Dynamic behavior of MR suspensions at moderate flux densities

In many proposed applications, magnetorheological (MR) fluids are subjected to a dynamic stimulus with finite deformation. Dynamic behavior of reduced iron based MR suspensions under oscillatory shear is experimentally investigated using a parallel-plate rheometer. The effects of strain amplitude, oscillation frequency, and magnetic field strength on the dynamic behavior are studied. MR fluids behave as linear viscoelastic materials for only sufficiently small strain amplitudes. At large strain amplitudes, MR fluids are nonlinear viscoelastic or viscoplastic, where the storage modulus shows a decreasing trend with the strain amplitude. At large enough strain rate amplitudes, the yield stress contribution is negligible and the suspension response is Newtonian. The dependence of the dynamic behavior on the strain amplitude and oscillation frequency is qualitatively summarized in the form of a Pipkin diagram.