| Magnetorheological fluid (MR fluid) damper, as a kind of the semiactive and controllable dampers, has been focused for the academia and engineering region since the MR effect was discovered. MR fluid, as the damping medium of the damper, is a stable disperse system composed of two phases, such as micro sized magnetic particles, carrier oil and stabilizer. Although fully commercial, mass-produced MR fluids and devices have been available via the retail market and applied, the high cost of MR fluid damper is still a barrier to widespread commercial acceptance in many areas. The typical MRF dampers need large volume of MR fluid and specific sealing component to restrict MRF leakage make them very expensive. Beside this, the wear produced by the magnetic particles will also shorten the life of the damper.The motivation of the work is to overcome the large volume of MRF and costly seal needed by conventional MRF dampers. Referring to the porous sponge MR fluid damper, this dissertation presents an original idea to use porous foam metal to hold magneto-rheological fluid (MRF) when unexcited and the MR fluid can be propelled when excited with external magnetic field. The feasibility and theory on the porous foam metal used to store MR fluid and produce the damping effect is studied.The main research works of this dissertation are as followings:1) The principles for selection of the porous materials are put forward. The relationship between the MR fluid capillary force and the pore size, the change of MR fluid characteristics in the micro tube such as density are investigated. The MRF storing ability and the penetrability of different porous materials have been evaluated. These experimental works are much useful for the selection of the suitable materials to store MRF.2) The performance of porous foam metals is studied and tested. The porosity of porous foam metal (Fe, Ni and Cu) is measured using fusible paraffin. The relationship between the penetrability of porous foam metal and the change of characteristics of MR fluid is obtained by measuring of MR fluid after flowing through the porous foam metal. The relative permeability of three porous foam metals are measured by vibrating sample magnetometer. The effect of the different materials and thickness of porous foam metals on the distribution of magnetic field is studied.3) The mechanism of the rising phenomenon of MR fluid under magnetic field is investigated. The computing model of the rising height of MR fluid is built up. A test rig is developed to evaluate the rising height under the different magnetic field; the experimental results validate the computing model of the rising height. These works provide the theoretic and experimental basis for the damping effect of MRF soaked porous metal foam (also named porous foam metal MRF damping materials).4) A shearing plate-on-plate test-rig is developed so as to investigate the performance of MRF soaked metal foam. The effect, shearing gap, current and different metal foams on the shearing performance, are investigated experimentally. The porous foam metal Cu, which could provide the maximal shear torque, is found out. At the same condition of magnetic field and shear gap, the shearing performance is sensitive to the volume of the propelled MRF.5) The performance of dynamic response of the MRF soaked porous metal foam is investigated. The three time parameters are defined to describe the dynamic response. The effect, shearing gap, current (or magnetic field) and different metal foams on the dynamic response, are investigated experimentally. The computing model on the response time is built up to explain the shear performance and dynamic response. |
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