QUASI-STATIC MEASUREMENTS ON A MAGNETORHEOLOGICAL FLUID

The shear stress tau-shear strain gamma behavior of suspensions of car bonyl iron particles in silicone oil was determined at a shear rate ga mma = 0.042 s(-1) as a function of applied magnetic induction B-0 (0.5 -6.0 kG), volume fraction of particles phi(0.05-0.30), and roughness o f the shearing surfaces. At low fields, the steady-state shear stress tau(S) was significantly higher for a roughened surface compared to a smooth surface, but became only slightly dependent on roughness at hig h fields. In accord with theoretical considerations, the ratio tau(S)/ phi was proportional to the square of the calculated magnetic field H- 0 inside the suspension at low fields, but its dependence on H-0 becam e smaller as the field increased. The smaller dependence may result fr om the magnetic saturation of the particles or the slipping boundary c ondition. (C) 1996 Society of Rheology.