Shrimp inspired 'Super-tough' Composites

When you look around, every invention seems to show a glimpse of nature. Be it the head lights of a car inspired from human eyes or a light bulb prompting the working of Sun. There are direct or indirect influences of nature in our advancements. They all seem to make sense considering the powerful bodies that inspired them. However, strange is the case to find how on earth a 'shrimp' would become a root study for developing the next generation of airplanes, body armour and helmets.

The creature is known as Mantis Shrimp also called as stomatopods. The shrimp has an evolutionary technique of  killing their prey in two ways. One using a spear that is driven through the prey and the other is a club that smashes the skin of the prey by pulverising it with high speed and force. The 'Dactyl club' can achieve accelerations of 10,000g unleashing great amount of impact with speed equivalent to .22 caliber bullet.

The idea of generating such large force onto another object can be considered suicidal if the right mechanism of absorption is ignored. But the mantis shrimp is assimilate the force onto itself thanks to the herringbone structure it possesses. This structure is the main inspiration for developing composite that can absorb large impact forces without fracturing.

The dactyl club when studied is found to be heavily mineralised, containing chitin fibers in hydroxyapatite matrix, allowing it to withstand repeated impacts without failure. The strength relies on the factor of arrangement of the fibers which are rotated by a small angle with respect to each layer below forming a herringbone structure.

The herringbone not only provides the failure resistance but also gives the shrimp to damage its prey severely by the transfer of momentum. The properties can be further simplified by understanding the structure in more detail the researchers found that the mineralized did not break because the crack is propagated by the structure and restricting it to the fibers and disallowing the crack to propagate to the surface.

A group of researchers imitated the structure of the dactyl club using carbon fiber epoxy composite. Forming helicoidal structures with different low angle rotations and then compared their performance to conventional unidirectional and quasi-directional fiber composites. The latter two when tested with 'drop weight' test were found to be fractured by the impact whereas the helicoidal structure showed a lower dent than the two, on average a 49% shallower dent. Following up with compressional tests also proved durability of the structure as 15-20% increase in residual strength was observed in the composites compared to the conventional structures.