Repulsive normal force by an excited magneto-rheological fluid bounded by parallel plates in stationary or rotating shear mode

This article reports results from an experimental study undertaken to determine the magnitude of the repulsive force exerted by a magnetorheological fluid on two bounding parallel and concentric plates under different magnetic field strengths. The plates are stationary without circumferential external loading or in a forced rotational rate for a constant inter plate gap separation. The results show that with stationary plates, the repulsive force increases with the magnitude of the excitation. Upon the addition of a steady-relative rotational speed, the force increases further. The increase in the shear-enhanced repulsive force rose up to a peak and then decreased as the test running, i.e., further increase in the shear strain. The force eventually settled at a steady value which was higher than that due to magnetic field only (no rotation). The main characteristics of the repulsive force against the strain curve are well described by a mathematical model which is derived on the basis of the particle chain tilt phenomenon. The critical twist angles of the plate in the current experimental set up under different magnetic flux densities, which give the maximum repulsive forces, were found to approach a constant value as predicted by the tilt particle chain model. © 2011 The Author(s).