Jenike shear tests

Hollenbach et al. (1982) showed compressibility to be a more reproducible index than parameters such as angle of internal friction or unconfined yield stress obtained from the Jenike shear test (ASTM D 6128). 

To these ends, the WPMPS decided that the Jenike shear cell and the Jenike shear testing technique, as described in the well-known Bulletin 123, was of great practical use for bulk... 

Although estimation of tensile strength, adhesion and cohesion from a Jenike shear test yield locus is the easiest and less demanding way of assessing powder stresses, there are other types of equipment which attempt to measure cohesion and tensile strength. 

Akers, R.J. (1992) Certification of a Limestone Powder for Jenike Shear Testing. CRM116. Commission of European Committees, BCR, Office for Official Publications of the European Communities, Brussels, Luxembourg. 

R.J. Akers, The certification of a limestone powder for Jenike shear testing. Community Bureau of Reference-BCR, CRM 116, Brussels, 1991. 

Standard Shear Testing Method for Bulk Solids Using the Jenike Shear Cell. ASTM Standard D6128-00. ASTM International, 2000. 

Bilgili E, Yepes J, Stephenson L, Johanson K, Scarlett B. 2004. Stress inhomogeneity in powder specimens tested in the Jenike shear cell Myth or fact Part. Part. System Charact. 21(4) 293-302. 

In a shear cell, such as the Jenike shear cell,22 the test powder is consolidated in a shallow cylindrical chamber which is split horizontally. The lower half of the cell is fixed and a shear force is applied to the upper moveable part at a constant low rate (see example E5, section 7.5.5, where experiments were obtained at a constant rate of 0.03 rpm, corresponding to a linear velocity of 1 mm min-1). Shearing can be carried out for each of a series of normal loads on pre-consolidated samples, so that at the end of the test the relationships between the shear stress and normal stress at various bulk densities are obtained. 

Introductory concepts A review of the differences between fluids and bulk solids. Cohesive strength tests A review of different shear test methods, the Jenike Direct Shear Test method, and the calculation of the design parameters to prevent arching and ratholing. 

FIGURE 10 Jenike direst shear test, cohesive strength test set-up. 

The data generated experimentally from the Jenike direct shear test can be used to determine the following derived parameters ... 

Studies have also been conducted comparing the Jenike direct shear test method to other test methods used to measure a powder s flowability (3), including the Hosokawa Micron Powder Characteristics Tester (Hosokawa Micron, Osaka, Japan), Peschl shear tester, and Johanson Hang-up Indicizer (Johanson Innovations, San Luis Obispo, California, U.S.A.). This is not an exhaustive list of all the powder testers available. In general each tester has its own test method, which measures some property of the powder that changes as the flowability changes. As stated previously, however, the term flowability must be taken in context. 

The so-called shear cells are used for direct shear tests, where the powder specimen is consolidated in the vertical direction and then sheared in a horizontal plane. There are basically two types of shear cells in use today the Jenike shear cell (sometimes referred to more generally as the translational shear box) and the annular (or ring) shear cell (the rotational shear box). As the equipment needed is highly specialized (and hence outside the scope of this Guide) and as manufacturers instructions are usually adequate, the following contains only an outline description of both the hardware and the test procedures. 

Fig. 17 shows the Jenike shear cell in a schematic diagram a circular (internal diameter 95 mm), open-ended shear box is split horizontally, the base is immobile and the ring can slide freely in the horizontal direction. The normal stress, which is applied via the lid, is first used to consolidate the specimen and then to load it during test. 

In the Jenike shear cell, the failure is forced to be in a lenticular space around the horizontal shear plane rather than throughout the whole sample and shear strains cannot therefore be determined. This disadvantage is overcome to some extent in the simple shear apparatus which confines the powder specimen in a rubber membrane or a hinged box, thereby allowing the failure to occur in the whole of the sample. As the whole thing distorts during test, shear strains can be evaluated. The shear stresses are not, however, uniformly distributed and the method has not been widely used other than in research. 

The failure function can be measured directly in a number of ways. Some are rather complex and still under development, like the new plane strain biaxial tester with flexible boundaries30, but the simplest method so far is the uniaxial compression test. Only the version developed by Williams et al,24 gives results close to those obtained indirectly with the Jenike shear cell, the other versions yield relative measurements only. 

A mould in the form of a ring, like the Jenike shear cell ring for example, is used and a lid which just fits inside it. The base of the cell and the lower face of the lid are covered with sellotape on which a glue is spread. The cell is filled with the powder to be tested and it is scraped level with top of the cell the lid is placed in position, on top of the sample. 

The Cohesion Tester has been used in industry, mainly as a quality control-type test. It can be useful as an aid to assessment of flow properties and of power requirements in mixers, bulk conveyors and feeders. The original developers of the tester, Warren Spring Laboratories35, have even tried to correlate the cohesion value with unconfined yield stress determined with the Jenike shear cell and found a good correlation for some powders (fc = 6 x C). The tester is, quite obviously, only useful with fine, cohesive powders because ... 

American Society for Testing and Materials 1997. Standard shear testing method for bulk solids using the Jenike shear cell. American Society for Testing and Materials, Baltimore, MD. 

There are basically three types of shear cells available for powder testing (a) the Jenike shear cell, also known as the translational shear box (b) the annular or ring shear cell, also called the rotational shear box and (c) the rotational shear cell, which is a fixture of a powder rheometer. 

The Jenike shear cell has been considered for long time the testing cell for establishing standard procedures in industrial applications and research. It has been recognized as one of the standards for testing bulk solids in the United States and in Europe, being especially focused on cohesive powders. The complexity of this method is such that errors due to poor technique can easily arise. A reference material has therefore been produced with which laboratories can verify both their equipment and experimental technique. The reference material consists of 3 kg of limestone powder packed in a polyethylene jar. It is accompanied by a certificate giving shear stress as a function of normal applied stress for four different powder compaction stresses. 

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