Buckling force chains in dense granular assemblies: physical and numerical experiments

This paper focuses on the columnar particle structures known as force chains, and their failure via buckling. The local kinematics and frictional dissipation of this failure mechanism are examined quantitatively for dense, cohesionless granular assemblies, under quasistatic and strain-controlled compression. Data are taken from a physical experiment and a discrete element simulation of bidisperse assemblies of circular particles undergoing shear banding. Particular attention is paid to the deformation and dissipation within a class of particle clusters, each composed of a buckled force chain segment and its laterally supporting neighbours. These particle clusters are found to be confined to the shear band. We establish measures of their local micropolar deformation, including nonaffine deformation, and the evolution of these quantities with strain. Temporally and spatially, the kinematics of this class of particles exhibits trends consistent with the particle motions that form the major contributors to deformation on the mesoscopic and macroscopic scales. The predominant mode of contact failure in a force chain undergoing buckling, and in the contacts with and within its laterally supporting neighbours, is frictional rolling. Rolling friction thus serves as one of, if not the main control valve for the energy flow from the force chain to its surrounding medium.