Microcapillary magnetorheometer

Abstract

Magnetorheological fluids, (MR fluids) have been around since the 1940's. After their discovery many applications followed, such as the MR clutch and MR damper. In these applications the fluids are subjected to ultra high shear rates although no knowledge is available on what happens to the rheological properties under these conditions. In general, the characteristics determined on lower shear rates are extrapolated and used to design new devices. Magnetorheological fluids have potential in the high tech and high precision applications and their properties need to be known in particular at shear rates around 106 [1/s]. Commercially available magnetorheometers are not able to measure these fluids at ultra high shear rates and are limited to 105 [1/s]. Therefore a new magnetorheometer is required to measure ultra high shear rates. In this thesis the physical limitations of current measuring principles are analysed and a concept is designed for ultra high shear rate rheometry in combination with a magnetic field. A prototype is fabricated and the techniques used are described. The prototype is tested and compared to a state of the art commercial rheometer. The test results of the prototype rheometer for MR fluids show its capability to measure fluids to a range of 10^4 [1/s] to 1.16x10^6 [1/s] and the capability to measure the magnetorheological effect of MR fluids.