Study On Magnetorheological Effect Of Silicon Rubber Based Magnetorheological Elastomer Under Compression Loading

Magnetorheological elastomers（MREs）are mainly composed of elastomer matrix and magnetic particles.Owing to the inter-particle magnetic interactions,the mechanical properties such as stiffness and damping properties of the MREs can be rapidly changed by adjusting the external magnetic field.At present,MRE has been applied in many fields as a kind of smart materials.Unfortunately,there are still many problems nowadays that need to be improved and resolved.For example,the magnetorheological effect（MR effect）that determines the adjustment range of the MRE-based smart components is not high enough,and it is lack of studies on the magnetorheological behavior of MREs under the alternating magnetic fields.Furthermore,many researches have been carried out on the MR effect of the MREs under the shear loadings.On the contrary,the MR effect of the MREs under compressive loading has not been studied as extensively as under shear loading,and it is still insufficient.In many engineering applications,such as the active vibration absorbers and smart engine mounts,the MRE-based smart components may work under the compressive loadings.According to these problems,two aspects of works were carries out.The first is that,by changing the pre-curing time,the viscosity of liquid silicone rubber was adjusted,and its effects on the particle chain structure in the anisotropic MREs as well as the MR effect of the MREs were studied.The second is that,the effect of the nanoscale graphene oxide（GO）sheets on the microstructure and viscosity of rubber matrix and the particle chain structure in the anisotropic MREs were studied,and the influences of the alternating magnetic field on the MR effect of the anisotropic GO/MRE were experimentally investigated.The main research work and results of this work are as follows:1.An experimental system that can apply the compressive loading with the direction paralleling to the external magnetic field to the MRE samples was developed,and the effect of the pre-curing time on the particle chain structure in the anisotropic MREs as well as the MR effect of the MREs were studied.The results show that with the increase of pre-curing time,the particle chain structures changes from the long chains with closely packed particles to short chains with loosely arranged particles.With the increase of magnetic field strength,the maximum bearing capacity,compression modulus and energy loss per loading-unloading cycle of MRE increase gradually.With the increase of pre-curing time,the maximum bearing capacity,compression modulus and energy loss of MRE decrease gradually,and both the absolute and relative MR effects of the anisotropic MREs reach the maximum at 20min of pre-curing time.2.The effect of GO additive on the MR effect of the anisotropic MREs under the quasi-static compressive loadings was studied.The results show that the addition of GO causes the decrease in the crosslinking density of rubber matrix.With the increase of magnetic field strength,the maximum bearing capacity,compression modulus and energy loss of GO/MRE increase gradually.With the increase of GO content,the maximum bearing capacity,compression modulus and energy loss of MRE decrease gradually.The addition of GO leads to the enhancements in both the relative and absolute MR effects of the GO filled anisotropic MRE,and the MRE with GO mass content of 0.1wt%has the highest relative and absolute MR effects.3.The effects of constant magnetic field,alternating magnetic field and stepwise magnetic field on stress relaxation behavior of GO/MRE with different GO content under different compression strains were studied.The results of the relaxation experiment show that the ratio K of long-term modulus E_∞to initial instantaneous modulus E₀ increases with the increase of strain and decreases with the increase of GO content.In the constant magnetic field,the magneto-induced stress increases with the increase of the magnetic field and strain,and it increases first and then decreases with the increase of GO content.In alternating magnetic fields,the magneto-induced stress decreases gradually with increasing number of the magnetic field cycles.In the stepwise magnetic field,the magneto-induced stress increases first and then decreases in both the loading and unloading process,but the magneto-induced stress in the unloading stage is generally less than that during the loading stage.