Electrical properties of magnetorheological fluids

The phase change form Newtonian fluid to semi-solid in a magnetorheological fluid commences with chain formation of the suspended magnetic particles. The resulting physical effects do not take place immediately and the mechanical response times of magnetorheological fluids quoted in the literature vary widely. This is not surprising given that they are often measured using different devices under diverse magnetic and dynamic conditions. Furthermore, the application of a magnetic field also requires time which can be considerably longer than that of any mechanical influences. However, the initial phase change is easily measurable as the onset of chain formation results in abrupt changes in the electrical properties independent of the ensuing mechanical effects. This work concerns the analysis of electrical properties, including capacitance, resistance and the respective time constants for magnetorheological fluids based on carbonyl iron powder suspended in silicone oil under mechanically and magnetically static conditions. Both parallel and series electrical time constants appear to be functions of the magnetic flux density rather than CIP concentration.