CHAPTER 4: MR Fluids at the Extremes: High-Energy and Low-Temperature Performance of LORD^® MR Fluids and Devices

LORD Corporation first successfully commercialized Magneto-Rheological (MR) fluids and devices in 1998. Patented and/or proprietary improvements to the MR fluid formulation have resulted in commercial fluids that have met both the high- and low-temperature requirements of the automotive industry for the past decade. This chapter will explore recent work on the effects of extreme environments on LORD^® MR fluid properties. Extreme conditions include off-road and military applications that place great demands on the fluid in terms of high temperature and high shear, highly oxidizing conditions, and low-temperature operating conditions. Changes in MR fluid physical properties and chemical composition after automotive and high-energy tests show that the fluid survives several times the required durability with no substantial base oil oxidation or iron particle degradation and undergoes rheological changes that improve iron particle settling. Improved high-temperature oxidation resistance of LORD MR fluids has been demonstrated, which may be of importance under conditions in which oxidation is an important fluid degradation mechanism. At very low temperatures, comparison of a conventional hydraulic damper with an MR damper designed for the same application show that the MR damper has much less variation with temperature than the conventional damper, illustrating that both fluid properties and device design must be considered when evaluating low-temperature performance. Further improvements in low-temperature MR fluid performance are possible, but such improvements may compromise high-temperature performance and redispersibility.