Incipient movement of spheres subjected to vibration and centrifugal forces

VALENZUELA ARACENA, K.A.; UÑAC, R.O.; IPPOLITO, I.; VIDALES, A M; BENITO, J.G.

Santiago de Chile

Workshop; Southern Workshop on Granular Materials 2015, Santiago de Chile; 2015

We perform two kinds of experiments to study the initiation of the movement of spheres deposited onto a surface.The first experiment consists in vibrating the surface following a harmonic oscillation and determining the criticalfrequency necessary to detach half of the particles at a given amplitude. The second experiment subjects a circularsurface, on which particles are deposited, to centrifugation at a lineal increasing rate. The critical rotation frequency at which half of the particles are detached from the surface is measured.The materials employed consist in glass and steel beads deposited on rough and smooth surfaces. Humidity is controlled to avoid the presence of capillary effects. Different grain sizes were inspected.The results show that as the size of the spheres increases the critical frequencies are higher. For vibration, these frequencies slightly depend on the surface roughness. Humidity is an important factor in both experiments. For the case of centrifugation, the critical force for detachment increases with the size of the sphere and remains almostindependent of its position on the surface.