This paper reports measurement results of ultrasonic propagation velocity in MR fluid under compression. Experiments were conducted by applying different pressures in MR fluid at constant magnetic flux density. At low magnetic flux densities (100 and 200 mT), the ultrasonic propagation velocity in MR fluids changes when subjected to pressure. This change is related to cluster formation in MR fluid. The ultrasonic propagation velocity change is smaller when higher pressures are applied, indicating that cluster size in MR fluid becomes thinner under higher pressures. However, at higher magnetic flux densities (300 and 400 mT), ultrasonic propagation velocities under different pressures are nearly similar. These results indicate that at higher magnetic flux densities, pressures do not affect cluster formation in MR fluids.

We carried out an impact experiment in order to investigate the influence of magnetic field intensity and inner diameter of the orifice on MR fluid motion under an impact load. The experiment was conducted by measuring the piston displacement. From the piston displacement, its velocity and acceleration were calculated.

An experimental study in ultrasonic propagation characteristics of a magnetic fluid under AC magnetic fields was conducted. Sound velocities in a magnetic fluid increased with elapsed time of the AC magnetic fields. Moreover, rapid decreases in sound velocities in a magnetic fluid were observed when the AC magnetic fields were stopped. These results were similar to those for DC magnetic fields. Dependence of frequencies and magnitudes of AC magnetic fields on sound velocities in a magnetic fluid was observed. Moreover, anisotropy was found in each frequency of the AC magnetic fields.

This study is an investigation on the effect of a chamfered orifice inlet on magnetorheological (MR) fluid subjected to shock loading. Three different orifices (without chamfer, chamfered at 60°, and chamfered at 120° on the inlet area) are used. MR fluid is subjected to shock loading, and a magnetic field is generated on the orifice area. Experiments are conducted by measuring piston displacement and damping force. Piston velocity is calculated from the piston displacement data. The results indicate that a chamfered orifice inlet affects the piston stroke, piston velocity, and damping force. The characteristics of piston velocity between the orifice without chamfer and the chamfered orifices are different. The post-peak decrease in piston velocity in the chamfered orifices is more refined than that in the orifice without chamfer. However, the chamfered shape in the orifice inlet reduces the shock loading performance of MR fluid.

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