Unbalanced force emanating from stored elastic energy in granular packing: Fundamental insight from quasi-static DEM simulation

Unbalanced force is poorly understood in discrete simulation of granular packing. During simulation of 'wall friction test' of granular iron ore, sharp peaks of unbalanced force were observed even during a quasi-static condition, contrary to the expected behavior. Particles having maximum unbalanced force were identified and the dynamic behavior of the particle and its neighborhood was thoroughly investigated (no explicit long range force was present in the simulation). It is inferred that the peaks occur due to storage of elastic energy within particles, followed by a sudden/gradual release. Finding of this article might have far reaching consequences in many disparate and diverse disciplines, such as Shear Transformation Zones (STZs) in metallic glasses, identifying tiny but non-trivial configurational changes at the onset of glass transition as well as for its relaxation behavior, origination of specific structural features (say, origin of stacking faults) in High Entropy Alloys (HEAs), kinetic instability induced symmetry breaking in granular media, Self-Organized Criticality (SOC) induced avalanching in granular systems etc. The unbalanced force index can turn out to be a very important metric for analyzing the configurational instability of those particulate ensemble for quasi-static and static conditions.