An Experimental Investigation of the Properties of a Magneto-Rheological Fluid in Squeeze Mode - The Segregation Problem

The latest outcomes [1, 2, 3] addressing the squeeze mode of a magneto-rheological fluid (MRF), report a maximum compressive stress of about 10bar. These results were achieved with a minimum squeeze gap of 0.5mm. One of the aims of this work is to reduce the minimum squeeze gap in order to get much higher compressive stresses. Reducing the minimum squeeze gap down to 0.15mm at a gap thickness compression ratio of 0.87 leads to measured compressive stresses up to 30bar. These results are only valid for a well mixed MRF for the very first squeeze cycles. Especially during the measurements at high magnetic fields an enormous increase of the compressive stress from squeeze cycle to squeeze cycle is observable. Such an increase is related to segregation effects which so far have been reported only rarely in published scientific work (see e.g. [4]) without any experimentally proven method for its avoidance. Thus, the second aim of this work is to check different physical approaches to minimize the segregation effect. Three different ideas are studied: a very simple mechanical wiper, a zero coil-current approach in case of increasing MRF gap and finally the reduction of the MRF reservoir.