The Theoretical Research On The Shear Stresses Of Magnetorheological Fluids Based On BCT Model

When an external field is applied to the magnetorheological(MR) fluids, the magnetic particles are polarized and acquire dipole moments. The dipole-dipole interactions between the particles cause the particles to form chains aligned with the magnetic field. Further the chains aggregate into three-dimensional structure, and thus can suffer shear stress. It is reported that the most stable formation of MR fluids is body-centered-tetragonal (BCT) structure under equilibrium conditions. There are also some other structure model, such as the cylinder structure, the layer structure, the fiber structure and so on. The main research object of the paper is BCT structure model.Based on Ampere' Molecular Current Hypothesis, Dipole theory and Ampere Law, the interaction force formulation of two spherical particles which aligned with the external field is firstly deduced. Thereafter, research is done on MR fluids sheared by a small angle based on BCT model and the formula of the shear stress is obtained.In order to proof the above theoretical formula, some experiments are carried out on the mechanical property of the MR fluids. The experimental results show, in the case of small shear deformation, the shear stress increases linearly as the strain increases and also the shear stress increases along with the rising of the particle volume fraction. However when the particle volume fraction is oversize, the shear stress varies slowly. Then the experimental results are compared with the theoretical results, and the outcomes show, the value of the shear stress which is obtained from the experiments has the same order of magnitude with that of theoretical one, these two values have the same changing tendency, but the theoretical values are larger than the experimental one.Finally in this paper the theoretical formula is analyzed, and the effects of the particle volume fraction, particle magnetization and the external magnetic field onthe shear stress are studied. The results show that the shear stress increases as the rising of the particle volume fraction, and the shear stress is proportional to the square of the magnetization. Moreover, the value of shear stress increases along with the rising of the external magnetic field, but when the MR fluids begin to exhibit gradual magnetic saturation, the shear stress becomes relatively constant.