Granular potential and compactivity of jammed particles.

Abstract

Granular materials exhibit complex behavior because of their nonequilibrium nature and dissipative mechanism. This study investigates the role of granular potential in bidisperse granular packings and its influence on thermodynamic properties such as entropy, compactivity, and density of states. Experimental tests using x-ray tomography were performed to examine the microstructure and volume fluctuations of bidisperse mixtures with varying composition ratios. Using a statistical mechanics approach and the fluctuation equation framework, the free-volume index and granular potential for an ensemble were quantified, revealing their direct correlation with packing structure and jamming behavior. The results show that granular potential significantly contributes to excess free volume, thereby influencing packing efficiency and stability. The findings offer insights into the implications of granular thermodynamics for natural and engineered systems, such as soil stability, landslides, and vascular flow regulation.