Systematic Experimental studies and Computational Perspectives of the non-linear squeeze Mode behaviour of Magneto-Rheological Fluids
Sprache des Titels:
Power Transmition and Motion Control, PTMC 2005
Magneto-rheological (MR) fluids are suspensions of micron-sized ferromagnetic particles in a non-magnetic carrier fluid. The essential characteristic behaviour is the rapid and reversible transition from the state of a Newtonian-like fluid to the behaviour of a stiff semi-solid by applying a magnetic field of about 0.1-0.4 Tesla. This feature can be understood from the fact that the particles form chain-like structures aligned in field direction. The MR-fluid offers three modes of operation, namely the direct shear mode, the valve mode and the squeeze mode. The latter is of particular interest due to its highly non-linear behaviour, which is still not fully understood and therefore expected to give rise to new industrial applications. A test rig for the exploration of the MR-fluid behaviour was designed for experimental purposes. The present paper describes the results of measurements under sinusoidal loading modes. Special emphasis was put on the dependence of the MR-fluid response with respect to parameter variations of the applied static magnetic field, the cyclic loading amplitude and frequency values. Cavitation effects have been investigated and partially suppressed by pre-pressurising the MR-fluid, which enables a more thorough insight into particle chain disruption and segregation effects. Well pronounced hysteresis loops are observed and exhibit characteristic kinks, which cannot be understood within the frame of elementary constitutive laws such as for Bingham fluids. Therefore, highly sophisticated continuum mechanical theories or particle dynamics simulations seem to be essential to recover the measurement curves in full detail.