Magnetorheology: Measurements, mechanisms and modeling

Tuesday, September 15, 2009 - 9:50am - 10:35am
EE/CS 3-180
Daniel Klingenberg (University of Wisconsin, Madison)
Magnetorheological (MR) fluids are suspensions of small particles
whose apparent rheological properties can be altered dramatically
by applying a magnetic field. For example, magnetic flux
densities of the order of 1 Tesla can induce a yield stress of the
order of 100 kPa in an otherwise essentially Newtonian fluid.
After a brief introduction to magnetorheology, including a few of
the more common applications, four vignettes of experimental
observations and resulting modeling challenges will be presented.
In the first vignette, transients in shear flow rheology observed
for large applied magnetic field strengths are addressed. These
transients are associated with the formation of lamellae within
the suspension, whose dynamics can be modeled at the particulate
or continuum levels. In the second vignette, unexpectedly large
yield stresses observed for suspensions with bidisperse particle
size distributions are described. Particle-level modeling reveals
the mechanism, but predicting the magnitude of the enhancement
remains a challenge. The third vignette examines effects of
friction, which only appear at large concentrations. Observations
are similar to jamming transitions observed in similar systems.
The last vignette examines a surprising enhancement caused by
replacing magnetizable particles with nonmagnetizable particles in
MR fluids.
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