A study on Sedimentation Issue in Magnetorheological Fluids

Abstract

The purpose of this dissertation is to investigate the sedimentation problem in magnetorheological fluids (MRFs). MRFs are the class of smart materials since some of the physical properties can be changed with the application of an external magnetic field. In particular, the shear stress and viscosity characteristics which can modify by varying the intensity of the magnetic field can be varied. The main property of MRFs is the capability of changing their rheological behavior within milliseconds and reversibly with off-state and on-state magnetic field conditions. At present, MRFs are very attractive for a large number of applications such as vibration-dampers, clutches, brakes up to the recent biomedical applications and virtual reality devices. MRFs typically consist of 1-10 m micron-sized magnetic particles dispersed in a carrier liquid. Sedimentation stability is the main problem that restricts the application of MRFs, and the main factors affecting the stability are high-density magnetic particles, volume fraction, and type of carrier liquids. Therefore, studying the preparation and performance of the MRFs is crucial to use MRFs extensively for various applications. To minimize the settling of magnetic particles used in MRFs various new types of additives, surface modifiers, different carrier fluid with varying viscosity, ferrite particles, and changing the particle volume fraction are used to address the sedimentation issue in the present work. First, the effects of three different clay additives are added in carbonyl iron particles along with poly-alpha-olefin oil for sedimentation effect in MRFs are investigated. Experimental investigations have been carried for sedimentation testing for MRFs which contain with and without additives to know the damping force of fabricated mono-tube magnetorheological (MR) damper. Further, the effect of different surface area fumed silica additive added in silicone oil to minimize the settling of carbonyl iron particles in MRFs. The carrier fluid with varying viscosity plays a major role in the stability of MRFs, so the MRFs were prepared with three different carrier fluids with varying viscosity. The ferrite particles based MRFs are stable against settling than the CIPs based MRFs due to the density of the particles used is very less. The rheological properties of the MRFs, including field-dependent yield-stress, were measured at off-state and magnetic fields applied using a parallel plate design magnetorheometer. Hence, in this present work minimize the sedimentation of the particles in MRFs with slight variation in the rheology properties have been formulated in lab-scale at cost-effective than the commercial available MRFs.