PARTICLE MATERIAL, MORPHOLOGY AND LOAD EFFECTS ON INTERNAL-FRICTION IN POWDERS

The frictional behaviour of dry ceramic and metal granular materials (spherical beads, sand and iron powders) has been studied. The coefficient of internal friction determined from shear cell measurements was used as the reference characterisation of this frictional behaviour. Other measures compared with this were standardized flow time, apparent and tap densities, the Hausner index and coefficient of internal friction deduced from the radial stress developed during die pressing. Of the simple measures, the Hausner index gave the least scatter, but showed poor sensitivity to changes in the coefficient of internal friction. The coefficient of internal friction calculated from shear cell measurements at normal stresses of 0.4-1.4 MPa was in good agreement with that deduced from die stresses during die pressing to about 300 MPa. Internal friction in loaded granular material was also studied in terms of particle size, shape and specific surface area. It was found to increase with decreasing particle size and deviations from sphericity, but in a highly non-linear way. There was no obvious effect of specific surface area over the range considered in this work.