The giant foam outsoles of modern running shoes aren’t just for show. These advanced materials can capture and rebound so much energy that they can make people run quantifiably faster—enough for anyone to shave minutes off their marathon time with the right pair of shoes.
That’s the power of foam on your feet. But now, one researcher imagines a new purpose: Protecting our buildings from car crashes and earthquakes. In a new paper published in Smart Materials and Structures, Tatheer Zahra, an investigator at the QUT Centre for Materials Science, demonstrates that the same sorts of foams we use in sneakers, memory pillows, and mattresses could be just as important for supporting buildings as they are for our bodies. After 3D-printing her own structures made of PLA foam (the same type of foam found in many of the aforementioned products), she estimates that a barrier of foam that’s less than an inch thick could stop a car moving 37mph. Zahra imagines that these delicate-looking mesh foams could replace the protective walls that surround buildings in many major cities—and that’s only the beginning.
How is any of this possible? How can shoe foam be so strong? PLA is what’s known as an “auxetic material.” When under pressure, auxetic materials behave differently than any other. Stretch a strip of rubber, or even steel, and it will become thinner and narrower as it grows longer. But when you stretch an auxetic material in such a way, it will paradoxically get wider as it grows longer.
This means auxetic materials can ultimately absorb considerable energy because when they encounter a force, they can contract or expand in multiple directions at once—diffusing that energy instead of snapping—before returning to their shape.
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