Vibration damping of hollow shaft by using magnetorheological elastomer

This paper presents a solution of the vibration reduction in the hollow shafts by MR elastomer. Generally, the vibration mode in hollow shafts can be divided into the bending and torsional vibrations. And the bending vibration is significant factor when it excites with the resonance frequencies in the hollow shafts. However, since the torsional vibration is also the critical source of vibration problem in the shaft, it is necessary to analyze bending and torsion vibration together with the natural frequencies. In this paper, active vibration control system of the shafts is introduced to actively absorb the combined bending and torsional vibrations. Proposed active damping structure is built by embedding the Magnetorheological(MR) elastomers whose elastic modulus is controllable by an applied magnetic field. MR elastomers consist of natural or synthetic rubber filled with micron-sized magnetizable particles. Therefore the stiffness can be changed variously according to the magnetic flux density. By using this property, the material can be applied to vibration absorber used in many parts of structures. However, the performance of MR elastomer on vibration reduction is various depending on different magnetically polarization direction and dimension during the manufacturing process. In this paper, a series test using MR elastomers with different types and dimensions are conducted. The extent of natural frequency shifted against magnetic field at various excitation frequencies can be measured. For the desired vibration damping performance of a shaft, the tests of MR elastomers as different direction, thickness are analyzed. For reduction of vibration, dynamic damper of the shaft is designed by using MR elastomer and equipped in the shaft. Finally, control results are shown through the experiments to confirm the effect of MR elastomer dynamic damper for vibration reduction.