BEHAVIOR OF MR FLUIDS AT HIGH VELOCITIES AND HIGH SHEAR RATES

Abstract

The objective of this work is to characterize the performance of MR fluid at high shear rates and high velocities. A slit-flow rheometer has been built which allows for high speed testing of MR fluid under varying field strengths. Fluid velocities range from 3.9 m/s to 27 m/s with resulting shear rates ranging from 0.23×105 s -1 to 1.6×105 s -1. In order to evaluate the performance of the fluid, the force required to drive the fluid through the slit is measured and force-velocity characteristics are generated. The zero-field viscosity is found and results indicate that shear thinning is still present even at these high shear rates. Two magnetic field strengths were considered for the field testing (50 kA/m and 100 kA/m). Results indicate that a yield stress is still being developed in the fluid. However, as fluid velocity increases, the yield stress being developed in the fluid decreases. This reduction in the yield stress could be attributed to the dwell time, or the amount of time the fluid spends in the presence of a magnetic field.