Researchers from the University of Sydney and San Diego State University have discovered new compaction patterns for brittle porous material that could explain a range of phenomena from avalanches to crater formation.
Professor Itai Einav and Dr Francois Guillard from Sydney’s School of Civil Engineering used puffed rice to explain the movement and crushing of porous materials when compressed. This research is published in the journal Nature Physics.
“Before we started we knew that brittle porous materials such as rocks, foams or even snow exhibit irreversible compaction patterns,” Einav said.
“We see such patterns in Sydney’s sandstone all around us, but this geological imprint doesn’t tell us much about the internal motions and the process of pores collapsing within the rock mass. We know rocks move, but it takes millions of years.”
He says what they didn’t know was in what ways the rocks move and deform, and specifically what types of internal patterns develop.
“We picked puffed rice because they are highly porous and compliant and typify generic brittle porous materials when being compressed,” he said.
“We wanted to understand how packs of brittle grains coordinate motion when crushed. Many of us have tried this at home as kids – crushing puffed rice cereal with a spoon. For us this simple experiment revealed surprisingly rich compaction patterns that were due to the competing processes of internal collapse and recovery.”
Guillard said the research model offered a new perspective on jerky flows in metallic alloys.
“We used a robust spring-lattice model to capture the process of internal collapse and recovery and are now able explain the dynamics of previously and newly observed patterns,” he said.
“The lattice model we have created can address other brittle porous media such as natural rocks, bones and snow, and man-made ceramics, foams and pharmaceutical powders.”
Video of puffed rice being crushed
Professor Itai Einav (left) and Dr Francois Guillard experiment with cereal.