Force/Strain/Load/Torque

The Muhammed Ali of Crustaceans

June 1, 2005 By: Stephanie vL Henkel, Sensors Sensors


The peacock mantis shrimp (Odontodactylus scyllarus) is distinguished by its brilliant coloration–and its mighty punching ability. This shrimp, about 9 cm long, can deliver a 51 mph jab delivering more than 200 lb. of force with its forelegs. And why? To crack the shell of a snail it intends to eat.



When UC Berkeley researchers led by Dr. Sheila N. Patek wanted to quantify the shrimp's kick and learn more about the mechanism that actually kills the snail prey, they set up a tank with a video camera and Model W200B02 ICP single-axis quartz impact force sensors from PCB Piezotronics. The sensors have a sensitivity of 50 mV/lb. (11 mV/N). To entice the shrimp to smack the detectors, the investigators coated them with shrimp paste (the creatures don't shy away from cannibalism).

For a slow-mo capture of the shrimp's action, Patek's colleague Roy Caldwell and graduate student Wyatt Korff used a camera shooting 5000 frames/s. The sensor data revealed that a heel structure on the shrimp's forelegs delivered a blow at speeds of 23 meters/s. The photographic record captured a secondary phenenomon: Negative pressure near the point of impact arising from the speed of the kick caused a cavitational effect. That implosive collapse of bubbles coming 0.5 ms after the strike proved the snail's undoing.

Contact Dr. Sheila N. Patek, University of California, Berkeley, Berkeley, CA; 501-643-9159,
patek@socrates.berkeley.edu.

Or Peter Munschauer, PCB Piezotronics, Depew, NY; 888-684-0004,
pmunschauer@pcb.com ,
www.pcb.com.


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