A mechanistic framework for the characterisation of cohesive, frictional and interlocking effects on powder flow behaviour

Powder flow behaviour is the result of countless combinations of interparticle forces of different natures: frictional, interlocking, cohesive and adhesive forces. We identify the rheological tests where one mechanism is most likely to dominate over the rest, and we propose the best descriptors of uniquely cohesive or frictional effects. We describe the procedure for a Fluidization test and the features of the results linked to powder cohesivity. We contrast these features against Shear test results to determine powder frictional properties, explaining the conditions and limitations of the analysis. We use Solid Volume fraction and Compressibility measurements to assess the extent to which the different mechanisms influence natural packing and forced flow in intermediate stress regimes. The proposed experimental protocol and framework of interpretation is applied to a wide range of powdered materials, representing typical industrial issues. The qualities of the characterization are discussed and compared to those associated with traditional rheological testing methods. The framework successfully differentiates the effects of the various interparticle interaction mechanisms on powder flow, enabling a comprehensive prediction of powder behaviour in a variety of handling and processing settings. The metrics used are all normalised, allowing for a universal direct comparison of flowability across completely different materials.