Study On Suspension Stability Of Magnetorheological Fluid Under Transverse Magnetic Field

Magnetorheological fluid(MRF)is a intelligent material with engineering application value.Generally,It is composed of micron-sized soft magnetic particles,non-magnetic carrier liquid and functional additives.After application of the magnetic field,MRF will converted from a Newtonian-like fluid to a solid-like in milliseconds,and the apparent viscosity will significantly increased.After the magnetic field is removed,it returns to the liquid state.This controllable rheological property makes it wildly used in the fields of automobiles,biomimetic robots,construction,and medical.MRF has encountered the problem of suspension stability in practical applications.Specifically,a significant difference in density between the soft magnetic particles of the MRF and the carrier liquid causes the soft magnetic particles to settle.In order to solve the settlement problem,scholars have carried out a lot of researches on the structural system,surface treatment and physical chemistry of soft magnetic particles.For long-term stationary installations,the settlement problem of MRF has not been completely solved.Based on the chaining of soft magnetic particles under an applied magnetic field,a suitable transverse magnetic field can be used to attenuate or even eliminate the sedimentation problem of the particles under gravity.For this reason,this paper analyzes the stress characteristics of soft magnetic particles under the action of transverse magnetic field,and designs the transverse magnetic field experimental device and the inductive method test settling device.The suspension stability of magnetorheological fluid under transverse magnetic field is studied experimentally.The main work of this paper are as follow:(1)Analysis of the MRF settlement problem from the perspective of the suspension phase itself,the core-shell structure,the carrier fluid and the study of new magnetorheological colloids.However,changing the material itself will change the rheological properties of the magnetorheological fluid,and these methods are not suitable for the MRF in the long-term stationary device.Therefore,the transverse magnetic field is used to solve the problem of MRF settlement.(2)The force analysis of the magnetorheological fluid under no field and magnetic field,and the force balance condition of the particles in the vertical direction after the application of the transverse magnetic field is determined,and the transverse magnetic field strength required for the suspension stability of different concentration samples is obtained.The suspension batch sedimentation theory is introduced to quantify the sedimentation process.(3)The volume fraction of the suspended phase in MRF is directly proportional to its own magnetic permeability.Therefore,by measuring the inductance of different regions of MRF,the volume fraction of soft magnetic particles in different regions can be reflected.Based on this design,the MRF settlement test system mainly includes a screw drive frame,an altimeter,an inductor head and an LCR test instrument.Due to magnetic flux leakage at the end of the inductor coil,a pure iron-clad coil is selected to reduce the leakage phenomenon,so that the measured inductance value can reflect the true concentration information.In designing the transverse magnetic field experimental device,in order to make the transverse magnetic field of the MRF sample at different heights close to the uniform magnetic field,the two permanent magnets with symmetric phase suction provide a transverse magnetic field.The magnetic field between the permanent magnets is simulated and analyzed,and the magnetic field strength at the MRF sample is changed by adjusting the spacing of the permanent magnets.(4)According to the theoretical analysis,the magnetic field required for the suspension stability of different concentrations of MRF samples was calculated and verified by experiments.The sedimentation characteristics of different concentrations of MRF samples are tested under zero field and transverse magnetic fields.Considering the error in the calculation,for the 32 vol% sample,the theoretically calculated magnetic field strength is used as a reference for the experiment,and multiple magnetic fields are designed for comparative analysis.According to the experimental results,26 vol% sample experiments were further planned,and the experimental verification of theoretical calculations has guiding significance.Further fitting the MRF sedimentation rate model under zero field and a transverse magnetic field respectively,according to the concentration propagation velocity and the solid flow function obtained by fitting,the minimum concentration of the MRF without sedimentation under a transverse magnetic field is obtained,and the verification application is performed.After applied the magnetic field,the suspension stability of the MRF sample is greatly improved.