The grapefruit-like pomelo, the world’s biggest citrus fruit, has a hefty peel that protects the delicate flesh inside. That peel could help inspire more shock-absorbent naval ships.
Boston University (BU) College of Engineering researchers are studying the pomelo’s ability to fall from up to 50 feet without smashing into pieces. (Watch the video!) With a U.S. Navy grant, they’re combining biology, materials science and computational mechanics to engineer lightweight materials that replicate the pomelo’s energy absorption mechanisms on a larger scale.
“I’ve always been intrigued by bioinspired engineering,” says project lead J. Gregory McDaniel, a BU associate professor of mechanical engineering and of materials science and engineering. “Nature keeps building things and testing them all the time, right in front of our eyes.”
The team’s Naval Engineering Education Consortium grant is aimed at developing materials that mitigate impact, shock and blast. “Those are three different things, but they all happen on a very short timescale of high stress or force on something that might break,” says McDaniel.
Searching for solutions in biology literature, McDaniel found a host of papers praising the pomelo. “It’s regarded as having this kind of magical impact resistance,” he says. “There seem to be a lot of design features in the pomelo fruit that are there for a reason and are not random.”
Every season, ripe pomelos plummet to the ground, traveling at 30 miles per hour. But instead of bursting upon impact and then laying around rotting, the fruit survives the fall and keeps its enticing appearance. Wandering animals gobble it up and leave its seeds far away.
The key lies in the peel’s three-layered construction. Inner and outer membranes encase a spongy, foamlike layer consisting of up to 18 mini layers pockmarked throughout with pores or voids. “It’s what’s called viscoelastic — kind of a rubbery elastic,” says McDaniel. “If you squish it, it deforms itself to absorb the shock, then slowly rebounds,” not unlike a memory foam mattress.
Working with BU PhD student Aidan Jimenez, McDaniel’s task is to figure out precisely what the pomelo peel is doing right and translate that knowledge into building a protective covering for a ship’s hull. Any advances could later have broad civilian uses, too, such as a more shock-absorbent cell phone case.
“There are interesting questions we need to answer,” in designing the covering, says McDaniel. “What should be the size of the voids in the foam in the inner layer? What should be the thicknesses and stiffnesses of the membranes?”
The team will ultimately fabricate and test a first-of-its-kind “peel” made of engineered rubbers and polymers that the Navy can use to protect ships.
“We’re absolutely not the pioneers in identifying the qualities of the pomelo fruit,” says McDaniel. “What we are trying to do is go a little further in finding the optimal parameters that will allow us to steal (these qualities) and take this all the way to (creating) a coating or layer that actually goes on a structure and works to absorb impact.”
Source: Boston University
Share this Post