An effective damper is required to give good performance over a wide range of vibrational frequencies. To achieve this, the damping coefficient of the damper must be variable. The Magneto-Rheological (MR) fluids are the fluids used in this type of dampers to achieve the objective. In this paper, a mathematical design of the MR damper is presented. For this, the magnetic circuit of the MR damper is designed and analyzed, which subsequently determines the damping force at different magnetic fields applied to it. The magnetic field can be controlled by the current input given to the electromagnet. A Finite Element Analysis (FEA) on ANSYS platform is carried out to obtain magnetic flux density in the working space of the damper. The damping force of the FEM model is determined for the damper. Lastly, these two models are validated experimentally in terms of damping force at various input current levels. For this purpose, a prototype of the MR damper is fabricated and tested in the newly setup vibration control laboratory of the department. A comparative analysis of the three models shows that the maximum percentage error in the damping force is within the 12% level with the experimental one and thus validates the mathematical and FEM modeling. The results obtained will be helpful for the automobile designers to create more efficient and reliable MR dampers and also to predict its damping force characteristics.

Smart materials have the ability to change their shape/size/state simply by adding a little heat or under some field. Magneto-Rheological (MR) fluids are one such smart material that changes from liquid to solid state almost instantly and reversibly when placed near a magnet. These fluids exhibit drastic and reversible changes in their rheological properties (elasticity, plasticity, viscosity, etc.) which mainly depend on the intensity of the magnetic field induced around it (Kumar and Mangal, 2012). The discovery of the MR fluids is credited to Jacob Rabinow, US National Bureau of Standard in 1948 (Rainbow, 1948). A typical MR damper (Figure 1) consists of cylinder, piston, electromagnetic coil and MR fluid which are enveloped by a cylinder. The piston of the MR damper behaves as an electromagnet. The yield shear stress of the MR fluid varies with the magnetic field intensity induced by the electromagnet. This intensity is controllable by the input current supplied to the electromagnet. Under a given magnetic field, the ferro-particles of the MR fluid align along the magnetic flux line in the working clearance of the damper, which in turn makes the fluid more viscous. The number of alignments of the particles, i.e., density of the alignments, is reversible and varies with the magnetic flux intensity, thus producing a variable and controllable damping force in the damper. It will, thus, make the vibration isolation more effective in a wide spectrum of frequencies, which is very much needed for automotive and civil applications.

Mechanical Engineering Journal, Magnetc circuit, MR damper, Damping force, FEM, Design.