Experimental Research Of Shear Yield Stress For Magneto-Rheological Fluid

As a kind of new intelligent material,magneto rheological fluid is a kind of stable suspending liquid which can be controlled by the magnetic field.In the magnetic field,magnetorheological fluid from the fluid into semi solid milliseconds and the process is reversible,the apparent viscosity can be increased by 10⁵¹0⁶times,the maximum yield stress reaches 50¹00kPa,which determine the MRF has very broad application prospects.The yield stress is one of the main performance parameters of magnetorheological fluid and the demarcation point of solid-liquid transformation performance.At present,there is no uniform test standard on the yield stress,so it is significant to design a test device that can accurately test the yield stress of the magnetorheological fluid.First of all,constructed the MRF shear yield stress calculation model using Maxwell stress tensor equation based on the test theory of the shear yield stress of magnetorheological fluids.Taking MRF-122EG and MRF-132LD of Lord company as the research object,the maximum relative error between the calculation results of yield stress for two kinds of MRF and the technical parameters provided by Lord were 6%and 9%based on the magnetic field simulation function of the finite element software ANSOFT,which proved that the calculation model of yield stress for magnetorheological fluid is reasonable.Secondly,designed testing device of the yield stress based on pull method.The magnetic circuit adopts an annular closed magnetic circuit,the pull block materials made of Q235steel,copper and iron in testing device,the wall groove shape of pull block made of rectangular and triangular,the depth of the wall grooves were divided into 1mm and 2mm,the gap of coupling surface were divided into 3mm,5mm,7mm and 9mm.At the same time,the design process of testing device for shear rate and testing bench were described in detail,and its rationalities were analyzed.Finally,tested the yield stress of MRF-132LD and MRF-122EG based on the testing device,value error between the test results and the technical parameters of the yield stress of Lord company as the selection standard.The optimum test plan:the gap of coupling surface is 5mm,the depth of the wall groove is 1mm,the pull block material is copper,the maximum relative error is 5%.At the same time,tested four kinds of MRF with 20%,33.3%,45.9%and 58.9%volume percentage based on the optimum test plan.The results showed that the yield stress of MRF with solid particle volume percentage increase has increased.The yield stress of 58.9%solid particles volume percentage for MRF more than50kPa.Then explored the effect of temperature on the yield stress of MRF.The test results showed that the yield stress of MRF decreases with the increase of the temperature.The test results of MRF shear rate and viscosity showed that when the shear rate was lower than 10s^-1,the yield stress increased with the increasing of shear rate,when the shear rate was higher than 10s^-1,the yield stress increased slightly but the trend was not obvious.The fluid viscosity decrease with the increase of shear rate.Finally,indirect tested B-H curve of four kinds of MRF.The purpose of this paper is to design a testing device to accurately test the yield stress of MRF and carry out relevant tests.The designed device can be applied to test the yield stress of MRF with the different volume percentage,which has guiding significance for the practical application of the magnetorheological fluid.