Rheometer

About: Rheometer is a research topic. Over the lifetime, 5759 publications have been published within this topic receiving 125849 citations.

The Measurement of Wall Shear Stress

Abstract: Knowledge of the wall shear stress is of both fundamental and practical importance The mean stress is indicative of the overall state of the flow over a given surface while the fluctuating stress is a “footprint” of the individual processes that transfer momentum to the wall The measurement techniques can be divided into two main categories: direct and indirect The indirect techniques can be further divided into momentum balance methods and correlation methods

Rheology of Sulfonated Polystyrene Solutions

Abstract: We report the apparent viscosity of aqueous solutions of a well-characterized synthetic polyelectrolyte, the sodium salt of polystyrene sulfonate. Using two rheometers we measure the apparent viscosity over more than five decades of shear rate to determine the Newtonian viscosity and the onset of shear thinning, which is inversely proportional to the relaxation time. We study five decades of polyelectrolyte concentration, from the dilute to the entangled regimes, and three decades of added salt (NaCl) concentration, on a single polyelectrolyte sample. Much of the viscosity data in the literature are shown to be in the shear thinning regime and are not indicative of the Newtonian viscosity. Our data for viscosity and longest relaxation time are qualitatively consistent with a recent scaling theory. There are systematic deviations from this simple theory, including the failure of the well-established Fuoss law, which is shown to be obeyed by the apparent viscosity only at higher shear rates.

Analysis and testing of Bingham plastic behavior in semi-active electrorheological fluid dampers

Abstract: Electrorheological- (ER-) fluid-based dashpot dampers have smart capabilities because ER fluids undergo large changes in yield stress as electric field is applied. Our objective is the development and experimental validation of quasi-steady dashpot damper models, based on an idealized nonlinear Bingham plastic shear flow mechanism, for purposes of preliminary design and performance predictions. The data required for the Bingham plastic model is normally supplied by ER fluid suppliers, that is, plastic viscosity and dynamic yield stress as a function of applied field, as determined from a shear stress versus shear strain rate diagram. As force is applied to the dashpot damper, the ER fluid flows through an annulus between the concentric inner and outer electrodes. The idealized Bingham plastic shear flow mechanism predicts that three annular flow regions develop as a function of the local shear stress. In the central pre-yield or plug region, the local shear stress is less than the dynamic yield stress, so that the plug behaves like a rigid solid. The remaining two annular regions, adjacent to the electrodes, are in the post-yield condition and correspond to the shear stress exceeding the dynamic yield stress, so that the material flows. Equivalent viscous damping performance of an ER fluid dashpot damper is strongly coupled with the plug behavior. For a constant force, as the applied field increases, so does the plug thickness and equivalent viscous damping. For a constant applied field, as the force increases, the plug thickness and equivalent viscous damping both decrease. The passive and active or field-dependent damping behavior of an ER-fluid-based dashpot damper can be designed for a specific application using these quasi-steady Bingham plastic models.