Computer Aided Design and Optimization of a Test Rig for Magneto-Rheological Fluid Behaviour

Magneto-rheological (MR) fluids are liquids whose rheological properties can be controlled by the application of an external magnetic field. Commercial applications of MR fluids can be found in vibration dampers and brakes. The MR fluid offers three modes of operation. Only two of them are frequently used in applications: Either the direct shear mode, where the relative motion of two magnetic poles separated by the fluid generates shear forces, or the valve mode, where the magnetorheologial effect is used to restrict the flow through passages and the resulting pressure difference is used for hydrostatic force generation. Because of its non-linear behaviour, the third mode of operation, the so called squeeze mode is up to now used for small amplitude vibration damping only. A better insight into the behaviour of MR fluids in the squeeze mode is expected to give rise to new applications. The present paper describes the design of a test rig for the exploration of the fluid behaviour in the squeeze mode. While the basic task of squeezing the MR fluid out of a narrowing gap can easily be accomplished, the measurement of hydrostatic pressure and shear stress at the boundary of the MR fluid film is very demanding. Finite element analysis is used for the design and optimization of both the mechanical and electromagnetical properties of the shear stress sensor.