What Makes a Good MR Fluid?

Experience in manufacturing magnetorheological (MR) fluids for commercial application has shown that some of the greatest barriers to commercial success are not factors or conditions normally considered in the laboratory. The present paper looks at conditions found in MR fluid devices operating in real-world applications where shear rates may exceed 10 ⁵ s 1 and devices are called upon to operate for very long periods of time. The problem of “In-Use-Thickening” wherein a MR fluid subjected to long-term use progressively thickens until it eventually becomes an unworkable paste is presented. The search for a solution to this heretofore unrecognized problem delayed commercial introduction of the Lord truck seat damper system for several years. Today, good fluids are able to operate for long periods with minimum in-use-thickening.