Magnetic-enhanced normal force of magnetorheological fluids

摘要

In this study, the static and dynamic normal forces of magnetorheological (MR) fluids with and without shearing were investigated by using an advanced commercial rheometer. The effects of time history, shear rate, and temperature under sweeping magnetic field on the normal force of MR fluids were systematically studied. Moreover, the influence of shear stress, gap distance, and the comparison of static and dynamic normal force in various magnetic field were also studied. The experimental results indicated that the normal force of MR fluids largely depend on magnetic field, more than 170% normal force increased when the magnetic field increases from 0 to 1 T. This behavior can be regard as the magnetic field-dependent of normal force, moreover, the mechanism of interaction between the magnetic field and normal force was investigated by microstructure analysis. The results show that the gap distance changes step-wise with increasing the magnetic field instead of continue increase. When imposing shearing, three regions can be found in the relationship between normal forces and shear rate, the normal force first decreases to a minimum value and then increases by increasing shear rates. The temperature effect of the normal forces is also measured and the normal force would increase with increasing of temperature. Comparing between with static and dynamic normal force shows that the dynamic normal force is larger than static normal force. And the average normal force is also larger than the shear stress. Finally, a normal force was calculated based on the magnetic field energy theory.