Theoretical and Experimental Studies of an Electro-Rheological Grease Shock Absorber

One method of achieving fail-safe, semi-active damping is to utilize a controllable fluid with a high zero-field damping capacity. To this end, this paper introduces a prototype electrorheological grease (ERG) as a new concept in electro-rheological fluids (ERF's). The general properties of grease-like fluids imply a non-Newtonian post yield viscosity. The fluid model developed in this paper considers the influence of a non-Newtonian post yield viscosity by using a power law model to account for shear thinning behavior. This model can be applied to all controllable fluids since it reduces to a Newtonian viscosity as a special case. The theoretical study includes a lumped parameter dynamic system model to predict the behavior of an actual damper, which takes into consideration inertial and compressibility effects. To validate the proposed models, a prototype damper was designed and used to collect data for a known ERF and the new ERG. Results from the ERG test data indicate that a good match between experimental and theoretical data was achieved. A sensitivity analysis shows that the model was insensitive to the mass of the fluid, but sensitive to the bulk modulus of the fluid. Comparisons are also made between the performance of the ERG and the existing ERF. The ERG demonstrates higher zero-electric field damping capacities than those of the ERF, yet produces an increase in damping when an electric field is applied.