The Theoretical Research On The Shear Stresses Of Magnetorheological Fluids

Based on the single-chain structure model of magnetorheological(MR) fluids, a formula for the calculation of shear stresses is established in present paper. The interaction force of two magnetic particles in an infinite single-chain is deduced using a new theoretical model which is founded on Ampere' molecular current hypothesis, Dipole theory and Ampere' law. Further more, the resultant force on a particle is then educed taking into account of action caused by all the other particles in the single-chain. A predictive formula for shear stresses is finally made corresponding to the interaction force of particles in the infinite single-chain.Under the external magnetic field, particles in a MR fluid will form into a fixed structure and thus could afford shear stresses. Traditionally it is considered that particles are formed into the single-chain structure, while the Body-Centered Tetragonal (BCT) structure comes into being when the particle volume is a little high. And the other structure models such as the layer model, the fiber model, the column model and so on. The single-structure model is researched in present paper.Based on the infinite single-chain structure model, research is done on MR fluids sheared by a small angle. The shear stresses are calculated according to the interaction force of two magnetic particles firstly, then to the resultant force on a particle in an infinite single-chain. The later is about 5% greater than the former, but both fit well on the order with the yield stresses of commercial MR fluids.Based on the research hereinbefore, research is also done on MR fluids sheared by arbitrary angles. Similarly the shear stresses are calculated according to the interaction force of two magnetic particles firstly, then to the resultant force on a particle in an infinite single-chain. The later is about 10% greater than the former, but both is a little higher than the value of the yield stresses of commercial MR fluids.Summarizing the present paper shows that: (1)the resultant force on a particle in an infinite single-chain is determined by its neighboring particle' action. (2)the shear stresses vary as the relative permeability of the matrix fluids, the volume fraction of particles, and the square of the particles' magnetization. The shear stresses increase with the external magnetic field, but have saturation values. (3)The saturation shear stresses vary as the relative permeability of the matrix fluids, the volume fraction of particles, and the square of the particles' saturationmagnetization. (4)the static yield shear angle may be a fixed value as 20.6 degree.