Magnetorheological (MR) fluids are promising in controllable damping based on regulated apparent viscosity under magnetic field control, and they are employed in various damping devices such as automotive dampers and energy absorbers for artillery or landing gears by medium substitution with structural adaptations. In this study, we designed and fabricated a magnetorheological energy absorber (MREA) with disc springs as recoiling parts, modeled the MR fluid flow based on the Bingham constitutive model, and then carried out unsteady extension based on the quasi-steady model. The experimental tests of the MREA show that the unsteady extension of the quasi-steady model can designate the behaviors of the MREA in different impact speeds better than the original; thus, the controllability of the MREA is verified. An interesting phenomenon, where a rippled MREA peak force is observed at the saturated excitation when the impact speed is not so high and disappears when the impact speed is high enough, is accounted from the viewpoint of flow modeling and finally verified by more experimental results.

Despite several salient benefits of numerous control systems utilizing magnetorheological (MR) fluid, practical realization of commercial products is limited due to the particles sedimentation. To overcome this problem, several measures have been proposed to optimize MR fluid settling through the viewpoints of dispersing medium viscosity, suspension force of dispersed phase and additives innovation, but the settling of MR fluid can be alleviated to an extent only. An active dispersing mechanism (ADM) proposed in the previous work is one of attractive ways to resolve the sedimentation problem in a level of device and it is promising to fulfil good serviceability for MR dampers even if the settling remains. In this work, attributive to the investigations in stirring devices, rotary blades are employed to fulfil the redispersing of settled MR fluid under the theory of solid-liquid two phase flow. The parameters and working conditions of the rotary blades are optimized to guide experimental verification in a damper-sized vessel. The vessel can be seen as a prototype for real MR damper. An immersed induction method (IIM) for the characterization of the localized MR fluid concentration is proposed to designate the dispersing process when ADM is started. With the experiments of different MR fluid volume fractions and rotating speeds of the rotary blades, it is fully testified that the faster the blades rotate, the shorter the mixing time, and the more the inclination angle of blades close to 45°, the better the dispersion capability. In addition, it is also identified that the ADM is effective to disperse the settled MR fluid and promising to the sedimentation immunity of MR damper.