Material Design via Particle Shape
Stronger under compression
These twisted-Z particles were made out of recycled plastic bottles and now form a recyclable building material. Under compression, the particles interlock and provide their own confinement; surprisingly, this granular material gets stiffer with more weight on it! When agitated, it flows and can be poured like a liquid. After experimenting in the lab on small 3D-printed particles, we scaled up and built human-scale structures with around 12,000 of the hand-sized particles.
Find out more here: Aleatory construction based on jamming
and here: Freestanding loadbearing structures with Z-shaped particles
Designed to fail
One of the great properties of granular materials is that they can restructure again and again without loss of strength. This self-healing capability makes sense in light of the disordered configuration the particles are in: a rearrangement just takes the packing from one random state to another.
As an energy dissipating material, a granular packing of tetrahedra differs greatly from one of disks. Shown above are raw stress-strain data for granular columns made up of the five shapes at the bottom; can you tell which shape is responsible for which jagged plastic deformation?
With dozens of different particle shapes we find a wide range of plastic failure and can connect it to the broader study of amorphous plasticity that includes metallic glasses, earthquakes, and much more!
Find out more here: Transforming granular plasticity through particle shape
With a homemade computed tomography (CT) setup, we can connect the mechanical properties of a granular packing with the configuration of its particles. Here is a cross section of a tomography of a packing of saddle particles. A packing like this will compress more than 25% its original size as if it were a linear spring and then, suddenly and violently, snap inward. The ordering in this tomography points to the likely culprit: pringles in a can save a lot of volume, and likewise the particles here jump onto each other once the stress is high enough.