Experimental analysis of magnetorheological dampers when subjected to impact and shock loading

The vast majority of the investigations for controllable magnetorheological (MR) dampers have focused on their low velocity and low frequency applications. The extensive work in this area has led to a good understanding of MR fluid properties at low velocities and frequencies. Many of the issues pertaining to MR damper behavior in impact and shock applications are relatively unknown. This study provides an experimental analysis of magnetorheological dampers when they are subjected to impact and shock loading. To this end, a drop-tower is developed to apply impulse loads to the dampers. The drop-tower design uses a guided drop-mass, which is released from variable heights to achieve different impact energies. The nominal drop-mass is 55 lb and additional weight may be added to reach a maximum of 500 lb. The nominal drop-mass of 55 lb is used throughout this study. Five drop-heights are investigated: 12, 24, 48, 72 and 96 in., corresponding to impact velocities of 86, 127, 182, 224 and 260 in./s, respectively. Two MR damper configurations are tested, a damper with a single-stage, double-ended piston and a mono-tube damper with a two-stage piston. The results indicate that the two damper configurations exhibit different force–displacement characteristics during impulse loading. For the single-stage, double-ended damper, the peak force occurs close to the beginning of the impact. Conversely, the two-stage, mono-tube damper does not reach the peak force until after the nitrogen accumulator bottoms out. To verify this behavior, a theoretical model of the accumulator is derived and compared to the experimental data. Additionally, the results show that at large impact velocities, the peak force does not depend on the current supplied to the damper, as is commonly the case at low velocities. This phenomenon is hypothesized to be the result of the fluid inertia preventing the fluid from accelerating fast enough to accommodate the rapid piston displacement. Thus, the peak force is primarily attributed to fluid compression, rather than the flow resistance (“valving”) associated with the fluid passing through the MR valve.