Assessing contact forces in granular materials from experimental measurements of kinematics Mathias Tolomeo, Vincent Richefeu, Gaël Combe, Jean-Noël Roux and Gioacchino Viggiani EPJ Web Conf., 140 (2017) 02012 Published online: 30 June 2017 DOI: 10.1051/epjconf/201714002012