The relative transient response of MR fluids subjected to magnetic fields under constant shear conditions

This paper concerns the transient response of MR fluids and factors that can influence the response performance of the material. In this study, the MR fluid is subjected to a constant shear between two parallel discs, one of which is rotating at a constant speed and the other fixed. When a step current is applied, the closed-loop controller increases the torque delivered to the rotating disc in order to maintain the speed. By examining the transient response of this delivered torque, the relative response time and rise time for the MR fluid can be determined. Results showing the relative response time dependency on five variables, (i) applied current (from 0.25 A to 2.00 A), (ii) shear rate (from 50 rpm to 300 rpm), (iii) particle volumetric concentration (from 10% to 40%), and (iv) particle properties, are presented. It was found that the rate of shear does not have much influence on the relative response time, but the other four factors can affect the response characteristics quite significantly. For example, the relative response time increases with a decrease in concentration of the material, and using silicone oxide-coated magnetically active particle improves the response of the material.