Fabrication And Performance Investigation Of Composite Magnetorheological Elastomers

Magnetorheological (MR) materials are kinds of smart materials and Magnetorheological elastomers (MREs) are a class of MR materials. The mechanical properties of the MREs can be controlled by an applied magnetic field. Besides the modulus and damping, other properties such as magnetostriction and piezoresistivity are also controllable. These unique characteristics enable the MREs be applied in many areas, such as adaptive tuned vibration absorbers (TVAs), stiffness tunable mounts and suspensions, and variable impedance surfaces. Unfortunately, the present MREs products can not fully meat the requirments of the practical application due to their low MR effect, weak mechnical properties and large dynamic damping. To this end, more research should be done to prepare high-performanced MREs with improved mechanical properties. This dissertation is focused on the preparation of high-performance MREs which exhibits high MR effect, good mechanical performance and small dynamic damping. The influences of the preparation condition on the properties of MREs are systematically studied.The preparation of high-performance MREs based on rubber natural rubber (NR) and cis-Polybutadiene rubber (BR) was studied at first. The synthetic parameters were optimized to produce MREs materials with high MR effect, good mechanical performance and small dynamic damping. MREs samples based on the mixed rubber were fabricated according to our previous reported method and the synthetic route was optimized. The hybrid MREs materials with different mass ratios (BR/NR) were prepared by using the high temperature vulcanization method and the mechanical property of the products was improved.To evaluate the performances of the as-prepared MREs under the applied magnetic field, a mechanical-magnetic coupled quasi-static shear mode load device was established. We first investigated the durability properties of the hybrid MREs under cyclic loading and high temperature conditions. The results revealed that the MR effect and modulus of all samples depended on the testing conditions, such as number of loading cycles, load amplitude, aging temperature and time. The relationship between the durability properties, cyclic loading and aging conditions were also analyzed.According to the results of the aging test,their mechanical properties, including modulus and damping capability, depend both on an external magnetic field and an environmental temperature. In order to systematically investigate their temperature-dependent mechanical properties, six different kinds of MREs samples which based on a mixed rubber matrices (cis-Polybutadiene rubber and natural rubber), were fabricated in this part. The steady-state and dynamic mechanical properties of the samples were measured under different conditions by using a rheometer. An improved constitutive equation was developed to model these properties under different magnetic fields and temperatures. The comparison between modeling predicting results with experimental data demonstrated that the model can well predict the modulus of MRE in different conditions.To further improve the mechanical performance of MREs, two novel hybrid MREs which were embed with MR fluids (MRFs) and MR gels (MRGs) were fabricated. In this work, MRF and MRG were injected into different numbers of holes, which were punched on MREs specimens regularly. The mechanical properties of MR fluid-elastomers (MRFEs) and MR gels-elastomers (MRGEs) investigated in the presence of externally applied magnetic fields. The modulus and loss factor have been evaluated by using a modified dynamic mechanical analyzer (DMA) and researched respectively. Dependence of the rheological response on volume fraction was also investigated. As a results, not only the foundation modulus of two novel hybrid MR materials were higher than both MRF's and MRGs's but also their MR effects were better than MREs's. The loss factor of two new hybrids was different from traditional MREs'. Moreover, their dynamic properties changed according to the difference volume ratio of MRFs and MRGs injected in MREs specimens. These results suggest that the two novel hybrid MREs are an improved system with volume fraction dependent rheological response. The mechanical properties of MREs can be improved by embedding with MRFs and MRGs. All their mechanical properties, especially MR effect, exhibit significant improvement compared with traditional MREs. A new model based on theory of composite materials and MRFs were used to explain the nonlinear mechanical properties of the hybrids, and it fit the experimental data well.