Particle fractal and load effects on internal friction in powders

This paper describes a study of the influence of particle shape on internal friction. In this work, fractal measures of particle shape have been applied to a range of commercially available copper powders chosen for their contrasting particle shape but similar size ranges. The flow and packing properties of powders under gravity loading conditions were examined using flow time tests for known mass, apparent density and tap density. In addition to these tests, a ring shear cell provided the internal friction of the powders under applied load with applied normal stresses of approximately 0.35 MPa. Fractal measures have been found to be better discriminators of shape than conventional two-dimensional shape factors. There was good correlation between fractal measurements of particle shape complexity and the Hausner ratio, flow time and coefficient of internal friction.