Preparation And Properties Of Silicone Rubber Based Magnetorheological Materials

Magneto-rheological elastomers(MRE), a new type of smart materials, belong to a new branch of magneto-rheological materials. They are prepared with ferromagnetic particles which are aligned in chain form and high polymer. Their dynamic mechanical properties can be controlled by the magnetic field. Thus MRE can be applied in many vibration fields, such as the device in the need of variable stiffness or avoiding resonance.The article deeply investigated the MRE prepared with different components ratio and pre-magnetic field, using micron carbonyl iron powder as a filler and two-component silicone rubber (type RTV) as the matrix. The details are as follows.The density and shore hardness of different samples were tested. The results show that the density of anisotropic samples is less than that of isotropic samples due to the change of volume of silicone rubber. The hardness difference among the samples is little. With the carbonyl iron content increasing, the density and hardness enhance. The microstructure of samples with different components ratio were observed using Laser Scanning Confocal Microscope. The filling particles in MRE are aligned in strong magnetic field during the curing of the polymer matrix.The static shear properties of MRE with different concentrations of carbonyl iron powder were tested. The static shear modulus increases with the filler fraction, and the shear modulus of the anisotropic samples is larger than that of isotropic samples. When the filler's content is 70%, the shear modulus of anisotropic MRE is 1.536MPa, and the shear modulus of isotropic sample is only 0.873MPa. When the shear force is applied to the anisotropic samples, the perpendicular direction's shear modulus is greater than the parallel direction's shear modulus. The maximum difference between them is 0.436MPa.A dynamic test set-up was established and the formula of dynamic shear modulus was given. The frequency response function was tested using the above-mentioned system in the magnetic field from OmT to 700mT. Then, the dynamic shear modulus could be acquired. The results show that the resonance frequency and MR effect enhance with the testing magnetic field and carbonyl iron content increasing. When the magnetic flux density is 700mT and carbonyl iron content is 75%, the amplitude increase of resonance frequency of MRE reaches 30%, the characteristics of frequency shift is better, and the largest change of dynamic shear modulus attains 66%.The influences of three parameters, such as magnetic particle size, admixture content and pre-adding structured magnetic field, on the MR effect were studied. Experiments show that, the increase of MR effect can be due to larger particles, silicone oil and pre-adding structured magnetic field. The MR effect reaches about 59% for materials with large particle (5.23um), and only 42% for materials with particle size of 2.25μm; The MR effect is 61.2% for materials with 10% silicone oil, and 34.2% for materials with 0% silicone oil; the MR effect is 18% for materials with OmT pre-adding structured magnetic field, and 35% for materials with 500mT pre-adding structured magnetic field.