VDW Verein Deutscher Werkzeugmaschinenfabriken e.V.

The Automated Shear Cell modules for the FT4 Powder Rheometer allow assessment of powders in terms of shear strength. Using a shear cell on the high-specification FT4 platform enables the automatic generation of accurate and reproducible shear information. This is in addition to bulk properties data and the comprehensive flowability data provided by a standard FT4 measurement (in accordance with ASTM Standard D7891).

A range of shear cell options is available to suit different sample sizes and applications:

• 85ml powder volume using 48 mm diameter shear head
• 10ml powder volume using 24 mm diameter shear head
• 1ml powder volume using 24 mm diameter shear head

Fully automated testing

Each shear cell is delivered with a library of testing programs in which the following stages are fully automated:

• The standard conditioning cycle that prepares the sample for testing
• A 'pre-shear' stage during which the powder bed is sheared to maximize the major principal stress
• A single series of tests at a particular pre-consolidation stress, which may be sufficient for powder characterization. For example, a powder may be pre-consolidated to 10 kPa and then sheared at 9, 6 and 3 kPa, with pre-consolidation to 10 kPa between each test
• More comprehensive, multi-stage testing to produce a range of yield loci corresponding to different pre-consolidation stress levels. Usually a given sample will be suitable for repeated shear testing to obtain the required set of yield loci. In this case the entire evaluation is automated.

Parameters derived from shear testing:

• Yield loci – shear strength vs normal applied stress
• Cohesion – shear strength at yield when normal stress is zero
• Internal angle of friction
• Unconfined yield strength or compression strength
• Major principal stress
• Flow function (the plot of unconfined yield stress versus major principal stress)

Particular benefits of the Freeman shear cells:

• Relatively low cost – being an FT4 accessory
• Pre-conditioning of sample to obtain a homogenous powder bed
• Fully automated shear testing and data analysis
• Ability to evaluate non-consolidated powders
• 1 ml minimum sample size

For more information on the FT4 Powder Rheometer, please visit the Freeman Technology website.