Qifan Yan

Squeeze behavior of magnetorheological fluids under constant volume and uniform magnetic field

In this work the experimental investigation of magnetorheological fluids in squeeze mode has been carried out under constant volume with a self-developed device. The magnetorheological fluids were forced to move in all directions in a horizontal plane as the two flat surfaces came together. A pair of Helmholtz coils was used to generate a uniform magnetic field in the compression gap. The normal forces within the gap were systematically studied for different magnetic field, squeeze velocity, particle concentration, viscosity of carrier fluid and initial gap distance. Two regions of behavior were obtained from the normal force versus gap distance curve: elastic deformation and plastic flow. A power law fitting was appropriate for the relation between the normal force and the gap in the plastic flow. The index of the power law was smaller than that predicted by the continuum theory, possibly due to the squeeze strengthening effect and the sealing effect. (Some figures may appear in colour only in the online journal)

Compression behaviors of magnetorheological fluids under nonuniform magnetic field

This work is concerned with an experimental and theoretical study on compression properties of magnetorheological fluids under the nonuniform field. Experimental tests of unidirectional monotonic compression were firstly carried out under constant area operation using a commercial plate–plate magneto-rheometer where the magnetic field radial distribution was nonuniform. Normal forces increased with decreasing of the gap distance, and two regions were found through the normal force versus gap distance curves: elastic deformation and plastic flow. High normal forces could be obtained in the case of high magnetic field, high compression velocity, low initial gap distance, high volume fraction, and high medium viscosity. In the plastic flow region, the normal force with the gap distance could be fitted with a power law relation

Magnetorheological Damper Working in Squeeze Mode

F_{\textrm {N}} \propto h^n

The rheological responds of the superparamagnetic fluid based on Fe3O4 hollow nanospheres

, and the index n was around well in the range (−3, −2). Taking nonuniform magnetic field into account, the theoretical modeling in the plastic flow was then developed to calculate the normal force under compression based on the continuum media theory. Compared to the uniform field, there existed a magnetic field gradient-induced normal force under nonuniform field. Considering the sealing and squeeze strengthening effect, the gap distance-dependent shear yield stress was proposed, and a good correspondence between the theoretical and experimental results was obtained.

Magnetically controllable generation of ferrofluid droplets

This research is focused on evaluation of the magnetorheological fluids (MRFs) based damper which works in squeeze mode. The operation direction of this damper is parallel to the direction of the external magnetic field. Before testing, commercial software ANSYS was used to analyze the magnetic field distribution inside the damper generated by charging current in the coil. The performance of the damper was tested by using the MTS809 (produced by MTS Systems Corporation, USA). For simulation of this damper, a mathematical model was set up. Experimental results showed that the small squeezed MR damper could produce large damping force; for example, the maximum damping force is nearly 6 kN, while the amplitude is 1.2 mm, the frequency is 1.0 Hz, and the current is 2.0 A, and the damping force was controllable by changing the current in the coil. The damping force versus displacement curves are complex. We divide them into four regions for simulation. The maximum damper force increased quickly with the increasing of the current in coil. This kind of damper can be used in vibration isolation for precise equipment.