| Magneto-rheological elastomer(MRE)is an important part of magneto-rheological materials which are emerging smart materials,its stiffness and damping are controllable and can be changed quickly and reversibly in the external magnetic field,these excellent performances provide solutions to the problem of designing vibration control structure with high frequency bandwidth.MRE sandwich structure is an application of magneto-rheological materials in semi-active control,the purpose of controlling the vibration of the sandwich structure can be achieved by controlling the change of the damping and stiffness of the MRE in sandwich structure under the external magnetic field.At present,the application of MRE in practical engineering are mostly concentrated in the fields of dampers,clutches and vibration isolators at home and abroad,there is not much research on the application of sandwich structure,the experimental and comparative analyzes of MRE sandwich structures under the clamped-clamped and cantilever boundary conditions and under the action of uniform magnetic field and local magnetic field are rarely reported.Based on the above situation,this paper manufactured the magneto-rheological elastomers which had different ratio of ferromagnetic powder,silicone oil and silica gel,their rheological properties were experimentally tested and analyzed by rheometer.The test results show that the rheological properties of MRE are closely related to the proportion of ferromagnetic powder and silicone oil.The storage modulus and loss modulus of the elastomers with high content of iron powder and silicon oil will be larger.Under the effect of magnetic field,the storage modulus and loss modulus of MREs increase with the increase of magnetic field strength.Dynamic models of magneto-rheological elastomer sandwich beams were established,the vibration equations were deduced,and the natural frequencies of magneto-rheological elastomer sandwich beams were analyzed numerically.MRE sandwich beams with different ratio or core layer thickness were also manufactured,set up an experimental table for investigating the vibration response characteristics.The MRE sandwich beams were fixed on the test table with both clamped-clamped and cantilever boundary conditions.Their vibration response characteristics were tested and analysis under the action of two different types of applied magnetic fields with uniform magnetic field and local magnetic field and different magnetic field intensities.Some conclusions can be drawn from the vibration response experimental results of MRE sandwich beams,the natural frequencies of the MRE sandwich beams withclamped-clamped and cantilever boundary conditions are both gradually increased under the action of a uniform magnetic field,the higher the proportion of ferromagnetic powder in the core of the sandwich beam,the greater the natural frequency;the natural frequency of clamped beam with the same intensity and the same ratio is larger than that of the cantilever beam.Under the action of local magnetic field,the MRE clamped-clamped sandwich beam has the lowest natural frequency in the middle part,the natural frequency increases when the magnetic field moves to both ends,the natural frequency of the MRE cantilever sandwich beams gradually decreases as the magnetic field moves from the fixed end to the free end,and will gradually decrease with the increase of magnetic field intensity at the same location,it will show the same trend with the iron powder and silicone oil content increases.The experimental results are consistent with the trend of theoretical calculations.The results of this study show that different sandwich structures can be combined and optimized by changing various factors appropriately which affect the vibration characteristics,and an adaptive sandwich vibration control structure with the wide frequency variation range also can be designed to meet various working environments and application requirements of vibration control engineering. |
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