Rheological controllability of double-ended MR dampers subjected to impact loading

The vast majorities of the applications of MR dampers have been for transportation applications-mainly shock absorbers for automobile suspensions, heavy truck seats, and racecar suspensions-where the MR device is not subjected to very high velocities. For these applications, as well as many others, although the MR device is most often subjected to relatively low velocities, the MR fluid which passes through a narrow piston gap can experience very high velocities and shear rates. Yet, there is very little known about the dynamics of MR fluids at these very high shear rates. This study will provide some of the results from an extensive experimental study that was conducted on the impact dynamics of MR dampers, at the Advanced Vehicle Dynamics Laboratory of Virginia Tech. For brevity, the results that are included in this paper are limited to those for a double-ended MR damper, which is most suitable for impact applications. For an impact velocity of 160 in/s and drop mass of 55 lb, the results indicate that the double-ended MR damper transmits relatively large forces, which are hypothesized to be due to the large size of the damper and the large amount of MR fluid that needs to be accelerated in the damper. For all of the tests on the double-ended MR damper, the fluid became controllable once the piston velocity dropped below a threshold value. The relationship between the threshold value and fluid characteristics showed that the transition to controllable tended to occur at about the same point as the transitioning of the fluid flow from turbulent to laminar.