Shear Stress Of Electrorheological Fluids Research Articles

Research on shear stress of electrorheological fluid containing piezoelectric powders

This paper describes experimental trials that were performed to increase the electrorheological (ER) effect in ER fluids (ERFs) by introducing piezoelectric particles (PEPs). Five sample solutions were made using different PEPs, ER powders, and liquids that included ERFs provided with different solutions and silicone oil. The shear stress of each sample was measured by shearing the sample between parallel plate electrodes. Samples containing the PEP showed the same shear stress under steady voltage inputs but showed somewhat higher shear stress under sinusoidal voltage inputs. This suggests that mixtures of the piezoelectric powders (at approximately 5 wt.%) and the ERF may shorten the response time of the ERF to DC inputs or increase the response frequency to AC inputs.

The influence of alternating current and direct current electric fields on the rheological behavior of electrorheological fluids with particles of the different crystalline structure

The rheological behavior of electrorheological fluids with dispersed fillers whose particles have different crystalline structures is investigated in direct and alternating electric fields. The dielectric characteristics of the materials were measured and the influence of the strength, frequency, and shape of the signal of electric field was investigated, and the influence of temperature on the shear stress in electrorheological fluids was estimated in direct current electric field.

Features of the Mechanisms of Conductivity of the Electrorheological Fluids With Double Doped TiO2 Particles Under External Temperature Effects

Electrophysical and rheological characteristics of ER fluids with TiO2 particles doped with alumi-num and phosphorus and having anatase structure are considered in an extended temperature range (5 - 100 ° C). The mechanisms of leakage currents in the ER fluid in electric fields up to 3.5 kV/mm are determined. Conduction mechanisms such as thermionic ionization, electron injection from an electrode, thermal excitation of charges, field emission of electrons from an electrode, thermionic emission of electrons from an electrode, and field emission of electrons from traps are identified. Based on the analysis of the current-voltage characteristics of the ER fluid, the positive role of the additional doping of the dispersed phase particles with phosphorus compared with the known results for ER fluid with TiO2/Al particles was established. The use of double doping of particles of the dispersed phase made it possible to obtain stable dependences of the shear stress of electrorheological fluids on the electric field strength in the range of the temperature effects under study.

Influence of particle size on shear behavior of amine-group-immobilized polyacrylonitrile dispersed suspension under electric field

Different-sized particles dispersed electrorheological (ER) fluids were fabricated with poly(acryloamidino diethylenediamine) to observe the influence of the particle size on ER behaviors. The fine particles dispersed ER suspension showed stable shear stress under a DC electric field. On the other hand, the rough particles dispersed suspension showed trembling shear stress which is divided into four regions in a plot of shear stress against shear rate. Our suggested spring–damper model equation treated the wide range of shear rate and specific (trembling) behaviors of shear stress in ER fluids. In this study, we successfully obtained various ER fluids showing different behaviors just by changing the size of particles in the ER fluids. All of the curves of the shear stress plotted against shear rate were fitted well by our spring–damper model.

Trembling Shear Behavior of a Modified‐Chitosan Dispersed Suspension under an Electric Field and its Model Study

AbstractAn electro‐rheological (ER) fluid showing trembling shear behavior was fabricated with chitosan particles that had benzene, amine and azo‐pendent side groups. This modified‐chitosan dispersed suspension showed four regions in a plot of shear stress against shear rate at high electric field. We analyzed this specific behavior with our suggested model. The model was developed with the spring‐damper model. Our suggested model equation treated the wide range of shear rate and specific behaviors of shear stress in ER fluids. In this study, we successfully obtained various ER fluids showing different behaviors just by changing the side functional groups of the particles in the ER fluids. All of the curves of the shear stress plotted against shear rate were fitted well by our spring‐damper model.magnified image

A new approach of enhancing the shear stress of electrorheological fluids of montmorillonite nanocomposite by emulsion intercalation of poly- N-methaniline

Poly- N-methaniline/montmorillonite (PNMA–MMT) nanocomposite particles with high dielectric constant as well as suitable conductivity were synthesized by an emulsion intercalation method and characterized by FT-IR, XRD, and TEM spectrometry, respectively. The electrorheological (ER) properties of the suspensions of PNMA–MMT particles in silicone oil (20 wt%) were investigated under DC electric fields. It was found that the shear stress of poly- N-methaniline/montmorillonite electrorheological fluid (ERF) is 6.0 kPa in 3 kV/mm (74.5 s −1), which is 3.6 times that of electrorheological fluid at zero field, and also much higher than that of pure poly- N-methaniline (PNMA) and montmorillonite (MMT). In the range of 10–90 °C, the shear stress changes slightly with the temperature. The sedimentation ratio of PNMA–MMT ERF was about 97% after 60 days. Furthermore, the dielectric constant of PNMA–MMT nanocomposite was increased 3.74 times that of PNMA and 1.99 times that of MMT at 1000 Hz, the dielectric loss tangent also increased about 1.58 times that of PNMA. It is apparent that the notable ER effect of PNMA–MMT ER fluid was attributed to the prominent dielectric property of the poly- N-methaniline/montmorillonite nanocomposite particles.

STRUCTURE-ENHANCED YIELD SHEAR STRESS IN ELECTRORHEOLOGICAL FLUIDS

A new technology, compression-assisted aggregation, is developed to enhance the strength of electrorheological (ER) fluids. The yield shear stress of ER fluids depends on the fluid microstructure. The unassisted electric-field induced ER structure mainly consists of single chains, whose weak points are at their ends. This new technology produces a structure consisting of robust thick columns with strong ends. As the weak points of the original ER structure are greatly enforced, the new structure makes ER fluids super-strong: At a moderate electric field and moderate pressure the yield shear stress of ER fluids at 35% volume fraction exceeds 100 kPa, well above any requirement for major industrial applications.

Temperature dependence of particle–particle interactions in electrorheological fluids

We report on the temperature dependence of particle–particle interactions in electrorheological (ER) fluids for the temperature range 20–100 °C. The attraction force between polyamide spheres immersed in silicone oil is measured as a function of temperature. The force–temperature characteristic shows a broad maximum around 40 °C, corresponding to an increase of about 30% compared to the force measured at room temperature. In view of these results we proposed that the temperature dependence of the shear stress in ER fluids is directly related to the variation of the local particle–particle attraction forces. Data are discussed in light of models which were proposed in the literature to describe particle–particle interactions. At high electric fields “conduction models” could explain the observed temperature dependence through the variations of the oil breakdown field with temperature. However, limitations of such models are also clearly evidenced by data obtained at low electric fields.

Computer Simulation of Electrorheological Fluids in the Binary System of Particle Size

One of the typical electrorheological (ER) fluids consists of suspension of fine particles in the liquid of low dielectric constant. Particles for ER fluids generally have a size distribution, and some experimental results were reported which showed the effect of particle size on the shear stress of ER fluids. On the other hand, the simulation by dielectric polarization model concluded that the shear stress calculated did not depend on the particle size under the same volume fraction of particles. In order to understand the effect of particle size, the two dimensional computer simulation was carried out for a system containing particles of different size, by using a model similar to that reported by Klingenberg et al. It was found that the shear stress of uniform size system did not depend on the particle size. When small and large particles, with the diameter ratio of 1:2, were mixed in equal numbers of particles, the chain-like clusters consisiting of both sizes of particles were formed. The shear stress and the response time of the binary size system were close to those of uniform size system, if the total volume fraction of particles was kept constant.

The conductivity dependence of the shear stress in electrorheological fluids

A ferroelectric KNO3/silicone oil electrorheological (ER) fluid is introduced to investigate the conductivity dependence of the ER effect under dc electric fields where the ER effect is conductivity dominated. By measuring the temperature dependence of the shear stress across the Curie temperature of particles, the dependence of the ER effect on conductivity has been quantitatively obtained in experiments. There is a critical conductivity ratio Γc (or mismatch factor βc2): when Γ<Γc, the shear stress increases with Γ; when Γ>Γc, the shear stress decreases with Γ. An agreement is obtained between theory and experiment when Γ (or β2) is lower. In the higher Γ(or β2) range, the experimental data are not in agreement with the theoretical prediction and the interfacial effect should be taken into account. The experimental data are more reliable due to the same conditions, such as the chemical nature, the surfacial property of particles, and the interfacial property between particles and suspending liquid as well as the size and shape of the particles.

The dependence of particle permittivity on the shear stress of electrorheological fluids

A ferroelectric TGS particle/silicone oil electrorheological (ER) fluid is introduced to investigate the dielectric dependence of the ER effect. The dielectric constant of ferroelectric changes violently with temperature at the Curie temperature (Tc). By measuring temperature dependence of shear stress across Tc, the effect of dielectric constant on shear stress can be directly obtained. All the results are more reliable due to the same conditions, such as size, shape, composition of particles, as well as the same chemical nature of particles and interface property between particles and liquid. The measurement was carried out under a high-frequency (1000 Hz) ac electric field where ER effect is dielectric constant dominated. For the first time, the dependence of the ER effect on dielectric mismatch has been quantitatively obtained experimentally. There is an obvious deviation of available theoretical calculations from our measured data. A more rigorous theoretical study should be developed to quantitatively interpret the relation of the shear stress and the permittivity mismatch factor.

Static shear stress of electrorheological fluids.

We have calculated the static shear stress of an induced electrorheological solid for a single-chain structure, double-chain structure, triple-chain structure, and body-centered tetragonal (bct) lattice. When the shear strain is small, all of these four structures prefer slanted configurations which will come back to the original configurations if the load is removed. As the shear strain exceeds a yield point, the structures break into parts which cannot return to the original configurations in a short time. The bct lattice is found to have the strongest shear modulus. The triple-chain structure is weaker than the bct lattice, but much stronger than the single-chain structure and double-chain structure. The single-chain structure has the Peierls-Landau instability if the chain is very long. A double chain is stronger than a single chain if the chains are quite long and the situation is reversed if the chains are short.

Shear stress and aggregation kinetics of electrorheological fluids under alternating electric fields

The effect of periodic ac and pulse electric fields on the shear stress of an electrorheological fluid is investigated by computer simulations. It is observed that as the frequency of the applied field (ω) is increased under a constant rate of shear (γ), the shear stress passes through a minimum. It is found that there is a distinct difference in the aggregation processes due to the induced electric dipoles at frequencies above and below this critical frequency; for low frequencies the clustering follows the electric field variation, while at high frequencies the clusters are unable to completely break up. These considerations of the clustering process lead us to propose a scaling law for the shear stress: σxy=σxy(ω/γ). This result agrees with experiments and with computer simulations.The effect of periodic ac and pulse electric fields on the shear stress of an electrorheological fluid is investigated by computer simulations. It is observed that as the frequency of the applied field (ω) is increased under a constant rate of shear (γ), the shear stress passes through a minimum. It is found that there is a distinct difference in the aggregation processes due to the induced electric dipoles at frequencies above and below this critical frequency; for low frequencies the clustering follows the electric field variation, while at high frequencies the clusters are unable to completely break up. These considerations of the clustering process lead us to propose a scaling law for the shear stress: σxy=σxy(ω/γ). This result agrees with experiments and with computer simulations.

Shear Stress and Aggregation Kinetics of Electrorheological Fluids under Alternating Electric Fields

The effect of periodic ac and pulse electric fields on the shear stress of an electrorheological fluid is investigated by computer simulations. It is observed that as the frequency of the applied field (ω) is increased under a constant rate of shear (γ), the shear stress passes through a minimum. It is found that there is a distinct difference in the aggregation processes due to the induced electric dipoles at frequencies above and below this critical frequency; for low frequencies the clustering follows the electric field variation, while at high frequencies the clusters are unable to completely break up. These considerations of the clustering process lead us to propose a scaling law for the shear stress: σxy=σxy(ω/γ). This result agrees with experiments and with computer simulations.The effect of periodic ac and pulse electric fields on the shear stress of an electrorheological fluid is investigated by computer simulations. It is observed that as the frequency of the applied field (ω) is increased under a constant rate of shear (γ), the shear stress passes through a minimum. It is found that there is a distinct difference in the aggregation processes due to the induced electric dipoles at frequencies above and below this critical frequency; for low frequencies the clustering follows the electric field variation, while at high frequencies the clusters are unable to completely break up. These considerations of the clustering process lead us to propose a scaling law for the shear stress: σxy=σxy(ω/γ). This result agrees with experiments and with computer simulations.