Small and large Ring Shear Tester
The principle of both testers is the same: A powder or bulk solid specimen is contained in a ring-shaped (annular) trough, called the bottom ring, covered by an annular lid and subjected to a vertical load through the lid. The specimen is then subjected to a shear deformation by rotating the bottom ring relative to the lid. From the normal stress and the shear stress measured following different procedures a couple of quantities is determined, e.g., the unconfined yield strength (compressive strength), the flowability, the internal friction, the bulk density.
The major difference between the testers is the size of the shear cells. which determines the maximum particle size that can be tested. This limitation results from the conditions that a sufficient number of particles must be contained in the shear cell to obtain a continuum, i.e., a "powder" or "bulk solid" instead of "some particles".
If the materials to be tested do not contain particles greater than about 1 mm, the small tester is sufficient. If larger particles have to be tested, the large tester is preferable. Since the maximum particle size is the critical point, it is no problem to test very fine particles in the range of micrometers or even nanometers in a large tester.
The selection guide shows further criteria to identify the best tester for your application: