| Magnetorheological elastomers (MREs) are a kind of magneto-sensitive materials, which are composed of microsized soft magnetic particles and low-permeability elastomers materials. During the preparation, the particles form an anisotropic ordered pre-configuration such as chains or more complex three-dimensional structures under applying a magnetic field. It is noted that the rheo logical or mechanical properties can be changed continuously, rapidly and reversibly by an external magnetic field. Based on these unique characteristics, MREs have attracted increasing attention and have been considered for a wide range of applications in vibration reduction and noise reduction, etc.Tremendous efforts have been devoted to the modulus of MREs in the past ten years, while the damping properties which are very important in practical application have not attracted considerable attention. For MRE-based vibration absorbers, low damping will contribute to the vibration reduction. Furthermore, for MRE-based vibration isolators, the tunable damping is preferred for vibration reduction effect when the excitation signal is located in different resonance frequency bands of the system. However, the high and uncontrollable damping is detrimental to some applications of MREs. Therefore, to develop high-efficiency MRE-based vibration reduction devices, it is very practical and important to study the damping properties.To overcome the above-mentioned problems, cis-polybutadiene rubber (BR) was used as matrix. The corresponding fabrication processes were studied to prepare BR based MREs and their mechanical properties were also investigated. In order to optimize the damping properties and obtain the practical MREs, the interface and the matrix of MREs were designed and improved. Details are described as following:1. The effect of interface between the two phases on the mechanical performances of the material is very important. In this study, the interfacial friction damping properties of MREs were investigated experimentally by using two kinds of carbonyl iron particles. The damping properties of MREs were measured under different magnetic fields and different shear strain amplitudes. The results demonstrated that the interfacial friction damping mainly comes from the frictional sliding at the interfaces between the free rubber and the particles, which is guidable for establishing interfacial model of MREs. 2. The interface and elastic matrix need to be improved to obtain the MREs with low damping. Maleic anhydride (MA) was selected as the compatibilizer to modify the interfaces of MREs. The experimental results indicated that the compatibility between the magnetic particles and rubber matrix was enhanced with the increase of MA. The enhancement of the bond between two phases led to different mechanical properties:the reduction of the loss factor, the increase of shear storage modulus, the enhancement of the tensile strength, and the reduction of the MR effect. In MREs, the matrix also plays a very significant role in damping properties. The graphite nanoplatelet (GNP) was selected as the reinforced component in the BR based MREs and their damping properties were investigated. MREs with different contents of GNP were prepared and the mechanical performances including loss factor, modulus, tensile strength and thermal diffusivity were measured. The effect of GNP on the damping properties under different shear strain amplitudes, magnetic fields and temperatures was studied. The results indicated that the flaky GNP could obstruct the sliding friction between the matrix molecular chains. The reinforcement of the matrix resulted in the reduction of loss factor. Consequently, the above methods were hopeful to optimize and reduce the damping of MREs, and helpful for practical application in MRE vibration absorbers.3. The controllable damping properties of MREs have also been investigated. The effect of crosslink density of the matrix on the controllable damping properties was firstly studied. The experimental results showed that the crosslink density of the matrix influenced the controllable damping properties of MREs directly. When the crosslink density of the matrix was low, the effect of plasticizer and frequency on the magneto-induced change of loss factor was remarkable. In addition, by reducing crosslink density, the magneto-induced modulus and the relative MR effect increased. A mechanism for the magneto-induced change of loss factor was proposed and the analysis implied that the rearrangement of particles played an important role in controlling the damping properties of MREs. Based on the mechanism of controllable damping properties, the polycaprolactone (PCL) was selected as the temperature-controllable component in the BR matrix and a novel kind of MREs with controllable damping properties was developed. The experimental results showed that the damping properties of the MREs can be controlled by varying the PCL weight ratio, the temperature, and the magnetic field. In practical applications, the effect of MREs with controllable damping properties on the properties of MREs based devices (MRE vibration isolators) is very important. These results will lead them to be widely applied in practical applications. |
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