The influence of viscometer dynamics on the characterization of an electrorheological fluid under sinusoidal electric excitation

Abstract

The dynamic response of a controlled‐strain, Couette viscometer employed for the characterization of the frequency response of an electrorheological (ER) fluid is studied both numerically and experimentally. In the numerical model, the ER fluid flow between the cup and bob elements of the viscometer is coupled with the mechanical response of the cup–torque sensor system. The Bingham model is used for describing the ER fluid, with various functional forms for relating the electric field strength to the Bingham stress. Variation in the shear‐rate dependency of the Bingham stress response is also represented. Dynamic resonance tends to dominate the cup rotation response and the shear rate of the fluid. The Bingham stress response contains higher harmonic components whenever it does not follow a second power‐law relationship exactly with the electric field strength. Higher harmonics induce their own resonances at relatively lower values of excitation frequency. Experimental results obtained with zeolite‐based ER fluids generally agree with those predicted through the numerical analysis. The characterization of an ER fluid will be reasonably accurate only if the excitation frequency of the electric field is low, say less than 0.1 times the natural frequency of the cup–torque sensor assembly.