Study On Bidirectional Mechanical Properties Of Variable Stiffness Isolator Of Magnetorheological Elastomer Under Low Frequency Conditions

In the traditional structure control,device parameters are fixed.Therefore,the stiffness is fixed or the adjustable range is small.It cannot adapt to random load and the change of natural vibration frequency caused by structural aging.Magnetorheological elastomer（MRE）has good dynamic mechanical properties and can adjust stiffness in real-time,reversibly and rapidly.It has broad application prospects in intelligent isolation and vibration reduction devices.Over the years,scholars have conducted in-depth research on MRE intelligent vibration damping devices,but mainly focused on unidirectional vibration control of highfrequency structures.In fact,buildings are subjected to seismic action and wind vibration in multiple directions.Wind vibration is frequent,and highly flexible and low-frequency structures are most susceptible.The existing bidirectional vibration controls are mostly fixed parameter devices,which are difficult to adapt to the changes of natural frequency of the structure and external load.The bidirectional mechanical properties of MRE intelligent devices are unclear.In this paper,MRE is used as the core intelligent component to design and manufacture a bidirectional variable stiffness isolator.The bidirectional mechanical properties of the MRE variable stiffness isolator under low frequency conditions are mainly studied.The specific research contents and results are as follows:（1）Based on the existing literature,appropriate raw materials and ratios are selected to prepare magnetorheological elastomers.Dynamic mechanical properties of magnetorheological elastomers under different frequencies,magnetic induction intensity and shear strain are tested by rheometer.The results show that the magnetorheological elastomer has three mechanical characteristics of magnetorheological effect,viscoelasticity and nonlinearity.Based on the test results of dynamic mechanical properties of magnetorheological elastomers,Maxwell-Kelvin-Bouc-Wen nonlinear and constitutive model is established.A method of identifying Maxwell model parameters by MRE skeleton curve and determining Kelvin and Bouc-Wen model parameters by hysteresis curve characteristics is proposed.（2）The magnetorheological elastomer is used as the intelligent component of bidirectional MRE variable stiffness isolator.In view of the large size and energy consumption of MRE variable stiffness isolator,it is difficult to apply it to macrostructure.Structural design and magnetic circuit design are determined from the perspective of energy saving and device portability.The electromagnetic model is established by Ansys,and the magnetic induction intensity of each layer of MRE is calculated.The results show that the magnetic induction intensity of the top MRE is up to 341.6 m T,which verifies the rationality of the design.（3）Mechanical properties of one-way Y-axis and two-way X-axis and Y-axis of bidirectional MRE variable stiffness isolator are tested.It is found that the maximum control force,equivalent stiffness and equivalent stiffness change rate of single direction increase with the increase of magnetic induction intensity,and decrease with the increase of shear deformation amplitude,which are almost unaffected by frequency.Energy dissipation capacity increases with the increase of magnetic induction intensity,shear deformation amplitude and shear frequency.In contrast,bidirectional loading has effects on the maximum control force,equivalent stiffness and energy dissipation capacity in one direction : When the bidirectional loading displacement increases,the maximum control force and equivalent stiffness in the single direction decrease first and then increase relative to the unidirectional loading.The nominal shear strain at the critical point is 30%.The energy consumption capacity increases with the increase of bidirectional displacement loading.