Effect of Temperature on Magnetorheological Fluid and Its Performance In Magnetorheological Fluid Damper and Magnetorheological Fluid Brake

Abstract

Magnetorheological fluid (MRF) is the dispersion of magnetic particles in a base liquid. They are controllable fluids whose flow properties can be changed by applying an external magnetic field. The design of the MR system and composition of MR fluid significantly impact the performance. Sedimentation stability and high yield stress of an MRF are essential parameters for better damping performance for any practical MR application. Initially, investigations have been carried out on carbonyl iron particles to determine the morphology, particle size, crystal structure, and saturation magnetization for their feasibility of synthesizing magnetorheological fluids in-house. In the first section of the study, the synthesis of various MRFs from commonly used carrier fluids and additives was carried out. The MRF samples were prepared for 25 % volume fractions of carbonyl iron (CI) powder in either silicone oil (350 cSt) or hydraulic oil (50 cSt) and by using lithium or calcium-based additives or a combination of both additives. The sedimentation stability and yield behaviour at different temperatures show a remarkable drop in sedimentation rate and yield stress for all the MR fluid samples. The characterization of the prepared MR fluids reveals that silicone oil fluid samples are more stable and have high yield stress values. One of the samples among the silicone oil based MRF is selected to further characterize its dynamic performance in magnetorheological fluid damper fabricated based on geometric dimensions obtained from the response surface optimization technique. The results indicate a 164.45 % and 135.48 % increase in damping force at higher amplitude and frequencies at 0 A and 1 A currents. Further, similar tests have been carried out by synthesizing one more MRF with silicone oil (50 cSt) + lithium base grease as the additive. The samples stability and yield stress with temperature are carried out, and performance analysis shows a remarkable change in damping force than earlier MRFs in the present study. The dynamic range obtained is practically more viable in 50 cSt silicone oil carrier fluid MRF than 350 cSt and 50 cSt in MRF samples, with less variability. iv The second part of the study aims to evaluate the temperature effect of MR fluid on performance while the damper is working. The range of critical parameters used to fabricate the MR damper is selected using the Technique for Order of Preference by Similarity to Ideal Solution performance score (TOPSIS). The temperature of the MR fluid is measured using an embedded thermocouple while the damper is operating at different loading parameters. The results reveal that the fluid temperature rises significantly from atmospheric to 125.39 °C, decreasing damping force by 66.32 % at higher loading parameters. The theoretical model predicts a temperature increase similar to the experimental values, with an average error of 10.24 % in the on-state condition. Particle characterization after dynamic testing reveals particle morphology has not changed, but the saturation magnetization of the particles reduced by 57 % at higher temperatures (127 °C). It is observed through thermogravimetric analysis (TGA) that the fluid's life is reduced by 0.25 %, which is negligible after dynamic testing of the liquid for approximately 85000 cycles. Finally, to imitate the temperature effect on the particle, particles were heat-treated at 200 °C, 400 °C, and 600 °C. Through scanning electron microscope (SEM) images, it is confirmed that deterioration of the particle starts after 200 °C if the fluid is operated for a prolonged amount of time. Along similar lines, the better MR fluid, which gives good sedimentation and yield stress, is further used to study the torque generation in two-rotor MR brake. The objective of this study is to know the torque generation capacity of the MR brake (Total mass=1.62 kg). The fabrication of MR brake is based on the Finite Element Method Magnetics (FEMM), which shows approximately 0.145 T magnetic flux density in the shearing gap. The MR brake's characterization shows an increase in torque with increased current and speed. Lastly, the tests have been carried out to identify the effect of sedimentation on torque generation at 52 °C after 15 hours of sedimentation. TGA and SEM analysis of the MR fluid and particles shows that 322 °C is the start of destabilization of the fluid, and after complete destabilization, the particle starts to melt at 400 °C, which acts as critical point in controlling the MR fluid system input parameters.