Measuring Force-Chains in Opaque Granular Matter Under Shear

Microstructural information, such as inter-particle forces and particle kinematics, plays a key role in understanding the continuum behavior of complex granular structure. Although micromechanical techniques have provided tremendous insights, they still lack quantitative accuracy and, associated with this, capacity to predict macroscopic behavior. We report here a set of experiments performed on a novel mechanical device in which we have successfully extracted particle-scale kinematics and inter-particle forces in a two-dimensional idealized granular assembly. This mechanical device allows a specimen composed of a two-dimensional analogue granular assembly to be subjected to quasi-static shear conditions over large deformation. Digital Image Correlation (DIC) is employed to measure particle kinematics. The inter-particle forces are inferred using the Granular Element Method (GEM), provided that average particle strains are measured and that the location of the contact points in the array is known. DIC combined with GEM allow us to observe and assess the force distribution in the complex granular assembly. These results represent an important step in our understanding of the micromechanical response of a complex granular assembly to applied macroscopic strains and stresses.