Dynamic patterns of compaction in brittle porous media

Brittle porous media exhibit a variety of irreversible patterns during densification, including stationary and moving compaction bands in rocks(1-3), foams(4), cereal packs(5) and snow(6). We have recently found moving compaction bands in cereal packs(5); similar bands have been detected in snow(6). However, the question of generality remains: under what conditions can brittle porous media disclose other densification patterns? Here, using a new heuristic lattice spring model undergoing repeated crushing events, we first predict the possible emergence of new types of dynamic compaction; we then discover and confirm these new patterns experimentally in compressed cereal packs. In total, we distinguish three observed compaction patterns: short-lived erratic compaction bands, multiple oscillatory propagating compaction bands reminiscent of critical phenomena near phase transitions, and diffused irreversible densification. The manifestation of these three different patterns is mapped in a phase diagram using two dimensionless groups that represent fabric collapse and external dissipation.