Memory of the Unjamming Transition during Cyclic Tiltings of a Granular Pile

TL;DR

This study uses numerical simulations to explore how granular piles remember their unjamming transition through hysteresis in micro-structure during cyclic tilting, highlighting the role of weak contacts near the unjamming point.

Contribution

It reveals the hysteretic behavior and memory effects in granular piles during cyclic tilting, emphasizing the importance of weak contact networks near unjamming.

Findings

Hysteresis in stress and fabric variables during cycles.

Memory of unjamming stored in weak contact network.

Irreversible modifications near the unjamming transition.

Abstract

Discrete numerical simulations are performed to study the evolution of the micro-structure and the response of a granular packing during successive loading-unloading cycles, consisting of quasi-static rotations in the gravity field between opposite inclination angles. We show that internal variables, e.g., stress and fabric of the pile, exhibit hysteresis during these cycles due to the exploration of different metastable configurations. Interestingly, the hysteretic behaviour of the pile strongly depends on the maximal inclination of the cycles, giving evidence of the irreversible modifications of the pile state occurring close to the unjamming transition. More specifically, we show that for cycles with maximal inclination larger than the repose angle, the weak contact network carries the memory of the unjamming transition. These results demonstrate the relevance of a two-phases description -strong and weak contact networks- for a granular system, as soon as it has approached the unjamming transition.