High viscosity linear polysiloxane magnetorheological fluid (HVLP MRF) was demonstrated with excellent suspension stability. Such material is suitable for application in the magnetorheological energy absorbers (MREAs) under axial impact loading conditions. On this basis, a new energy absorber incorporating a radial valve with high magnetic field utilization and a corrugated tube is proposed. In energy absorption applications where the MREA is rarely if ever used, our MREA takes the ultra-stable HVLP MRF as controlled medium in order for a long-term stability. For MREA performing at very high shear rates where the minor losses are important contributing factors to damping, a nonlinear analytical model, based on the Herschel-Bulkley flow model (HB model), is developed taking into account the effects of minor losses (called HBM model). The HB model parameters are determined by rheological experiments with a commercial shear rheometer. Then, continuity equation and governing differential equation of the HVLP MRF in radial flow are established. Based on the HB model, the expressions of radial velocity distribution are deduced. The influences of minor losses on pressure drop are analyzed with mean fluid velocities. Further, mechanical behavior of the corrugated tube is investigated via drop test. In order to verify the theoretical methodology, a MREA is fabricated and tested using a high-speed drop tower facility with a 600 kg mass at different drop heights and in various magnetic fields. The experiment results show that the HBM model is capable of well predicting the impact behavior of the proposed MREA.
The quasi-static model, without considering the inertia effect, is usually used to design and evaluate magnetorheological energy absorbers (MREAs). Although the quasi-static model is generally acceptable to describe the behavior of MREA operated at low velocity and low frequency, it is not sufficient to predict that under high-speed impact conditions. For this situation, we develop an analytical model inclusive of fluid Inertia as well as Minor losses based on the Bingham-plastic model (called BPIM model). In particular, instead of using area-averaged acceleration (assuming fluid acceleration uniformly distributes over the flow cross-sectional area), we directly take the non-averaged acceleration to analyze fluid inertia. Then, the governing equation is obtained from Navier–Stokes equations and continuity equation, in which the time-related term representing inertia effect is no longer neglected. In addition, the expression of damping force is derived by solving the initial-value problems obtained from the governing equation, boundary conditions and initial conditions using the method of separation of variables. Further, the influence of inertia effect and minor losses on MREA force is quantitatively analyzed. Besides, the MREA coupled with disc springs as the storage element is presented, and the nonlinear model of disc spring is employed. To validate the theoretical model, two identical MREAs are fabricated, and a high-speed drop tower is set up to test the two MREAs placed in parallel. It is shown that the BPIM model is capable of well predicting the dynamic behavior of the MREA.
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