Utilizing an approximate model and the experiment results we were able to clarify the characteristics tendencies during the transition of torque on rotating-disk and rotating-concentric-cylinder device types utilizing electro-rheological fluid (ER Fluid) with smectite particles. From the approximation of experiment data and parameters in the approximate model, the transition of torque was clarified to depend on three patterns of the creation of clusters.
When the electric field strength is large and the shear rate is small the torque has a pattern of overshoots. However, when the shear rate increases, torque takes on a different, second order time-lag pattern (over-damping) in the case of the rotating-cylinder type, and another, bent curve function in the case of rotating-disk type. Regarding the case of rotating-cylinder type, the cause can be considered to be that the clusters first aggregate and then are broken when the shear rate increases. In the case of the rotating-disk type the particles do not disperse and are promoted to aggregate.