Performance Analysis of Magnetorheological Energy Absorbers Under Impact Conditions

Magnetorheological energy absorbers (MREAs) can provide adaptive vibration and shock mitigation capabilities to adapt to varying payloads, vibration spectra, and shock pulses, as well as other environmental factors. To effectively utilize these adaptive capabilities, the dynamic range (defined as the ratio of the force at maximum field to the force in the absence of field) or turn-up ratio is a key issue. Previous studies found that the dynamic range of a MREA significantly degraded at velocities even as low as nominally 6 m/s. To improve understanding of MREA behavior and to enable effective MREA design, which implies maintaining sufficient dynamic range over its design speeds range, this study focuses on the design, fabrication, testing, and transient impact analysis of a MREA for which the primary design objective was a dynamic range, D≥2, for nominal impact speeds of up to 6.75 m/s. The MREA was tested using the drop tower facility at GM R&D Center under nominal drop speeds of up to 6 m/s. The drop test experimental results showed that the MREA achieved a dynamic range of ≥2 for nominal speeds up to 6 m/s. However, the design analysis, based primarily on a laminar Bingham-plastic model (Re < 2300) failed to properly account for passive viscous losses for drop speeds above 2 m/s. Suggestions for improving the design analysis are described. To accurately predict the transient MREA force response behavior in this impact speed range, a hydromechanical model was developed and experimentally validated using results from the drop tests for nominal speeds up to 6 m/s. It was concluded that: 1) maintaining a low Reynolds number is essential to achieve a useful dynamic range, where in our case, a Re<850 led to a predicted dynamic range of D≥2; and 2) the hydromechanical analysis is a useful and accurate tool for predicting this MREA transient force behavior for these drop test data.