Research Of Properties Of Magnetic Powders Under Shear And Compression Excited By Magnetic Field And Their Application

Magnetic powders form columnar structures excited by magnetic field, similar as magnetorheological fluids and electrorheological fluids, thus it can be used in the control of friction. This property enables magnetic powders to be used in clutches and brakes, such as the application of magnetic powder clutch in vehicles and magnetic powder brakes in tension control. A large quantity of reports on magnetorheological fluids and electrorheological fluids were published, while few researches on rheological properties of magnetic powders can be found.The thesis mainly introduces the experimental investigation on shear and compressive properties of magnetic powders excited by magnetic field. The application of magnetic powders in dampers is also discussed and a damper was adapted from a magnetic powder clutch. In addition, a small magnetic powder damper were designed.Firstly, the influencing factors on shear stress were experimentally studied on a commercial rheometer, including magnetic field, gap distance, shear rate, particle volume fraction and fluids. Secondly, transient behaviors of magnetic powders in commercial magnetic clutch were experimentally studied. A test rig was built to investigate the torque output of a magnetic powder clutch when the excited current was applied. The response of shear stress of the magnetic powders under stepwise magnetic field was analyzed and compared with that of magnetorheological fluids and electrorheological fluids. Ways to reduce the response time of magnetic powder clutch was put forward and experimentally verified. In addition, squeeze behaviors of magnetic powders under magnetic field were investigated on the rheometer. A power-law equation between the compressive stress and gap distance was achieved and the index was discussed. A magnetization model was used to describe the dependence of compressive stress on magnetic flux density. A damper adapted from a magnetic powder brake was introduced. Lastly, a small magnetic powder damper was designed, which might be used in the actuator for virtual reality.