Researchers have found that packed rice grains weaken under rapid compression but remain stronger under slow pressure. This unusual property has been used to create a metamaterial that automatically adjusts its behavior based on the speed of applied forces.
An international team led by the University of Birmingham made the discovery and published the results in the journal Matter. The phenomenon, called rate softening, occurs because friction between rice grains drops sharply during fast loading, weakening internal force networks.
The team combined rice-based units with sand to build a granular metamaterial. It can bend, buckle, or stiffen differently under slow movements versus sudden impacts without any electronics or sensors.
Dr. Mingchao Liu of the University of Birmingham said the work turns a common granular material into an engineered system that responds through its own mechanical properties. Potential uses include soft robots for surgery and protective equipment that absorbs impacts more effectively.
