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Proceedings of the International Conference on 239
Advances and New Challenges in Earthquake
Engineering Research, Hong Kong Volume
RHEOLOGICAL BEHAVIOR OF MR
MATERIALS IN FLOW MODE
X. Wang 1 , F. Gordaninejad 1 , G. H. Hitchcock 1 ,
A. Fuchs 2 , M. Xin 2 and G. Korol 3
1 Department of Mechanical Engineering, University of Nevada, Reno, NV 89557, USA
Department of Chemical Engineering, University of Nevada, Reno, NV 89557, USA
3 Visteon Automotive Systems, Dearborn, MI 48126, USA
ABSTRACT
A flow mode type rheometer is developed to evaluate the tunable rheological properties of magnetorheological
(MR) materials. The proposed method is simple, and provides measurement of the
apparent viscosity and yield stress of MR materials. In addition, a theoretical shear stress-shear strain
rate relationship is developed based on a non-Newtonian fluid flow analysis. The rheological
properties of a commercial MR fluid and a newly developed magneto-rheological polymeric gel
(MRPG) are investigated. Experimental shear stress results are presented for a shear strain rate range
of 20s" 1 to 20,000s" 1 . The results for apparent viscosity, dynamic and static shear yield stress under the
influence of different applied magnetic fields are reported.
INTRODUCTION
Typically, the design of an original equipment manufacturer (OEM) damper consists of one or more
orifices which either are located within the piston or are external by-passes. For most applications, a
magneto-rheological (MR) fluid damper can have a similar orifice design characteristic to an OEM
damper (Gordaninejad and Breese, 2000, Gordaninejad and Kelso, 2000). Available measurements
for rheological properties of MR fluids are mainly in the shear-mode and low shear stain rates (Li,
2000). The focus of this study is to determine the shear stress of a MR fluid in the flow mode for a
wide range of shear strain rates. This may be important for the force estimation and the controller
design of a MR fluid damper where the working fluid operates at high shear strain rates.
Recently, a piston-driven slit channel rheometer has been developed to estimate the shear yield stress
of MR fluids under a magnetic field by Nakano et al. (1999). The slit rheometer utilizes an applied
uniform magnetic field normal to the slit channel flow direction where forced convection assists in
heat dissipation at high shear strain rates. However, it is difficult to determine the velocity gradient for
a non-Newtonian fluid in such a device.
In general, although it is important in some MR fluid based applications, relatively little attention has
been paid to the behavior of MR suspensions in pressure driven flows. In addition, conventional
rotational rheometry encompasses shear strain rates only up to a few thousand I/sec, while shear strain