Since interest in ER fluids has increased, recently numerous and quite diverse application fields has been proposed. In the studies concerning devices using ER fluids, the behavior of the fluids has been assumed to be almost that of bingham plastics. Also, many differences have been observed between experimental and theoretical result of application devices. But the behavior of ER fluid differs from bingham plastics in the region of low shear rate. Almost all the research concerning application devices using ER fluids is based on the assumption similarity with bingham plastics. And studies have not been performed in this area because of the nonlinear behavior in the region of low shear rates. In spite of the use of improved control methods, research concerning the application of devices using ER fluids has encountered many problems due to modeling error of the basic governing equations. In this study, the motion of particles of an ER fluid in a cylindrical ER clutch is visualized by video camera in order to examine the mechanism of ER effects under the shear mode. The particle type ER fluid is used in this study. The particle size of ER fluids used in the devices is very small, and the response times are in the range of milliseconds. Hence, ER fluids that have a slow response time, fluids with extremely large particles and low concentration were selected. A cylindrical ER clutch is consists of input and output rotational cylinders and ER fluid between them. The cylinders also serve as electrodes. The torque of a cylindrical ER Clutch/Break is measured by torque meter. And then discuss the behavior of cylindrical ER clutch/Break influenced of the nonlinear behavior of ER fluid through results of visualization. As result, the shear stress of a cylindrical ER Clutch/Break is nonlinear at low shear rate because ER fluid in a cylindrical ER clutch is different to form the cluster according to the strength of electric field.

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