Creature Feature: Twisting Cracks Impart Superhero Toughness to Animals

Crack twisting and toughening strategies in Bouligand architectures.

The helicoidal architecture of a mantis shrimp's dactyl club is naturally designed to survive repeated high-velocity blows. (credit: University of California, Riverside, Scanning Electron Microscope image/David Kisailus)

July 30, 2018 | Source: Purdue University, purdue.edu, 25 June 2018, Emil Venere

WEST LAFAYETTE, Ind. – Super-resilient materials found in the animal kingdom owe their strength and toughness to a design strategy that causes cracks to follow the twisting pattern of fibers, preventing catastrophic failure.

Researchers in a recent series of papers have documented this behavior in precise detail and also are creating new composite materials modeled after the phenomenon. The work was performed by a team of researchers at Purdue University in collaboration with University of California, Riverside.

The researchers studied the preternatural strength of a composite material in a sea creature called the mantis shrimp, which uses an impact-resistant appendage to pummel its prey into submission

"However, we are seeing this same sort of design strategy not just in the mantis shrimp, but also in many animals," said Pablo Zavattieri, a professor in Purdue’s Lyles School of Civil Engineering. "Beetles use it in their shells, for example, and we also are seeing it in fish scales, lobsters and crabs."

New findings show that the composite material of the club actually becomes tougher as a crack tries to twist, in effect halting its progress. This crack twisting is guided by the material's fibers of chitin, the same substance found in many marine crustacean shells and insect exoskeletons, arranged in a helicoidal architecture that resembles a spiral staircase.

"This mechanism has never been studied in detail before," Zavattieri said. "What we are finding is that as a crack twists the driving force to grow the crack progressively decreases, promoting the formation of other similar mechanisms, which prevent the material from falling apart catastrophically. I think we can finally explain why the material is so tough."

The findings are now helping the development of lighter, stronger and tougher materials for many applications including aerospace, automotive and sports.