Granular Beams

Abstract

Granular beams are a composite material consisting of a membrane filled with particles. Composite materials are a unique type of material in which constituent materials are crudely combined to form a product whose physical properties are different than that of the original constituent materials. Unlike other combinations of materials, the constituents are not chemically bonded or atomically intertwined; therefore, composite materials are often cheaper and easier to produce. Such is the case for granular beams. Liquid silicone rubber is poured over a mold consisting of a length of pipe and left to harden. This rubber membrane is filled with particles; these are items of any shape or size and will give the beam its characteristic rigidity. The ends of the membrane are plugged and sealed, and a pump attached to one end to extract or inject air into the interior of the granular beam. Withdrawing air from the beam causes its particles to pack tightly into a certain configuration which gives the beam its structural rigidity. In my research, I conducted 3-point bend tests of these granular beams, changing their cross-sectional area, particle size and shape, and internal pressure to see how these changes affected the beam’s rigidity. Given this data, I derived a formula for the rigidity of a granular beam, given by the rigidity metric of shear modulus, as a function of a constant multiplied by the beam’s internal pressure and the cross-sectional area, with the shape of the particles contributing to the value of the constant. At the end, I give some potential directions future research could take, along with some applications.