Experiment And Study On Mechanical Properties Of High Stability MR Fluid

Magneto rheological (MR) fluid is a kind of suspension liquid formed by micro or nano magnetic particles scattered in the base fluid, and its main components are magnetic particles, carrier fluid and various additives. Under the action of magnetic field, it can transform rapidly from the liquid state into solid state in milliseconds, and restore the flow state once again without the magnetic field. The rheological property of MR fluid can be used to design MR damper. As a new type of intelligent material, the intelligent adjustable features of MR fluid result in MR damper’s advantages of large output, low energy consumption, real-time control and high precision, so that it has good damping effect. Therefore, the performance of MR liquid directly affects whether MR damper can work well or not. In order to achieve the above advantages of MR damper, MR fluid should have the characteristics of good stability, hard to agglomerate, low zero field viscosity and high shear yield stress. So far, domestic and foreign scholars have done many researches on MR liquid and achieved some results, but there still are some problems to be solved, such as the preparation of high performance MR fluid, the build-up of microscopic model to describe the magneto rheological fluid behaviors, the design of shear yield stress testing device, etc. There still should be some further and deeper research on MR fluid. By combining experiments and theory analysis at both the macro-and the micro-level, starting from the basic properties of MR fluid, this paper studies the preparation methods, rheological properties and mechanical behaviors of MR fluid.and then puts forward to the initial tilt chain model adding the carbon-coated particles by preparing high stability MR fluid, and improves the shear yield stress testing device of MR fluid. The paper involves in the ferromagnetic mechanics, fluid mechanics, electromagnetism, material chemistry and other fields, and obtains some conclusions with certain reference value through experiments and theoretical analysis. The researches of this paper mainly manifest as in the following aspects:1) The multi-walled carbon nanotubes (MWCNTs) coated magnetic particles are prepared, and the dosage of various materials and the preparation process of the coated particles are studied. Finally, the composite magnetic particle which have the best effects of coating are selected.2) Combining the prepared MWCNTs coated magnetic particles and the surface active agent modified magnetic particles which are prepared by research group earlier and by adding different amount of additives, different volume fraction of MR fluids are prepared.3) Through the test of stability, zero field viscosity and shear yield stress of MR fluids, the effects of the ratio of two kinds of composite magnetic particles, volume fraction of magnetic particles and the dosage of additives on the properties of MR fluid are studied, and better performances of MR fluids are got. At the same time, the beneficial effect of adding MWCNTs coated magnetic particles to improve the stability of MR fluid is verified.4) Based on the work mode of MR fluid, a parallel disk type shear yield stress testing device is designed and improved. Through the researches on the device of material, structure, sensor and data acquisition, the uniform magnetic field and easy-using integration test device is developed.5) According to the chain mechanism of MR fluid and based on dipole theory, the initial tilt chain model of MR fluid added the carbon-coated particles is deduced. The influence of magnetic induction intensity, volume fraction and other factors on the shear stress yield are analyzed from the microcosmic level, and the comparison results between the theory analysis and experiment show that the initial tilt chain model added the carbon-coated particles is verified to be correct.The innovations of this paper lay in:1) The MWCNTs coated magnetic particles are obtained, and together with the surface active agent modified magnetic particles as mixed magnetic particles, MR fluid is prepared. The performance test results show that the adding MWCNTs coated magnetic particles can improve the stability of MR fluid. Meanwhile the influences of the ratio of two kinds of composite magnetic particles on the sedimentation rate, zero field viscosity of MR fluid are got.2) A parallel disk type MR fluid shear yield stress integration testing device is developed and improved.3) The initial tilt chain model adding the carbon-coated particles of MR fluid is proposed and verified with the results of experiment.