“Shear Cell for Direct Determination of Yield Locus

of Particulate Materials”

Inventors: V.M. Puri, et al.

PSU Invention Disclosure No. 96-1674

Issued U.S. Patent No. 6,003,382

In many applications involving handling, flow and storage of bulk solids such as tableting, pelletizing, particle size reduction, mixing, packaging and quality control, it is important to be able to design bulk solids handling systems to precise engineering specifications. To design a reliable system, using rational principles, it is necessary to characterize the flow properties of the bulk solids.

Two Penn State researchers have built and tested a shear tester for powders that allows for the successful determination of a yield locus from single tests. The principle of this invention is that yield states can be maintained in a test cell over a range of normal and shear stresses in the same test. This leads directly to a yield locus. This invention is a versatile tester which minimizes the effects of operator error by allowing consistent consolidation, without the need for trial-and-error in determining the required number of twists for consolidation of powder mass in Jenike-type shear tests. It also eliminates error introduced by ring-to-ring contact during shearing by maintaining any specific gap between upper and lower rings or cell walls. The amount of time and material needed to generate a yield locus is also greatly reduced.

Because of its flexible design, this invention can also be used as a Jenike shear cell, yield locus tester (YLT) or a direct shear cell. In the Jenike procedure, the initial yield point from separate samples is used to establish each discrete data point on the yield locus, while in the YLT, the yield locus is a dynamic set of post yield stress states in the same sample. Therefore, if shear stress values change significantly after the initial yield point for a given normal stress, then the Jenike and YLT yield loci are expected to be different.