Mechanical Mechanism Of Magnetorheological Fluids

In the dissertation, the mechanism of magnetorheological (MR) fluids and a series of related key issues due to the application of the external magnetic field have been systematically investigated on the basis of microscopic and macroscopic scale. The method adopted throughout the present studies is a combination of theoretical analysis, experimental investigation and numerical calculation. The dissertation focuses on the mechanical mechanism of MR by the applied magnetic field. The rheological property, the characteristic of magnetorheological effect as well as the influencing factors and the mechanical behavior are studies in detail and in depth. The main research is as follow:(1) Designing and making the device testing the rheological property by the using the basic principle of mechanical design based on the theory of electromagnetics, electrodynamics, fluid mechanics and experimental mechanics. It keep away from the slide of the surface. The testing property of that is stable and the testing range is wide, the maximum stress up to 160kPa. The magnetic field is well-distributed and the range of magnetic field is able to change from zero to 6kGs. The shear rate is changeable from zero to 360 rod/min. (2) Testing the rheological property and magnetic property of MR fluids. It shows that the rheological property depend upon the strength of the applied magnetic field. The yield stress and the viscosity change with the magnetic field strength. The yield stress and the viscosity increase when the strength increasing. The magnetic property has been determined by the magnetic property of the particle consisting of MR fluid. The relative permeability and the susceptibility of MR fluid are not constant, which change with the magnetic field strength.(3) Investigating the characteristic of magnetorheological effect as well as the influencing factors based on the experiment. The main factors of influencing magnetorheological effect include the applied magnetic field strength, relative permeability and susceptibility of particles, particle size, volume fraction of particles, an additive as well as manufacture technology. The stress response of MR is on the increase with the growth of the magnetic field strength, particle size, volume fraction of particles. The influence of additive and manufacture technology on magnetorheological effect can not be neglected. The magnetorheological effect is adipole effect by the applied magnetic field. The dipole includes the internal dipole of the particle, which is a key of magnetorheological effect, and the dipole of a carrying oil along with the surface dipole of the particle. (4) Under the condition of noncompressible plasticity and small deformation as well as a little temperature change, develop a constitutive model based on a simple mechanical pattern for Magnetorheological(MR) fluids in the presence of an applied magnetic field by adopting the theory of continuum. A constitutive equation of MR fluids based on the simple mechanical model is given. It describes that macroscopic stress response of MR fluid changes with the shear strain by the applied field. The results consent well with the experimental results, which shows that the model of MR fluid setting up is reasonable.(5) Based on the microstructure during the application of external magnetic field to a MR fluid, analysis the interactive force between the particles when the particles aggregate into chains of dipoles aligned in the field direction due to the dipole moment exceeding thermal energy. The microscopic mechanical model has been presented to describe the mechanism of MR fluid. The interactive force changed with the magnetic field strength has been simulated by the using numerical method. The response of shear stress changed with the shear strain has been simulated. The results consent well with the experiment results.(6) Using the basics theory of electromagnetics and fluid dynamics, develop a model coupling electromagnetics with dynamics for MR fluids applied the magnetic field. Analysis the...