Experimental evidence and structural mechanics analysis of force chain buckling at the microscale in a 2D polymeric granular layer

Abstract

The force chain concept underlies a significant fraction of our current understanding of the mechanics and stability of granular solids. One of the more interesting physical questions that remain unanswered relates to how a granular solid traverses the transition in state to that of a granular fluid. One possibility is that the transition is initiated by the buckling of loaded columns of particles. Here we explore the physics of force chain buckling through a combination of experiment and theory, for the first time explicitly verifying the phenomena. In our idealized experiments, a monolayer of micron scale particles is adhered to a soft elastomer foundation and a uniaxial stress is applied to the system. Above a critical threshold stress, the particles buckle and form a dramatic sinusoidal topography reminiscent of a common elastic instability involving a continuum plate (wrinkling). We use Laser Scanning Confocal Microscopy (LSCM) to make a complete observation of the buckled film in three dimensions, which allows us to show the subtle differences between a continuum and granular film. We go on by comparing measurements to recent theoretical predictions and discuss some simple scaling relations relating the emergent sinusoidal structure to the details of the underlying particles. © 2013 AIP Publishing LLC.