Rheological properties of magnetorheological fluids

Abstract

The effects of dispersed phase saturation magnetization and applied magnetic fields on the rheological 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 µm (grade A) and 2 µm (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% 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 ∼0.8 T. The yield stresses of 33 and 40 vol% 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. For example, the yield stresses for 33 and 40 vol% grade B based MR fluid were 80 ± 8 and 102 ± 2 kPa, respectively at 0.8 ± 0.1 T. The yield stresses at the flux density approaching magnetic saturation in particles (B ∼ 0.8T) were found to increase quadratically with the saturation magnetization (µ 0 M s ) of the dispersed magnetic phase. This is in good agreement with the analytical models of uniformly saturated particle chains developed by Ginder and co-workers. 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.

Optimal Design Methodology of Magnetorheological Fluid Based Mechanisms

“…In contrary, some of the ferrimagnetic materials such as Mn-Zn ferrite, Ni-Zn ferrite and ceramic ferrites have low saturation magnetizations and are therefore suitable to be applied in low yield stress applications [1]. MR particles are typically in the range of 0.1 to 10μm [4,5], which are about 1000 times bigger than those particles in the ferrofluids [6]. In the MRF, magnetic particles within a certain size distribution can give a maximum volume fraction without causing unacceptable increasing in zero-field viscosity.…”

“…ss ma M = πµ (4) where μsMs is the saturation magnetization of the particle, which is about 1.7 x 10 6 A/m for bulk iron and 0.48x10 6 A/m for the magnetite.…”

Synthesis and Viscosity Analysis of Magneto-Rheological Fluid

“…This change in the state of the fluid with respect to the magnetic field is based on the phenomenon of the change in the viscosity of the fluid. The MR fluid constitutes micron sized particles over the range of 0.1 μm to 10 μm [7], which can be polarized magnetically, thus changing the rheological characteristics of the fluid. These micron sized particles are dispersed in the carrier fluid.…”

Impact of Nanowires on the Properties of Magnetorheological Fluids and Elastomer Composites

“…The viscosity and yield stress of the fluid is scalable with the magnitude of the applied magnetic field until magnetic saturation of the particles is reached (Jones & Saha, 1990). At high fields, the fluid is converted to a semi-solid with a five to six orders-of-magnitude change in apparent viscosity (Genç & Phulé, 2002). As the particle loading approaches 40 vol.…”

“…While increasing the volume fraction of particles in the suspension results in an increase in the yield strength of the material, it also results in an increase in the off-state viscosity. The shear strength of the suspensions increases with an increase in size of the particles (Genç & Phulé, 2002); however, spherical particles larger than about 10 !m tend to settle rapidly, even with the addition of special additives. Suspensions composed of nanometer-sized particles tend to settle more slowly, if at all, due to Brownian motion.…”