This research details a novel method of increasing the shear yield stress of magnetorheological (MR) fluids by combining shear and squeeze modes of operation to manipulate particle chain structures, to achieve so-called compression-assisted aggregation. The contribution of both active gap separation and particle concentration are experimentally measured using a custom-built Searle cell magnetorheometer, which is a model device emulating a rotary Magnetorheological Energy Absorber (MREA). Characterization data from large (1 mm) and small (250 μm) gap geometries are compared to investigate the effect of the gap on yield stress by compression enhancement. Two MR fluids having different particle concentrations (32 vol% and 40 vol%) are also characterized to demonstrate the effect of solids loading on compression-assisted chain aggregation. Details of the experimental setup and method are presented, and a chain microstructure model is used to explain experimental trends. The torque resisted by practical rotary MREAs is directly related to the strength of the MR fluid used, as measured by the shear yield stress. This study demonstrates that it is feasible, utilizing the compression-enhanced shear yield stress, to either (1) design a rotary MREA of a given volume to achieve higher energy absorption density (energy absorbed normalize by device volume), or (2) reduce the volume of a given rotary MREA to achieve the same energy absorption density.
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Demonstration of Combined Shear and Squeeze Strengthening Modes in a Searle-Type Magnetorheometer
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Becnel, AC, & Wereley, NM. "Demonstration of Combined Shear and Squeeze Strengthening Modes in a Searle-Type Magnetorheometer." Proceedings of the ASME 2013 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. Volume 1: Development and Characterization of Multifunctional Materials; Modeling, Simulation and Control of Adaptive Systems; Integrated System Design and Implementation. Snowbird, Utah, USA. September 16–18, 2013. V001T03A036. ASME. https://doi.org/10.1115/SMASIS2013-3244
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