Effect of Particle Shape Anisotropy on the Performance and Stability of Magnetorheological Fluids

Abstract

The effect of shape anisotropy of a magnetic particle on the performance and stability of the magnetorheological (MR) suspension was investigated using a rotational rheometer and a vibrating sample magnetometer. A flaky Sendust (FS) suspension demonstrated surprisingly high MR performance at low magnetic field strength because of the shape anisotropy effect which induced a rapid ascent of the particles' magnetic moment and, thus, suspension's high yield stress. Despite its lower iron content (85%) than carbonyl iron (almost pure iron), the Sendust suspension exhibited a yield stress value greater than that of the carbonyl iron suspension at low magnetic field strength. Because of the low demagnetization factor in a nonisometric Sendust particle, the alloy particles were easily magnetized along the easy axis direction, which led to an unexpectedly high yield stress of the suspension at a low magnetic field strength. At a high magnetic field strength, all of the tested suspensions of flaky Sendust, bulk Sendust (BS), and carbonyl iron (CI) displayed similar MR behaviors but different yield stress values. The highest yield stress value at high magnetic field strength was that of the carbonyl iron suspension, followed by those of the FS suspension and the BS suspension; however, the difference between the yield stress values of the two Sendust suspensions was not substantial. A master curve for different MR fluids was obtained by plotting dimensionless viscosity as a function of the shear rate and the square of the magnetic field strength, which indicates that the particle suspensions exhibited similar responses to the external magnetic stimuli. Though the density of FS is larger than the bulk Sendust, the FS suspension demonstrates remarkably improved stability compared with the CI suspension or the BS suspension because of the large drag coefficient of the flaky Sendust particles.

Non‐Settling Super‐Strong Magnetorheological Fluids

“…The apparent viscosity η is the ratio between the shear stress ( τ ) and the shear rate ( γ ), equal to τ / γ , which is proportional to the inverse of the Mason number (Mn −1 ). [ 21,22 ] The Mason number (equivalent to $${\mathrm{\dot{\gamma }}}$$/M 2 , where M is the magnetic field strength; see Supporting Information for more details) is then an independent variable that collapses the experimental data collected at various magnetic field strengths and shear rates onto a single master curve (Figure 6b). [ 42,43 ] Under a fixed particle concentration, the master curve for the specific viscosity (i.e., the ratio of the apparent viscosity and the medium viscosity) and the volume fraction correction versus $$\dot{\gamma }$$/ μ 2 at different magnetic field strengths can be obtained.…”

“…[ 42,43 ] Under a fixed particle concentration, the master curve for the specific viscosity (i.e., the ratio of the apparent viscosity and the medium viscosity) and the volume fraction correction versus $$\dot{\gamma }$$/ μ 2 at different magnetic field strengths can be obtained. [ 22–24 ] The behaviors of different MR fluids are compared for pure CI, 95% CI, and 90% CI fluids at two different magnetic field strengths, as shown in Figure 6b. All six curves overlap well with each other, which means the behaviors of the three fluids were the same because they followed the same scaling law ( Figure a) and therefore the same particle magnetization model.…”

“…As a solution to this problem, researchers have attempted to fabricate magnetic composites by combining magnetic particles with low‐density materials. [ 17–38 ] However, the use of composite particles to reduce the density mismatch inevitably degrades the MR performance of composite particle‐based fluids because non‐magnetic materials are added. [ 1,2 ] As an alternative, researchers have tried to solve the sedimentation problem by using surfactants.…”

Liquid-crystalline ferroferric oxide nanocomposites: self-assembly and magnetorheological effects

“…, silicon oil and hydrocarbon oil) that can control their magnetorheological properties by an external magnetic field. 19,20 For most MR fluids, when an external magnetic field is applied, the particles are magnetized along the field direction and induced their aggregation to form chain-like structures, resulting in an increase of viscosity. While they will become random once the external magnetic field strength is removed.…”

Experiments and Analysis of the Limit Stresses of a Magnetorheological Fluid

“…In the present work, attention is paid to the problem of limiting stresses. The main factors that affect the ability to achieve a suitable value of this parameter are the magnetic field strength acting on the fluid and the composition of the MR fluid, especially the quantity, size and magnetic parameters of the ferromagnetic particles used to prepare the suspension [5,[22][23][24][25][26].…”