Insights on the local dynamics induced by thermal cycling in granular matter

In this letter, we report results on the effect of temperature variations on a granular assembly through molecular-dynamic simulations of a 2D granular column. Periodic dilations of the grains are shown to perfectly mimic such thermal cycling, and allow to rationalize the link between the compaction process, the local grains dynamics and finite-size effects. Through extensive simulations, we show quantitatively that the individual disks properties, namely their roughness and elastic modulus, define a critical cycling amplitude of temperature . Below , the dynamics is intermittent and spatially heterogeneous while confined into localized regions, whereas above , the whole column flows and the disks dynamics ranges continuously from cage-like at the bottom of the column to purely diffusive at the top. Our results rationalize a series of experimental results reported in the literature on dry or immersed granular materials and provide a simple simulation method for the study of thermal cycling as an alternate driving method for soft glassy materials.