Effects of the non-uniform magnetic field on the shear stress and the microstructure of magnetorheological fluid

Abstract

A particle-level 3D simulation was carried out to explore the difference between the shear stress and the microstructure of magnetorheological fluid in the present of different distributions of non-uniform magnetic field. The non-uniform magnetic field used in the simulation was generated by a permanent magnetic. Three types of non-uniform magnetic field distributions with the same average magnitude were obtained by locating the simulation box at different positions above a permanent magnet. The quasiequilibrated structures were first examined before the beginning of the shear simulation. Then, the typical evolution of shear stress under non-uniform magnetic field was investigated. The shear stress curve included a sharper growth region in the beginning compared to the stress curve under the vertical uniform magnetic field. At the same shear rate, the shear stresses under non-uniform magnetic fields were different from these under the vertical uniform magnetic field. The chain-like structures inside magnetorheological fluid were responsible for the difference of the shear stresses. Specially, the chain-like structures with inclination θ>90° and azimuth φ≈90° were beneficial for improving the shear stress. The volume average magnetic field was employed to quantitatively describe the characteristics of the non-uniform magnetic field. The shear stress curve of magnetorheological fluid under the volume average magnetic field matched well with the stress curve under the corresponding non-uniform magnetic field.