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.