Research On Rheological Behaviors Test Instrument For Magneto-rheological Fluids

Because of the field-dependent properties and rapid time responses, MR fluids have attracted considerable attention recently as controllable components of engineering devices. To develop high quality and practicable in engineering MRF materials and to design MR fluid devices for engineering application, much attention has been paid to study on test methods for rheological behaviors of MRF over the past decade. Although several test apparatus have been designed and fabricated lately at home and over sea, test results from different test apparatus show some diversity due to lack of reasonable evaluation criterions and rational test methods. In the interest of development of new MRF rheometer, the double-side shear test theories based on rotational coaxial cylinder have been presented, some techniques in magnetic circuit design and mechanical structures design have been analyzed, and test apparatus have been designed and fabricated on the basis of test theories above-mentioned. Primary researches in this dissertation are stated as follows:According to the working modes of the MRF testing instrument, the dissertation gives an overview of its current situation and development tendency of the testing technique from two ways: shear mode and flow mode. It also analyses the main problem existing in the field of MRF testing technique and the academic value for developing the research on the testing method of MRF rheological characteristics. At the same time, in view of the high-shearing strain rate and the high saturated magnetization, double-side shear test methodology based on rotational coaxial cylinder is presented for development of new MR fluid rheometers.In this dissertation, the flow characteristics of MR fluid are simply presented, and for describe the flow characteristics of MRF, four constitutive models have been summarized. Author comes to conclusion that MR fluid rheological behaviors can be expressed by shear stress function of magnetic induction strength and shear rate, by analyzed comprehensively those constitutive models. Differential equations and their rational boundary conditions in two channels are set up by analyzing stress equilibrium of MRF micro-unit. The flow characteristics and shear stress distribution function of MRF under zero magnetic field and non-vanishing magnetic field in two shear channels are respectively characterized by Newton constitutive model and Bingham model. In this foundation, the theory relationships between nominal shear stress and transmission torques are comprehensively established, and the theory relationships between rotor angular velocity and nominal shear strain rate are comprehensively established too. An approximation algorithm is put forward.The magnetic circuit structure and magnetic principle of this instrument have been determined; and the importance of magnetic circuit design was analyzed. Direct-current series magnetic circuit equation was established in the basis of magnetic circuit design criterion, and obtains the relationship between the magnetic field intensity and excitation current, combined the rigidity requirement for the instrument, the magnetic parameters of this instrument was determined. Using digital teslameter, we test the magnetic field intensity in the channel, and the relationship between magnetic field intensity and excitation current was determined. It's indicated that the magnetic circuit design method is reasonable.According to the torque transmission traits of the MRF testing instrument, combining its system demand, we reasonably choose torque sensor, torque measuring instrument, power equipment, high-accuracy laser tachometer, instrument of temperature measurement etc, which are suitable for this instrument, assemble and successfully debug it, the results shows that the way of double-side shear test methodology based on rotational coaxial cylinder is reasonable. A kind of MRF have been tested by the instrument designed in this paper, the result shows that: MRF viscosity becomes stronger with the increase of the magnetic field; MRF shear stress is related to the allocated proportion of the liquid itself; the shear stress becomes stronger with the increase of the shear rate; when the magnetic field is stronger , the increase change of the shear stress is comparatively small, which indicates that it tends towards the magnetic saturation; MRF viscosity decreases with the rise of the temperature.