Study On Shear Properties Under Stiffness Softening Stiffness Of Magnetorheological Elastomer

Smart isolation is the development trend of isolation technology in the future.The research on isolation system based on magnetorheological elastomer(MRE)has opened up a new direction of smart isolation.So far,few research on the negative equivalent stiffness of MRE has been reported.Based on the fact that permanent magnet can provide an initial magnetic field for MRE)a rigidity softening shear test device of MRE is designed by applying current to the coil to weaken its magnetic field.The magnetic field produced by the coil can adjust the magnetic field of the magnet to change the rigidity of MRE and realize the rigidity softening performance of MRE.This paper achieves the following work to address these problems:Initially,the excitation fixture is designed,which is composed of core,coil,permanent magnet,MRE and clamping device.The magnetic field generated by the coil regulates the magnetic field of the magnet to change the equivalent stiffness of MRE and realize the equivalent stiffness softening performance of MRE.A numerical investigation using Ansoft Maxwell is conducted to simulate and analyze the test device.The current applied is 0.9A,0.66 A,0.43 A,0.2A,0A and-0.45 A respectively.The simulation results show that when positive current is applied,the flux produced by the coil is opposite to the flux produced by the permanent magnet,and the positive current can reduce the Magnetic Flux(B)value in MRE.When the applied current increases from-0.45 A to 0.9 A,the flux density of MRE decreases from 1.01 T to 0.02 T.At 1.01 T,the effect of magnetic field on MRE adjustability is saturated.According to the designed excitation fixture model,the entity manufacture is carried out,and the test platform is built up.The shear properties of MRE under different carbonyl iron powder(CIP)volume fractions,current intensities,shear displacements and excitation frequencies were studied.The excitation frequency is 0.1Hz,0.5Hz,1Hz and 2Hz,the amplitude is 1mm,2mm and 3mm,and the sinusoidal excitation is used in this research.The applied current of the coil is 0.9A,0.66 a,0.43 a,0.2A,0A and-0.45 a respectively.For each scenario,the test are repeated 4 time to obtain stable performance data of MRE,and the sampling rate of the data acquisition device is set to 500 Hz.The test results are processed and analyzed.The hysteresis curve and the stiffness and damping changes under different excitations are drawn by Origin software.The results show that with the increase of applied current from-0.45 a to 0.9A,the equivalent stiffness of all MRE samples decreases with the increase of current,and the equivalent stiffness of all MRE samples decreases to the lowest value at 0.9A.It effectively realizes the characteristics of stiffness softening.When the volume fraction of CIP in the sample is the same,the anisotropic sample has higher stiffness,damping performance and greater adjustability than the isotropic sample.The higher the content of CIP,the greater the equivalent stiffness and damping.When the excitation amplitude increases from 1mm to 3mm,the stiffness growth rate of anisotropic material is about 40%,and that of isotropic material is about 30%.However,the performance of MRE is almost independent of the excitation frequency.