Dynamic Viscoelasticity of a Magnetorheological Fluid in Oscillatory Slit Flow

The nonlinear dynamic viscoelasticity of an MR fluid in oscillatory slit flow under magnetic flux normal to the flow has been investigated by using a newly developed oscillatory pressure flow type rheometer. An MR fluid consisting of micron-sized, magnetically polarizable particles dispersed into a carrier medium is evaluated. The dynamic viscoelasticity remarkably depends on a fluid strain amplitude and a magnetic field strength. Both of the storage modulus (G′) and loss modulus (G″) increase dramatically with the increase of applied magnetic field strength H from 0 to 160 kA/m. And for the increase of the strain amplitude, both of them dramatically decrease, while the loss tangent ( tan δ) increases remarkably, showing the dominance of viscoelastic plastic property. The above results are discussed in terms of three deformation regions of the MR fluid; pre-yield, yield, post-yield.