31 July 2003 Impact of varying concentrations of nanometer-sized particles in a bidisperse magnetorheological fluid
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Conventional magnetorheological fluids are suspensions of micron sized particles in a hydraulic or silicone oil medium. Recently, research has been conducted into the advantages of using bidisperse fluids, which is a mixture of two different powder sizes in the MR suspension. The MR fluids investigated here use a mixture of conventional micron sized particles and nanometer sized particles. The settling rate of such bidisperse fluids using nanometer sizes particles is reduced because of thermal convection and Van der Waals experienced by the nanometer sized particles compete favorably with gravitational forces. This reduction in the settling rate comes at a cost of a reduction in the maximum yield stress that can be manisfested by such an MR fluid. There is a measurable and predictable variation in rheological properties as the weight percent of the nanometer sized particles is increased, relative to the weight percent of micron sized particles, while maintaining the solids loading in the MR fluid as a constant. In this context, this study investigates the effect of varying the weight percent of nanometer sized particles on rheological characteristics such as yield stress and postyield viscosity. The goal of this study is to find an optimal composition of the bidisperse fluid to obtain best combination of high yield stress and low settling rates based on empirical measurements. The applicability of rheological models, such as the Bingham-plastic and the Hershel Buckley models, to the measured flow curves of these MR fluids is also presented.
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Julian Trihan, Jin-Hyeong Yoo, Norman M. Wereley, S. Kotha, A. Suggs, Radhakumar Radhakrishnan, T. Sudarshan, B. J. Love, "Impact of varying concentrations of nanometer-sized particles in a bidisperse magnetorheological fluid", Proc. SPIE 5052, Smart Structures and Materials 2003: Damping and Isolation, (31 July 2003); doi: 10.1117/12.483987; https://doi.org/10.1117/12.483987

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