Interpretation of T-Bar Tool Measurements for Yield Stress Materials

Abstract

The T-bar rheometrical tool (Brookfield Engineering Laboratories, Inc.) is a slender rod which is placed in a material and rotated horizontally about its short axis by a vertical shaft. The torque on the shaft from laminar flow of material around the rod is determined by the material’s rheological properties. T-bar experiments for a Newtonian liquid are shown to agree closely with existing theory. For yield stress materials an approximation is derived for the torque on a rotating T-bar which is supported by experiments on a range of materials. The torque for very slow rotational speed is insensitive to boundaries beyond a few T-bar diameters and is shown to correlate with the material’s yield stress and other non-Newtonian parameters. A step-decrease in torque for each half-revolution of the T-bar was shown by some materials and possible origins of this effect are discussed.

Keywords

• rheometry
• t-bar
• vane
• yield stress
• thixotropy
• viscoplasticity