Granular Rod Flows

Motion down a frictional, inclined plane is a classic example presented in first year physics classes, yet the concept serves as a standard method to study the flow of granular materials. A parameter of interest remains the inclination angle at which a flowing system comes to rest, also known as the angle of repose, or the friction angle. For a block on an incline, the angle of repose is related to the static friction coefficient that can be readily derived. However, for more industrially relevant situations and materials, both particle shape and friction properties affect the angle of repose. Sometimes these relations follow standard reasoning: for example, the angle of reponse for monodisperse spheres of larger surface friction lies at circa 20^o, whereas smoother particles stop flowing at much lower angles. While for particles with aspect ratios different from unity, the angle of repose will typically increase, as is the case of granular rods. Here we explore how the properties of a granular rod, namely it's aspect ratio and surface roughness, influence the angle of reponse for systems of varying size, flowing down an inclined plane, using the discrete element method, that is fully accessible to students at any level.