Mechanism of Shear-Thinning Effects of Magnetorheological Fluid: Particle Chains Breaking Off

MR fluid, a typical non-Newtonian fluid, has shear-thinning characteristics, which is shown that the shear stress increases non-linearly with the shear rates. To be more precise, shear stress increases with shear rates but its increasing rate gradually slows down. The broken particle chains after shear rotate at the same velocity as the upper shear disk, and there is a velocity difference with base carrier fluid, resulting in a hydrodynamic force. Besides, the particles at the end of rotating particle chains move outward by centrifugal force, which increases the rotating radius. At the same time, the angular velocity also increases with shear rates. With the combination of these two effects, the linear velocity of rotating particles increases exponentially, causing a higher hydrodynamic force. When the hydrodynamic force is higher than the magnetic force, the particle will fall off. As fewer particles rotate with the upper shear disk, the shear stress increases nonlinearly with the shear rate. The higher particle concentration will lead to more serious shear-thinning effects, while the increasing magnetic field strength will weaken it. The experiment results confirm that the mechanism of shear-thinning effects of MR fluid is particle chains breaking off. This work will provide guidance for the preparation of MR fluids, which is beneficial to improve the performance of MR fluids, as well as the precise control of MR devices.