ON THE EXTENDED RUTGERS–DELAWARE RULE FOR MR SUSPENSIONS UNDER MAGNETIC FIELDS

Abstract

The interrelation between apparent viscosity in steady shear flow and complex viscosity in oscillatory shear flow for magnetorheological (MR) suspensions is investigated. Series of experiments have been conducted using a MR rheometer. An extended Rutgers–Delaware rule is proposed, in which an effective shear rate for oscillatory shear flow is defined as ωΔh. Here ωΔh is the shift factor dependent on strain amplitude (γ0), which was found to be similar for different MR suspensions under different magnetic fields. At high strain amplitudes (γ0≥100%), Δh≈γ0, the Rutgers–Delaware rule is approximately obeyed. At low strain amplitudes (γ0<100%), the curves of Δh fall between the line of the Cox–Merz rule and that of the Rutgers–Delaware rule. The curve of Δh at low strain amplitudes depends on the ingredients of the MR suspension. For samples with the same ingredients, a unified curve of Δh can be identified in a range of magnetic fields and/or for a range of volume fraction of magnetic particles.