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16 May 2005 A study on MR fluids subjected to high shear rates and high velocities
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This study intends to identify the behavior of MR fluid subject to high rates of shear and high flow velocities. A high shear rheometer is built which allows for the high velocity testing of MR fluids. The rheometer is capable of fluid velocities ranging from 1 m/s to 37 m/s, with corresponding shear rates ranging from 0.14x105 s-1 to 2.5x105 s-1. Fluid behavior is characterized in both the off-state and the on-state. In the off-state, the MR fluid was shown to exhibit nearly Newtonian post-yield behavior. A slight thickening was observed for growing shear rates. This slight thickening can be attributed to the behavior of the carrier fluid. The purpose of the on-state testing was to characterize the MR effect at high flow velocities. MR fluid was run through the rheometer at various flow velocities and a number of magnetic field strengths. The term "dwell time" is introduced and defined as the amount of time the fluid spends in the presence of a magnetic field. Two active valve lengths were considered, which when coupled to the fluid velocities, generated dwell times ranging from 12 ms to 0.18 ms. The yield stress was found from the experimental measurements and the results indicate that the magnitude of the yield stress is sensitive to fluid dwell time. The results from the on-state testing imply that high velocity applications may be subject to diminished controllability for falling dwell times.
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Fernando D. Goncalves and Mehdi Ahmadian "A study on MR fluids subjected to high shear rates and high velocities", Proc. SPIE 5760, Smart Structures and Materials 2005: Damping and Isolation, (16 May 2005);

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