(13c) A Novel Method to Analyze Shear Cell Data of Powders for Different Initial Consolidation Stresses

The shear cell methodology is commonly used during material characterization to measure powder flow properties. Flow indices, such as cohesion, angle of internal friction, unconfined yield strength, major principal stress and flow function coefficient can be extracted from yield loci by Mohr circle analysis, which can be used to describe the flow regime. Despite its popularity, the methods to compare shear cell data are limited, especially when materials are tested under different initial consolidation stresses. The yield loci are dependent on the initial consolidation stress applied to powder beds, and are thus difficult to interpret for comparisons between materials or between shear cells. This study identified the mathematical relations between the different attributes quantified in the Mohr circle analysis, and investigated the effect of initial consolidation stress on flow indices with rigorous statistical analysis. The aim was to develop a comparison method, which indicates material characteristics, and is independent of the initial consolidation stress. As a case study, 24 powders were analyzed by a rotational shear cell under four initial consolidation stresses. The results have shown that the effects of initial consolidation stress on angle of internal friction were minimal. The linear relation between unconfined yield strength and cohesion was used to re-scale the yield loci under different initial consolidation stresses into a single “master” line for each material. The effect of initial consolidation stress on angle of internal friction was identified as a material property. Using the proposed methodology, it is possible to compare materials tested under different initial consolidation stresses.