Shape of the grains

Over the last decade we have researched the relationship between the shape of the particles composing a granular mixture and their macroscopic properties. Various particle shapes have been used with particular attention paid to the role played by the presence of flat faces. Initially, "static" situations such as a deposit of particles in a container were treated, where it was found, for example, that square particles tend to be oriented tip-up (with the faces at 45 Degrees with respect to the horizontal). As the particles became more elongated, their preferred orientation became closer to the horizontal, producing a very important change in stress transmission within the vessel [1.2.]

Subsequently, we start to deal with dynamic situations by analysing the flow patterns inside a silo when it is unloaded. In this scenario, we show that the shear stresses generated inside the silo lead to a significant alignment of the particles, mainly due to the geometrical constraints imposed by the flat faces of the particles[3]. Taking advantage of this phenomenon of "alignment of particles with flat faces under shear stress", we have devised a highly effective mechanism to pack cubic particles into a cylindrical container.

We are currently studying stacks of square particles and the rheological properties of a mixture of particles with flat faces when flowing in an inclined plane.