Modeling and Experimental Investigation on Rheological Characteristics of Magnetorheological Fluids and Greases Under Steady and Large-Amplitude Oscillatory Shear

This study systematically investigates the complex nonlinear rheological behavior of magnetorheological fluids (MRFs) and greases (MRGs) through comparative experiments under two shear modes (steady-state shear and large-amplitude oscillatory shear) at room temperature. Results demonstrate that during steady-state shear tests, the apparent viscosity of both materials decreases with the increasing shear rate, exhibiting shear-thinning behavior at high shear rates that aligns with the Herschel–Bulkley constitutive model. Throughout the logarithmically increasing shear rate range, the viscosity and shear stress of MRF consistently exceed those of MRG. Under low-frequency, large-amplitude oscillatory shear (LAOS) conditions, both materials display pronounced viscoelasticity and hysteresis. At higher current levels, the maximum shear stress of MRF surpasses MRG, but its hysteresis loops exhibit reduced smoothness. The Bouc–Wen model accurately characterizes the nonlinear hysteresis of both materials, with model parameters successfully identified via a genetic algorithm. This work establishes a universal framework for the dynamic mechanical response mechanisms of magnetorheological materials, providing theoretical guidance for designing and predicting the performance of smart damping devices.