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.

MR流体是一种典型的非牛顿流体，具有剪切稀化特性，表明剪切应力随剪切速率非线性增加。更准确地说，剪切应力随着剪切速率的增加而增加，但其增加速率逐渐减慢。剪切后破碎的颗粒链以与上剪切盘相同的速度旋转，与基础载液存在速度差，从而产生水动力。此外，旋转粒子链末端的粒子在离心力的作用下向外运动，从而增大了旋转半径。同时，角速度也随着剪切速率的增加而增加。通过这两种效应的结合，旋转颗粒的线速度呈指数增加，从而产生更高的水动力。当水动力大于磁力时，颗粒就会脱落。随着上剪切盘旋转的颗粒减少，剪切应力随剪切速率非线性增加。颗粒浓度越高，剪切稀化效应越严重，而磁场强度的增加会减弱这种效应。实验结果证实，磁流变流体剪切稀化效应的机制是颗粒链断裂。这项工作将为磁流变流体的制备提供指导，有利于提高磁流变流体的性能，以及磁流变器件的精确控制。