lot of MR fluid based devices are rotary devices, this paper investigates the behaviour of MR fluids under pressure when a rotation is applied to shear the fluid. The system is designed in order to apply both the magnetic field and the pressure following a Design of Experiment method. The experimental apparatus comprises a cylinder in which a piston is used both to apply the pressure and to apply a prescribed rotation. The magnetic circuit is designed to provide a nearly constant induction field in the MR fluid. The experimental apparatus measures torque as a function of the variables considered and the yield shear stress is computed. A statistical analysis of the results shows that there is a positive interaction between magnetic field and pressure, which enhance the MR fluid performances more than two times.

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