Study On Mechanical-electro-magnetic Coupling Properties Of Magnetorheological Elastomers

Magnetorheological elastomer(MRE)is a kind of intelligent materials.Similar to other MR materials,MRE is also prepared by dispersing ferromagnetic particles into the matrix.The difference is that the solid matrix of rubber is used instead of other materials such as liquid or gel,so it has more stable performance and higher modulus.When the external magnetic field is applied to the MRE,its mechanical performance response can be controlled precisely,quickly and reversibly.Because of this unique magnetorheological behavior,MRE has wide applications in the field of vibration control,building constructions,noise reduction and so on.The microstructure of MRE,especially the direction,diameter,length of the chain and the interface between the particles and the matrix,plays a critical role in determining MRE's mechanical behaviors.However,the hysteresis phenomenon of mechanical behavior has been observed comparing to the change of microstructures.In practice,the life of MRE is often assessed by testing its mechanical properties,but this method is not real-time and will damage the microstructures during the tests.Iron particles are the most commonly used ferromagnetic particles in MRE,so MRE has the piezoelectric characteristics as a typical conductive polymer composite,and its electrical properties are very sensitive to the structural change induced by external stimuli.In addition,MRE's microstructure damage and other problems caused by the fatigue loadings also could be reflected through testing and characterizing its electrical performances.Therefore,in this paper,the electrical performance of MRE under the excitation of force,electricity and magnetic field was studied,as well as the fatigue dependent impedance-mechanic coupling properties.In order to improve the mechanical and electrical properties of MRE in different directions,it was reinforced by introducing flax fiber weaves.Details are described as follows:1.The impedance change of the MRE samples under different external mechanical loading and magnetic field stimuli were investigated.The electrical properties of the materials were characterized by taking advantage of the impedance spectrum.The coefficient Rd was defined to characterize the microstructure damage.After building an equivalent circuit model,all parts of the circuit components were presented and analyzed.In addition,all circuit components were correlated to its physical meanings.Aiming at the preloading conditions in the electrical performance tests,a possible basis was provided.The result shows that tiny damages on the interface layer could greatly influence the impedance spectroscopy of an MRE.On the basis of the experimental results,a new quick and nondestructive method was developed to characterize the degree of the microstructure change.2.The impedance change of the MRE samples under different fatigue loadings was investigated.Same to the mechanical characteristics,the electric properties of the MRE varied with the loading cycles due to the change of the microstructure.The curves of capacitance could be divided into four sections with the cyclic loading numbers increased.The greater the magnetic field strength,the more obvious this performance.A coupling effect was found between the electrical performance and mechanical performance,and the platform segments of curves were correlated to the yield stage of MRE.In addition,the dependence of cycling loading on both the mechanical and electrical properties was investigated,and the detailed mechanism was discussed.Through the analysis to the impedance spectrum,both of the magnetostrictive phenomenon and interface damage can be reflected.Since the simplicity of the testing process,the non-destructive impedance spectrum method presented high potential in real-time detecting the damage of the MRE microstructure and predicting the fatigue life in practical applications.3.Based on the study of MRE's electro-mechanical coupling properties,the flax fiber weaves were added into the MRE to strengthen the matrix and enhance the properties.The gap among the strands of fibres could be well filled with the PDMS-based MRE,and the matrix combined well with the fibres.The CI particles can form aggregation structure along the fibre direction through this method.The influence of loading directions,density and layer numbers of the FFWs on the mechanical and electrical properties of the FFW-MRE were studied.When parallel to the fibre layers,the conductivity of MRE greatly increased,but in the vertical direction,the insulation and adjustable range of resistance were greatly improved.Besides,the mechanisms of structure formation and enhancement performance were discussed.Because of the simple and environmental fabricating process,it is a potential method to broaden the practical applications of MREs.