Rheometer

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

New Universal Extensional Rheometer for Polymer Melts. Measurements on a Polystyrene Sample

Abstract: A new universal extensional rheometer, which makes it possible to investigate the elongational properties of polymer melts, is described. Measurements under a wide variety of constant stretching rates and constant tensile stresses can be undertaken and recoil and relaxation experiments can be performed on a small amount of material. The operation modes of the apparatus are demonstrated on a polystyrene sample. For this polystyrene the viscosity and the recoverable strain in the steady state of elongation were measured over more than three decades of the tensile stress. At small stresses the recoverable strain is proportional to the stress, i.e., the compliance is constant and the viscosity gives a constant value which is three times the zero‐shear viscosity. At higher stresses the recoverable strain seems to level off and the viscosity runs through a maximum which lies 30% above the stress‐independent value.

Shear thickening in low-concentration solutions of wormlike micelles. I. Direct visualization of transient behavior and phase transitions

Abstract: Shear thickening of low-concentration solutions of wormlike micelles is investigated using simultaneous rheological and visualization measurements. Shear-induced structures (SISs) are directly visualized in transparent Couette cells using a laser light scattering technique similar to dark-field microscopy. From these measurements, four different regimes of behavior are identified. In regime I, which occurs below a critical shear stress σc, the shear rate increases monotonically with stress and no shear thickening or SISs are observed. In regime II, which occurs for stresses greater than σc but less than σs, SISs nucleate inhomogeneously and grow from the inner cylinder of the Couette cell. In this regime, the steady state shear rate initially decreases with increasing stress and then increases again as the stress is raised. The steady state in regime II is characterized by two coexisting states separated by a cylindrical interface (concentric with the Couette cylinders). Near the inner cylinder, viscous S...

Correlation between yield stress and slump: Comparison between numerical simulations and concrete rheometers results

Abstract: Results of numerical flow simulations for two slump geometries, the ASTM Abrams cone and a paste cone, are presented. These results are compared to experimental results in the case of a cone filled with cement pastes in order to validate the proposed numerical method and the chosen boundary conditions. The correlation between slump and yield stress obtained numerically for the ASTM Abrams cone is then compared to the experimental correlations obtained by testing concrete with different rheometers during comparative studies that were organized at LCPC Nantes (France) in 2000 and MB Cleveland (USA) in 2003.