Electrorheological and magnetorheological fluid lag dampers for helicopter rotor systems

A nonlinear viscoelastic-plastic model is developed to describe electrorheological (ER) and magnetorheological (MR) fluid dynamic behavior. The model combines linear mechanisms with nonlinear shape functions to bring about transition through yield. Experimental ER fluid data is used to estimate the five model parameters and validate the model.; The Bingham plastic fluid model is used to derive the flow equations through the annulus of different damper configurations, and the damping coefficient is obtained as a function of the damper model geometry, the fluid yield stress and plastic viscosity. Using these equations, a moving electrode, mixed mode ER fluid damper is fabricated and tested for quasi-steady behavior. The damper is also tested dynamically for sinusoidal excitations at a frequency of 10 Hz. The force vs. displacement hysteresis data is measured for different excitation amplitudes and varying electric fields. The hysteresis results demonstrate the viscoelastic-plastic nature of the damper. An augmented nonlinear damper model based on the viscoelastic-plastic fluid model is developed with additional parameters included to account for built-up damper effects such as stiction and inertia.; Scaled {dollar}{lcub}rm Fluidlastic{rcub}sp{lcub}TM{rcub}{dollar} and MR fluid helicopter lag dampers are tested under various conditons. The MR fluid dampers are tested with the magnetic field in the ON and OFF conditions. The damper pairs are tested for zero preload and preloaded conditions, and under single and dual frequency excitation conditions. The {dollar}{lcub}rm Fluidlastic{rcub}sp{lcub}TM{rcub}{dollar} and the MR (OFF) dampers show linear behavior, whereas the MR (ON) dampers show a significant nonlinearity. A linear Kelvin chain model is used to describe the {dollar}{lcub}rm Fluidlastic{rcub}sp{lcub}TM{rcub}{dollar} and MR (OFF) damper hysteresis behavior with good success. The MR effect is extracted from the single frequency built-up MR (ON) damper data. The viscoelastic-plastic model is used to describe the MR effect hysteresis. The model captures the MR (ON) damper behavior well. When tested under dual frequency conditions, the {dollar}{lcub}rm Fluidlastic{rcub}sp{lcub}TM{rcub}{dollar} and the MR (OFF) dampers show minimal effect. The MR (ON) dampers show a significant drop in stiffness and damping under dual frequency excitation conditions. The viscoelastic-plastic model predictions for the MR (ON) dual frequency hysteresis match well with experimental results.