Freeman Technology has added a uniaxial powder tester to the FT4 Powder Rheometer, extending the system’s ability to efficiently and reproducibly measure properties that directly correlate with a powder’s in-process behaviour. Uniaxial testing complements the FT4’s existing test methodologies for shear, bulk and dynamic powder measurement.
Uniaxial testing involves measuring the force needed to break or fracture a column of consolidated powder. It is probably the most simple and direct method of measuring unconfined yield strength, a parameter related to cohesivity. In the past, use of the technique has been inhibited by the difficulties inherent in repeatably producing a uniformly packed and consolidated powder column for testing. As a result, unconfined yield strength data are routinely derived from shear testing, a less direct but practical alternative.
Freeman Technology has developed a new accessory that, in combination with a well-defined consolidation methodology, produces a homogeneous, uniform powder column for testing. Measuring the normal stress required to fracture the column directly identifies the unconfined yield strength. Comparative tests show that the new solution produces data closely comparable to those derived from shear test data, but offers improved repeatability.
Uniaxial testing is not suitable for powders with very low cohesive strength, but is a quick and intuitive method for measuring unconfined yield strength of more cohesive materials. It complements rotational shear testing which in contrast requires less sample, can be used for less cohesive materials and is essential for measuring wall friction data in support of material of construction choice.