A novel class of relatively stable and redispersible MR fluids based on meso-scale magnetic particles of iron or nickel zinc ferrite and nano-scale additives is described. For a flux density B ~ 1 Tesla, the iron based MR fluids exhibited yield stresses of ~100 kPa. For ferrite based fluids the yield stress values were as high as ~15 kPa at B ~ 1T. The yield stresses at the flux density required for magnetic saturation increase quadratically with the saturation magnetization of the particulate material, in good agreement with a model for the yield stress of uniformly saturated particle chains. At lower flux densities, the yield stress was generally observed to increase as B3/2, consistent with models of the role of local saturation of the particle magnetization. The additives were found to enhance the stability and redispersibility of the MR fluids: they appeared to promote a small non-zero yield stress in the absence of a field but were found not to have a substantial effect on the field-dependent yield stresses.
[1]
J. M. Ginder,et al.
Shear stresses in magnetorheological fluids: Role of magnetic saturation
,
1994
.
[2]
R. E. Rosensweig,et al.
On magnetorheology and electrorheology as states of unsymmetric stress
,
1995
.
[3]
Georges Bossis,et al.
Yield stress in magnetorheological and electrorheological fluids: A comparison between microscopic and macroscopic structural models
,
1997
.
[4]
L. C. Davis,et al.
RHEOLOGY OF MAGNETORHEOLOGICAL FLUIDS: MODELS AND MEASUREMENTS
,
1996
.
[5]
C. Rogers,et al.
Magnetorheological Fluids: Materials, Characterization, and Devices
,
1996
.
[6]
W. M. Winslow.
Induced Fibration of Suspensions
,
1949
.