Simulation And Experimental Research On Magnetic Circuit Of MRF Yield Stress Meter

Magnetorheological fluid(Magneto-rheological fluid,MRF)is a new intelligent material whose rheological properties can take a sharp change under magnetic field,and its rheological properties can be controlled continuously by magnetic field.With changing magnetic field intensity,its yield stresscan be controlled.Based on this characteristic,the MRF devices have some advantages,such as smooth braking,simple structure,be easily controlled,fast response,low energy consumption,and so on.So,these have extensive application prospect in the field of engineering.Yield stress is one of the main performance parameters of magnetorheological fluid,and it has a very important position in the study of the theory and application of MRF.Meanwhile,stable and controllable magnetic field is the precondition of accurate measurement of magnetorheological fluid yield stress.At present,the common MRF yield stress test device usually choose the electromagnetic coil to control the magnetic field,therefore,it is very necessary to put forward a new magnetic circuit design scheme to measure the MRF yield stress accurately.This subject adoptsa method of finite element analysis combined with experimental study to research the magnetic circuit of MRF yield stress test device based on MRF.Incombination with the structure characteristics of magnetorheological fluid yield stress testing device based on pulling method,complete the design of three kinds of magnetic circuit scheme:permanent magnet,the current excitation type and composite.Three kinds of magnetic circuit model is established using the finite element analysis software,and do simulation calculation,then get the magnetic induction intensity contours and magnetic induction line profile.The biggest magnetic induction intensity ofthese three scheme can meet 0.35 T based on the analysis comparison.But the magnetic field of permanent magnet working gap can’t continuous change and cannot be equivalent in accordance with the requirements;and composite magnetic circuit structure is complex,combined surface is more,these may affect the accuracy of test.The structure of current excitation type magnetic circuit is simple,and the magnetic field can change continuously by controlling the electric current,so choose this solution for the optimal design of magnetic circuit.According to the independent designed MRF yield stress test equipment,build magnetic field loading test bench,and do the four kinds of volume fraction of magnetorheological fluid field loading test,test the magnetic induction intensity between working gap with 20%,33.3%,45.9% and 58.9% of four kinds of MRF,then get the B-I curve.It can be seen that the biggest magnetic induction intensity of four kinds of magnetorheological fluid samples can reach more than 0.35 T,so the magnetic circuit of this test devicemeet the design requirements.Test the magnetic induction intensity at different positions in the working gap.Take six points in the middle of working gap vertically up from the bottom of reservoirand(d(28)0mm is the bottom of reservoir): d(28)4mm,d(28)10mm,d(28)20mm,d(28)30mm,d(28)40mm and d(28)50mm,and test the six points of magnetic induction intensity,then make the relation curve between work position and magnetic induction intensity.It can be found that the magnetic field of working gap reduces evenly with the increase of excitation current.The magnetic induction intensity of middle and lower MRF in the reservoir is bigger than the top,and the magnetic induction intensity is basically linear decrease with the increase of the height.