A Nonlinear Analytical Model for Magnetorheological Energy Absorbers Under Impact Conditions

Abstract

Linear stroke magnetorheological energy absorbers (MREAs) can be used to adaptively control load-stroke profiles under impact loads. An appropriate and controllable dynamic range, defined as the ratio of the force at maximum field to the off-state force, as well as the off-state (minimum) damping force, must be specified in order to account for varying payload mass over a wide range of MREA operating velocities. A key challenge when designing MREAs for high speed impact conditions is that the high shaft speeds in linear stroke MREAs induce high Reynolds number flows in the magnetic valve of the MREA, so that high dynamic range canbe a design challenge. Previous studies demonstrated that the dynamic range, D, of an MREA under high speed drop impact test dramatically dropped to D≈1 as velocity rose to 6.6 m/s, where Reynolds number, Re>2000. Also, past research on MREAs typically assumed that the off-state force increases linearly with speed, but at the higher shaft speeds occurring in impact events, the off-state damping exhibits nonlinear velocity squared damping effects. This problem was recognized in our prior work where it was shown that minor losses are important contributing factors to off-state damping. In this study, a nonlinear analytical MREA model, based on the Bingham-plastic nonlinear flow model (BP model), is combined with semi-analytical minor loss factors to develop a BPM model. From this BPM model, an effective design strategy is presented for conventional MREAs and an MREA designed. The BPM model was validated via finite element analysis (FEA), so that MREA performance could be verified before manufacture. The MREA was fabricated and tested up to effective piston velocity of 5 m/s using the high speed drop tower facility at GM R&D Center. Comparison of our analysis with measured data shows that the BPM model can accurately predict off-state (passive) MREA performance under impact conditions, and the effective deign of the MREA using the BPM was validated.