Measuring shear properties and normal stresses generated within a rotational shear cell for consolidated and non-consolidated powders

Powder behaviour and particularly the measurement and prediction of flow properties remains of great importance to industry. Analytical studies over many decades have increased understanding, but it is modern instrumentation, sometimes using empirical methodologies that is providing new means of characterising powders and better understanding of the elements of powder processing. Progress is rapid and every study reveals the potential for further research. This work uses a rotational shear cell to evaluate five very different powders from a large particle ceramic (bimodal size distribution: 60 and 170 pm) to 4 pm limestone. The focus of the study was firstly to determine the yield loci of all materials after 9 kPa pre-consolidation and then to use a different shear cell control methodology to investigate the stresses automatically generated normal to the shear plane, as shearing proceeds. Non-consolidated or unstressed powders are of special interest and shear tests were done at close to zero consolidation stress, including the measurement of generated normal stress. The ratio of this generated normal stress to applied shear stress was derived for a wide range of pre-shear conditions and the results suggest that this parameter is differentiating and useful. Values for the coarse and the fine powders varied by a factor of about 2 and up to 3 when the powders were non-consolidated. (C) 2008 Elsevier B.V. All rights reserved.