An attempt in assessing contact forces from a kinematic field

In granular materials, it is not so simple to assess experimentally the contact forces. Photoelasticity is generally used for this purpose but this technique involves some constraints that may limit its use. We propose a different solution, which implements both the digital image correlation (DIC) technique and the non-smooth contact dynamics (NSCD) formalism. In a nutshell, the technique aims to find a set of contact forces mechanically admissible given a set of measured contact velocities. We used photographs of a simple shear test of a two-dimensional analogue granular material (about 1000 aluminum rods) to apply the solution, and we showed that valuable information about the contact forces can be extracted from the kinematic field provided that no major rearrangement occurs for at least five image shots.