Magnetorheological fluids (MRFs) were synthesized to investigate potential enhancements in magnetorheology when replacing magnetic particles with nonmagnetic micro-scale glass beads, that is, to increase yield stress, while reducing density and particle settling rate. Two MRF samples having 40 volume percent (vol%) of particles were synthesized: MRF-40 and MRF-37. MRF-40 had 40 vol% of carbonyl iron (CI) particles, and MRF-37 contained 35.7 vol% of CI particles and 4.3 vol% of glass beads. A comparative study of MRF characteristics was conducted to determine the impact of the nonmagnetic glass beads on yield stress, as well as viscosity, and settling rate. Both MRFs were characterized as follows: 1) magnetorheology as a function of magnetic field, 2) sedimentation rate in a fluid column measured using an inductance-based sensor, and 3) cycling of a small-scale damper undergoing sinusoidal excitations at frequencies of 1 Hz for characterization and 4 Hz for endurance tests. Optical micrographs of the glass beads were taken before and after damper cycling to assess durability. The MRF with glass beads initially doubled the damper yield force (relative to the MRF with no glass beads) at high field strengths in damper tests. This increase in yield force did not persist as the damper was cycled in an endurance test and the glass beads eroded. Fe particle sedimentation rate was reduced by about 4% in the MRF with glass beads.Index Terms-Magnetorheological fluids, nonmagnetic glass beads, yield stress.
Magnetorheological fluid composites were formulated in this study to investigate their performance for potential use in landing gear hydraulic systems, such as shock struts. The magnetorheological fluids synthesized here utilized three hydraulic oils certified for use in landing gear, two average diameters of spherical magnetic particles, and a lecithin surfactant. The magnetorheology of these fluids was characterized, including (a) magnetorheology (yield stress and viscosity) as a function of magnetic field, (b) sedimentation analysis using an inductance-based sensor, (c) cycling of a small-scale magnetorheological damper undergoing sinusoidal excitations at frequencies of 2.5 and 5 Hz, and (d) impact testing of an magnetorheological damper for a range of magnetic field strengths and velocities using a free-flight drop tower facility. The goal of this research is to analyze the performance of these magnetorheological fluid composites, compare their behavior to standard commercial magnetorheological fluid, and determine their feasibility for use in helicopter landing gear.
Adaptive landing gear dampers that can continuously adjust their stroking load in response to various operating conditions have been investigated for improving the landing performance of a lightweight helicopter. In prior work, adaptive magnetorheological (MR) landing gear dampers that maintained a constant peak stroking force of 4000 lb f across sink rates ranging from 6 to 12 ft s −1 were designed, fabricated and successfully tested. In this follow-on effort, it is desired to expand the high end of the sink rate range to hold the peak stroking load constant for sink rates ranging from 6 to 26 ft s −1 , thus extending the high end of the speed range from 12 (in the first study) to 26 ft s −1 . To achieve this increase, a spring-based relief valve MR landing gear damper was developed. In order to better understand the MR landing gear damper behavior, a modified nonlinear Bingham Plastic model was formulated, and it incorporates Darcy friction, viscous forces across the MR and relief valves to better account for the damper force behavior at higher speeds. In addition, gas pressure inside the MR damper piston is considered so the total damper force includes a gas force. The MR landing gear damper performance is characterized using drop tests, and the experiments are used to validate model predictions data at low and high nominal impact speeds up to 26 ft s −1 (shaft velocity of 9.6 ft s −1 ).
Articles you may be interested inRheological characterization of a magnetorheological ferrofluid using iron nitride nanoparticles Magnetorheological behavior of magnetite covered clay particles in aqueous suspensions J. Appl. Phys. 112, 043917 (2012); 10.1063/1.4748878Magnetorheology and sedimentation behavior of an aqueous suspension of surface modified carbonyl iron particles Magnetorheological (MR) fluids are suspensions of micron-scale magnetizable particles suspended in a carrier fluid. When field is applied, MR fluids develop a field controllable yield stress and a field independent post-yield viscosity. However, this viscosity has substantial temperature dependence, varying by up to an order of magnitude over the operating temperature range of MR fluid devices. We apply non-Brownian suspension theory to explain this result and find that the majority of this effect should be caused by the temperature dependent behavior of the carrier fluid. Thus, if two fluids share the same carrier fluid, then their fluid properties should scale in temperature similarly. This result is first validated by measuring viscosity across temperature for custom model fluids designed to conform to theory, showing temperature scaling within 5% for both the MR fluids and their carrier fluid. Then, on a series of related commercially available fluids with unknown additive content, we show that the MR fluids exhibit common scaling to within 4%. We also investigate the effects of magnetic hysteresis and find that it induces a negligible increase in yield stress and no measurable change in viscosity. We conclude that our non-dimensional analysis enables the temperature dependence of novel MR fluids to be characterized with fewer experiments. V C 2015 AIP Publishing LLC. [http://dx.
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