Abstract
Keywords:
Magnetorheological, MR fluids
Abstract
Magnetorheological (MR) fluids are materials that respond to a magnetic field with a dramatic change in rheological behavior. These fluids can reversibly change instantaneously from a free-flowing liquid to a semi-solid with controllable yield strength when exposed to a magnetic field. In the absence of an applied field, MR fluids are reasonably well approximated as Newtonian liquids. For most engineering applications a simple Bingham plastic model is effective in describing the essential, field-dependent fluid characteristics. The rheological properties of MR fluids depend on the concentration, size, distribution and shape of the iron particles, the carrier oil properties, additional additives, applied field, temperature and other variables. Two areas of performance that received particular attention during Lord’s decadelong MR development program in the 1990s were settling stability and durability (wear and seal life) as MR fluids, when first invented, were not stable to long-term settling and could be quite abrasive in use.This paper describes the scientific improvements required to create viable MR fluids and systems as well as the physical principles under which successful MR fluid devices are designed.