Alexander A. Alexandridis

Wear Testing of Seals in Magneto-Rheological Fluids©

Magneto-rheological (MR) fluid-based dampers can be used in suspensions to modify ride, handling, and suspension frequencies in autos. We have developed a unique seal wear test method to simulate the wear of rod seals in Magneto-rheological fluid-based dampers. In this test, seal material samples in the form of rectangular coupons are immersed in a bath of MR fluid, and a section of the rod is brought into contact with the seal coupon. The rod is loaded against the coupon with a known normal force, and a variable-frequency reciprocating machine is used to stroke the rod back and forth across the material coupon surface. Test conditions such as normal load, frequency and amplitude of oscillation, and temperature are adjusted to simulate desired conditions. This bench test method ranks various seal materials qualitatively in the correct order (as determined in field tests with these seal materials) in terms of wear and abrasion resistance and constitutes a valid test procedure for the screening of seal materials, MR fluids, and rod surface coatings.

Medium- and high-frequency analysis of magnetorheological fluid dampers

Controllable dampers based on smart fluids contain internal passages through which the working fluid flows and wherein the controlled pressure drop occurs under the influence of magnetic or electric fields. In this paper, the dynamics of such dampers are analysed through a series of theoretical dynamic models of increasing detail and complexity. The models capture the medium- and high-frequency dynamics of the damping force output of the damper and include the lumped mass of the fluid contained in the internal flow passages, the piston and rod assembly mass, and the compressibility of the fluid and pressurized gas contained within the chambers of the damper. The models are derived in state-space form from which transfer functions and natural frequencies are obtained analytically and then calculated for each of the systems. The results are presented in the form of frequency responses (Bode plots). Finally, the effects of the key geometric parameters of the damper and of the relevant fluid properties on the damper force output dynamics are presented and discussed.