A Study On Electrorheological(ER) Fluid Materials And Vibration Control

The research in smart materials and structure systems has been an active research area in recent years. As a typical smart material, the rheological properties of electro-rheological (ER) fluid such as viscosity, shear modulus as well as yield stress are reversibly changed by applying to electric field to the fluid domain. Since its mechanical properties can be easily controlled and tuned and transmitted within a wide range, the ER fluid could be used as an electric and mechanical interface in various industrial areas. For example, it could be used in the automotive industry for clutch, brake, and damper. It could also be used in the robot. The salient properties of the ER fluid itself are that it has a very fast response to electric field, a low power consuming and an easy access to control. These inherent characteristics encourage it's applications in semi-active suspension systems in vehicle and in construction vibration control. However, the ER fluid has also some problems such as a limited shear yield stress under electric field, dispersion and temperature stability, at the same time, it is difficulty to obtain a stable chain under a high shear rate, and this in turn results that the damping force of ER shock absorber varies in a narrow range and could not work in a high velocity. Therefore, the researching ER fluids with excellent properties and manufacturing a good ER shock absorber have also many difficulties. The main work and result of this dissertation including the following aspects: â‘ Although TiO₂ has a high dielectric constant, but as an anhydrous ER fluid, it's ER activity is rather weak. In this dissertation, a method is presented to improve the ER activity of TiO₂ by doping with cerium and yttrium ions so that its internal structure or microstructure is modified and an optimal dielectric and conduction properties are obtained. The experiments show that doping of Ce, Y into TiO₂ is found to greatly improve the ER activity due to lattice distortion and defects in crystal TiO₂ originated from doping of Ce, Y. â‘¡The ER particular materials of TiO₂ doping with cerium and yttrium ions were obtained by means of Sol-gel technique. The experiments show that the ER activities of TiO2 doping with cerium and yttrium ions are affected greatly by their fabrication conditions due to the change in phase components, uniformity, particle size and dielectric properties. It is very importment to control the fabrication conditions in order to obtain a good ER activity. â‘¢The ER particular materials were characterized by means of scanning electron microscopy(SEM), X-ray diffraction(XRD) and FT-IR. The experiments found that the micrographs of particles has polygon feature. The particle size is about 30～50μm. The heat decomposition process of xerogel powder is divided into three stages: the first stage(below 200℃) is assigned the desorption and decomposition of water and organic agent in xerogel powder, the second stage (200℃～400℃) is assigned to the breaking, decomposition and combustion of organism, the third stage(above 400℃) is assigned to the crystallization of amorphous TiO2 continuously. No crystallization temperature is observed. Cerium and yttrium accelerate the crystallization process, but they obstract the crystallization transformation of anatase to rutile. The effect of yttrium is more obvious than that of cerium. â‘£The dielectric properties of TiO2 doping with cerium and yttrium ions such as dielectric constant, conductivity and dielectric loss are studied. The experiments found that the doping leads to a large increase in dielectric constant, conductivity and dielectric loss. Dielectric loss tangent is increased from 0.05 to 0.565, conductivity from 3×10-9S/m to 8.25×10-7 S/m, dielectric constant in low frequency from 90.5 to 273, which are responsible for the improvement of their ER activity. â‘¥The rheological equations based on the plate and axisymmetrical model are derived from N-S equation in hydromechanics by applying the Newton fluid and Bingham plastic model. The design parameters are determined by means of the plate model. A ER shock absorber is designed and it's characteristics in different velocities are calculated and simulated. ⑦The ER shock absorber for mini-bus is manufactured, it's characteristics such as the damping force vs. displacement and the damping force vs. velocity is tested. The experiments show that the damping force can be controlled continuously by applying different electric field. ⑧The error between the damping force calculated and measured is analyzed. Modification constants for the plate model are presented. The damping force calculated is in agreement with the damping force measured when the model is modified. ⑧The dynamics model for vibration in vehicle and road model are built. LQG optimal control, sliding mode control and fuzzy logic control for semi-active suspension systems with ER shock absorber are studied. The numerical simulations are implemented. The results show that the optimal control demonstrated a good control effect and made a good tradeoff among performances in suspension system whenparameter variation in dynamic model and possibility in system implementation are not considered. The sliding mode control has also a good control effect, but it's possibility in system implementation is higher than the optimal control. Otherwise, it has also a good robustness to model parameter variation. Although the fuzzy control is not as well as LQG optimal control and sliding mode control, its possibility in system implementation is enhanced.