The Development And Mechanical Characterization Of Magnetorheological Elastomers

Magnetorheological(MR) elastomers are a class of smart materials.They consist of polymer and soft magnetic particles.Their properties such as modulus and damping can be controlled by an applied magnetic field.MR elastomers have been applied in adaptive tuned vibration absorbers and vehicle suspension bushings because of their controllable stiffness.They will play an important role in the vibration control and other application areas.For engineering application,MR elastomers must own high MR effect(often evaluated by the change of modulus),and other mechanical properties.However,until now,the reported MR effect was not large enough and little research foused on other properties,such as the damping and the mechanical performance.Moreover,current therectical models had too many assumptions to obtain the high accuracy.This dissertation aims to solve the above problems.A fabrication system was established to prepare MR elastomers based on the high-elastic and high-toughness materials.The effects of several basic factors in fabrication and measurement on the properties of MR elastomers were experimentally investigated.Two theoretical models were established according to the microstructure of the MR elastomers. Finally,the MR elastomers were optimized,and high properties were obtained.In the segment of Introduction,the history,classification and application of the MR materials were firstly introduced,and then the recent progresses in MR elastomers were detailed.Besides,the main scientific and applied problems were also pointed out.A fabrication system for MR elastomers based on matrix of the high-elastic and high-toughness materials such as natural rubber was established.To prepare the matrix/particle visco-plastic mixtures,the organic solvent and machine mixing methods were used respectively.By comparing the two options in technology, efficiency and feasibility,the machine mixing method was ultimately perferred. Furthermore,the thermal-magnetic coupled pre-configuration and vulcanization systems were set up,and the scheme for developing MR elastomers based on high-elastic and high-toughness materials was explored.The effects of several basic factors,such as the pre-configuration magnetic flux density and temperature,content of plasticizers and iron particles used in the fabrication and strain amplitude and driving frequency set in the test,on the dynamic properties of MR elastomers were experimentally investigated.In addition,a mechanical-magnetic coupled quasi-static shear mode load device was established. The shear stress-strain relationship of the MR elastomers with different contents of iron particles was obtained under an adjustable magnetic field.The basic mechanical properties concluding tensile and tear strength,hardness,elasticity,thermal-oxidative aging and anti-abrasion performance of MR elastomers were also evaluated according to rubber testing criterion.The microstructure of the MR elastomers prepared under different magnetic flux densities was observed by the scanning electron microscopy.The results indicated that the iron particles gradually aggregated into the cylindrical structure after application of the magnetic field in preparation.As the increment of the magnetic flux density,the length and breadth of the cylindrical structure were both raised.Based on above observed microstructure,a finite-column model which assumed MR elastomers containing several column structures with random length and the same breadth was proposed.Through the effective permeability approach,MR elastomers' field-induced modulus was derived.Further research on the microstructures and properties of MR elastomers showed that the length of column structures in MR elastomers obeyed the Gaussian distribution.So a Gaussian distribution model was established to study the effects of particle column size,external magnetic field density and shear strain on the field-induced properties of the MR elastomers.The simulation results of the Gaussian distribution model were also compared with other conventional models(such as model respectively proposed by Jolly and Davis) and the relevant published data.Results showed that this model agreed well with the experimental evidence and indeed improved the accuracy on predicting the behavior of the MR elastomers.The damping properties of MR elastomers were studied by the dynamic experiments and the numerical simulations.The experimental results indicated that the MR elastomers were also a kind of controllable damping materials.A method of magnetic field dependent interfacial slipping was proposed to explain the experimental phenomena.After picking the three-dimensional representative volume as a unit model,the stress-strain response was simulated in a dynamic periodic load by using the finite element analysis software ANSYS.The results of stress-strain relationship presented a hysteresis loop.The damping ratio was calcutated from the loop and approached to the previous experimental results.Based on above theoretical and experimental results and combined with the application requirements,the MR elastomers were optimized.It was noted that addition of the carbon black into the matrix resulted in high MR effect,low damping ratio and strong tensile strength.These results were hopeful to solve the extinct shortcoming existing in conventional MR elastomers,and helpful for application in adaptive tuned vibration absorber.