Experimental and Numerical Investigation of the Squeeze Mode of Magneto-Rheological Fluids
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Schriftreihe der Technischen Universität Wien
Magneto-rheological (MR) fluids represent a class of smart materials, the rheological properties of which can be controlled by the application of an external magnetic field. 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 magneto-rheological 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. A test rig for the exploration of the fluid behaviour in the squeeze mode, Ref  was used to obtain measurement data. The present paper describes the results of measurements from this test rig in single squeeze as well as periodic squeeze experiments showing the highly complex material properties of MR-fluids. Distinct hysteresis behaviour and cyclic hardening takes place due to the formation and disruption of iron particle chains along the magnetic field lines which is part of further investigations and has to be understood in more detail. Describing this material behaviour numerically is a challenging task. Finding a material law goes far beyond using rather simple elasto-viscoplastic material laws implemented in commercial Finite Element codes. Therefore, highly sophisticated continuum theory techniques have to be applied in principle.