Puffed rice is a brittle porous material very interesting to observe various behaviors of porous media when compressed. For example, when compressed at constant medium velocity, horizontal compaction bands can be seen moving from bottom to top in the sample.
The precise detail of how this correlated motion happen is still unclear, as well as the precise dynamics of the bands (from bottom to top or from top to bottom for example). To better understand this phenomenon, we perform simulations of lattice of spring that display very similar behaviour, with different patterns of compaction.
The phenomenon emerges from the strain-rate softening sensitivity of the material:
[Download] F. Guillard, P. Golshan, L. Shen, J. R. Valdes, I. Einav. Dynamic patterns of compaction in brittle porous media. Nature Physics 11, 835 (2015)
[Download] Valdes, Julio R., François Guillard, and Itai Einav. “Evidence that strain-rate softening is not necessary for material instability patterns.” Physical review letters 119.11 (2017): 118004.