bouncing back

Protecting fragile objects and people from impacts requires materials that can absorb energy without transmitting large forces. Cellular structures, observed in natural materials like sponge and bone, provide a template for reducing density and absorbing impact energy. In my final year of PhD research, I partnered with Sandia National Laboratories and combined numerical modeling and experimental approaches to characterize a new class lattice materials which absorb impact energy then recover elastically.

My approach uses a custom constructive geometry toolbox, the most challenging finite element simulations I have executed, and a custom test apparatus for recording performance in high speed impact scenarios.

The fixture subjects a sample under test to a prescribed impact velocity and mass, then captures the sample’s force/displacement response. Sounds simple - yet this actually took six months of design, development, and debugging!

The fixture consists of an aluminum carriage that slides freely on a vertical rail. As the impact carriage falls towards the object under test, a magnetic switch is tripped, commanding a data acquisition card to begin streaming load cell data, a high speed camera to record video, and floodlamps to properly expose the image.

Experimental and numerical results indicate these metamaterials transmit up to six times more useful impact energy at equivalent density compared to isotropic foams.

Experimental and numerical results indicate these metamaterials transmit up to six times more useful impact energy at equivalent density compared to isotropic foams.

The work was published in Advanced Materials Technologies and reported in the Denver Post and Boulder Daily Camera.