Design, development and analysis of a magnetorheological damper

Magnetorheological Dampers or MR Dampers are advanced shock absorbers known for their fast response rate, wide dynamic range, mechanical simplicity and low power requirement. MR dampers use smart fluids called MR Fluids which can change dynamic yield stress when acted upon by a magnetic field. The damping force is changed by varying the rheological properties of the fluid magnetically. MR dampers are usually used in high-end automobiles. In this paper, an attempt has been made to make an alternative damper to the existing high-priced MR dampers which can be used in the mid-segment vehicles of today. A new design is proposed by the authors which incorporate the flow of the MR fluid through a hollow passage and focuses on making use of the strong magnetic field created at its center. Silicone oil as a carrier fluid, Carbonyl Iron power and White lithium grease as an additive are selected after studying fluid components. Before fabrication of the new design, numerical calculations are made to evaluate the strength of the magnetic field that is needed to provide suitable yield stress. A permeability around 3000 NA⁻² is expected. This is estimated from the B-H curve for a commercial MR fluid called MRF - 32D. It is noted that a 43 SWG is the most suitable for the damper and with 4 - 5 windings, a maximum induced field of 1.2T (theoretically) can be produced at the center of the primary fluid column. This fluid column exists to a length of 80 mm while the coiling spanned up to 65 mm of the column. It is also concluded that these design parameters will be sufficient to create a strong magnetic field which can exert enough yield stress to give the desired results needed for damping.