Transient behaviors of a compressed electrorheological (ER) fluid based on zeolite and silicone oil have been experimentally investigated. The ER fluid is purely compressed between two parallel plates. Compressive speed and voltage amplitude effects on the transient process and randomly applied on/off voltages have been studied. Through normalizing compressive stress of the ER fluid, the characteristic compressive strain and the response time constant corresponding to the rise of compressive stress have been fitted with exponential equations. Results show that the rising time of the transient compressive stress is greatly affected by the compressive speed and the compressive strain position applying voltages, while the amplitude of the applied voltage has little effect on the rising time. The obtained transient compressive strain for the compressive stress to rise to its stable value is much smaller than that working in the transient process of ER fluids under shearing. The decay time and decay strain of compressive stress are much less than for stress rising. The half decay compressive strain is as small as 0.0003 in the experiment. Results show that the response time of compressed ER fluids is quick enough for the usual working conditions of squeezing ER dampers.

The transient process of an electrorheological (ER) fluid based on zeolite and silicone oil sheared between two parallel plates to which a square-wave electric field is applied has been experimentally studied. The transient shear stress response to the strain or time is tested. The characteristic constants of time under different applied electric fields and shear rates have been determined. The response time is found to be proportional to shear rate with an exponent of about −0.75 in the tested shear rate range, which agrees with the theoretical predictions made by others. But it only shows a small dependence on the strength of the applied electric field. The results show that the transient process of ER fluids is related to the structure formation in the shearing. When the required shear strain is reached, the shear stress rises to a stable value under constant electric field. Although the electric field strength greatly affects the yield strength, it shows little effect on the stress response time. Also, experiments showed the electric field-induced shear stress decreased with an increase of shear rate.

This paper discusses the effect of the electric double layer on a very thin water lubricating film with and without consideration of the elastic deformation of the opposing surfaces. A modified Reynolds equation that considers the electric double layer is used in a numerical analysis. The effect of zeta potential on the film thickness and pressure is numerically calculated. For both hydrodynamic and elastohydrodynamic cases, the electric double layer significantly increases the lubricating film thickness. The pressure is also marginally increased, as illustrated in the hydrodynamic analysis. However, the effect on pressure is almost unnoticeable in the elastohydrodynamic analysis. Overall, the electric-double-layer effect is only significant for a water-film thickness of less than approximately 100 nanometers

Particulate volume effect on electrorheology of suspensions at three volume fractions based on zeolite and silicone oil with strong electrorheological (ER) effect was determined and discussed. Experiments showed that ER effect was very weak at a low particulate volume fraction, and increased quickly with the increase of the particulate volume fraction. Based on the conduction model, interaction force between particles, particle chains in unit area, saturation of local electric field between particles, and the many body effect, were employed to explain the volume effect. This investigation showed that the ER effect could be effectively improved by increasing the particulate volume fraction.

The atomic force microscope (AFM) has become a main instrument in observing nano/microtribological characteristics of sample surfaces. In this paper, we investigated the micro-scale adhesive contact between the AFM tip and the sample surface based on the Maugis-Dugdale contact model, and analyzed the energy conversion and dissipation process during the AFM scanning process. A dimensionless stick-slip number ŋ=8U1h/(kθR2s) was defined, which can serve as a characteristic index for the appearance of nano/microtribology stick-slip behavior. If the stick-slip number is less than one, i.e., ŋ<1; the AFM tip slides on the sample surface and no stick-slip behavior occurs in the AFM lateral force signal. When the stick-slip number equals one, i.e., 1; the tip jumps on the sample surface and the AFM lateral force signal begins to exhibit a stick-slip behavior but without energy dissipation. Only in the case of ŋ>1 does the stick-slip behavior appear in the AFM lateral force signal accompanied by an obvious energy dissipation. The defined stick-slip number demonstrates that the nano/microtribological stick-slip behavior is due to the adhesive hysteresis as well as the instability motion of the AFM tip during the scanning process. Finally, the influence on nano/microtribology stick-slip behavior of sample surface energy, surface topography, scanning velocity, spring constant of AFM cantilever probe, etc. are investigated theoretically and experimentally. Various experimental results of nano/microtribology stickslip behavior under AFM are successfully interpreted according to the stick-slip number.

In an atomic force microscope (AFM), the cantilever probe, probe tip and sample surface form a micro system in which micro contact, elastic deformation, relative sliding and friction occur during scanning with the contact mode. In this paper, the energy conversion and dissipation during scanning process in the micro system is investigated based on the Mauges-Daules contact model. A dimensionless stick-slip number 221sh=8Uh/(kqR) is defined to describe the micro stick-slip behavior under AFM. Through numerical simulation of the dynamics of the probe tip, it is shown that AFM lateral force is dependent on the defined stick-slip number. If ŋ<1, lateral force is weak and stick-slip phenomenon disappears. When ŋ=1, the probe tip jumps between the asperities on sample surface, showing stick-slip behavior but without energy dissipation. In the case of ŋ>1, the tip moves off the sticking points with an adhesion hysteresis, resulting in an energy dissipation. Therefore, the stick-slip number can serve as a characteristic parameter. Numerical simulation of AFM lateral force with different stick-slip numbers is in agreement with experimental results. Finally a method to extract frictional force from the AFM lateral force signal is proposed.

Stepwise compression of electrorheological (ER) fluids based on zeolite and silicone oil under constant voltages was experimentally investigated. The difference between peak compressive stress and stable compressive stress obtained during the stepwise compression changed with the change of applied voltages and compressive strains. The decay ratio of compressive stress, which may depict the solidification level of ER fluids under external electric fields, decreased with the increase of electric field and compressive strains. Also both the peak compressive stress and the stable compressive stress were shown to be determined by the electric field under low applied voltages. With the increase of the applied voltage, ER fluids were shown to be described by the mechanics of compressing a continuous fluid. At a much stronger ER effect, a deviation from the prediction of the continuous media theory occurred, and structure strengthening of ER fluids by compression should be considered

Electrorheological (ER) fluids are usually described by the continuous theory, Newtonian model and Bingham model. But during recent years, experiments showed that the mechanical properties of ER fluids were much complex than the traditional definitions. Many-body effect, modeling mechanical properties of ER fluids from particle chains or columns, and other problems are thought to be some key issues in ER effect and for ER mechanism.

The tribology behaviors of the brass/silicon dioxide sliding couple under controlled electrode potential were investigated on self-made friction tester. The results showed that the electrode potential of the brass had a dramatic influence on the tribological behaviors of the frictional couple. An interesting phenomenon is that during certain electrode potential range the friction coefficient of the couple was controllable. The SEM morphologies of worn surfaces of the brass also showed different wear mode under different electrode potentials.

A Zeolite-based ER fluid was sheared in a cup-bob unit under stepwise electric field excitation. The shear stress of the ER fluid, electric current and the applied electric potential during the transient phase were recorded simultaneously with a data-acquisition system. The experiment results show that there exists a delay time of approximately 0.3ms in shear stress following the change in electrical potential. The delay time corresponded to the time needed for the charging and the discharging of the ER fluid cell at the moments of field-on and field-off respectively, and was not influenced by the field strength and the shear rate. This result implies that the shear resistance of ER fluid does not change in the polarization and de-polarization processes. With the increase in shear rate, transient periods of stress build up and decay occurred at the switching on and switching off moments following an exponential pattern. The response time of ER fluid is discussed in the context of the designing of ER devices.