Rheological properties of magnetorheological fluids

The effects of dispersed phase saturation magnetization and applied magnetic fields on the theological properties of magnetorheological (MR) fluids are described. MR fluids based on two different grades of carbonyl iron powder with different average particle size, 7-9 microns (grade A) and 2 microns (grade B), were prepared. Vibrating sample magnetometer measurements showed that the saturation magnetization values were 2.03 and 1.89 T for grades A and B, respectively. Rheological measurements were conducted for 33 and 40 vol pct grade A and grade B based MR fluids with a specially built double Couette strain rate controlled rheometer at flux densities ranging from 0.2 to about 0.8 T. The yield stresses of 33 and 40 vol pct grade A were 100 3 and 124 3 kPa, respectively at 0.8 0.1 T. The yield stress values of MR fluids based on finer particles (grade B) were consistently smaller. The results presented here show that the decrease in yield stress for finer particle based MR fluids is due to the relatively smaller magnetization of the finer particles. (Author)