How a shrimp's 200-lb. punch could lead to better football helmets
Scientists have marveled at how the mantis shrimp breaks open its prey, but only now are engineers learning how the shrimp's club is built – and how that could help humans.
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Tread lightly around the mantis peacock shrimp. Up to 7 inches long, this crustacean sports gregarious colors – and an extraordinarily powerful, resilient club for whacking its prey.
Now, a team of scientists has uncovered the secrets of the club's construction, unrolling a blueprint that holds the promise of a new generation of lightweight, impact- and shock-resistant materials for products ranging from body armor and electric cars to football helmets that better shield players from head injuries.
Indeed, the researchers already have designed composite materials based on the club's natural design that have successfully withstood several types of high-velocity munitions, says David Kisailus, an assistant professor of engineering at the University of California at Riverside, who along with colleagues from six other institutions conducted the study.
The peacock mantis shrimp feeds on some of the hardest nuts to crack in the ocean – snails, other crustaceans, as well as other forms of shellfish. It does so by unleashing its club repeatedly at unusually high speeds until the shells of its prey crack open enough to expose the shrimp's meal.
How it does this is crucial to understanding the enormous stresses it is able sustain.
Like a praying mantis, the shrimp have a folded appendage near their heads. The appendage resembles a football punter's tightly draw leg just before he unleashes the kick. The appendage has a latch that locks the joint until a muscle in the upper portion of the appendage has fully contracted. When the shrimp releases the latch, it unleashes the pent-up energy in the muscle, flinging the appendage outward, explains Shelia Patek, a biologist at the University of Massachusetts at Amherst, who uncovered a spring-like material at the joint that further energizes the strike.
Dr. Patek and fellow researchers have clocked the shrimp's punt at more than 45 miles an hour – underwater. That makes it the new world champ for so-called feeding strikes – the movement animals make to nail their prey. It's nearly twice as fast as a punch a boxer typically throws in open air and delivers a force of more than 200 pounds, with the club accelerating with a force of some 10,000 Gs – 500 times more acceleration force than humans can endure.
And that isn't all. Patek's team also found that the strike imparted a second rattling impulse to a creature's shell that came quickly on the heels of the first strike. When the researchers examined high-speed video, they saw a brief flash of light at the point of contact – the telltale signs of cavitation.